Molecular Cytogenetics. Protocols and Applications
Methods in Molecular Biology TM VOLUME 204 Molecular Cytogenetics Protocols and Applications Edited by Yao-Shan Fan ...
Author: Yao-Shan Fan
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Methods in Molecular Biology
Molecular Cytogenetics Protocols and Applications Edited by
Yao-Shan Fan
HUMANA PRESS
Molecular Cytogenetics
1 Molecular Cytogenetics in Medicine An Overview Yao-Shan Fan 1. Introduction The word "chromosome" was introduced over a century ago from the Greek language meaning "colored body." While cytogenetics refers to the study of chromosomes, the term molecular cytogenetics is used to describe the analysis of genomic alterations using mainly in situ hybridization based technology. Fluorescent in situ hybridization (FISH) was initially developed in the late 1980s from radioactive hybridization procedures used for mapping human genes (1–4). Soon, this technology was utilized for the characterization of chromosomal rearrangements and marker chromosomes (5,6), the detection of microdeletions (7), and the prenatal diagnosis of common aneuploidies (8,9) in clinical cytogenetics laboratories. At the same time, numerous DNA probes have been commercialized, further promoting the wide-spread clinical applications of molecular cytogenetics. Many new FISH techniques have been developed, including primed in situ labeling (PRINS [10]), fiber FISH (11,12), comparative genomic hybridization (CGH) (13), chromosome microdissection (14,15), spectral karyotyping (SKY [16]), Multiple color FISH (M-FISH [17,18]), color banding (19), FISH with multiple subtelomeric probes (20), and arraybased CGH (21,22). With the current FISH techniques, deletion or rearrangement of a single gene can be detected, cryptic chromosome translocations can be visualized, the copy number of oncogenes amplified in tumor cells can be assessed, and very complex rearrangements can be fully characterized. Using interphase FISH, genomic alterations can be studied in virtually all types of human tissues at any stage of cell division, without the need of cell culture and chromosome preparation. The development of FISH technology in the past two decades has brought cytogenetics into the molecular era, and made the "colored bodies" more colorful and brighter.
From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
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2. FISH Techniques 2.1. DNA Probes All types of human DNA sequences have been used as probes for molecular cytogenetic studies. These include unique sequences, repetitive sequences such as α-satellite and telomere DNA, locus specific DNA obtained by PCR amplification, large genomic DNA sequences cloned into cosmids, bacterial artificial chromosomes (BACs), P1-derived artificial chromosomes (PACs), yeast artificial chromosomes (YACs), chromosome band or arm specific sequences generated by microdissection, and DNA libraries established by chromosome flow sorting. To make the probes, DNA sequences are labeled directly with fluorescent dyes or indirectly with biotin or digoxigenin, which are then detected with immunofluorescent staining. DNA sequences can be labeled with a single color, dual colors, or multiple colors. Single or multiple probes can be used for each hybridization. In recent years, numerous fluorescent labeled DNA probes have been commercially available, making the FISH protocols much simpler, more cost-effective, and reliable for clinical applications.
2.2. FISH with Unique DNA Sequences FISH with unique DNA sequences represents the most basic molecular cytogenetic technique. The DNA segment used as a probe may represent a functional gene, or a particular chromosome region or locus. The basic steps of FISH procedure include labeling of DNA probes, preparing interphase or metaphase chromosome slides, in situ hybridization, and visualization with a fluorescence microscope (4). FISH with unique sequences is most commonly used for the diagnosis of microdeletion syndromes, and for the detection of gene fusion or rearrangements in cancer cells.
2.3. Chromosome Painting Chromosome painting refers to a FISH procedure using probes generated from specific chromosome libraries (23), Alu and L1 PCR (24) or chromosome microdissection (25). When the probe contains unique and repetitive sequences from an entire chromosome, whole chromosomes of a homologous pair in metaphases are illuminated with fluorescence (painted). The short or long arm of a particular chromosome can be painted with an arm-specific probe. Using a device containing a 3 × 8 array, all 24 chromosomes can be painted simultaneously and detected sequentially on a single slide using a standard fluorescent microscope (26). Chromosome painting is usually performed as an adjunctive tool for identification and characterization of structural rearrangements.
2.4. Spectral Karyotyping (SKY) SKY is an automated chromosome painting procedure (16). The probe mixture is composed of chromosome specific libraries generated from flow-sorted human chromosomes. The probes are directly labeled with combinations of 5 fluorochromes: Rhodamine, Texas-red, Cy5, FITC, and Cy5.5. By the means of computer classification of the spectra, all 24 human chromosomes can be simultaneously visualized in different colors. SKY has been proven to be a powerful tool for the characterization of complex chromosomal rearrangements in cancer cells (27–29) and de novo constitu-
tional structural abnormalities (30,31). With a visual sensitivity to DNA alterations of 1–2 Mb in size, SKY is a useful tool for detecting cryptic translocations (32).
2.5. Multiple Color FISH (M-FISH) M-FISH has also been called multifluor FISH or multiplex FISH (17,18). Similar to SKY, the probes are labeled with the combinations of multiple fluorochromes. Different from spectral analysis, 24 chromosomes in unique colors are detected by a series of fluorochrome specific filters with the assistance of computer software. Whereas a wheel containing multiple filters can be installed onto a fluorescence microscope, the software designed for 24 color analysis can be added into an existing imaging system used for conventional karyotyping. Therefore, an additional imaging system is not required for M-FISH studies.
2.6. FISH Following Microdissection (MicroFISH) To perform MicroFISH (14,15) a whole chromosome, a marker, or a particular chromosome band is scraped from metaphase spreads using a micromanipulator. The scraped DNA is amplified by PCR, and labeled as probes. FISH of such probes with normal reference metaphase chromosomes reveals the composition of chromosomes or the chromosome regions in question. The term reverse in situ hybridization has been used to describe this procedure. This technique is useful for characterizing structural rearrangements and marker chromosomes. Microdissection has been used as a tool to produce commercial DNA probes for specific chromosomes, specific arms, or particular chromosome regions.
2.7. Comparative Genomic Hybridization (CGH) CGH gained its name from a FISH procedure that compares test DNA with normal reference DNA (13,33), and is also called reverse in situ hybridization. The test DNA is traditionally labeled with a green color and the normal reference DNA with a red color. The DNA mixture is then hybridized to normal metaphase chromosomes prepared from a blood culture. By measuring the ratio of green to red color, gains or losses of chromosomes or chromosomal regions in the test DNA can be detected. The size of DNA segments that CGH can detect is estimated to be in the range of 10–20 Mb. CGH is useful in the characterization of de novo unbalanced constitutional anomalies (34). Since the entire genome can be scanned for gains or losses without preparing metaphase chromosomes of the cells or tissues tested, CGH has been widely used in investigations of solid tumors (33).
2.8. Primed In Situ Labeling (PRINS) PRINS refers to a process of reannealing short oligonucleotide primers to target sequences in situ, followed by elongation of the sequences with a Taq polymerase and simultaneous labeling of the target sequences with a fluorochrome (10). The target sequences are examined under a fluorescence microscope. PRINS primarily targets short stretches of α-satellite DNA unique to each chromosome. The reaction can be completed in less than 2 h. This technique has been used as an efficient alternative tool to detect aneuploidies (35,36).
2.9. Color Banding This technique is also called cross-species FISH (Rx FISH) because it utilizes DNA obtained from flow-sorted gibbon chromosomes by PCR amplification (19). The genome of gibbons (Hylobates concolor and Hylobates syndactylus) has a high degree of homology with human DNA but with extensively rearranged chromosomes. When hybridized with a set of gibbon DNA probes labeled with a combination of FITC, Cy3, and Cy5, human metaphase chromosomes show a distinctive color banding pattern. This technique has been used in cancer cytogenetics studies with commercially available probes (37).
2.10. FISH with Multiple Subtelomeric Probes (Multi-Telomere FISH) The technique of multi-telomere FISH utilizes a device containing 41 subtelomeric probes for all 24 different chromosomes (not including the short arms of acrocentrics [20]). Each of these probes is composed of unique sequences of 100–200 kb mapped in the subtelomeric regions (~300 kb from the chromosome end) of human chromosomes (38). The probes for the short arms and the long arms are dual labeled with a green and a red fluorochrome respectively. This allows detection of submicroscopic deletions or translocations in all subtelomeric regions with a single hybridization, and therefore can be used as screening a tool.
2.11. Fiber FISH Fiber FISH is a hybridization of DNA probes to extended chromatin fibers (i.e., free chromatin released from lysed cells) on a microscope slide (11). A modified method hybridizes probes to unfixed DNA fibers prepared from cells embedded in pulsed-field gel electrophoresis (PFGE) blocks (12). This technique has been used for high resolution gene mapping (11,12), and for direct visualization of gene duplication and chromosome breakpoints involved in translocations (39–41).
2.12. Combined Immunophenotyping and FISH The term FICTION, standing for fluorescence immunophenotyping and interphase cytogenetics as a tool for the investigation of neoplasms, was originally created to describe this technique (42). FICTION is a simultaneous analysis of cell surface immunologic markers and interphase FISH. The strategy of combining immunophenotyping with FISH enables correlation of chromosome aberrations of interest with cell lineage and differentiation stages of tumor cells, and therefore provides a useful tool for studies of leukemia and lymphomas (43,44).
2.13. Microarrays, Fluorescence Genotyping, and Other Molecular Approaches Many other molecular approaches have been developed for delineating chromosomal disorders and screening of submicroscopic genomic alterations. PCR-based microsatellite CA repeat analysis and methylation studies have been routinely used for detecting uniparental disomy and imprinting (45). Microsatellite markers have been utilized for a genome wide screening of chromosomal aberrations (46). A fluores-
cence-based genotyping technique has been recently developed for screening subtelomeric rearrangements (47). The techniques of tissue microarrays (48), array CGH (21,49), and c-DNA microarrays (22) are being rapidly developed and utilized in many areas of biomedical research, including molecular cytogenetic studies.
3.1. FISH for Structural Abnormalities The incidence of constitutional structural chromosome abnormalities which are visible at the level of 400 bands is approximately 1/200 at birth, including all balanced de novo, 1/1000; all balanced inherited, 1/400; all unbalanced de novo, 1/1000; and all unbalanced inherited, 1/2000 (50). While an inherited abnormality can usually be determined by its banding pattern and parental studies, FISH analysis is necessary for the identification and characterization of most unbalanced de novo structural rearrangements, including marker chromosomes. Numerous acquired aberrations which lead to gains or losses of chromosomal material have been described in leukemia, lymphomas, and solid tumors. It is important to know whether or not a particular chromosomal region or a particular gene is involved in a chromosomal aberration, so that a correct clinical diagnosis can be made and appropriate treatment initiated. In many cases, however, this may not be possible without FISH or other molecular studies. Chromosome painting (51–53), SKY (27–31), M-FISH (54), CGH (33,34), and color banding (37) have all been utilized in the studies of structural abnormalities in conjunction with G-banding analysis. In many cases, however, FISH with unique sequences is necessary to determine the involvement of a particular gene in a structural abnormality. An example is the rearrangement of the MLL gene in a translocation with a breakpoint at 11q23 in acute myeloid leukemia (55,56). Nevertheless, a comprehensive molecular cytogenetic approach may be necessary depending on the nature of the disease and the particular aberration (57–59).
3.2. FISH for Microdeletion Syndromes More than thirty microdeletion syndromes have been described in the past two decades (7,60). Williams, Prader-Willi/Angelman, Smith-Magenis, 22q11.2 deletion, and 1p36 deletion, are the most common microdeletion syndromes. These syndromes are usually caused by a deletion of a 2–4 Mb DNA sequence, undetectable by standard chromosome analysis. The term "contiguous gene syndrome" is also used to describe these disorders because the deleted chromosome segment may contain a number of functional genes. The deletion of 22q11.2 is associated with a number of syndromes and psychiatric illnesses including DiGeorge, velocardiofacial, conotruncal anomaly face syndromes, and an increased risk of schizophrenia. Recently, these disorders have been considered to represent varying expression of the same genetic defect (61). The prevalence of 22q11.2 deletion alone was estimated to be 1/4500 in the general population (62,63). The deletion of 1p36 is believed to be the second most common microdeletion, with an estimated incidence of >1/10,000 newborns (64). Thus, the overall incidence of microdeletion syndromes is likely in the range of 1/1000–2000
newborns, or higher given that the number of microdeletion syndromes described is growing, and that clinical recognition is difficult for many of these syndromes. With an assumed incidence of 1/1000, the risk for one individual to be affected with two different microdeletion syndromes is 1/1,000,000 or 1/106. Such a case has indeed been reported (65). With the improvement of the quality of chromosome preparation, the deletion of 17p11.2 in Smith-Magenis syndrome can be detected by G-banding analysis without difficulties (66). For the majority of microdeletion syndromes however, a definitive diagnosis cannot be made without FISH analysis. Studies of microdeletion syndromes have created new concepts such as uniparental disomy and genomic imprinting, and opened exciting areas in human and medical genetics research. In return, the knowledge obtained from research has led to a combined diagnostic approach for Prader-Willi and Angelman syndromes, i.e., conventional karyotyping to exclude structural abnormalities, FISH to detect microdeletion, and DNA testing for uniparental disomy or gene mutation (45). While the detection rate may vary in different laboratories, the data from our laboratory is shown here as an example of FISH utilization for the diagnosis of microdeletion syndromes. From 1996 to the end of 2000, a total of 550 blood samples were received for testing of common microdeletions. The diagnosis of a microdeletion syndrome was made in 59 of these cases (10.73%) by FISH, including 37/300 (12.33%) cases referred for 22q11.2 deletion, 10/167 (6%) for Prader-Willi/Angelman, 11/73 (15%) for Williams, and 1/10 (10%) for Miller-Dieker syndrome. FISH for SmithMagenis syndrome is performed in our laboratory only when the chromosomal finding is inconsistent with the clinical indication. Although 1p36 deletion has been considered to be the second most common microdeletion syndrome, no case has been referred to our laboratory for testing of this deletion. This may reflect the difficulties in the clinical recognition of such a syndrome, or simply the level of awareness of this syndrome among local clinicians.
3.3. Detection of Subtelomeric Aberrations in Patients with Unexplained Mental Retardation Genomic alterations in the subtelomeric regions appear to be an important cause of developmental disabilities (67). It was suggested that subtelomeric anomalies may be second only to Down syndrome as the most common cause of mental retardation (68). Patients with unexplained mental retardation or developmental disabilities have been studied by FISH with multiple subtelomeric probes. In an earlier large study reported by Knight et al. (69), subtelomeric aberrations were detected in 7.4% of patients with moderate to severe idiopathic mental retardation. Our recent study (70) and two other large reports (71,72) have estimated that the frequency of clinically significant subtelomeric aberrations is 3–5% in the study population. FISH with multiple subtelomeric probes has been considered to be a valuable tool for a definitive diagnosis of patients with unexplained mental and developmental disabilities (70).
3.4. Interphase FISH for Prenatal Diagnosis of the Common Aneuploidies Aneuploidies of chromosomes 13, 18, 21, X, and Y account for about 95% of the chromosomal aberrations causing live-born birth defects. Extensive studies have been done in the past 15 yr to establish, refine, and assess the techniques of interphase FISH prenatal diagnosis of these common aneuploidies with uncultured amniocytes (8,9,73,74). DNA probes and FISH protocols were commercially standardized in the late 1990s. The currently used AneuVysion assay kit (Vysis, Downers Grove, IL) includes two sets of multicolor probe mixtures, one for chromosomes 13 and 21, and the other for chromosomes 18, X, and Y. The standardized probes and protocols have been proven to be accurate and very sensitive for prenatal diagnosis of the most common aneuploidies. This technique is particularly valuable for high risk pregnancies as indicated by ultrasonography or maternal serum screening (75). Since 1998, our laboratory has routinely provided rapid interphase FISH prenatal diagnosis for patients with a high risk pregnancy noted at a late gestational age (≥ 20 wk), i.e., either a positive maternal serum screening for trisomy 18 or 21, or an abnormal ultrasound indicating a probable chromosomal anomaly. FISH was performed using AneuVysion assay kits and the results were reported to the referring physicians. Among the 196 cases studied, aneuploidies were detected in 30 cases (15.3%), including 12 cases with trisomy 21, 10 cases with trisomy 18, 2 cases with trisomy 13, 2 cases with 45, X, and 2 cases with triploidy. All FISH results were confirmed by conventional G-banding analysis which showed 100% accuracy and zero false positive/false negative result. It is strongly believed that interphase FISH prenatal diagnosis is very beneficial to this group of patients and should be routinely provided as a standard diagnostic tool.
3.5. Prenatal Diagnosis of Chromosomal Disorders Using Maternal Blood Fetal nucleated red blood cells which pass into the maternal circulation during pregnancy provide a cell source for noninvasive prenatal genetic diagnosis. Cytogenetic analysis of fetal cells by FISH is a potentially useful method for prenatal diagnosis of chromosomal disorders, but requires relatively pure samples of fetal cells isolated from maternal blood (76). Many methods including density gradient centrifugation, magnetic activated cell sorting, fetal cell culture, and immunocytochemical staining have been developed for the isolation, enrichment and identification of fetal cells (77–80). Currently, noninvasive prenatal genetic diagnosis is still in the investigational phase. However, an approach of combined cell sorting, immunophenotyping, and FISH appears to improve the sensitivity and specificity of the methods, and thus offers new promise to the future of noninvasive prenatal genetic testing (81).
3.6. Preimplantation Diagnosis of the Common Aneuploidies Preimplantation diagnosis is a prepregnancy genetic test for in vitro fertilization (IVF) patients. A large proportion of patients undergoing IVF are at the age of ≥35 yr. It was
estimated in this group that about 50% of embryos are chromosomally abnormal with aneuploidy being the major contributor (82). Since most aneuploidies arise as the products of a maternal meiosis I non-disjunction, they can be detected by FISH analysis on the first and/or second polar bodies removed from oocytes following maturation and fertilization. DNA probes for chromosomes 13, 18, and 21 have been used most commonly for FISH studies on polar bodies (82–85). Many other chromosomes have been tested on single blastomeres biopsied from embryos at an early stage of development (d 3 [86–88]). Preimplantation diagnosis of aneuploidies has provided an accurate and reliable approach for the prevention of age-related aneuploidies in IVF patients with advanced maternal age (84,85). Selecting embryos with a normal chromosome complement can also improve the implantation rate in patients with advanced age or carriers of an altered karyotype (88).
3.7. Studies of Mosaicism and Its Effect on Early Human Development The recent molecular cytogenetic studies of chromosomal mosaicism and its effect on early human development represent a very interesting area of research. Constitutional mosaicism is the result of postfertilization mitotic error, i.e, a somatic event. Two types of mosaicism, meiotic and somatic, have been defined by molecular studies in determining the origin of the extra chromosome in the trisomic cell line. While meiotic mosaicism refers to the occurrence of a mitotic error producing a diploid cell line in a trisomic conception, somatic mosaicism means a trisomic cell line occurred in a conception which was initially diploid (89). Other terms, such as generalized vs confined mosaicism, are also commonly used. A generalized mosaicism involves all cell lineages of the conceptus, including both the placenta and the embryonic/fetal tissues. A mosaicism when occurred only in the placenta is called confined placenta mosaicism. Studies using FISH, CGH, and other molecular techniques have facilitated our understanding of the biological and clinical significance of chromosomal mosaicism in early embryonic/fetal development (89–92).
3.8. Detection of Specific Translocations and Gene Rearrangements in Human Cancer Over 100 recurrent chromosomal translocations in hematologic neoplasms, malignant lymphomas, and solid tumors have been identified, and rearrangement of a specific gene is known in most of these translocations (93). FISH has been a powerful tool in the characterization of these translocations. Clinically, the identification of specific chromosomal translocations and gene rearrangements is not only diagnostic, but also important for determining a therapy plan, monitoring treatment, and predicting prognosis. For patients with chronic myeloid leukemia, it has been shown that interphase FISH is highly sensitive in detecting the BCR/ABL fusion, and therefore is very useful for following patient's response to therapy (94–96). FISH is necessary to detect involvement of specific genes in many cases of acute leukemia, for example, the involvement of the MLL gene in an 11q23 rearrangement (55,56), and the TEL/AML1 fusion in childhood acute lymphoblastic leukemia (97,98). FISH probes for several rearranged genes in non-Hodgkin lymphomas are now commercially available. The
technique of interphase FISH detection of the BCL2 rearrangement in follicular lymphoma using breakpoint-flanking probes has shown advantages over the standard PCR method (99). Many specific chromosomal and gene rearrangements have been characterized in solid tumors. These rearrangements, for example, the translocation t(X;18)(p11.2;q11.2) in synovial sarcoma and the EWS/FLI1 fusion in Ewing sarcoma/ peripheral primitive neuroectodermal tumor, can be detected by dual color interphase FISH in formalin-fixed, paraffin-embedded tumor tissues (100,101). It is apparent that interphase FISH detection of specific gene rearrangements in solid tumors has potential value for diagnosis and treatment, but an expanded variety of FISH probes needs to be made commercially available to clinical laboratories.
3.9. Analysis of Gains and Losses of Chromosomes or Chromosomal Regions in Tumors Conventional cytogenetic studies of solid tumors were hampered due to the difficulties of cell culture and chromosome preparation, as well as the complexity of their genomic alterations. With the interphase FISH approach, however, chromosomal aneuploidies can be detected without cell culturing in virtually any given tissue or cell source, such as touch preparations, sections of frozen tumor, and paraffin-embedded tissue (102,103). Similarly, almost all types of clinical specimens can be used for CGH studies of tumors (33). Many reports have shown gains or losses of individual chromosomes or chromosome regions correlating with particular tumors, different stages of the tumor, and the prognosis of patients (104–107). These studies have yielded extremely important information for our understanding of the biologic behavior of solid tumors.
3.10. Testing Deletion of Tumor Suppressor Genes and Amplification of Oncogenes Deletion of tumor suppressor genes, such as p53 and RB-1, and amplification of oncogenes, such as N-myc, C-myc, and HER-2/neu, can be detected by FISH or CGH studies of tumor tissues. FISH has provided reliable estimates of N-myc amplification in neuroblastoma. FISH also has advantages over Southern blot analysis in terms of speed, technical simplicity, ability to discern heterogeneous gene amplification among tumor cells in the same specimen, and capacity to determine the source of the amplified N-myc signals (108). The interphase FISH method has been considered to be more accurate than the Southern blot method in detecting N-myc amplification when the number of cells with N-myc amplification is low, or when intra-tumor heterogeneity is present (109). In addition, FISH has also shown a strong correlation between 1p abnormalities and N-myc amplification (110). Amplification of C-myc has been detected by FISH in many different types of tumors, including medulloblastoma, malignant melanoma, lung cancer, nasopharyngeal carcinoma, ovarian cancer, and prostate cancer. Testing of the HER-2/neu (also known as erbB-2) gene in breast cancer has become very important for patient management owing to its association with more aggressive clinical and pathologic features. Amplification and/or overexpression of HER-2/neu can be assessed by either FISH, PCR, or immunohistochemistry. The
methods of immunohistochemistry and FISH have been compared in recent studies (111–116), and a combined approach has been suggested to make the test more sensitive and cost-effective (114–116). The status of many other oncogenes have been tested in human cancers, and amplifications of multiple oncogenes are known in some tumors. While the changes in copy number of multiple oncogenes can be simultaneously tested using CGH microarrays (21,49), a large number of tumor tissue specimens can be rapidly analyzed with FISH performed on consecutive tissue microarray sections (48).
3.11. Genome-wide Screening for Constitutional and Acquired Alterations As mentioned above, unbalanced constitutional or somatically acquired alterations can be screened by CGH in a single experiment, but the resolution is limited. The technique of array CGH has provided a high resolution screening method for DNA copy number changes (21). A cDNA microarray-based CGH method has also been developed to identify gene amplifications and deletions genome-wide (22). In a very recent report, the use of array CGH has achieved a resolution of approx 1 Mb in the analysis of the genome and demonstrated its sensitivity of detecting single copy gains and losses (49). Submicroscopic chromosomal aberrations can also be screened using genome-wide microsatellite markers (46). Automated fluorescent genotyping using microsatellites has been shown to be a very sensitive method for screening cryptic rearrangements of the telomeric regions (47).
4. Standards and Guidelines for Clinical Applications It is necessary that all cytogenetics laboratories have their protocols and standards established for the clinical applications of molecular cytogenetic techniques according to the guidelines provided by professional organizations. It is also important that the standards and guidelines be updated as new technologies evolve and the data on their clinical applications accumulates. In North America, the guiding principles of genetic testing have been provided by the American Society of Human Genetics (ASHG), the American College of Medical Genetics (ACMG), and the Canadian College of Medical Geneticists (CCMG). In 1993, the ACMG recognized prenatal interphase FISH to be of diagnostic potential when the investigational nature of testing was stressed (117). The guidelines, including clinical indications, requirements of test validation, analysis standards, and reporting of FISH studies, were provided by the ACMG in 1996 (118), and were updated in 1999 (119). In 1997, the CCMG also provided guiding principles for clinical applications of FISH technology to Canadian cytogenetics laboratories (120), which were basically consistent with the ACMG policies. A Joint ASHG/ACMG Test and Technology Transfer Committee published a report on diagnostic testing for Prader-Willi and Angelman syndromes with recommended testing approaches including FISH in 1996 (45). Recently, the same committee published the first part of an ACMG/ASHG position statement on technical and clinical assessment of FISH (121). It was recommended in this statement that:
"FISH testing be considered a highly useful and accurate test for the diagnosis of microdeletions and for the identification of unknown material in the genome. In disorders in which FISH testing provides results not possible from standard cytogenetic testing, the testing is standalone and should be accepted as such."
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Labeling FISH Probes for DNA Targets
2 Labeling Fluorescence In Situ Hybridization Probes for Genomic Targets Larry E. Morrison, Ramesh Ramakrishnan, Teresa M. Ruffalo, and Kim A. Wilber 1. Introduction Fluorescence in situ hybridization (FISH) requires nucleic acid probes, including deoxyribonucleic acid (DNA), ribonucleic acid (RNA), or nucleic acid analogs, labeled directly with fluorophores, or capable of indirect association with fluorophores. The nucleic acid provides the FISH assay with its specificity through complementary pairing of the probe nucleotides with nucleotides of the target nucleic acid. The appended fluorophores provide the ability to visually detect the homologous regions within the cellular structure using a fluorescence microscope. Photographic or electronic cameras can also be used to provide permanent images of the fluorescence staining patterns, and the latter can be used to provide quantitative measurements of the probe fluorescence. This chapter describes a variety of methods by which DNA can be coupled to fluorophores to form FISH probes directed toward genomic targets. Following a brief discussion of labeling methodologies, fluorophore selection, and sources of probe DNA, a number of detailed protocols are provided that describe both enzymatic and chemical labeling of FISH probes.
1.1. Direct and Indirect Fluorophore Labeling Fluorophores can be associated with nucleic acid probes by chemical conjugation to the nucleic acid, or by chemical conjugation of the nucleic acid with a nonfluorescent molecule that can bind fluorescent material after hybridization. The former method is called "direct labeling" and the latter method is called "indirect labeling." In indirect labeling, the molecule directly attached to the nucleic acid probe is typically either biotin or a hapten, such as dinitrophenol (DNP) or digoxigenin. The in situ hybridization is performed with the hapten- or biotin-labeled probe, after which the specimen is incubated with fluorophore-labeled antibody or avidin. Because a number of From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
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fluorophores can be attached to each antibody or avidin molecule, the indirect method allows for the association of multiple fluorophores with each directly attached binding moiety. Furthermore, additional rounds of antibody binding, sometimes referred to as "sandwiching," can be utilized to further increase the number of bound fluorophores. For example, if goat IgG anti-DNP was used to bind to DNP-labeled probes, then fluorophore-labeled anti-goat IgG can be used to amplify the signal in a second round of indirect labeling. In addition to binding multiple rounds of avidin and/or antibody secondary reagents, the amount of fluorescence staining can be increased using enzyme conjugates of avidin or antibodies. For enzyme conjugates to be effective in FISH, fluorescent products of the enzymatic reaction must remain localized near the site of probe binding. Two approaches to dye localization include the generation of a precipitating fluorescent product (ELF reagent, Molecular Probes, Inc., Eugene, OR) (1–3), and generation of highly reactive fluorescent compounds that covalently attach to neighboring cellular material (CARD/TSA system, NEN, Boston, MA) (4–6). While indirect labeling has the potential for generating greater fluorescence signal, it also has the disadvantage of requiring additional incubation steps to bind the antibody and avidin reagents. The introduction of fluorescent antibodies also can increase the background fluorescence owing to nonspecific binding of the antibodies and avidin proteins to extraneous cellular material on the microscope slide, and the slide surface itself. Furthermore, when multicolor FISH is utilized to simultaneously identify several different genomic targets, a different, spectrally distinct fluorophore must be used to unambiguously identify each of the targets. For direct-labeled probes, this means finding N spectrally distinct fluorescent labels to identify N different targets. For indirect-labeled probes this means not only selecting N different labels, but also finding N different binding pairs (hapten-antibody or biotin-avidin pairs) for binding each of the N fluorescent labels. For very small genomic targets, for example, targets less than 70 kilobases (kb), indirect labeling may be required to achieve visually interpretable staining. However, larger targets are usually detectable using direct labeling alone. For research applications where probes or particular targets may be used infrequently or are under initial investigation, individual laboratories may opt for small target probes, such as plasmid or cosmid clones, for which indirect labeling may be a necessity. However, with the availability of bacterial artificial chromosome (BAC) libraries generated in connection with the Human Genome Project, large target probes can be easily generated and discerned with little difficulty when directly labeled.
1.2. Survey of Nucleic Acid Labeling Chemistry For either direct- or indirect-labeling, the probe nucleic acid must be modified to attach a fluorophore, biotin, or hapten. Both chemical and enzymatic reactions have been used for this purpose. Early fluorescence in situ hybridization was performed with a chemically modified probe, using periodate oxidation of a 3'-terminal ribonucleotide to form the dialdehyde, coupled in turn with a hydrazine derivative of fluorescein (7). Biotin or a hapten could presumably be added by this same chemistry,
however, the chemistry is restricted to RNA probes or DNA probes to which a 3'-terminal ribonucleotide has been added, using terminal transferase, for example. Other chemical modifications reported for in situ hybridization probes include a reaction to introduce the hapten aminoacetylfluorene (AAF) (8–12), and mercuration (13). Mercurated probes are reacted post hybridization with a bifunctional molecule containing the detection moiety and a thiol group (14,15). A convenient method of chemical labeling that is described in more detail below uses platinum complexes (16). In this method, the detection moiety is derivatized to form a coordinating ligand of a platinum complex. The labeled complex is further reacted with nucleic acid resulting in the formation of a coordinate covalent bond between the platinum and primarily guanine residues of the nucleic acid. Other chemistries employed in labeling hybridization probes include, bisulfite mediated transamination of cytosine (17,18), photochemical reaction with photobiotin (19), bromination of thymine, guanine, and cytosine with N-bromosuccinimide; followed by reaction with amine-containing detection moieties (20), and condensation of terminal phosphate groups with diamines, followed by coupling with amine reactive detection moieties (21,22). Enzymatic reactions, especially those using polymerases to incorporate labeled nucleoside triphosphates, have been the most popular means of labeling nucleic acids by far. Of these, nick translation to incorporate biotinylated nucleoside triphosphates is the oldest and most frequently used method (23–25). Other haptens incorporated by this method include dinitrophenol (26), digoxigenin (27), and fluorescein (28). In addition to being used as an indirect label with anti-fluorescein antibodies, fluorescein incorporated by nick translation has been used for directly detected probes (26,28). A variety of fluorophores are now commercially available that can be incorporated by polymerases for directly detected FISH (e.g., from Molecular Probes Inc., Eugene, OR; New England Nuclear, Boston, MA; or Vysis, Inc., Downers Grove, IL). In addition to nick translation, DNA polymerases have been used to incorporate labeled nucleoside triphosphates into FISH probes by PCR. This has included PCR with flanking primers that amplify DNA inserts within plasmids (29), as well as PCR with random and degenerate (30) primers. Examples of these important enzymatic labeling protocols are provided below. (See Subheadings 3.1.–3.3.). Note that in situ hybridization probes perform best when the probe lengths are 40 mM) or EDTA (>5 mM), Mg acetate (>100 mM), NaCl (>100 mM), and restriction enzyme digestion buffers should be avoided because of their rate-limiting effect on the labeling reaction. 18. The molar excess of reactive fluorophore-to-protein, and the protein concentration will determine the extent of protein labeling. The labeling ratio required for optimal perfor-
mance of the labeled protein reagent will depend upon which fluorophore and protein are used, and will need to be determined experimentally. Too low a labeling ratio results in weak fluorescence signals, while too high a ratio can inhibit the specific protein binding reaction and increase nonspecific binding. 19. The amount of 20 mM fluorophore solution added to the protein should not result in the organic solvent concentration exceeding 20% of the total reaction volume, necessary to prevent denaturation of the protein. 20. As an alternative to gel permeation chromatography, the unconjugated fluorophore can be separated from the protein by dialyzing in TBS or PBS, changing the buffer solution at several hour intervals until the dye color is no longer imparted to the buffer. 21. Alternative protein labeling protocols abound in the literature and are available from suppliers of labeling reagents (e.g., see the "Amine-Reactive Probes" information sheet from Molecular Probes, Inc., or "Procedure for Labeling Proteins with Fluorochromes" by Research Organics, Cleveland, OH).
References 1. Bueno, D., Skinner, J., Abud, H., and Heath, J. K. (1996) Double in situ hybridization on mouse embryos for detection of overlapping regions of gene expression. Trends Genet. 12, 385–387. 2. Diwu, Z., Klaubert, D. H., and Haugland, R. P. (1999) Spectral properties and biological applications of ELF enzyme substrates that generate bright fluorescent precipitates at the enzymatic activity sites. Proc. SPIE-Intl. Soc. Opt. Eng. 3602, 265. 3. Jowett, T. and Yan, Y. L. (1996) Double fluorescent in situ hybridization to zebrafish embryos. Trends Genet. 12, 387–389. 4. Bobrow, M. N., Harris, T. D., Shaughnessy, K. J., and Litt, G. J. (1989) Catalyzed reporter deposition, a novel method of signal amplification. Application to immunoassays. J. Immunol. Methods 125, 279–285. 5. Raap, A. K., Van De Corput, M. P., Vervenne, R. A., Van Gijlswijk, R. P., Tanke, H. J., and Wiegant, J. (1995) Ultra-sensitive FISH using peroxidase-mediated deposition of biotin- or fluorochrome tyramides. Hum. Mol. Genet. 4, 529–534. 6. Speel, E. J., Ramaekers, F. C., and Hopman, A. H. (1997) Sensitive multicolor fluorescence in situ hybridization using catalyzed reporter deposition (CARD) amplification. J. Histochem. Cytochem. 45, 1439–1446. 7. Bauman, J. G., and Van Duijn, P. (1981) Hybrido-cytochemical localization of specific DNA sequences by fluorescence microscopy. Histochem. J. 13, 723–733. 8. Cremer, T., Landegent, J., Bruckner, A., et al. (1986) Detection of chromosome aberrations in the human interphase nucleus by visualization of specific target DNAs with radioactive and nonradioactive in situ hybridization techniques: Diagnosis of trisomy 18 with probe L1.84. Hum. Genet. 74, 346–352. 9. Cremer, T., Tesin, D., Hopman, A. H., and Manuelidis, L. (1988) Rapid interphase and metaphase assessment of specific chromosomal changes in neuroectodermal tumor cells by in situ hybridization with chemically modified DNA probes. Exp. Cell Res. 176, 199–220. 10. Landegent, J. E., Jasen in De Wal, N., Baan, R. A., Hoeijmakers, J. H., and Van Der Ploeg, M. (1984) 2-Acetylaminofluorene-modified probes for the indirect hybridocytochemical detection of specific nucleic acid sequences. Exp. Cell Res. 153, 61–72. 11. Nederlof, P. M., Robinson, D., Abuknesha, R., et al. (1989) Three-color fluorescence in situ hybridization for the simultaneous detection of multiple nucleic acid sequences. Cytometry 10, 20–27.
12. Nederlof, P. M., Van Der Flier, S., Wiegant, J., et al. (1990) Multiple fluorescence in situ hybridization. Cytometry 11, 126–131. 13. Dale, R. M. and Ward, D. C. (1975) Mercurated polynucleotides: New probes for hybridization and selective polymer fractionation. Biochemistry 14, 2458–2469. 14. Hopman, A. H., Wiegant, J., Tesser, G. I., and Van Duijn, P. (1986) A nonradioactive in situ hybridization method based on mercurated nucleic acid probes and sulfhydryl-hapten ligands. Nucl. Acids Res. 14, 6471–6488. 15. Hopman, A. H., Wiegant, J., and Van Duijn, P. (1987) Mercurated nucleic acid probes, a new principle for nonradioactive in situ hybridization. Exp. Cell Res. 169, 357–368. 16. Van Belkum, A., Linkels, E., Jelsma, T., Van Den Berg, F. M., and Quint, W. (1994) Nonisotopic labeling of DNA by newly developed hapten-containing platinum compounds. Biotechniques 16, 148–153. 17. Draper, D. E. (1984) Attachment of reporter groups to specific, selected cytidine residues in RNA using a bisulfite-catalyzed transamination reaction. Nucl. Acids Res. 12, 989–1002. 18. Reisfeld, A., Rothenberg, J. M., Bayer, E. A., and Wilchek, M. (1987) Nonradioactive hybridization probes prepared by the reaction of biotin hydrazide with DNA. Biochem. Biophys. Res. Commun. 142, 519–526. 19. Keller, G. H., Huang, D. P., and Manak, M. M. (1989) Labeling of DNA probes with a photoactivatable hapten. Anal. Biochem. 177, 392–395. 20. Keller, G. H., Cumming, C. U., Huang, D. P., Manak, M. M., and Ting, R. (1988) A chemical method for introducing haptens onto DNA probes. Anal. Biochem. 170, 441–450. 21. Chu, B. C., Wahl, G. M., and Orgel, L. E. (1983) Derivatization of unprotected polynucleotides. Nucl. Acids Res. 11, 6513–6529. 22. Morrison, L. E., Halder, T. C., and Stols, L. M. (1989) Solution-phase detection of polynucleotides using interacting fluorescent labels and competitive hybridization. Anal. Biochem. 183, 231–244. 23. Langer, P. R., Waldrop, A. A., and Ward, D. C. (1981) Enzymatic synthesis of biotinlabeled polynucleotides: novel nucleic acid affinity probes. Proc. Natl. Acad. Sci. USA 78, 6633–6637. 24. Langer-Safer, P. R., Levine, M., and Ward, D. C. (1982) Immunological method for mapping genes on Drosophila polytene chromosomes. Proc. Natl. Acad. Sci. USA 79, 4381–4385. 25. Manuelidis, L., Langer-Safer, P. R., and Ward, D. C. (1982) High-resolution mapping of satellite DNA using biotin-labeled DNA probes. J. Cell. Biol. 95, 619–625. 26. Ried, T., Landes, G., Dackowski, W., Klinger, K., and Ward, D. C. (1992) Multicolor fluorescence in situ hybridization for the simultaneous detection of probe sets for chromosomes 13, 18, 21, X and Y in uncultured amniotic fluid cells. Hum. Mol. Genet. 1, 307–313. 27. Arnoldus, E. P., Wiegant, J., Noordermeer, I. A., et al. (1990) Detection of the Philadelphia chromosome in interphase nuclei. Cytogenet. Cell. Genet. 54, 108–111. 28. Wiegant, J., Ried, T., Nederlof, P. M., Van Der Ploeg, M., Tanke, H. J., and Raap, A. K. (1991) In situ hybridization with fluoresceinated DNA. Nucl. Acids Res. 19, 3237–3241. 29. Ried, T., Baldini, A., Rand, T. C., and Ward, D. C. (1992) Simultaneous visualization of seven different DNA probes by in situ hybridization using combinatorial fluorescence and digital imaging microscopy. Proc. Natl. Acad. Sci. USA 89, 1388–1392. 30. Telenius, H., Pelmear, A. H., Tunnacliffe, A., et al. (1992) Cytogenetic analysis by chromosome painting using DOP-PCR amplified flow-sorted chromosomes. Genes Chromosomes Cancer 4, 257–263.
31. Morrison, L. E. and Legator, M. S. (1999) Multi-color fluorescence in situ hybridizations techniques, in An Introduction to Fluorescence in situ Hybridization: Principles and Clinical Applications (Andreeff, M. and Pinkel, D., eds.), Wiley-Liss, New York, pp. 77–118. 32. Sambrook, J., Fritsch, E. F., and Maniatis, T. (1989) Molecular Cloning, A Laboratory Manual. 2nd ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor. 33. Collins, C., Kuo, W. L., Segraves, R., Fuscoe, J., Pinkel, D., and Gray, J. W. (1991) Construction and characterization of plasmid libraries enriched in sequences from single human chromosomes. Genomics 11, 997–1006. 34. Deaven, L. L., Van Dilla, M. A., Bartholdi, M. F., et al. (1986) Construction of human chromosome-specific DNA libraries from flow-sorted chromosomes. Cold Spring Harb. Symp. Quant. Biol. 51, 159–167. 35. Carter, N. P., Ferguson-Smith, M. A., Perryman, M. T., et al. (1992) Reverse chromosome painting: A method for the rapid analysis of aberrant chromosomes in clinical cytogenetics. J. Med. Genet. 29, 299–307. 36. Telenius, H., De Vos, D., Blennow, E., Willat, L. R., Ponder, B. A., and Carter, N. P. (1993) Chromatid contamination can impair the purity of flow sorted metaphase chromosomes. Cytometry 14, 97–101. 37. Guan, X. Y., Meltzer, P. S., and Trent, J. M. (1994) Rapid generation of whole chromosome painting probes (WCPs) by chromosome microdissection. Genomics 22, 101–107. 38. Telenius, H., Carter, N. P., Bebb, C. E., Nordenskjold, M., Ponder, B. A., and Tunnacliffe, A. (1992) Degenerate oligonucleotide-primed PCR: General amplification of target DNA by a single degenerate primer. Genomics 13, 718–725. 39. Cherif, D., Bernard, O., and Berger, R. (1989) Detection of single-copy genes by nonisotopic in situ hybridization on human chromosomes. Hum. Genet. 81, 358–362. 40. Kelly, R. B., Cozzarelli, N. R., Deutscher, M. P., Lehman, I. R., and Kornberg, A. (1970) Enzymatic synthesis of deoxyribonucleic acid. XXXII. Replication of duplex deoxyribonucleic acid by polymerase at a single strand break. J. Biol. Chem. 245, 39–45. 41. Feinberg, A. P. and Vogelstein, B. (1983) A technique for radiolabeling DNA restriction endonuclease fragments to high specific activity. Anal. Biochem. 132, 6–13. 42. Feinberg, A. P. and Vogelstein, B. (1984) A technique for radiolabeling DNA restriction endonuclease fragments to high specific activity. Addendum. Anal. Biochem. 137, 266–267. 43. Speicher, M. R., Gwyn Ballard, S., and Ward, D. C. (1996) Karyotyping human chromosomes by combinatorial multi-fluor FISH. Nat. Genet. 12, 368–375. 44. Schrock, E., Du Manoir, S., Veldman, T., et al. (1996) Multicolor spectral karyotyping of human chromosomes. Science 273, 494–497. 45. Morrison, L., Legator, M., Ramakrishnan, R., Zimmerman, D., Volling-Kwasneski, M., and Koeppen, P. (1998) FISH karyotyping with combinations of whole chromosome probes directly labeled with five visible fluorescent labels. Cytometry Supplement 9, 150. 46. Morrison, L. E. (1995) Detection of energy transfer and fluorescence quenching, in Nonisotopic probing, blotting, and sequencing (Kricka, L. J., ed.), Academic Press, San Diego, pp. 429–471. 47. Van Belkum, A., Linkels, E., Jelsma, T., Houthoff, H. J., Van Den Berg, F., and Quint, W. (1993) Application of a new, universal DNA labeling system in the PCR mediated diagnoses of Chlamydia trachomatis and human papillomavirus type 16 infection in cervical smears. J. Virol. Methods 45, 189–200. 48. Garvey, J. S., Cremer, N. E., and Sussdorf, D. H. (1977) Methods in Immunology: A Laboratory Text for Instruction and Research. 3rd ed. W. A. Benjamin, Inc., Reading, PA. 49. Morrison, L. E. (1988) Time-resolved detection of energy transfer: Theory and application to immunoassays. Anal. Biochem. 174, 101–120.
Labeling FISH Probes for RNA Targets
3 Labeling Fluorescence In Situ Hybridization Probes for RNA Targets Ramesh Ramakrishnan and Larry E. Morrison 1. Introduction Ribonucleic acids (RNA) can be detected in cellular specimens by fluorescence in situ hybridization (FISH) using labeled RNA, deoxyribonucleic acid (DNA), or nucleic acids analogs. The RNA targets are often messenger RNA (mRNA) molecules that have been transcribed from the genomic DNA. Specific mRNA sequences can be selectively identified out of the many co-expressed mRNA molecules owing to the high specificity of nucleic acid base pairing. The analysis of selected mRNA sequences is an important measure of many cellular properties, including, for example, the identification of specific cell types, the identification of different stages of cell differentiation, and measuring abnormal mRNA expression, as often accompanies cancer development. RNA probes can be directly conjugated with fluorescent labels, or conjugated with labels that specifically associate with fluorescent compounds. Once hybridized, the presence and relative abundance of an RNA target can be qualitatively assessed visually based on the fluorescence intensity, or in a more quantitative fashion, by digital imaging and image analysis. Much of what is stated about genomic FISH probes in the preceeding chapter is also applicable to FISH probes for RNA targets, including statements related to direct and indirect labeling, amplified detection reactions, and fluorescent label selection. Since DNA probes are often used for RNA detection, DNA probe labeling methods described in the preceding chapter may also be employed in making DNA probes for mRNA detection. In addition to the methods described in the preceding chapter, some enzymatic labeling reactions are unique to working with RNA. Reverse transcriptase can be used to incorporate labeled nucleoside triphosphates into DNA using an RNA template (1–4), and RNA polymerase can be used to incorporate labeled nucleoside triphosphates into RNA strands (5–8). From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
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Synthetic oligonucleotides are more easily applied to RNA detection because many copies of an mRNA molecule are synthesized in vivo, in contrast to the diploid nature of the genomic DNA. Synthetic oligonucleotides, including DNA, RNA, and analogs such as peptide nucleic acids (PNA) can be synthesized relatively inexpensively and can have any of a number of different fluorophores incorporated terminally or attached to internal sites during the oligomer synthesis process. The following protocols provide some common methods for labeling probes used to detect RNA targets via FISH. Owing to the ease of obtaining synthetic oligonucleotides, the methods presented here are entirely enzymatic, relying on reverse transcriptase, DNA polymerase I, and RNA polymerase.
1.1. Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) The first method described below generates fluorophore or hapten labeled DNA probes to RNA transcripts using the technique of RT-PCR (9,10). The process involves an initial reverse transcriptase reaction, using either random hexamer primers, or degenerate oligonucleotide primers (DOP), as described in the preceding chapter, resulting in single-stranded cDNA. Double stranded cDNA is generated using E. coli DNA polymerase I, followed by an amplification using Taq polymerase and either the same degenerate DOP primers, or transcript-specific PCR primers.
1.2. Single-Stranded Probes It is important to be able to generate single-strand-specific probes (antisense sequences) when using FISH to detect mRNA transcripts. Although double-stranded probes can, and are, used in many FISH applications for detection of transcripts in cells, there are two major reasons to prefer the single-stranded variety. The first reason is that although double-stranded probe can be denatured before hybridization, the solution-phase kinetics of reannealing is considerably faster than that of probe hybridizing to surface-immobilized target sequences. This results in a large portion of probe being titrated out of the hybridization mix, even before encountering the target. The second reason is that the use of the sense probe serves as an excellent negative control for the FISH assay, since its complementary sequence should not be present in the mRNA population to be studied. There are a number of different methods for generating single-stranded probes for use in FISH. In Subheading 1.2.1. is described a method for generating single-stranded DNA probes, as well as, a method for generating antisense and sense RNA probes. Both of the methods make the assumption that the specific sequence of interest is available as a clone, or as part of a cDNA library.
1.2.1. Single-Stranded DNA Probes—Asymmetric PCR The first method involves altering the conditions of PCR such that one of the strands is preferentially synthesized. This technique is referred to as asymmetric PCR (11,12), and involves performing the assay with one of the primers (complementary to the desired single strand) in vast excess to the other, "limiting" primer. Primer ratios normally range from 50:1 to 100:1. For the first few cycles (normally 10–15), doublestranded DNA is predominantly produced in an exponential manner. As the limiting
primer is depleted, an excess of one strand is produced, in a linear fashion. Consequently, about 40 cycles of PCR are required to generate adequate amounts of singlestranded probe. By switching the ratios of the primers, it is possible to generate single-stranded probe to each strand in separate reactions. A method is described below for the generation of single-stranded DNA probes to the human HLA-G mRNA sequence.
1.2.2. Single-Stranded RNA Probes The second method involves attaching specific viral RNA polymerase promoter sequences to the 5' end of each sequence of interest. RNA polymerases are very sequence-specific. When the hybrid DNA molecule is transcribed in vitro in the presence of fluorescent ribonucleoside triphosphates, specific single-stranded cRNA molecules of high specific activity are generated. Different RNA polymerase promoter sequences (for example, T7 or SP6) can be attached to either end of the DNA molecule. By performing separate in vitro transcription reactions in the presence of the appropriate RNA polymerase, specific single-stranded transcripts to each strand (sense or anti-sense) can be generated. The in vitro transcription reaction typically results in a 50–100-fold linear amplification of the sequence of interest, in the presence of fluorescent ribonucleotides. A method is described below for the generation of singlestranded sense and antisense RNA probes to the human HLA-G mRNA sequence.
1.3. In Situ Reverse Transcriptase PCR (In Situ RT-PCR) In situ hybridization is limited in sensitivity when low levels of nucleic acid are involved. In situ PCR (13–15) and in situ RT-PCR (16,17) can be used to localize DNA or RNA respectively, in appropriately prepared tissue samples. Below is described an in situ technique to detect HSV-1 RNA on selected sections from latently infected rat trigeminal ganglia or cortical neurons (16,17). Specific oligonucleotide primers to the HSV-1 glycoprotein B (gB) gene and digoxigenin-labeled nucleotides are used to produce amplified digoxigenin-labeled DNAs in situ, which are localized using an alkaline phosphatase-conjugated anti-digoxigenin antibody detected with the BCIP/NBT. Neurons in infected trigeminal ganglia as well as cortical neurons containing HSV-1 transcripts have been identified using this method (16,17).
2. Materials 2.1. RT PCR 1. 10X PCR buffer I (Applied Biosystems, Foster City, CA). 2. PCR assay buffer: 10 µL of 10X PCR Buffer I, 2 µL dNTPs (10 mM each), 1 µL of primer (100 ng), 1 µL Taq polymerase, and nuclease-free water to 100 µL. 3. Deoxynucleoside triphosphates: 10 mM each (Promega Corp., Madison, WI). 4. PCR Labeling Buffer: same as PCR Assay Buffer, with addition of 1 µL of SpectrumOrange™ or SpectrumGreen™ dUTP, except the final volume is 99 µL. 5. 100 ng/µL primer (random hexamer (Promega Corp.) or DOP-PCR primer). 6. 50 nmol SpectrumOrange™/SpectrumGreen™ 2'-deoxyuridine-5'-triphosphate (Vysis, Inc., Downers Grove, IL) Reconstitute with 50 µL of nuclease-free water to give a 1 mM solution. Stable for up to 3 mo if stored at –20°C.
7. Taq polymerase: any commercial variety available can be used, but optimal concentration to be used must be first determined by titrating with appropriate substrate. 8. RNasin 40 U/µL (Promega Corp.). 9. Reverse Transcriptase: Superscript II at 200 U/µL (Gibco-BRL, Gaithersburg, MD). 10. 5X First strand buffer (Gibco-BRL). 11. E. coli DNA polymerase I–10 U/µL, (Gibco-BRL). 12. 0.1 M dithiothreitol (DTT). 13. RNase H—2 U/µL (Gibco-BRL). 14. 5× Second strand buffer (Gibco-BRL). 15. Glycogen: molecular biology grade, 5 mg/mL (Promega Corp.). 16. 5 M Ammonium acetate, (Sigma Chemical Co., St. Louis, MO). 17. Isopropanol: absolute, (Aldrich Chemical Co., Milwaukee, WI). 18. 70% Ethyl alcohol. 19. Nuclease-free water. 20. Mineral oil (if necessary), light white (Sigma Chemical Co.). 21. NuSieve GTG agarose (FMC BioProducts, Rockland, ME). 22. 1X Tris-borate buffer (TBE): 45 mM Tris-borate, 1 mM EDTA, pH 8.0, for gel electrophoresis (BioRad, Hercules, CA).
2.2. Asymmetric PCR 2.2.1. Buffers and Enzymes 1. 10X PCR buffer I (Perkin-Elmer Applied Biosystems, Foster City, CA). 2. PCR assay buffer: 10 µL of 10X PCR Buffer I, 1 µL dNTPs (10 mM each), primer pair (concentration as below), 1 µL of SpectrumOrange™ or SpectrumGreen™ dUTP (Vysis, Inc., Downers Grove, IL), 3 U of Taq polymerase, nuclease-free water to 99 µL. 3. 50 pmol of "excess" primer. 4. 1 pmol of "limiting" primer. 5. SpectrumOrange™/SpectrumGreen™ 2'-deoxyuridine-5'-triphosphate (Vysis, Inc.): reconstitute with 50 µL of nuclease-free water to give a 1 mM solution. Stable for up to 3 mo if stored at –20°C. 6. Taq polymerase: any commercial variety available can be used. 7. Nuclease-free water. 8. Mineral oil (if necessary): light white (Sigma Chemical Co., St. Louis, MO). 9. NuSieve GTG agarose (FMC BioProducts, Rockland, ME). 10. 1X Tris-borate buffer (TBE): 45 mM Tris-borate, 1 mM EDTA, pH 8.0, for gel electrophoresis (Bio-Rad, Hercules, CA).
2.2.2. Primers The primers used were designated: 1. HLA-A, sequence 5' TGG GAC TGA GTG GCA AGT. 2. HLA-B, sequence 5' TTC ATG GTG GCC TGA GCA.
2.3. Single-Stranded RNA Probes 2.3.1. Buffers and Enzymes 1. 10X PCR buffer I (Applied Biosystems, Foster City, CA). 2. PCR assay buffer: 10 µL of 10X PCR buffer I, 2 µL dNTPs (10 mM each), 1 µL of each primer (100 ng), 1 µL Taq polymerase, and nuclease-free water to 99 µL.
3. SpectrumOrange/SpectrumGreen 2'-deoxyuridine- 5'-triphosphate (Vysis, Inc., Downers Grove, IL): reconstitute with 50 µL of nuclease-free water to give a 1 mM solution. Stable for up to 3 mo if stored at –20°C. 4. Taq polymerase: any commercial variety available can be used. 5. Mineral oil (if necessary), light white (Sigma Chemical Co., St. Louis, MO). 6. SP6 RNA polymerase, 10 units/µL (Promega Corp., Madison, WI). 7. 5X SP6 transcription buffer (Promega Corp.). 8. T7 RNA polymerase, 10 Units/µL (Promega Corp.). 9. 5X T7 transcription buffer (Promega Corp.). 10. Fluorescein RNA labeling mix, 10× (Roche Biochemicals, Nutley, NJ). 11. Nuclease-free water. 12. In vitro transcription labeling buffer: 2 µL of fluorescein RNA Labeling Mix, 4 µL of 5X transcription buffer, 2 µL of specific RNA polymerase, nuclease-free water to 18 µL. 13. 0.5 M EDTA, pH 8.0. 14. NuSieve GTG agarose (FMC BioProducts, Rockland, ME). 15. 1X Tris-borate buffer (TBE): 45 mM Tris-borate, 1 mM EDTA, pH 8.0, for gel electrophoresis (BioRad, Hercules, CA).
2.3.2. Primers The primers used were designated: 1. SP6HLA, 5' AGG GAT CCA TTT AGG TGA CAC TAT AGA ACC CGG GGC TGG GAC TGA GTG GCA AGT. 2. T7HLA, 5' GGA TCC TAA TAC GAC TCA CTA TAG GGA G TTC ATG GTG GCC TGA GCA.
2.4. In situ RT PCR 1. 100 ng/µL primers. The primer pairs used were (1) for gB: 5' primer ATT-CTC-CTCCGA-CGC-CAT-ATC-CAC-CTT; 3' primer AGA-AAG-CCC-CCA-TTG-GCC-AGGTAG-T. (2) For LAT: 5' primer GAC-AGC-AAA-AAT-CCC-GTC-AG; 3' primer ACG-AGG-GAA-AAC-AAT-AAG-GG (3) for glyceraldehyde phosphate dehydrogenase (GAPDH): 5' primer ATT-GGG-GGT-AGG-AAC-ACG-GAA; 3' primer ACC-CCTTCA-TTG-ACC-TCA-ACT-A. 2. Graded ethanols: 100, 70, and 50% ethanol. 3. PBS: 10 mM Na2HPO4, 1.8 mM KH2PO4, 140 mM NaCl, 2.7 mM KCl, pH 7.5. 4. Xylene. 5. Taq polymerase: any commercial variety available can be used, but optimal concentration to be used must be first determined by titrating with appropriate substrate. 6. Reverse transcriptase: Superscript II at 200 U/µL (Gibco-BRL, Gaithersburg, MD). 7. DNase I, RNase free (Gibco-BRL). 8. NuSieve GTG agarose (FMC BioProducts, Rockland, ME). 9. In situ PCR Reaction mix: 1× PCR Buffer II (Applied Biosystems, Foster City, CA), 1 mM MgCl 2, 1× digoxigenin DNA labeling mix (Roche Molecular Biochemicals) 100 ng of primer mix, 50% glycerol, and 1 µL of Taq polymerase. 10. RNasin 40 U/µL (Promega Corp.). 11. DNase digestion buffer: 1 mM NaCl, 10 mM Tris-HCl, pH 7.5. 12. In situ reverse transcriptase assay buffer: 10 U of SuperScript II (Gibco-BRL), 5 U of RNasin, 5 µL of oligo(dT) primer (100 ng/mL), 10 mM DTT, 1 mM dNTP, in SuperScript II reaction buffer (Gibco-BRL) per 100 µL.
13. Antidigoxigenin antibody conjugated to alkaline phosphatase (Roche Molecular Biochemicals). 14. BCIP/NBT (Vector Lab.).
3. Methods 3.1. RT-PCR 3.1.1. Synthesis of cDNA 1. Denature RNA sample before assay, at 90°C, for 5 min. 2. Add 1 µg of poly (A)+ RNA to 4 µL of 5× first strand buffer, 2 µL of 0.1 M DTT, 1 µL of 10 mM dNTP mix, 100 ng of primer and 1 µL of Superscript™ II reverse transcriptase (200 U/µL). 3. Incubate at 37°C for 60 min. 4. To the reaction mix add 92 µL of nuclease-free water, 30 µL of 5× second strand buffer, 3 µL of 10 mM dNTP mix, 4 µL of E. coli DNA polymerase I (10 U/µL) and 1 µL RNase H (2 U/µL), and incubate at 16°C for 2 h. 5. Add 2 µL of glycogen (5 mg/mL), 0.4 vol of 5 M ammonium acetate and twice the final volume of absolute isopropanol. 6. Microcentrifuge at max × g force value for 10 min at room temperature, and discard supernatant. 7. Wash pellet with 0.5 mL of ice-cold 70% ethanol and air dry. 8. Resuspend pellet in 10 µL of nuclease-free water.
3.1.2. Amplification and Labeling of cDNA Amplify and label double-stranded cDNA according to the procedure described in Subheadings 3.3.1 and 3.3.2 of the preceding chapter. Alternately, use gene specific primers and appropriate PCR amplification/labeling conditions (see Notes 1–5).
3.2. Asymmetric PCR Amplify 1 µg of plasmid DNA (1 mg/mL) in PCR assay buffer, using the following conditions: 40 cycles at 94°C for 15 s, 55°C for 15 s, followed by a single extension at 72°C for 10 min, and then hold at 4°C. 10 µL of this reaction should then be electrophoresed on a 1% agarose gel. The yield of DNA from this reaction varies from 1.0–2.0 µg of labeled single-stranded DNA (see Notes 6–8).
3.3. Single-Stranded RNA Probes 3.3.1. Amplification of DNA Amplify 1 µg of DNA (1 mg/mL) in PCR assay buffer using the following conditions: 30 cycles at 94°C for 15 s, 55°C for 15 s, followed by a single extension at 72°C for 10 min, and then hold at 4°C.
3.3.2. In vitro Transcription of PCR Product 2 µL of cDNA is in vitro transcribed in in vitro transcription labeling buffer, for 2 h at 37°C. Stop the reaction by adding 2 µL of 0.5 M EDTA, pH 8.0, on ice. Make up the volume to 100 µL with nuclease-free water, and directly use for FISH (see Notes 9–11).
3.4. In Situ RT PCR 1. Perfuse animals with 4% paraformaldehyde, embed tissue in paraffin, and cut on a microtome. 2. Deparaffinize 6 µm sections of tissue on glass slides in xylene (3 × 2 min). 3. Successively rehydrate tissue with graded ethanols in the following order: 100% ethanol (2 × 2 min); 70% ethanol (2 min), and 50% ethanol (2 min). 4. Wash sections in PBS (pH 7.5) for 5 min, twice. 5. Permeabilize sections with 1% HCl in PBS for 5 min, and then wash in PBS (3 × 5 min) (see Note 12). 6. Treat sections with 400 U of RNase-free DNase, and 10 U of RNasin in 200 µL of DNase digestion buffer, at 37°C overnight (see Note 12). 7. Rinse samples with RNase-free PBS to remove excess DNase. 8. Samples are then reverse-transcribed in 100 µL of in situ reverse transcriptase assay buffer, at 37°C for 60 min. 9. Rinse samples repeatedly with RNase-free PBS. 10. Rinse samples with PCR buffer II (3 × 5 min). 11. Layer 25 µL of in situ PCR reaction mixture onto the sections, which are covered with a glass coverslip and sealed using nail polish, taking care to ensure that the polish does not seep into the reaction mix. 12. PCR amplification is carried out in a BioOven III Thermal Cycler (BioTherm Corp, St. John Associates, Inc., Beltsville, MD 20705) in two stages; first for 3 cycles at 92°C for 1 min, 54°C for 30 s, and 72°C for 30 s, followed by 25 cycles at 92°C for 15 s, 54°C for 15 s, and 72°C for 15 s (see Notes 13–15). 13. After amplification, remove the coverslips and wash the sections successively with 1X SSC (2 × 5 min), 50% formamide in 1X SSC (3 × 15 min, 56°C), and 1X SSC (2 × 15 min). 14. Following a rinse in Tris-buffered saline (pH 7.5) and 5% normal goat serum. Treat the digoxigenin-labeled amplified DNA with an antidigoxigenin antibody conjugated to alkaline phosphatase (1:250), and visualize with BCIP/NBT. 15. Monitor color development visually; reaction can be stopped typically after about 30 min, by washing with 0.1 M Tris-HC1 (pH 7.5), 1 mM EDTA.
4. Notes 1. To guard against nonspecific amplification resulting from contamination of PCR reagents, use the best quality of reagents possible, and use them exclusively for PCR. We routinely aliquot out all of our solutions and freeze them at –20°C. We also use aerosol resistant tips for pipetting to minimize cross-contamination. Designate one area in the lab exclusively for PCR work. 2. When possible, prepare DNA and RNA samples in separate rooms. In addition, it is absolutely essential to run suitable negative controls (i.e., without target sequence) each time an experimental PCR is performed. 3. Titrate the Taq polymerase with the specific target. Too much enzyme can result in nonspecific background. 4. Titrate primers from 50 ng to 1 µg. 5. Vary the number of cycles to find the appropriate number of cycles which gives the best signal-to-noise ratio. 6. For best results, the ratio of primers will have to be optimized by titration.
7. Since the reaction to generate single-stranded DNA by asymmetric PCR is not efficient, as many as 40 cycles will need to be run. At times, an aliquot may need to be removed after 40 cycles for a fresh round of asymmetric PCR. 8. Another method to enhance yield of single-stranded product is to double the amount of Taq polymerase used in a normal PCR reaction. A typical concentration is 3 U of enzyme per reaction. 9. As before, the quality of the labeled transcript can be monitored on a 1% agarose gel. 10. Do not stain gel with ethidium bromide, since fluorescein-labeled cRNA will autofluoresce on a UV-transilluminator. 11. Observe all precautions normally followed while handling RNA. 12. The most crucial steps in obtaining good results using this technique are determining the optimal time for tissue permeabilization and DNase treatment. 13. Include control samples in which the enzyme reverse transcriptase is not included; this should not produce any positive signals. 14. Include control samples that have been pretreated with RNase prior to reverse transcription; this should not produce any positive signals. A simple way to perform this step is to include RNase I (400 U) in the DNase digestion step, overnight. 15. Include control samples in which the in situ PCR is performed in the absence of specific primers; this should also not produce any positive signals.
References 1. Mcknight, S. L. and Kingsbury, R. (1982) Transcriptional control signals of a eukaryotic protein-coding gene. Science 217, 316–324. 2. Graves, B. J., Eisenberg, S. P., Coen, D. M., and Mcknight, S. L. (1985) Alternate utilization of two regulatory domains within the Moloney murine sarcoma virus long terminal repeat. Mol. Cell Biol. 5, 1959–1968. 3. Jones, K. A., Yamamoto, K. R., and Tjian, R. (1985) Two distinct transcription factors bind to the HSV thymidine kinase promoter in vitro. Cell 42, 559–572. 4. Sambrook, J., Fritsch, E. F., and Maniatis, T. (1989) Molecular Cloning, A Laboratory Manual. Second ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor. 5. Schenborn, E. T. and Mierendorf, R. C., Jr. (1985) A novel transcription property of SP6 and T7 RNA polymerases: Dependence on template structure. Nucl. Acids Res. 13, 6223–6236. 6. Milligan, J. F., Groebe, D. R., Witherell, G. W., and Uhlenbeck, O. C. (1987) Oligoribonucleotide synthesis using T7 RNA polymerase and synthetic DNA templates. Nucl. Acids Res. 15, 8783–8798. 7. Rosenberg, A. H., Lade, B. N., Chui, D. S., Lin, S. W., Dunn, J. J., and Studier, F. W. (1987) Vectors for selective expression of cloned DNAs by T7 RNA polymerase. Gene 56, 125–135. 8. Milligan, J. F. and Uhlenbeck, O. C. (1989) Synthesis of small RNAs using T7 RNA polymerase. Methods Enzymol. 180, 51–62. 9. Veres, G., Gibbs, R. A., Scherer, S. E., and Caskey, C. T. (1987) The molecular basis of the sparse fur mouse mutation. Science 237, 415–417. 10. Kawasaki, E. S. (1990) Amplification of RNA in PCR Protocols: A Guide to Methods and Applications (Innis, M. A., Gelfand, D. H., Sninsky, J. J., and White, T. J., eds.), Academic Press, New York, pp. 21–27. 11. Gyllensten, U. B. and Erlich, H. A. (1988) Generation of single-stranded DNA by the polymerase chain reaction and its application to direct sequencing of the HLA-DQA locus. Proc. Natl. Acad. Sci. USA 85, 7652–7656.
12. McCabe, P. C. (1990) Production of single stranded DNA by asymmetric PCR, in PCR Protocols: A guide to Methods and Applications (Innis, M. A., Gelfand, D. H., Sninsky, J. J., and White, T. J., eds.), Academic Press, New York, pp. 76–83. 13. Ramakrishnan, R., Levine, M., and Fink, D. J. (1994) PCR-based analysis of herpes simplex virus type 1 latency in the rat trigeminal ganglion established with a ribonucleotide reductase-deficient mutant. J. Virol. 68, 7083–7091. 14. Gressens, P. and Martin, J. R. (1994) In situ polymerase chain reaction: localization of HSV-2 DNA sequences in infections of the nervous system. J. Virol. Methods 46, 61–83. 15. Nuovo, G. J. (1992) PCR In Situ Hybridization: Protocols and Applications. Raven Press, New York. 16. Ramakrishnan, R., Poliani, P. L., Levine, M., Glorioso, J. C., and Fink, D. J. (1996) Detection of herpes simplex virus type 1 latency-associated transcript expression in trigeminal ganglia by in situ reverse transcriptase PCR. J. Virol. 70, 6519–6523. 17. Ramakrishnan, R., Poliani, P. L., Goins, W. F., Fink, D. J., and Glorioso, J. C. (1996) Studies of LAP1 and LAP2 function in LAT expression in vivo, in Proceedings of the 21st International Herpesvirus Workshop, Dekalb, IL.
Sample Preparation and Hybridization
4 Basic FISH Techniques and Troubleshooting Sue Van Stedum and Walter King 1. Introduction Fluorescence in situ hybridization (FISH) technology permits the detection of specific nucleic acid sequences in morphologically preserved chromosomes, cells, and tissue. The unambiguous detection of structural or copy number changes of whole chromosomes or chromosome specific regions is an important prognostic and predictive factor in human disease. The utility of FISH in chromosome analysis is divided into metaphase and interphase applications. This distinction is manifested primarily in the preparation of the cells prior to pretreatment and hybridization. The culturing of cells for metaphase analysis is identical to those used in standard karyotyping. FISH is particularly advantageous in samples of low cellularity, or containing a mixed population of cells. A wide variety of sample types are amendable to FISH making it particularly valuable in the study of archival material, such as formalin-fixed paraffin-embedded tissues. However, the success of probe hybridization is dependent on the optimal preparation of sample. In interphase applications, the efficiency of probe hybridization is greatly enhanced by treating the cell or tissue preparation with a variety of reagents that permeabilize the target while preserving important morphological features. Additionally, pretreatment will reduce the background autofluorescence of cells and tissue. A thorough understanding of the processes behind sample pretreatment will provide insight in troubleshooting efforts. Once the DNA in the sample is made available for hybridization, the conditions for optimal signal involves far fewer permutations. The purpose of this chapter is to review the salient features of FISH with respect to sample preparation and hybridization.
1.1. Interphase vs Metaphase Analysis Fluorescently labeled DNA probes can be hybridized to cells in both interphase and metaphase stages of the cell cycle. Interphase FISH is advantageous in the rapid screening of many nuclei without the need for cell culture and metaphase chromosome preparation. It is also beneficial in the study of samples with a low mitotic From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
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index such as most solid tumors. The major limitation of interphase FISH is the inability to detect unknown structural chromosomal changes. Conversely, metaphase FISH analysis allows for a visual analysis of specific chromosome regions that contain structural changes, making it particularly useful in a variety of applications including chromosome painting probes, centromere specific, and locus identification probes. Structural changes in the genome such as translocations, inversions, and marker chromosomes are often readily identified by metaphase FISH. Methods combining banding techniques and FISH have been optimized for confirmation of aberrant findings. Slide quality of interphase and metaphase preparations is a very significant factor in the success of FISH. A thorough understanding of the tissue of interest and of slide preparation techniques is the first step to obtaining high quality results. Each laboratory should validate a probe's performance on control specimens prior to use.
1.2. Slide Preparation 1.2.1. From Culture The spreading of condensed chromosomes involves the precise application of the cell preparation across a slide under favorable drying conditions (see Note 1). Temperature and relative humidity are controlled to optimize chromosome spreading and morphology, and to minimize the presence of cytoplasm. A phase contrast microscope is essential for reviewing slide quality. The chromosomes in a metaphase should appear medium gray in color, have sharp borders, be well separated, and have little to no visible cytoplasm. Chromosomes should not appear refractile under phase microscopy. If the slides do not meet these specifications, modify slide preparation conditions by adjusting the temperature or humidity levels, and if necessary, by adjusting the density of the cell suspension. These measures are aimed at optimizing the rate of evaporation of the fixative. After drying, slides are aged overnight at ambient temperature. For long term storage, slides should be stored with desiccant in a –20°C freezer.
1.2.2. From Fresh Specimens While slide preparation can be performed in either of the two formats listed below for cultured metaphase specimens, fresh specimens are usually less affected by controlled temperature and humidity. Nuclei in cells obtained from non-cultured sources such as amniocytes, squamous, and epithelial cell types contain significantly more cytoplasm than cultured cells which, in turn, prevents the swollen nuclei from spreading effectively in two dimensions across the slide. Consequently, fixed cells are simply dropped onto slides. With the aid of a microscope, additional sample can be applied to the slide until the desired cellularity is achieved. Cyto-centrifugation is also a popular method for depositing cells onto slides. If slides are to be hybridized the same day, they should be artificially aged in the same manner as cultured samples.
1.3. Slide Pretreatment 1.3.1. Fresh Cells The accessibility of DNA in metaphase chromosomes is optimized during slide dropping and usually does not require pretreatment. For interphase cells, following aging, cells are incubated in a protease solution to rid the cell of extracellular debris and further reduce the presence of cytoplasm. This step is particularly important in cell types that have a significant amount of cytoplasm, e.g., amniocytes. Following enzymatic treatment, cells are exposed to a 1% formaldehyde solution to stabilize nuclear morphology. Slides are incubated in a series of graded ethanol solutions to dehydrate the cells in preparation for denaturation. Pretreatment procedures are basically the same for each specimen regardless if the processing includes a cultured or uncultured format. The recommended protease concentration is lower for amniocytes than most other cell types due to their fragile nature. Many samples, particularly fresh cultured cells or lymphocytes do not require pretreatment. However, the use of a standard protocol may be warranted when hybridizing slides with excess cytoplasm or background debris. Pretreatment of uncultured bone marrow specimens is often beneficial and helps to minimize background noise while increasing specific signal intensity. Fixation in 1% formaldehyde prior to protease digestion may help maintain compact nuclear signals.
1.3.2. Paraffin-Embedded Solid Tumor Freshly excised specimens should be fixed as soon as possible in 10% buffered formalin. Fixation times between 24–48 h are optimal for FISH applications may help delays in tissue fixation, as well as over- and under-fixation will result in weak or absent hybridization signals. Sections are typically cut at 4–6 microns and should be mounted on positively charged slides, such as amino-silane treated, then allowed to air dry. The slide can be used immediately or stored for an extended period of time at ambient temperature. Prior to use, the mounted slides are baked in an oven or on a slide warmer overnight at 56°C to improve tissue adherence. Formalin is a stronger fixative than acid or alcohols. Consequently formalin-fixed specimens require significantly more protease digestion for optimal probe hybridization. To prepare paraffin-embedded samples for FISH, the paraffin must first be removed. There are commercial pretreatment kits available that are optimized to prepare tissue specimens for FISH. Samples are deparaffinized in a series of xylene or Hemo-D® solutions followed by dehydration in ethanol. The samples are then treated chemically with HCl, followed by sodium isothiocyanate at elevated temperatures prior to protease digestion.
1.4. Hybridization and Wash The process of specific and efficient hybrid formation of labeled DNA to partially digested chromatin involves denaturation of target and probe DNA, hybridization of labeled probe in the presence of unlabeled blocking DNA homologous to nonspecific repetitive sequences, and removal of unhybridized, or nonspecifically hybridized or
bound probe. Denaturation conditions for FISH are similar to those required for purified DNA, except that they are performed in the presence of formamide, a chaotrope, which lowers the melting point of duplexed nucleic acids (1). Hybridization of FISH probes made from large genomic DNA fragments, typically containing repetitive sequences, necessitates the use of excess blocking DNA. The suppression of probe hybridization to non-target sequences by blocking DNA constitutes the mechanism of FISH specificity. The amount of probe used in a hybridization is in the 10–900 ng range for a 10 µL hybridization volume. Less probe is required if made from highly repetitive sequences near the centromere, which can span hundreds of thousands of base pairs. Depending on the complexity of the probe, hybridization buffers may also contain accelerators such as dextran sulfate.
1.5. Enumeration Before a hybridized slide can be assessed, the operator needs to be aware of the quality characteristics of the probe in addition to the characteristics of the test sample. It is important to become familiar with the size, shape, and fluorescent intensity of each of the DNA probe signals in order to accurately evaluate the hybridization results. Signals should be bright, distinct, and easily enumerated. The background should be free of fluorescing particles and the probe should not cross-hybridize to other loci. The operator also needs to be familiar with the cell population of the test slide and recognize when to include or exclude cell types, or when to scan a population of cells for a specific malignancy. Certain probes are intended to target cells during interphase or metaphase stages of the cell cycle and the operator must adjust their focus accordingly. 2. Materials 2.1. Slide Preparation from Metaphase Cultures 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Waterbath. Humidifier. Plastic wrap. Hygrometer. Test tube racks. Carnoy's fixative (see Note 2). 3:1 Methanol:Glacial Acetic acid, cold (–20°C). Slides. 70% Ethanol. Water. Laboratory wipes, lint free. Cell suspension(s). Microscope, phase contrast.
2.2. Slide Preparation from Metaphase Culture Using a Controlled Cytogenetic Drying Chamber 1. Thermotron CDS-5 Cytogenetic Drying Chamber (Holland, MI). 2. Slides. 3. 70% Ethanol.
4. Laboratory wipes, lint free. 5. Cell suspension(s). 6. Microscope, phase contrast.
2.3. Slide Preparation from Primary Amniocytes 1. 2. 3. 4. 5.
Fixed cell suspension. Microscope slides. 70% Ethanol. Laboratory wipes, lint free. Microscope, phase contrast.
2.4. Slide Preparation from Uroepithelial Cells 1. 2. 3. 4. 5.
Fixed cell suspension. 6 mm-12 well masked slides (Shandon Inc., Pittsburgh, PA). 70% Ethanol. Laboratory wipes, lint free. Microscope, phase contrast.
2.5. Pretreatment of Fresh Cells 1. 2. 3. 4.
2X SSC. Prewarmed pepsin working solution (0.5 mg/mL Pepsin/0.01 N HCl). Phosphate buffered saline (PBS). Post fixation solution: 0.95% formaldehyde: 1 mL of 37% formaldehyde, 0.18 g MgCl2, and 39 mL of PBS. 5. 100% Ethanol. 6. 85% Ethanol. 7. 70% Ethanol.
2.6. Pretreatment of Paraffin Pretreatment 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Paraffin slides baked overnight at 56°C. Diamond-tipped scribe. Slide warmer at 45–50°C. Hemo-De clearing agent (Fisher Product No. 15-182-507A). 100% Ethanol. Hydrochloric acid, 0.2 N. Purified water (distilled or deionized or Milli-Q). Wash buffer: 2X SSC, pH 7.0. Waterbath at 37 and 80°C. Pretreatment solution: 1 M NaSCN. Protease solution: 0.5 mg/mL pepsin (2500–3000 U/mg) in NaCl, pH 2.0. Neutral buffered formalin (4% formaldehyde in PBS).
2.7. Hybridization and Wash 1. 2. 3. 4. 5.
Slides for hybridization. DNA Probe. Forceps. Denaturing solution: 70% formamide / 2X SSC, pH 7.0–8.0. 70, 85, and 100% Ethanol.
6. 7. 8. 9. 10. 11.
Waterbath at 73°C. 22 × 22 mm Glass coverslips. Rubber cement. Humidified hybridization chamber (airtight container with a piece of damp blotting paper). Incubator at 37°C. Post-Hybridization wash buffer: 0.4X SSC/0.3% NP40 for nonformalin fixed samples or 2X SSC / 0.3% NP-40 for formalin fixed paraffin embedded. 12. DAPI Counterstain.
3. Method 3.1. Slide Preparation from Metaphase Cultures 1. Place a waterbath and humidifier within a containment cabinet. Humidity should be approx 50%. Use a humidifier if the room hygrometer reading is below 45%. 2. Prewarm the waterbath to 67° ± 2°C. Place test tube racks in the center of the waterbath so that they do not touch the sides of the bath. Maintain the water level just below the top of the test tube rack throughout the procedure. 3. Optimize the cell pellet concentration with Carnoy's fixative so that the suspension is slightly cloudy (see Note 3). 4. Clean a microscope slide by flooding both sides of the slide with 70% ethanol. Wipe the slide dry with a laboratory wipe. 5. Dip the cleaned slide in a jar of water. Tilt the slide to evenly coat its upper surface. 6. Immediately hold the slide over the waterbath. Holding a Pasteur pipet 2–4 in above the slide, expel 3 to 4 drops of cell specimen suspension along the length of the slide. 7. Place the slide, specimen side up, on the top of the test tube racks in the waterbath. Let the slide dry for 5–10 min. 8. Remove the slide and view under a phase contrast microscope. Adjust slide dropping conditions as necessary.
3.2. Slide Preparation from Metaphase Culture Using a Controlled Cytogenetic Drying Chamber (see Note 4) 1. Turn on the Thermotron and set the temperature to 22°C and the relative humidity to 44%. Allow the unit to equilibrate. 2. Optimize the cell pellet concentration with Carnoy's fixative so that the suspension is slightly cloudy (see Note 5). 3. Clean a microscope slide by flooding both sides of the slide with 70% ethanol. Wipe the slide dry with a laboratory wipe. Place the slide on the interior surface of the Thermotron. 4. Holding a Pasteur pipet 2–4 in above the slide, expel 3 to 4 drops of cell specimen suspension along the length of the slide. 5. Observe the drying pattern of the suspension. Optimal slides are often prepared from suspensions that dry within 45–60 s. 6. Review the slide under a phase contrast microscope and adjust slide-dropping conditions as necessary.
3.3. Slide Preparation from Noncultured Samples (see Note 6) 1. Gently resuspend fixed cells. 2. Drop 15–20 µL of cell suspension per hybridization area (usually two areas per slide). 3. Air dry.
4. Check for cellularity under phase and repeat steps 2–3 as required. 5. Age overnight or incubate in a 73°C, 2X SSC solution for two min (see Note 7).
3.4. Slide Preparation from Uroepithelial Cells 1. Gently resuspend fixed cells and aliquot 3 µL, 10 µL, and 30 µL of the resuspended pellet onto 3 wells of the 6 mm masked slide. 2. Air dry. 3. Determine which sample contains the optimal cellularity where there are sufficient numbers of nonoverlapping cells. 4. Check for cellularity under phase and select appropriate well for hybridization. 5. Age overnight or incubate in a 73°C, 2X SSC solution for two min (see Note 7).
3.5. Fresh Cells Pretreatment 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Place slides in 2X SSC at 73°C for 2 min. Place slides in pepsin working solution at 37°C for 10 min. Wash slides in PBS at room temperature for 5 min. Place slides in post fixation solution at room temperature for 5 min. Wash slides in PBS at room temperature for 5 min. Dry slides. Immerse slides in 70% ethanol at room temperature for 1 min. Immerse slides in 85% ethanol at room temperature for 1 min. Immerse slides in 100% ethanol at room temperature for 1 min. Proceed to slide denaturation.
3.6. Paraffin Pretreatment (see Note 8) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.
Mark the paraffin area to be hybridized with a diamond-tipped scribe. Immerse slides in Hemo-De for 10 min at room temperature. Repeat twice using new Hemo-De each time. Dehydrate slides in 100% ethanol for 5 min at room temperature. Repeat with new ethanol. Air dry slides or place on a 45–50°C slide warmer for 2–5 min. Immerse slides in 0.2 N HCl for 20 min (see Note 9). Immerse slides in purified water for 3 min. Immerse slides in wash buffer for 3 min. Immerse slides in pretreatment solution at 80°C for 30 min. Immerse slides in purified water for 1 min. Immerse slides in wash buffer for 5 min. Repeat wash buffer rinse. Remove excess buffer by blotting edges of the slides on a paper towel. Immerse slides in Protease Solution at 37°C for 10 min (see Note 10). Immerse slides in wash buffer for 5 min. Repeat wash buffer rinse. Dry slides on a 45–50°C slide warmer for 2–5 min. Immerse the specimen in neutral buffered formalin at room temperature for 10 min (see Note 11). Immerse the slides in wash buffer for 5 min. Repeat wash buffer rinse. Dry slides on a 45–50°C slide warmer for 2–5 min. Proceed with hybridization protocol.
3.7. Hybridization and Wash The timing for preparing the probe solutions should be carefully coordinated with denaturing the specimen so that both will be ready for the hybridization step at the same time. 1. Immerse the slides in denaturing solution at 73°C for 5 min. Do not denature more than 4–6 slides at one time per Coplin jar (see Note 12). 2. Immerse slides in 70% ethanol at room temperature for 1 min. 3. Immerse slides in 85% ethanol at room temperature for 1 min. 4. Immerse slides in 100% ethanol at room temperature for 1 min. 5. Drain excess ethanol from the slide by blotting the edge of the slide to a towel and wipe the underside of the slide dry with a laboratory wipe. 6. Aliquot probe to a microfuge tube, cap tightly, and denature probe in a 73°C waterbath for 5 min. 7. Apply between 3–10 µL (depending on specimen area) probe mixture to target area of slide (see Note 13). 8. Immediately place a 22 × 22 mm or a 12-mm round (uroepitheliar hybridizations Subheading 3.4.)glass coverslip over the probe and allow it to spread evenly under the coverslip. 9. Seal coverslip by applying rubber cement around the periphery of the coverslip. 10. Place slides in a humidified chamber prewarmed to 37°C and cover. 11. Incubate slides at 37°C overnight (14–18 h, see Note 14). 12. Remove the rubber cement seal by gently pulling up on the sealant with forceps. 13. Immerse slides in post-hybridization wash buffer at room temperature and float off the coverslip. 14. Remove excess liquid by wicking off the end of the slide. 15. Immerse slides in post-hybridization wash buffer at 73°C for 2 min. Do not wash more than 4–6 slides at one time per Coplin jar for nonparafinembedded samples, incubate in 2X SSC/0.1% NP40 at ambient temperature for 1 min. (See Note 14). 16. Remove slide and air dry in the dark in a vertical position. 17. Apply 10 µL DAPI counterstain to the target area and apply a 22 × 22 mm glass coverslip. 18. Store the hybridized slide in the dark. Place slides in –20°C storage when not in use.
3.8. Signal Enumeration in Interphase Cells Evaluate slide adequacy using the following criteria (see Notes 15–20). 1. Probe signal intensity: The signal should be bright, distinct, and easily evaluated. Signals should be in either bright, compact, oval shapes or stringy, diffuse, oval shapes. 2. Background: The background should appear dark or black and relatively free of fluorescence particles or haziness. 3. Recognition of target signals: Use the prescribed filter. Adjust the depth of the focus, and become familiar with the size and shape of the target signals and noise (debris). 4. Using a ×40 objective, scan several areas to assess any heterogeneity of cell type. Select an area of even nuclei distribution; avoid areas of the target where hybridization signals are weak. 5. Using a ×63 or ×100 objective, begin analysis in the upper left quadrant of the selected area and, scanning from left to right, count the number of signals within the nuclear boundary of each interpretable interphase cell according to the guidelines. 6. Focus up and down to find all of the signals present in the nucleus.
7. Count two signals that are the same size and separated by a distance equal or less than the diameter of the signal as one signal. 8. Do not score nuclei with no signals or with signals of only one color when using two or more different fluorophores. Score only those nuclei with one or more FISH signals of each color.
4. Notes 4.1. Slide Preparation 1. The goal for optimal spreading of hypotonically swollen cells for metaphase or interphase analysis is the flattening of nucleus and cytoplasm. This flattening process is mediated by the combination of the evaporation and spreading rate of the fixative on the slide (2). This is particularly important in metaphase applications where over-spreading causes chromosomes from adjacent cells to overlap while under-spreading results in shorter chromosomes that are clustered on top of one another. 2. Optimal drying properties is a major reason that Carnoy's fixative is one of the most widely used fixatives in cytogenetics laboratories. The fixative is added slowly to cells to avoid rupture of the cell membrane that could lead to chromosome loss. Cold fixative is often preferred to accelerate fixation and maintain cell morphology. Carnoy's fixative should always be freshly prepared prior to use as the components lose their stability over time and fixative properties diminish. 3. Slides may be prepared directly from fixed cell pellet suspensions or the samples may be stored for extended periods of time at –20°C. Prior to slide preparation, cell pellets are usually washed several times in additional fixative to rid the samples of debris that could interfere with slide production and FISH interpretation. 4. Reproducibility in the slide preparation process is critical to FISH success. Laboratories are very diverse and creative in their slide preparation techniques, and often have the need to change slide dropping variables with daily and seasonal weather changes. The basis of slide preparation and cell spreading is related to the drying rate of cells as they are applied to the slide. Temperature and relative humidity have a profound effect on this process and therefore laboratories often attempt to control these variables as much as possible. Many laboratories have incorporated the use of the Thermotron CDS-5 Cytogenetic Drying Chamber into their daily procedures. The Thermotron is a self-contained unit with controlled relative humidity and temperature settings used to achieve optimum chromosome spreading routinely and in a highly consistent manner (2). Self-sealing arm ports allow the user to prepare slides in a controlled environment inside the Thermotron. A great number of additional variables affect the slide preparation process. 5. The density of the cell suspension, type of slide, air flow, fixative ratio, and cell type, in addition to culturing and harvesting techniques, all contribute to the overall process. Consistency in protocol is often the best means of controlling the slide making process. 6. Many procedures such as cytocentrifugation involve the application of a specimen directly to the slide with subsequent fixation. Specimens on slides are allowed to air dry at room temperature and are promptly fixed in a solution compatible with FISH. Carnoy's fixative and 95% ethanol are routinely used. Slides are immersed in a Coplin jar of fixative solution for 10 min, or alternatively the slide can be flooded in a series of fixative washes. Following slide aging, slides can be used immediately in the FISH procedure or stored at –20°C. 7. The aging process is thought to be an additional form of fixation. This step is of particular importance when running FISH assays the same day as slide preparation. Freshly pre-
Van Stedum and King pared specimens that are not aged often appear over-denatured following hybridization. If slides are to be hybridized the same day, they can be artificially aged by incubating in a 73°C, 2X SSC solution for 2 min. Alternatively samples can be aged briefly on a slide warmer at 90°C. However, excessive baking of slides prior to FISH should be avoided as this will decrease probe signal.
4.2. Slide Pretreament 8. Fixatives Fixatives Compatible with FISH: • 10% buffered formalin • Paraformaldehyde • Karnovsky's fixative (16% paraformaldeyde 50% Glutaraldehyde)
Fixatives Incompatible with FISH: • Bouin's fixative. • B5 fixative. • Acidic fixatives (e.g., picric acid). • Zenker's fixative. • Alcohols (when used alone). • Mercuric chloride. • Formaldehyde/zinc fixative. • Hollande's fixative.
9. Troubleshooting suboptimal FISH results may be difficult due to the number of processes involved between specimen procurement and FISH analysis. Proper preparation, embedding, and sectioning techniques are dependent on the type of tissue under investigation and can introduce many variables to processing (3). Specimen variability may also introduce difficulties relative to the tissue type and the amount of extracellular and cytoplasmic material present. The HCl and isothiocyanate treatments are thought to break the cross-linked basic histone protein bonds, thereby improving the efficiency of subsequent enzyme digestion (4). 10. Enzymatic digestion is usually performed with proteases such as pepsin or proteinase K. Increasing the concentration of the pepsin to 1.5 mg/mL in 0.2 N HCl often reduces background fluorescence and improves signal intensity. Proteinase K is a far more active enzyme and care must be given to avoid over-digestion that will result in loss of tissue and cellular architecture as well as loss of DNA. Optimization of nuclei enzymatic treatment is critical to assay success. Some tissues show greater resistance to enzymatic digestion and prove difficult to analyze by FISH. Often, the resistance is related to prolonged times of formalin fixation or the cellular composition of the tissue. Difficult samples may benefit from longer incubations and/or higher concentrations with sodium isothiocyanate pretreatment. Additionally, optimization of enzyme concentration and length of incubation is important. If samples are underdigested, autofluorescence will become problematic and underestimation of signal copy number may result. Overdigestion of tissue will decrease signal intensity and destroy nuclear morphology. 11. The specimen may be fixed prior to FISH in 10% buffered formalin to prevent additional tissue loss during denaturation and hybridization. The pretreatment process can be time consuming, however, but is essential for successful FISH results. Automation of these pretreatment steps has been reported to result in superior FISH results and greater consistency (5). Significant labor savings and batching of larger number of samples are also important benefits.
4.3. Hybridization and Wash 12. While the denaturation of the probe solution can be achieved by boiling the probe in TE, milder conditions are employed for the preservation of tissue, cell and chromosome morphology (6). The extent of DNA denaturation within chromatin is still dependent on the
well understood Tm parameter, which is defined as the point at which 50% of the DNA is single stranded. Tm is dependent on GC content, monovalent cation concentration, and length of the duplex strands (7). The sample needs to be denatured well beyond the Tm where close to 100% of the DNA is single stranded. Typically, these conditions are 70–75°C in 2X SSC in 50–55% formamide. Often the probe and the sample are simultaneously or co-denatured on the slide. This results in more favorable kinetics for rapid heteroduplex formation. If denaturation conditions of the sample significantly exceed these conditions, a broader more speckled hybridization pattern can result, which is the result of the "uncoiling" of the compact DNAhistone structures. Adequate fixation can circumvent this to some extent. Conversely, if the DNA strands are not adequately denatured, little or no hybridization signal will result. 13. The nature of blocking DNA is different depending on the complexity of the probe. A DNA probe made from highly repetitive sequences such as centromeric or paracentromeric DNA is hybridized in the presence of 10–100 fold excess of total human genomic DNA. If the probe contains unique sequences to a specific region of a chromosome arm, hybridization is conducted in the presence of a similar mass excess of highly repetitive DNA, termed Cot-1 DNA. Cot-1 DNA is composed of DNA from highly repetitive alphoid sequences and intermediate repetitive sequences such as Alu family of repeats (8,9). It is these latter sequences which are present on all chromosomes as well as in virtually all genomic DNA fragments from which FISH probes are made. 14. Hybridization time will be dependent on the sequence complexity of the probe. Probes with a significant fraction of unique sequences will typically require an overnight incubation at 37°C, while probes containing centromeric or pericentromeric satellite sequences only require a few hours of hybridization at 37–42°C. Slight variations in hybridization temperature are employed to differentiate between closely related repetitive sequences. However, crosshybridization is more effectively eliminated through high-stringency wash. For paraffin embedded samples, use of a higher salt concentration in the wash buffer achieves a similar degree of specificity as does the higher stringency conditions for nonformalin fixed samples. This is because of a lower melting point for probe; target hybrids in the formalin fixed samples that could result from a much shorter length of target sequences as a result of degradation or could be owing to the persistence of protein in the hybridized region that causes hybrid destabilization.
4.4. Enumeration 15. Guideline:
16. It is extremely important to incorporate control slides with FISH testing to check for hybridization adequacy. Both negative and positive controls, ideally near the cut-off for diagnosis, should be included each day FISH tests are run. The control slides should be evaluated prior to any test slides. If the slides are found to exhibit the appropriate quality, the slides should be enumerated and compared to known values to determine counting accuracy. If control slides meet the acceptance criteria but the enumeration values are outside the specified range, the enumeration may not have been performed correctly and an independent, repeat assessment of the same slide may be appropriate. FISH test results should not be reported if assay controls fail, interpretation of the hybridization signal is difficult, or if there are insufficient cells for analysis. 17. For paraffin embedded tumor samples, use a ×25 objective to view the hybridized area and locate the target of interest (tumor cells as identified by H & E stain). Avoid areas of necrosis and where the nuclear borders are ambiguous. Skip those nuclei with signals that require subjective judgment. Skip signals with weak intensity and nonspecificity, or with noisy background. 18. Skip nuclei with insufficient counterstain to determine the nuclear border. Enumerate only those nuclei with discrete signals. Enumerate hybridization signals only among tumor cells. Tumor cells in general are larger than normal cells, lymphocytes, and epithelial cells. Identify target areas by H & E stain on every 10th slide of the same tissue block. Identify these areas on the coverslip after the FISH assay is performed. Continue this process until 60 nuclei are enumerated and analyzed. 19. For single cell suspension samples, select an area where the specimen is distributed sparsely, few interphase nuclei or metaphase spreads are overlapping, and several interphase nuclei or metaphase spreads can be scanned within a viewing field. Avoid areas where the distribution of cells is dense, cells are overlapped, or the nuclear border of individual nuclei is unidentifiable. Identify the area of interest specific to the type of test being performed.
20. When more than one color fluorophore is involved, additional consideration is given to resolve signals that are randomly positioned in close proximity such that the colors blend. In some cases a color blend represents the confirmation of a translocation event. In other cases, the signals can be resolved with the use of filters specific to each fluorophore.
References 1. Trask, B., Pinkel, D. (1990) Fluorescence in situ hybridization with DNA probes. Methods Cell Biol. 33, 383–400. 2. Spurbeck, J. L., Zinsmeister, A. R., Meyer, K. J., and Jalal, S. M. (1996) Dynamics of chromosome spreading. Am. J. Med. Genet. 61(4), 387–93. 3. Lowery, M. C. Application of FISH Technology on Paraffin-Embedded Tissue, Procedural Tips and Trouble-Shooting Guide, Vysis, Ed. 2000, Downers Grove, IL. 4. Hopman, A. H. N., Poddighe, P., Moesker, O., and Ramaekers, F. C. S. (1991) Interphase cytogenetics: an approach to the detection of genetic aberration in tumours, in Diagnostic molecular pathology: A practical approach. (M. J. O. and H. C. S., eds.), IRL Press, New York, NY, pp. 141–167. 5. Jacobson, K., Thompson, A., Browne, G., Shasserre, C., Seelig, S. A., and King, W. (2000) Automation of fluorescence in situ hybridization pretreatment: a comparative study of different sample types. Mol. Diagn. 5(3), 209–220. 6. Ramesh, K. H., Macera, M. J., and Verma, R. S. (1997) Rapid denaturation improves chromosome morphology and permits multiple hybridizations during fluorescence in situ hybridization. Biotech. Histochem. 72(3), 141–143. 7. Wetmur, J. G. (1991) DNA probes: applications of the principles of nucleic acid hybridization. Crit. Rev. Biochem. Mol. Biol. 26(3–4), 227–259. 8. Britten, R. J., Baron, W. F., Stout, D. B., and Davidson, E. H. (1988) Sources and evolution of human Alu repeated sequences. Proc. Natl. Acad. Sci. USA 85(13), 4770–4774. 9. Hwu, H. R., Roberts, J. W., Davidson, E. H., and Britten, R. J. (1986) Insertion and/or deletion of many repeated DNA sequences in human and higher ape evolution. Proc. Natl. Acad. Sci. USA 83(11), 3875–3879.
Chromosome Microdissection
5 Chromosome Microdissection Xin-Yuan Guan 1. Introduction It has been known for decades that chromosome rearrangements exist in most if not all human tumors (1) and certain human hereditary diseases (2). Distinct chromosomal abnormalities in tumors lead to the activation of proto oncogene products, creation of tumor specific fusion proteins, or inactivation of tumor suppressor genes. Since chromosome banding techniques were developed, cytogenetic study of nonrandom chromosome abnormalities in malignant cells has become an integral part of the diagnostic and prognostic work up of many human cancers (3). However, not all cytogenetically visible chromosome rearrangements (e.g., complex chromosome rearrangements, small ring chromosomes, and unidentifiable de novo unbalanced translocation) can be determined by conventional cytogenetic banding analysis. This technique limitation prevents complete karyotypic analysis in many human cancers, particularly solid tumors. This technical limitation has been complemented by the combined use of chromosome microdissection and fluorescence in situ hybridization (FISH) techniques (4). Chromosome microdissection has been developed as a very powerful tool to proceed rapidly from cytogenetic observation to molecular analysis.
1.1. The Development of Chromosome Microdissection Chromosome microdissection was primarily developed to isolate DNA markers from a defined chromosomal region, which was first successfully applied to the Drosophila polytene chromosomes (5) and then mouse chromosome (6). In 1989, a significantly increased cloning efficiency was achieved when Lüdecke et al. (7) first developed an amplification strategy in which microdissected DNA was digested with Rsa I, ligated into a Sma I-cut pUC vector, and subsequently PCR amplified using vector sequences flanking the insertion site. This method was then modified by ligating the restriction digested DNA from microdissection to a 5' protruding linkeradaptor, which was constructed from oligonucleotides of 24- and 20-mer. The dissected DNA was then amplified by PCR with the 20-mer of the linker-adaptor as a From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
primer, and the amplified products were restriction digested and cloned into a plasmid vector (8–10). In these methods, microchemical manipulations are typically carried out in nanoliter-scale with the use of micropipettes controlled by microinjection. However, widespread application of these procedures was limited because of the extremely time consuming and labor intensive requirement for dissecting 20–80 copies of the selected regions, high risk of extraneous DNA contamination, as well as the difficulties in microchemical manipulations. As an alternative, the method presented here applies a strategy for direct PCR amplification of microdissected DNA using a degenerate oligonucleotide primer (4,11). This method was further improved by treating microdissected DNA with Topoisomerase I prior to the PCR amplification (12). It significantly simplifies the procedure of microdissection and provides several advantages over previously described methods. This method reduces the time and effort necessary for microdissection by reducing the copies of microdissected DNA while also limiting the risk of contamination with extraneous DNA, during the manipulation. The procedure of this protocol is streamlined by eliminating the needs for microchemical manipulations and allows the routine utilization of microdissection in cytogenetic laboratories.
1.2. The Applications of Chromosome Microdissection Although it was originally designed for the isolation of DNA markers from defined regions, chromosome microdissection has been widely applied in cytogenetic research and molecular cloning once it has been combined with the FISH technique. After a decade of effort, this approach has been developed into a useful and reproducible approach for the following purposes to date.
1.2.1. Construction of DNA Clones for Regions of Interest The primary application of microdissection prior to the human genome project initiative was to isolate chromosomal region specific DNA markers to fill in gaps found in a physical map. Several region-specific libraries have been constructed for positional cloning projects including 8q24 for the Langer-Giedion syndrome (7), 6q16–q21 for melanoma (13), and 2q35–q37 for alveolar rhabdomyosarcoma (14). In addition, microdissection was applied to obtain highly polymorphic markers from 2p16, which leaded to the identification of hMSH2 gene in hereditary nonpolyposis colorectal cancer (15).
1.2.2. Generation of FISH Probe Fluorescence in situ hybridization with different painting probes has been widely applied to detect previously unrecognizable chromosome abnormalities in tumors and hereditary diseases. To meet the increasing demand for high quality FISH painting probes, chromosome microdissection has been used to generate many different FISH probes, including human whole chromosome painting probes (WCP) (16), chromosome arm painting probes (Fig. 1A) (17), and band specific painting probes (Fig. 1B) (18).
Fig. 1. (A) Microdissection was used to generate chromosome arm painting probes from 12p (red) and 12q (green). (B) An example of band-specific probes constructed by microdissection. Terminal band probes of 1p (red) and 1q (green) were shown. (C) A small ring chromosome was characterized by microdissection. The dissected DNA (red) was hybridized to the small ring chromosome (indicated by an arrow) and centrimere region of chromosome 14. (D) Characterization of double minutes (DMs) by microdissection. The dissected DNA (red) was specifically hybridized to DMs.
1.2.3. Detection of Chromosome Rearrangement One of the most appealing features of chromosome microdissection is its ability to directly detect the chromosomal constitution of virtually any cytogetically visible chromosome rearrangement. This unique approach has been used to analyze different chromosome rearrangements including deletion, translocation, small ring chromosome (Fig. 1C), and amplification. Reinvestigation, using microdissection, of events which conventional banding analysis had cataloged as simple terminal deletions clearly demonstrated that the presumed terminal deletions were actually interstitial deletions or translocations (19–21). Application of microdissection to products resulting from gene amplification including homogeneously staining region (HSR) and double minutes (Fig. 1D) has revealed that the contents of these regions are usually composed of multiple chromosomal regions (22,23).
1.2.4. Selection of Region-Specific cDNA The availability of microdissected DNA from HSR has prompted the development of techniques for isolating transcribed sequences contained within the microdissected
region. One strategy, microdissection combined with hybrid selection, has been applied to identify genes associated with 12q13–q15 HSR in an osteosarcoma cell line (24) and 20q11–q13.2 HSR in breast cancer (25). Briefly, PCR products of microdissected DNA were immobilized on a nylon membrane, then hybridized with random primed cDNAs prepared from a cancer cell line with the target HSR. After hybridization and a stringent wash, the specifically hybridized cDNA clones were eluted and recovered by PCR.
1.3. Strategy for Chromosome Microdissection The chromosome microdissection technique described here includes two major parts: microdissection of a target chromosomal region, and subsequent amplification of the dissected DNA fragments with a degenerate oligonucleotide primer by PCR.
1.3.1. Chromosome Microdissection Metaphase chromosomes for microdissection are prepared from phytohemagglutinin (PHA)-stimulated normal peripheral blood lymphocytes. Metaphases are spread on clean coverslips (22 × 60 mm) and GTG-banded. Usually, 3–5 copies of a target chromosomal region are enough to obtain a high quality probe. The microdissection is performed with a glass-needle controlled by a micromanipulator attached to an inverted microscope. The microdissected chromosome fragments are transferred into 5 µL collection solution containing Topoisomerase I (Topo I).
1.3.2. Treatment of Dissected DNA with Topo I Before PCR amplification, the dissected DNA is treated with Topo I which can relaxes the very tight DNA coiling. This treatment has been shown to dramatically enhance the recovery of sequences from dissected DNA (12). After the desired number of dissected chromosomal region is collected, the dissected DNA is treated with Topo I by incubating at 37°C for 1 h.
1.3.3. Amplification of Microdissected DNA The most difficult part of amplification of dissected DNA is effective initiation of the PCR reaction. Taq polymerase is not efficient for PCR initiation because its extension temperature is 72°C, whereas the optimal annealing temperature for the primer, a partially degenerated primer (26), is about 30°C. To solve this problem, T7 DNA polymerase (Sequenase) is introduced in the first 5–8 cycles of PCR (27). The enzyme is added during each cycle at the annealing temperature (30°C). Following this preamplification step, a conventional PCR reaction catalyzed by Taq polymerase is performed.
1.3.4. Fluorescence in situ Hybridization FISH is a simple and rapid method to ensure the success of microdissection and to check the quality of the probe. PCR amplified dissected DNA is labeled with fluorochrome in a secondary PCR reaction. After labeling, the probe is purified and hybridized to normal metaphase chromosomes.
2. Materials 2.1. Preparation of Metaphase Chromosomes for Microdissection 1. Complete RPMI 1640 medium: RPMI 1640 medium, 15% fetal calf serum, 1% glutamine (200 mM), 1% Pen/Strep (10,000 U/mL). 2. Phytohemagglutinin (PHA) (Murex Biotech Ltd., Dartford, UK). 3. Colcemid (10 µg/mL) (Gibco-BRL, Gaithersburg, MD). 4. Hypotonic solution: 0.075 M KCl. 5. Carnoy's fixative: 3:1 methanol and glacial acetic acid. 6. 22 × 60 mm glass coverslip. 7. Trypsin working solution: 0.005% trypsin (Gibco-BRL, Gaithersburg, MD) in Hank's balanced salt solution (HBSS) without calcium and magnesium (Gibco-BRL, Gaithersburg, MD). 8. Giemsa stain working solution: 1 mL Giemsa stock solution (BDH Chemicals Ltd., Poole, UK) in 50 mL 0.01 M sodium phosphate (pH 7.0).
2.2. Microdissection and Topo I Treatment 1. Glass needle: prepare glass needle by pipet puller using glass capillary tube (1.2 mm wide and 4 in in length) (WPI, Sarasota, FL). 2. Kopf needle/pipet puller, Model 750 (Kopf, Tujunga, CA). 3. Stratalinker 2400 (Strategene, La Jolla, CA). 4. An inverted microscope. 5. A hydraulic micromanipulator, model MO-302 (Narishige, Japan). 6. Collection solution (final concentration): 4 mM Tris-HCl (pH 7.5), 2 mM MgCl2, 5 mM NaCl, 0.2 mM each dNTP (Pharmacia LKB, Piscataway, NJ), 1 µM UN1 (5' CCGACTCG AGNNNNNNATGTGG 3'), 1 U/50 µL Topo I (Promega, Madison, WI). 7. Thermal cycler and thin-walled PCR tubes.
2.3. Amplification of Dissected DNA 1. Sequenase version 2 (13 U/µL, US Biochemicals, Cleveland, OH). 2. Enzyme dilution buffer (US Biochemicals, Cleveland, OH). 3. PCR reaction mixture (final concentration): 10 mM Tris-HCl (pH 8.4), 2 mM MgCl2, 50 mM KCl, 0.2 mM each dNTP, 1 µM UN1 primer, 2 U/50 µL AmpliTaq LD (Perkin Elmer, Norwalk, CT) (see Note 1).
2.4. Fluorescence In Situ Hybridization 1. 2. 3. 4. 5. 6. 7. 8. 9.
Biotin-16-dUTP (Roche, Mannheim, Germany). 3 M sodium acetate (pH 5.2). TE buffer: 10 mM Tris-HCl, 1 mM EDTA. BioSpin P6 column (BioRad, Hercules, CA). Denaturing solution: 70% formamide, 2X SSC. Store the solution at 4°C and it can be repeatedly used for several months. Hybridization buffer: 70% formamide, 2X SSC, 10% dextran sulfate. Human Cot I-DNA (1 mg/mL, Gibco-BRL, Gaithersburg, MD). 20X SSC: 175.3 g NaCl and 88.2 g sodium citrate, pH 7.0, in 1 L distilled water. Washing solution I: 50% formamide, 2X SSC. Store the solution at 4°C and it can be repeatedly used for several months.
10. 11. 12. 13. 14.
Washing solution II: 4X SSC, 0.1% NP40 (Calbiochem, La Jolla, CA). Washing solution III: 4X SSC. Block solution: 2% (w/v) BSA in 4X SSC, 0.05% Triton X-100. Store the solution at –20°C. Avidin and Anti-avidin (Vector Laboratories, Burlingame, CA). PNM buffer: 95 mL 0.1 M sodium phosphate, 0.1 mL NP40, 20 mg sodium azide, and 5 g nonfat dry milk in 100 mL distilled water. Incubate the mixture in a 37°C waterbath for 2 h and shake several times during the period to allow all of the milk completely dissolved. Leave the solution at room temperature for 1 d, followed by spinning in a table top centrifuge to pellet the solids. Aliquot the supernatant and stored at 4°C until to be used. 15. Antifade solution: 100 mg p-phenylenediamine dihydrochloride in 10 mL PBS. Adjust to pH 8.0 and add 90 mL glycerol. Filter the solution with 0.22 µm membrane to remove undissolved particles and store it at –20°C. 16. 4', 6-Diamidino-2-phenylindole (DAPI).
3. Methods 3.1. Preparation of Metaphase Chromosomes for Microdissection 1. Mix 0.5 mL peripheral blood with 4.5 mL Complete RPMI 1640 medium containing PHA and culture the cells for 64–68 h at 37°C. 2. The cells are harvested by adding 25 µL colcemid (10 µg/mL) into the culture medium and incubated at 37°C for 20 min. 3. Transfer the cells to a 15 mL centrifuge tube and centrifuge at 250g for 5 min, then carefully discard the supernatant. 4. Resuspend the remaining cell pellet in 10 mL of hypotonic solution and incubate the cells in a waterbath at 37°C for 12–18 min. Centrifuge at 250g for 5 min and discard the supernatant. 5. Resuspend the remaining cell pellet thoroughly but gently in 8 mL freshly prepared Carnoy's fixative and place the tube on ice for a minimum of 2 h. Centrifuge at 250g for 5 min and then remove the supernatant carefully. 6. Wash the cells twice with 5 mL Carnoy's fixative by centrifuging at 250g for 5 min. 7. Resuspend the cell pellet in 0.5–1.5 mL Carnoy's fixative to obtain a lightly opaque cell suspension before preparing slides (see Note 2). 8. Drop 2–3 drops of cell suspension onto a clean coverslip held at 45° angle, allowing the cell suspension to run down the length of the coverslip. Do not blow the slide to avoid contamination. 9. Keep the prepared coverslips in a sterile container at 37°C for 3–5 d prior to G-banding (see Note 3). 10. Standard G-banding with trypsin-Giemsa (GTG) was performed prior to microdissection. Briefly, treat the slide with trypsin working solution at room temperature for 1–2 min. Transfer the slide to Giemsa working solution for 5 min at room temperature, then rinse the slide with distilled water and air dry. (All steps above should be performed under sterile conditions.)
3.2. Microdissection and Topo I Treatment 1. Find the target chromosome under an inverted microscope fitted with a stage that can be freely rotated to allow the target chromosome perpendicular to the axis along where the glass needle is moved. If possible, the microscope should reside on an anti-vibration table to dampen out vibration.
2. Dissect the target chromosomal region with glass needles controlled by a micromanipulator attached to the inverted microscope (see Note 4). 3. Pick up the dissected DNA fragment with the needle by positioning the tip of the needle directly above the DNA fragment and then moving the needle down and lightly touching the fragment. The DNA fragment will be held to the tip by electrostatic forces and then is transferred into a 5 µL collection solution by touching the needle tip to the fluid. 4. After the desired number of dissected DNA fragments (5 copies) are collected, the collection solution is covered with a drop of mineral oil. Before the amplification of dissected DNA, the DNA is treated with Topo I at 37°C for 1 h to relax the very tight DNA coiling.
3.3. Amplification of Dissected DNA 1. An initial PCR (5–8 cycles at 94°C for 1 min, 30°C for 2 min, and 37°C for 2 min) is conducted by adding approx 0.3 U of Sequenase at 30°C each cycle [Sequenase (13 U/µL) is diluted 1–8 in enzyme dilution buffer, and 0.2 µL is added to 5 µL reaction mixture]. 2. Following this pre-amplification step, a conventional PCR reaction catalyzed by Taq DNA polymerase is performed in the same tube. Fifty µL PCR reaction mixture is added and a 30-cycle reaction at 94°C for 1 min, 56°C for 1 min, and 72°C for 1.5 min is performed, with a final elongation time of 5 min at 72°C. 3. Add 2 µL of first round PCR products into another 50 µL PCR reaction mixture and perform 20 PCR cycles identical to that described in step 2. 4. The success of the process can be judged at this point by eletrophoresis analysis. Load 5 µL of the PCR products onto a 1% agarose gel. The size distribution of PCR products is 200–800 base pairs (see Note 5).
3.4. Fluorescence In Situ Hybridization 1. Prepare FISH probe by adding 2 µL of second round PCR products into a 50 µL PCR reaction mixture identical to that described in the above steps except for the addition of 20 µM Biotin-16-dUTP for final concentration. The PCR reaction is continued for 20 cycles at 94°C for 1 min, 56°C for 1 min, and 72°C for 2 min, with a 5 min final extension at 72°C. 2. Remove unincorporated Biotin-16-dUTP from the product by centrifuging on a Bio-gel P6 filtration column following the manufacture's instructions. 3. Recover the probe by precipitation with 1/10 vol of 3 M sodium acetate and 2 volumes of ethanol for 20 min at 4°C and centrifugation at 10,000g for 15 min at 4°C. Resuspend the probe in 40 µL TE buffer. 4. Hybridization of the FISH probes is based upon the procedure described previously (12). Briefly, for each hybridization, about 100 ng labeled probe is mixed in 10 µL hybridization mixture (7 µL hybridization buffer, 2 µL probe, 1 µL human Cot I DNA) which is denatured at 75°C for 5 min followed by a pre-hybridization at 37°C for 20 min. 5. Denature a slide bearing metaphase spreads for 2 min at 72°C in denaturing solution, then dehydrate the slide through a series of 70, 85, and 100% ethanol. 6. Place the hybridization mixture on the slide previously denatured and cover with a 22 × 22 mm coverslip, seal with rubber cement, and incubate the slide at 37°C overnight in a humidified container. 7. After hybridization, the coverslip is removed and the slide is washed 3× in washing solution I at 45°C for 5–10 min each. 8. Wash the slide 3× in washing solution II and 1× in washing solution III at room temperature for 2 min each.
9. Hybridization involving only directly labeled probes can be analyzed at this point. Hybridization involving biotin labeled probe is then treated with 40 µL FITC-conjugated avidin (5 µg/mL) in PNM buffer for 20 min at room temperature. The slide is then washed as described at step 8. 10. The fluorescence signal is then amplified by treating the slide with 40 µL anti-avidin antibody (5 µg/mL) in PNM buffer for 20 min at room temperature. The slide is then washed as described in step 8. 11. The slide is usually treated with one more layer of FITC-conjugated avidin as the identical to that described in step 9. 12. The slide is dehydrated through a series of 70, 85, and 100% ethanol washes and air dried. Counterstain the slide with 40 µL antifade solution containing DAPI (1 µg/mL). The slide is then coverslipped and examined with a fluorescence microscope equipped with appropriate filters.
4. Notes 1. To diminish the impact of contamination, all glassware for the preparation of reagents should be washed and autoclaved twice before use. Water with highest purified grade should be filtered through a 0.22 micron filtration unit, then autoclaved twice for 40 min before use. Likewise, salts solutions are prepared from reagents of the highest available purity, and are filtered and autoclaved in the same fashion as the water. 2. Fix cells with Carnoy's fixative solution (3:1 methanol and glacial acetic acid is acceptable). High quality FISH probe can be obtained using cells fixed in Carnoy's fixative within one year. 3. The age of coverslip with metaphase chromosomes for microdissection should be between 3–14 d. Exposure of coverslips to high temperature (>60°C) or prolonged the storage time may reduce the quality of the product from microdissection. 4. Glass needles are prepared on a spring-loaded, automated pipet puller. Needle diameters at the point of breakage should be the width of a chromosome. Needles are placed on plasticine strips in culture dishes for contamination-free storage. Once prepared, the needles are irradiated with UV light for 5 min in an ultraviolet cross linker to ensure that they are free of DNA contamination. 5. DNA contamination is a critical problem in the amplification of dissected DNA. Since the initial amount of dissected material is exceedingly small (in the range of 10–13 to 10 –14 g/fragment), even minute amounts of contaminating DNA can overwhelm the dissected DNA and lead to useless amplification products. The contaminated DNA may derive from a glass needles which touches DNA other than the target DNA, could be introduced into the collection drop from the air when the tube is repeatedly opened and closed, or even from one of the reagents which has been contaminated with extraneous DNA before microdissection. Therefore, all reagents used for microdissection should be tested for contamination prior to microdissection experiment. The test is carried out by regular PCR reaction with 0.1 ng total human genomic DNA or without DNA. After 40 cycles at 94°C for 1 min, 56°C for 1 min, and 72°C for 2 min, the purity of the tested PCR reagents can be checked by electrophoresis analysis. If the positive control produces extensive products in the size range of 200–800 base pairs, whereas the negative control produces little or no visible product, the test reagent is suitable for microdissection. Otherwise, it is necessary systematically to replace each of the reagents until a negative blank is obtained. After all PCR reagents are confirmed suitable for microdissection, Topo I and Sequenase should be also tested.
References 1. Miteiman, F., Kaneko, Y., and Trent, J. (1991) Human gene mapping 11: Report of the committee on chromosome changes in neoplasia. Cytogenet. Cell Genet. 58, 1053–1079. 2. Frezal, J. and Schinzel, A. (1991) Human gene mapping 11: Report of the committee on clinical disorders, chromosome aberrations and uniparental disomy. Cytogenet. Cell Genet. 58, 986–1052. 3. Sandberg, A. (1990) The Chromosomes in Human Cancer and Leukemia. Elsevier Press, New York. 4. Meltzer, P. S., Guan, X.-Y., Burgess, A., and Trent, J. M. (1992) Rapid generation of region specific probes by chromosome microdissection and their application. Nat. Genet. 1, 24–28. 5. Sclaenghe, F., Turco, K. E., Edstrom, J-E., Pirrotta, V., and Melli, M. (1981) Microdissection and cloning of DNA from a specific region of Drosophila melanogaster polytene chromosomes. Chromosoma 82, 205–216. 6. Rohme, D., Fox, H., Herrmann, B., et al. (1986) Molecular clones of the mouse t complex derived from microdissected metaphase chromosomes. Cell 36, 783–788. 7. Lüdecke, H.-J., Senger, G., Claussen, U., and Horsthemke B. (1989) Cloning defined regions of the human genome by microdissection of banded chromosomes and enzymatic amplification. Nature 338, 348–350. 8. Saunders, R. D., Glover, D. M., Ashburner, M., et al. (1989) PCR amplification of DNA microdissected from a single polytene chromosome band: A comparison with conventional microcloning. Nucl. Acids Res. 17, 9027–9037. 9. Johnson, D. H. (1990) Molecular cloning of DNA from specific chromosomal regions by microdissection and sequence-independent amplification of DNA. Genomics 6, 243–251. 10. Kao, F-T. and Yu, J-W. (1991) Chromosome microdissection and cloning in human genome and genetic disease analysis. Proc. Natl. Acad. Sci. USA 88, 1844–1848. 11. Wesley, C. S., Ben, M., Kreitman, M., Hagag, N., and Eanes, W. F. (1990) Cloning regions of the Drosophila genome by microdissection of polytene chromosome DNA and PCR with nonspecific primer. Nucl. Acids Res. 18, 599–603. 12. Guan, X.-Y., Trent, J. M., and Meltzer, P. S. (1993) Generation of band-specific painting probes from a single microdissected chromosome. Human Molecular Genet. 2, 1117–1121. 13. Guan, X.-Y., Meltzer, P. S., Cao, J., and Trent, J. M. (1992) Rapid generation of regionspecific genomic clones by chromosome microdissection: Isolation of DNA from a region frequently deleted in malignant melanoma. Genomics 14, 680–684. 14. Yu, J., Tong, S., Yang-Feng, T., and Kao, F.-T. (1992) Construction and characterization of a region-specific microdissection library from human chromosome 2q35–q37. Genomics 14, 769–774. 15. Leach, F. S., Nicolaides, N. C., Papadopoulos, N., et al. (1993) Mutations of a mutS Homolog in hereditary nonpolyposis colorectal cancer. Cell 75, 1215–1225. 16. Guan, X.-Y., Meltzer, P. S., and Trent, J. M. (1994) Rapid construction of whole chromosome painting probes by chromosome microdissection. Genomics 22, 101–107. 17. Guan, X.-Y., Zhang, H. E., Bitter, M., Jiang, Y., Meltzer, P. S., and Trent, J. M. (1996) Chromosome arm painting probes. Nat. Genet. 12, 10–11. 18. Guan, X.-Y., Meltzer, P. S., Burgess, A., and Trent, J. M. (1995) Complete coverage of chromosome 6 by microdissection probes. Human Genet. 95, 637–640. 19. Meltzer, P. S., Guan, X.-Y., and Trent, J. M. (1993) Telomere capture stabilizes chromosome breakage. Nat. Genet. 4, 252–255.
20. Guan, X.-Y., Horsman, D., Zhang, H., Meltzer, P. S., and Trent, J. M. (1996) Mapping a recurrent breakpoint on chromosome 6q11 in human follicular lymphoma by chromosome microdissection. Blood 88, 1418–1422. 21. Weimer, J., Kiechle, M., and Arnold, N. (2000) FISH-microdissection (FISH-MD) analysis of complex chromosome rearrangements. Cytogenet. Cell Genet. 88, 114–118. 22. Guan, X.-Y., Meltzer, P. S., Dalton, W. S., and Trent, J. M. (1994) Identification of cryptic sites of DNA sequence amplification in human breast cancer by chromosome microdissection. Nat. Genet. 8, 155–161. 23. Van Den Berg, C., Guan, X.-Y., Von Hoff, D., et al. (1995) DNA sequence amplification in human prostate cancer identified by chromosome microdissection: Potential prognostic implications. Clin. Cancer Res. 1, 11–18. 24. Su, Y. A., Meltzer, P. S., Guan, X.-Y., and Trent, J. M. (1994) Direct isolation of expressed sequences encoded within a homogeneous staining region by chromosome microdissection. Proc. Natl. Acad. Sci. USA 91, 9121–9125. 25. Guan, X.-Y., Xu, J., Anzick, S. L., Zhang, H. E., Trent, J. M., and Meltzer, P. S. (1996) Direct selection of transcribed sequences from microdissected DNA: Isolation of genes within a commonly amplified region at 20q11–q13.2 in breast cancer. Cancer Res. 56, 3446–3450. 26. Telenius, H., Pelmear, A. H., Tunnacliffe, A., et al. (1992) Cytogenetic analysis by chromosome painting using DOP-PCR amplified flow-sorted chromosomes. Genes Chromsom. Cancer 4, 257–263. 27. Zhang, J., Meltzer, P., Jenkins, R., Guan, X.-Y., and Trent, J. (1993) Application of chromosome microdissection probes for elucidation of BCR-ABL fusion and variant Philadelphia chromosome translocations in chronic myelogenous leukemia. Blood 81, 3365–3371.
6 Primed In Situ Labeling Jørn Koch 1. Introduction PRINS (Primed in situ labeling) produces the same type of result as FISH; namely a hybridization dependant staining of specific DNA sequences in cell and tissue preparations. However, the staining is obtained differently, as the probe used in PRINS is unlabeled and staining results from the synthesis of labeled DNA at sites binding the probe. To obtain this site specific DNA synthesis, the probe is hybridized in the presence of a primer-dependant DNA polymerase that can synthesize DNA from the 3'-end of the probe (primer) as it hybridizes, as well as labeled nucleotides serving as substrates for the DNA synthesis. The main advantages of the PRINS design are faster and cheaper detection of target sequences with probes that penetrate well (see Note 1), probes are readily available from any oligonucleotide synthesis facility, and can be designed to suit the purpose. The disadvantages are that PRINS requires a better quality of the specimen and better incubators than the more rough FISH technique (see Notes 2–4), fewer optimized probes are commercially available, and multiple single copy targets can not be detected simultaneously. An international PRINS working group has been established, and there is a website at www.icg-prins.org. A list of tested primer sequences will be published on that site. However, with the lack of commercial interest in the PRINS technique, these are not likely to be taken through official governmental approval procedures, which may limit the diagnostic use in some parts of the world.
1.1. Applications of the PRINS Technique 1.1.1. Sensitive, High Discrimination Detection of Tandem-Repeat DNA The technique was first designed to enable the discrimination between closely related tandem-repeat sequences (1), and detection of tandemly repeated target sequences in chromosomes and nuclei (in situ) by oligonucleotide probes is still the primary use of the technique (2). With a simple short procedure, such sequences can be efficiently From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
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detected down to small target sizes and with single nucleotide discrimination (3,4). Recently, this application was further enhanced by the development of the dideoxyPRINS (ddPRINS) approach. In ddPRINS, the absence of one or more nucleotides from certain repeat sequences is employed to further improve discrimination and signal/noise ratios in PRINS. The basis for ddPRINS is that such DNA can be efficiently synthesized also when the missing nucleotide is included as a dideoxyanalogue, whereas nonspecific synthesis of DNA is blocked. Telomeric repeats e.g., contain a G-rich strand missing cytosine, and a complementary C-rich strand missing guanine. Consequently, the G-rich strand can be produced in a ddPRINS including ddCTP, and the C-rich strand in a dd-PRINS including dGTP. Relative to a standard PRINS, the ddPRINS improve the signal/noise ratio of telomere staining by about an order of magnitude, increases the efficiency to virtually 100%, and lowers the detection limit to a few hundred bases of target DNA (presumably corresponding to 2–3 priming events per target site) (5–8). Furthermore, since one strand of the target is flanked at its 5'-end by one sequence, and the other strand by another, it is possible to also determine the orientation of the target. It has been possible to determine the relative orientation of various telomeric repeat variants with respect to each other by this method (6–8).
1.1.2. Quantitative Detection of DNA Sequences (Q-PRINS) As the PRINS design allows for high concentrations of small probes that penetrate the specimen well, targets can be effectively saturated, and the reaction made quantitative. This possibility has been used in particular for measuring the size of telomeric repeat domains at individual chromosome ends, based on the ddPRINS reaction (5). A similar approach can be applied to the sizing of other simple repeat domains that vary in size, such as trinucleotide repeats. Q-PRINS reactions can be evaluated in either of two ways. The first is simply to measure the staining frequency (how many out of 100 potential targets are actually stained). The higher the staining frequency, the larger the target (9). With the dd-PRINS, this often becomes impractical as the staining efficiency in many cases is close to 100%. In normal blood lymphocytes, the main telomeric repeat is stained with an average efficiency of 99.8% (see Fig. 1). In such cases, it is preferable to measure the light intensities of the PRINS signals instead. We have described a procedure for this, employing the pre-existing image analysis program QUIPS from VYSIS for the purpose (5). Another analysis program has become available from DAKO. This program seems equally suited for signal quantification. Expanded trinucleotide repeats are generally stained with a low enough efficiency to be evaluated for relative size by determining the percentage of cells labeled.
1.1.3. Detection of Single Copy Targets The detection of such targets has traditionally been the Achilles heel of the PRINS technique. However, it was recently reported that single copy sequences could be detected at high sensitivity, if multiple primers are used and signals are enhanced with the Tyramide amplification system (10,11). Apart from these two modifications, the single copy target detection procedure does not differ from previous PRINS protocols.
Fig. 1. ddPRINS on a spread of human chromosomes. Each chromosome is made of two chromatids, and each chromatid has two ends, so the number of targets/signals/cell is in principle 184. However, signals on neighboring chromatids may appear fused. The outline of the chromosomes is also visible, mainly owing to autofluorescence from the chromatin.
1.1.4. Self-Primed In Situ Labeling (SPRINS) In the absence of added primer, primed in situ labeling from endogenous priming sites (self-labeling) can be detected. In normal chromosome spreads it is seen as a very faint background staining (absent in ddPRINS). In spreads of low quality, the background staining is increased (see Note 2). However, most notably, the phenomenon can be employed to study the in vitro and in vivo activity of DNA modifying enzymes. Digestion of chromosome spreads with nucleases or restriction enzymes produce nicked chromosomes where the density of nicks (and thus sites of enzyme activity) can be displayed by SPRINS (Fig. 2). Similarly, if DNA is nicked in vivo as a consequence of cell processes, the resulting nicks can subsequently be detected by SPRINS (e.g., detection of apoptosis or topoisomerase activity) (12).
Fig. 2. SPRINS on a spread of human metaphase chromosomes digested with the restriction enzyme Msp I. The chromosomes appear with a chromosome specific banding pattern.
1.1.5. Combinatorial Labeling PRINS can be combined with PRINS, FISH, or immunostaining for the simultaneous detection of multiple targets (13–15). Doing a PRINS reaction ahead of a FISH reaction often eliminates the need for other pretreatments (e.g., proteinase treatment). PRINS is less destructive to the quality of the specimen than FISH, and also less destructive to the quality of a preceding immunostaining reaction. Thus, if the antibody has been "secured" at the site by fixation in paraformaldehyde, very little loss of antibody staining occurs as a result of the following PRINS reaction.
2. Materials 1. 2. 3. 4.
Chromosome spreads (see Note 3). Cover slips. Coplin jars, or other suitable containers for washing the slides. Standard nucleoside triphosphates, dideoxy nucleotides for ddPRINS (Lithium salt, Roche). Hapten or fluorochrome labeled nucleotides (digoxigenin-dUTP, biotin-dUTP, fluorescein-dUTP, rhodamine-dUTP [Roche]). 5. Tth or Taq DNA polymerase and 10× polymerase buffer (enzyme and buffer are supplied together by Roche).
PRINS 6. 7. 8. 9. 10. 11. 12.
5 M NaCl. 500 mM EDTA. 20X SSC. 20% Tween 20. Ice cold (–20°C) ethanol series (70, 90, 99% (vol/vol)) for PRINS on predenatured slides. Nonfat dry milk (powder). Fluorochrome labeled anti-digoxigenin for detection of digoxigenin labeled PRINS product (Fab fragment, Roche). Fluorochrome labeled Streptavidin for detection of biotin labeled PRINS product (Roche, Vector Laboratories). Antifade solution: Vectashield (Vector Laboratories) or p-phenylenediaminedihydrochloride (Sigma). Counterstain: either propidium iodide (Sigma) or DAPI (Sigma). 10X dNTP for basic PRINS (1.0 mM each of dATP, dCTP, and dGTP, 0.1 mM of labeled dUTP, mix in 50% glycerol). Can be stored at –20°C for at least 1 yr. The glycerol keeps the liquid from solidifying at 20°C so it is possible to aliquot from a stock without cycles of thawing and freezing. 10X dNTP for dideoxy-PRINS (with ddGTP) (1.0 mM each of dATP, dCTP, 1.0 mM ddGTP, 0.1 mM of labeled dUTP, mix in 50% glycerol). Can be stored at –20°C for 1 yr. Reaction mixture (for basic PRINS in a 50 µL volume): 38 µL ddH2O, 5 µL 10X polymerase buffer, 5 µL 10X dNTP, 1 µL DNA probe (from 500 ng and up), 1 µL DNA polymerase (1 U), mix gently by tapping a finger on the Eppendorf tube, and use immediately after inclusion of the polymerase.). Reaction mixture without polymerase may be stored at –20°C for months. Stop buffer: 50 mM NaCl, 50 mM EDTA, pH 8.0. Wash buffer: 4X SSC, pH 7.0 (1X SSC: 150 mM NaCl, 15 mM sodium citrate), 0.05% Tween 20. Blocking solution: 5% (w/vol) nonfat dry milk dissolved in washing buffer. Centrifuge for 2 min in an Eppendorf centrifuge and use supernatant). Can be stored at –20°C for years. When in use, it is preferable to store the blocking solution at 20°C and do not use it for more than 1 wk (the milk turns sour with time). Either two incubators (thermoblocks, waterbaths) where the slide can be put on a metal surface to ensure good heat transfer, one with a surface temperature of 94°C and the other with a surface temperature of 55–65°C. The temperature of the 94°C incubator should be measured very carefully, as it should not deviate more than 1–2°C from the desired value. To ensure this it may be helpful to cover the slide and the hot plate with an insulating lid (see Note 3), or a special PRINS/in situ PCR machine (from Hybaid, MJ-Research or Techne) preset (simulated slide function) to incubate the slide at 91–94°C for 2–4 min and at 55–65°C for 5–60 min (depending on the oligonucleotide used). The reason for the slightly lower setting during denaturation in this case stems from the build-in compensation for the 1.5°C temperature difference between the hotplate and the interior of the slide on a metal surface covered with a lid (see Note 4).
3. Methods 3.1. Standard One-Step Reaction The PRINS protocol comes in two variants. Either the slide is denatured in hot formamide, as for FISH, and immediately quenched in an ice cold ethanol series as described in Subheading 3.4., or the slide is denatured by heating the slide with the reaction mixture added to a denaturing temperature as follows:
1. Decide how large a region of the slide should be analyzed, and choose a cover slip and an amount of reaction mixture that fits the area. Use 1 µL reaction mixture for each mm of cover slip length. To cover a standard slide completely, prepare 60 µL reaction mixture and cover with a 24 × 60 mm cover slip. To cover a smaller area, prepare less reaction mixture (and use a smaller coverslip). 2. As soon as the reaction mixture has been spread with the cover slip, the slide is denatured by placing it on a hotplate covered with a lid for 4 min at 94°C (see Note 4). 3. Transfer the slide quickly to 55–65°C and incubate for 5–60 min for probe annealing and chain elongation. Probes for simple repeats anneal rapidly, more complex probes more slowly, and chain elongation is virtually instantaneous, so the annealing time determines the incubation time. 4. Place the slide in preheated stop buffer at the temperature used in step 3 for 1 min to terminate the PRINS reaction. 5. Transfer the slide to 50 mL of wash buffer and wash for approx 3 min at room temperature (the reaction can be paused at this step, and the slide stored overnight in wash buffer at 4°C). 6a. If fluorochrome labeled nucleotides have been used, the slide can now be counterstained, mounted and evaluated under the microscope. 6b. If digoxigenin labeled nucleotides have been used, they need to be visualized with antidigoxigenin antibody as described in Subheading 3.6.
3.2. Dideoxy-PRINS In the PRINS procedure, simply replace the nucleotide(s) not needed for DNA synthesis from correctly hybridized probes with the corresponding dideoxy-nucleotides (e.g., replace dGTP when synthesizing the CCCTAA element of the human telomere).
3.3. Combinatorial Labeling There are two basically different strategies to combinatorial labeling, either the PRINS is done first or the PRINS is done last. In PRINS-FISH, PRINS is done first to avoid PRINS reactions from the FISH probe(s), and the denatured FISH probe is added to the slide after the latter has been quenched in ice-cold ethanol. It is important that the slide is not (re)denatured after the PRINS, as this may cause the PRINS signal to disappear. In PRINS-immunostaining the PRINS is done last, and after the immunostaining the slide is fixed in 2% paraformaldehyde for 2 min at room temperature and dehydrated through an (70, 90, and 99%) ethanol series prior to the PRINS to enhance the survival of the immunostaining.
3.4. PRINS on Already Denatured Slides If it is preferred to use a slide which has been denatured in formamide, e.g., if the incubator is not sufficiently reliable for robust heat denaturation, the slide is denatured in 70% formamide, 70°C, for 2 min, or according to your standard protocol for FISH denaturation. The slide may have also been previously denatured if a previous PRINS reaction has been conducted. In both cases it is important that the slide is immediately quenched in a –20°C ethanol series to fix the target DNA in the denatured configuration. 1. Dehydrate the slide in a –20°C ethanol series (70, 90, and 99%, 3 min each) as soon as possible after denaturation.
2. Remove the slide from the 99% ethanol, drain and airdry. 3. Prepare a reaction mixture as above steps. If this is a second PRINS reaction, make sure to use a different label on the dNTP this time. 4. Annealing and chain elongation: the slide is preheated to 55–65°C for 1 min. Then, the likewise preheated reaction mixture is put on the slide and spread with a coverslip. 5. Incubate, stop and wash as above. The slide is now ready for antibody staining and counterstaining/mounting. 6. If a third PRINS reaction is desired, repeat steps 1–5.
3.5. Self-Primed In Situ Labeling (SPRINS) SPRINS can be done according to the above protocol, Steps 2–5 (the slide should not be denatured at any point, so there is no need for Step 1).
3.6. Visualization of Digoxigenin or Biotin Labeled PRINS Product 1. Apply 50 µL of fluorochrome conjugated anti-digoxigenin (or fluorochrome conjugated Streptavidin) in blocking solution (2 ng/µL) to the slide. Incubate under a coverslip for 30–60 min in the dark. 2. Wash 2 × 5 min in 50 mL of washing buffer. The slide is now ready for counterstaining and mounting.
3.7. Counterstaining and Mounting 1. Blue counterstaining of DNA is obtained by including 0.4 µM DAPI in the antifade solution. 2. Red counterstaining of DNA is obtained by including propidium iodide in the antifade solution. Mount the slide in 20 µL of antifade solution containing 0.5 µg/mL propidium iodide.
4. Notes 1. An advantage of the PRINS technique is that the probes are very small, and thus penetrate easily to the target, even when this is in a tight conformation. This is exploited by Franck Pellestor's group for efficient staining of target sequences in sperm cells (16). 2. An occasional problem in PRINS is "self-labeling" of certain regions of satellite DNA. In human chromosomes, satellite III on chromosome 9, and more rarely, satellite II on chromosomes 1 and 16 may self-label. This self-labeling is somewhat primer dependent, but may occur with any primer. Some primers always induce the self-labeling, but with most primers it is only seen in low quality chromosome spreads, and the solution to the problem therefore is to make better spreads. 3. The PRINS technique relies strongly on the intact nature of the target sequences. Nicked or broken DNA is not only a poor template for chain elongation, in situ, through endogenous chain elongation in situ nicks in the chromosomal DNA may also raise the otherwise low background staining associated with PRINS. As accessibility of the target is generally not a problem in PRINS on standard chromosome spreads, freshly prepared slides are the preferred starting point for an optimal reaction. If optimal slides can not be prepared, accessibility can be increased by treatment with a proteinase (DNAse-free!), vulnerable chromatin can be stabilized by fixation with paraformaldehyde, and damaged DNA can be repaired with a DNA ligase. The chromatin in "aged" slides may be so hardened that it requires long incubations to denature it by heat, e.g., 10 min for a slide aged one month at room temperature. 4. If heat denaturation of slides is used, a strict temperature control is needed to provide optimal denaturation of target sequences without destroying the polymerase. Suitable
Koch computerized incubators are available from a range of companies (we use incubators from Hybaid, and from MJ-Research). If specialized incubators are not available, stable waterbaths or hot-plates can be used. It is important that any such equipment is covered with an insulating lid to ensure the right and reproducible incubation temperature.
References 1. Koch, J., Kølvraa, S., Gregersen, N., and Bolund, L. (1989) Oligonucleotide-priming methods for the chromosome-specific labeling of alpha satellite DNA in situ. Chromosoma 98, 259–265. 2. Koch, J., Hindkjær, J., Kølvraa, S., and Bolund, L. (1995) Construction of a panel of chromosome specific oligonucleotide probes (PRINS-primers) useful for the identification of individual human chromosomes in situ. Cytogenet. Cell Genet. 71, 142–147. 3. Pellestor, F., Girardet, A., Andréo, B., and Charlieu, J. P. (1994) A polymorphic alpha satellite sequence specific for human chromosome 13 detected by oligonucleotide primed in situ labeling (PRINS). Hum. Genet. 94, 346–348. 4. Pellestor, F., Girardet, A., Lefort, G., Andréo, B., and Charlieu, J. P. (1995) Rapid in situ detection of chromosome 21 by PRINS technique. Am. J. Med. Genet. 56, 1–8. 5. Krejci, K. and Koch, J. (1998) Improved detection and comparative sizing of human chromosomal telomeres in situ. Chromosoma 107, 198–203. 6. Krejci, K. and Koch, J. (1999) An in situ study of variant telomeric repeats. Genomics 58, 202–206. 7. Serakinci, N. and Koch, J. (1999) Detection and sizing of human telomeric repeat DNA in situ. Nature Biotech. 17, 200–201. 8. Serakinci, N. Krejci, K., and Koch, J. (1999) Telomeric repeat organization—a comparative in situ study between man and rodent. Cytogenet. Cell Genet. 86, 204–211. 9. Therkelsen, A. J., Nielsen, A., Koch, J., Hindkjær, J., and Kølvraa, S. (1995) Staining of Human telomeres with primed in situ labeling (PRINS). Cytogenet. Cell Genet. 68, 115–118. 10. Kadandale, J. S., Tunca, Y., and Tharapel, A. T. (2000) Chromosomal localization of single copy genes SRY and SOX3 by primed in situ labeling (PRINS). Microbial and Comparative Genomes 5, 71–74. 11. Kadandale, J. S., Wachtel, S. S., Tunca, Y., Wilroy Jr., R. S., Martens, P. R., and Tharapel, A. T. (2000) Localization of SRY by primed in situ labeling in XX and XY sex reversal. Am. J. Med. Genet. 95, 71–74. 12. Andersen, C., Koch, J., and Kjeldsen, E. (1998) CpG islands detected by self primed in situ labeling (SPRINS). Chromosoma 107, 260–266. 13. Mitchell, A., Jeppesen, P., Hanratty, D., and Gosden J. (1992) The organization of repetitive DNA sequences on human chromosomes with respect to the kinetochore analysed using a combination of oligonucleotide primers and CREST anticentromere serum. Chromosoma 101, 333–341. 14. Hindkjær, J., Koch, J., Terkelsen, C., Brandt, C. A., Kølvraa, S., and Bolund, L. (1994) Fast and sensitive multicolor detection of nucleic acids in situ by PRimed IN Situ labeling (PRINS). Cytogenet. Cell Genet. 66, 152–154. 15. Hindkjær, J., Brandt, C. A., Koch, J., Lund, T. B., Kølvraa, S., and Bolund, L. (1995) Simultaneous detection of centromere specific probes and chromosome painting libraries by a combination of Primed in situ labeling and chromosome painting (PRINS-painting). Chromosome Res. 3, 41–44. 16. Pellestor, F., Girardet, A., Andréo, B., Lefort, G., and Charlieu, J. P. (1997) Incidence of chromosome 1 disomy in human sperm estimated by the primed in situ (PRINS) labeling technique. Cytogenet. Cell Genet. 76, 192–195.
Spectral Karyotyping
7 Spectral Karyotyping Jane Bayani and Jeremy A. Squire 1. Introduction Historically in clinical cytogenetics, G-banding has been the gold standard for detecting gross chromosomal abnormalities, ranging from simple numerical changes to the identification of complex structural rearrangements in clinical samples. The designation "marker chromosome" or "derivative chromosome" has been used to indicate that G-banding has been unable to provide a definitive identification of the aberration. This is often because the complexity of the rearrangement has resulted in the lack of a coherent and recognizable banding pattern. The advent of the various multicolor fluorescence in situ hybridization (FISH) chromosomal painting techniques (1,2) has greatly improved our ability to identify all marker chromosomes, but these techniques still need some careful planning in rapidly achieving the goal of identifying complex chromosomal rearrangements. Spectral karyotyping (SKY) involves the use of 24-color, whole chromosomepainting permitting visualization of each chromosome in one experiment. This technology is based on the principles of spectral imaging (3) and Fourier spectroscopy (4). Flow sorted chromosomes are PCR-labeled (5), either directly or indirectly, with fluorochromes or haptens. Five pure dyes that are spectrally distinct are used in combination to create the unique chromosome cocktail of probes. This probe cocktail is hybridized to metaphase preparations and detected using sophisticated image analytical methodologies. Image acquisition (Fig. 1) is accomplished by conventional fluorescence microscopy and the use of a specially designed triple filter (SKY CUBE™, Applied Spectral Imaging). In this design, light passes through a Sagnac interferometer focussed on a charged-coupled device (CCD) detector. Spectral images are acquired and analyzed with the commercially available SD 200 Spectral Bio-Imaging System (ASI Ltd., MigdalHaemek, Israel). The generation of a spectral image is achieved by acquiring ~100 frames of the same image that differ from each other only by the optical path difference (OPD). The collected images are Fourier Transformed and the data sorted in the software (SKYVIEW™). Each chromosome has a unique From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
07_Squire_85-104F[7.10.2]
Bayani and Squire
Fig. 1. Schematic representation of image acquisition using an interferometer housed in the optical head (Applied Spectral Imaging, Carlsbad, CA). Images from the hybridized specimen are collected, Fourier transformed and processed.
spectral "signature", generated by the specific combination of one or more of the five pure dyes. Once a spectral image is acquired, the SKYVIEW™ software compares the acquired spectral image against the combinatorial library containing the fluorochrome combinations for each chromosome and generates a "classified" image. The classified image pseudo-colors the chromosomes to aid in the delineation of specific structural aberrations where the RGB (Red-Green-Blue) display image, which displays the fluorescent colors of the chromosomes may appear quite similar (Fig. 1). For every chromosomal region, identity is determined by measuring the spectral emission pixel by pixel. Regions where sites for rearrangement or translocation between different chromosomes occur are visualized by a change in the display color at the point of transition (Fig. 2A). One of the most obvious limitations of SKY is its inability to readily detect deletions or other intrachromosomal structural changes such as inversions. However, there are some compelling reasons for the systematic use of SKY in the analysis of abnormal chromosome preparations of the type encountered in cancer cells. The ease of interpretation of the clearly assigned color patterns means that it is not essential to have a highly experienced metaphase analyst to perform the microscopy. In addition the acquired images can be analyzed objectively so that subtle translocations as small as ~2 megabases of DNA can be detected (6). Such a small chromosomal region would be difficult to detect with certainty by conventional banding analysis. SKY therefore provides a method for rapid high-resolution screening of the cancer karyotype and has applications both in the research and clinical cytogenetics laboratories. To date, spectral karyotyping is the most widely used method for 24-color FISH analysis. It has been used to examine a variety of neoplasms including hematopoietic malignancies (7–13), carcimomas (14–20), sarcomas (21–27), and brain tumors (28,29). Its contributions to clinical genetics is evident in the number of publications examining various syndromes (30–32) and it has been applied to examining assisted reproductive technologies (33–37). SKY has also been successfully applied to murine systems to address diverse research questions (Fig. 2B) often associated with mouse
Fig. 2. SKY analysis of cancer metaphase preparations. (A) SKY Analysis of a human soft tissue sarcoma. The (top left panel) illustrates the inverted DAPI banding of a metaphase which permits identification of chromosomal regions in using patterns similar to G-banding. The central (top panel) shows the display of the same metaphase with arrows indicating the rearranged chromosomes. The (top right panel) shows the aberrant chromosomes as detected by SKY analysis. The (central panel) shows the SKY karyotype using classified in which structural alterations of chromosomes 3, 7, and 18 can be clearly seen. (B) SKY analysis of a murine fibrosarcoma. The (bottom right panel) shows the display of a murine metaphase with arrows indicating the rearranged chromosomes. The (bottom central panel) shows inverted DAPI banding of the same metaphase. The (bottom right panel) shows the SKY karyotype in which structural alterations can be clearly seen.
models of human cancer (38–50). The increased interest in SKY over the last 4–5 yr stems from the convenience and interpretative ease of this powerful molecular cytogenetic screening technique.
1.1. Probe Labeling The SKY probes are available commercially and are created from flow-sorted chromosomes that are usually amplified and labeled using DOP-PCR (5). The 24-chromosome probe cocktail is generated by the combination of 5 pure dyes. This allows 2n–1 or 31 combinations. The color separation for each chromosome is based on individual spectral properties of each fluorochrome as detected by a specially created triple filter (SKYCube™) during a single acquisition step. The creation of customized probes is possible using flow cytometry (2) to sort each chromosome. Thereafter, it is necessary to use the correct spectral settings and fluorochrome combinations for data acquisition and analysis in the preference file of the supplied SKY software.
1.2. Chromosome Preparation from Tissues The utility of SKY in both clinical and research molecular cytogenetics laboratories lies in the ability to hybridize and detect all the chromosomes in the genome. Thus, metaphase chromosomes must be present in cytogenetic preparations. Whether the sample to be tested is derived from hematopoietic sources or solid tissues, the cells used must be mitotically active so that adequate good quality metaphases can be generated after short-term tissue culture. Agents such as colcemid prevent spindle formation and keep cells at metaphase. Finding the proper colcemid times and concentration is a matter of experience and practice. Cell fixation also involves hypotonically swelling the cells, then slowly introducing a methanol:acetic acid fixative. Careful attention to the hypotonic treatment and first methanol:acetic acid fixation can yield cell suspensions that are free from cellular and cytoplasmic debris. Most experienced cytogeneticists acknowledge that the quality of chromosomal preparations for both banding and all FISH procedures can be greatly influenced by the drying environment during slide making and by the age of the slide. Humidity and temperature will significantly influence the rate of fixative evaporation during slide making. The drying time should be well controlled so that when the overall humidity is less then than 30% slide making is performed near a steam source or humidifier. In recent years a controlled environmental evaporation chamber developed by Thermotron Inc. has made for more reproducible slide making and has gained in popularity in clinical laboratories. In view of the cost of performing SKY procedures, it is advisable to ensure that the target slides are consistently of optimal quality and age.
1.3. Slide Pretreatment and Denaturation Once metaphase preparations have been made, the slides must be assessed to determine the necessary slide pre-treatment. All slides should be assessed by phase contrast microscopy before SKY analysis. The presence of cellular and cytoplasmic debris that may contribute to the overall background is sometimes unavoidable, and can be removed by protease treatments. Once a protease treatment has been applied, the DNA must be denatured to a single stranded state to hybridize to the labeled probe. This is
achieved through heat denaturation using a 70% formamide solution. Formamide is used because it lowers the melting temperature of DNA, thus a 75°C solution of formamide is sufficient to denature DNA into single strands. Once the denaturation of the target DNA has been achieved, the slides must immediately be placed in 70% ethanol followed by an increasing alcohol series to keep the DNA target in its denatured state and to remove any residual moisture. The denaturation of the target DNA is the most critical step in any FISH-based assay. Too little denaturation causes poor hybridization efficiency and accessibility of the probe to the target DNA. Too much denaturation destroys the DNA also resulting in poor hybridization efficiency.
1.4. Probe Denaturation The SKY probe, like the target DNA, must also be denatured into its single stranded state in order for hybridization to occur. The probe comes already resuspended in a hybridization solution usually containing formamide and dextran sulfate. As described previously, the formamide allows the DNA to melt at lower temperatures. The use of unlabeled COT-1 DNA in FISH probes serves to suppress repetitive sequence hybridization that is widely dispersed throughout the human genome. Thus, the probe must first be heat denatured at 75°C, then allowed to pre-anneal at 37°C such that the COT-1 DNA can hybridize to and block background signals from these highly repetitive sequences. Because COT-1 DNA represents the fraction of DNA sequences, which have the fastest annealing properties, the 1 h incubation at 37°C will not cause the re-annealing of the labeled DNA.
1.5. Hybridization Once both the target DNA on the slides and the DNA probe has been denatured, the probe is applied to the slides and allowed to hybridize together at 37°C for a minimum of 48 h. The signal strength following hybridization will depend primarily on the completeness of the denaturation process of the target DNA. In addition, the presence of cellular and cytoplasmic debris surrounding the chromosomes, can greatly impair the accessibility of the probe to the target chromosomes.
1.6. Post-Hybridization Washes and Detection The post hybridization washes and detections take the bulk of the laboratory time. To remove any unbound probes, a lower concentration of formamide at 45°C is used followed by a treatment with 1X SSC also at 45°C. Like many hybridization assays, a blocking step is performed to reduce any background or noise present during the immunological detection steps to follow. The blocking solutions are usually made of some combination of bovine serum albumin and a detergent in an isotonic buffer. The commercial SKY probes are combinations of specific paints in which some chromosomal paints have been directly labeled with a fluorochrome, and others have been indirectly labeled with a hapten. The detection reagents provided in the kit contain antibodies to indirectly detect labeled paints. Between incubations with the antibody reagents, a detergent wash is carried out to remove any unbound residual antibodies that could contribute to background. Gentle agitation during these washes helps to reduce the background signals that may appear due to the presence of cellular and
cytoplasmic debris. The final step is the counterstaining of the DNA using DAPI, mixed with an antifading mounting medium. The slides can then be stored at –20°C where the signals can last for several months.
1.7. Image Acquisition For the greatest success in applying SKY analysis to cytogenetic cases, it is not only important to have the proper slide preparations, slide pre-treatment, DNA denaturation, and stringency in post hybridization washes, but to use the image acquisition and analysis software to its fullest potential. As discussed above, the differentially labeled whole chromosome paints are distinguished from each other by their unique spectral properties. Using a fluorescent microscope equipped with the SKYCUBE, light passes through a Sagnac interferometer focussed on a charged-coupled device (CCD) detector. The generation of a spectral image is achieved by acquiring ~100 frames of the same image that differ from each other only by the optical path difference (OPD). These collected images are Fourier transformed and the data sorted in the software (SKYVIEW™). The spectral properties for each pixel can then be compared to the spectral or combinatorial library that drives the SKYVIEW™ software. Acquisition times are generally dependent on the overall fluorescence intensity, although it is not necessarily the signal intensity that influences the accuracy of SKY analysis. Weak signal strength can give equally reliable results provided that the spectral properties of each dye is maintained. Thus, the fidelity of the fluorescence of the probe cocktail and subsequent immunochemical detections is important.
1.8. Hybridization of SKY probes to Previously G-banded Slides: Slide Pretreatment In some situations it may be necessary to perform SKY analysis on previously G-banded material. This procedure can be especially important for verifying an inconclusive chromosomal aberration on a specific metaphase cell. In this situation an image of the G-banded metaphase cell of interest should be captured, the microscope coordinates noted, and promptly prepared for SKY analysis as soon as possible (i.e., within 2 wk). For older samples, slide storage variables such as humidity and ambient temperature will greatly influence success. It is thus very important to find out how the sample was prepared and stored. If there are a limited number of slides remaining from the patient sample of interest, it is sometimes helpful to use a superfluous slide from another sample prepared the same week to derive the best conditions with respect to aging and storage.
2. Materials 2.1. Probes Vial 1 in kit from Applied Spectral Imaging (MigdalHaemek, Israel).
2.2. Chromosome Preparation from Tissues 1. Sample Tissue. 2. Tissue culture media appropriate for short term culturing. 3. Blades and scalpels.
Spectral Karyotyping 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
Sterile Petri dishes. Vented tissue culture flasks and sterile pipets. 37°C CO2 Incubator. Colcemid (10 mg/mL Gibco-BRL). 1X Trypsin (Gibco-BRL) prewarmed to 37°C. Citrate saline at room temperature. 0.075 M KCl prewarmed to 37°C. 37°C Oven or waterbath. 15-mL conical tubes. Tissue culture centrifuge. 3:1 (v/v) methanol:acetic acid. Glass slides (Fisher). 200-µL pipet and tips. Slide storage box.
2.3. Slide Pretreatment and Denaturation 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Metaphase slides aged for 2–3 d. Ethanol series: 70, 80, 95% in plastic or glass Coplin jars cold. Small forceps. 75°C Waterbath. Deionized, distilled high grade formamide. 20X SSC. 10% (w/v) Pepsin. 0.01 M HCl prewarmed to 37°C in an oven or waterbath. 1X PBS at room temperature. 1X PBS/50 mM MgCl2 at room temperature. 1% Formalin/1X PBS/MgCl2 at room temperature. Timer.
2.4. Probe Denaturation 1. Aliquoted labeled probe. 2. 75°C Waterbath or PCR machine. 3. 37°C Waterbath or PCR machine.
2.5. Hybridization 1. 2. 3. 4. 5. 6. 7. 8.
Denatured metaphase slides from Subheading 2.3. Denatured probe from Subheading 2.4. Glass or plastic coverslips (22 × 20 mm). 10-µL or 20-µL pipeter and tips. Rubber cement. Hybridization box. Plastic bag. 37°C Oven.
2.6. Post-Hybridization Washes and Detection 1. Forceps. 2. 45°C Waterbath. 3. Three glass or plastic Coplin jars containing 50% formamide/2X SSC at 45°C.
4. 5. 6. 7.
Three glass or plastic Coplin jars containing 1X SSC at 45°C. Seven glass or plastic Coplin jars containing 0.01% Tween-20/4X SSC at 45°C. One glass or plastic Coplin jar containing 2X SSC at room temperature. Commercially available kit from Applied Spectral Imaging containing: Vial 2: Blocking reagent; Vial 3: Detection reagent; Vial 4: Detection reagent; Vial 5: DAPI/Antifade solution. 8. Plastic slide box for storage at –20°C. 9. 22 × 30-mm glass coverslips.
2.7. Image Acquisition 1. Fluorescent microscope attached to Applied Spectral Imaging Optical Head. 2. Spectral Imaging Acquisition software (Applied Spectral Imaging). 3. SKYVIEW analysis software (Applied Spectral Imaging).
2.8. Hybridization of SKY Probes to Previously G-banded Slides: Slide Pretreatment 1. 2 Coplin jars of xylene. 2. 2 Coplin jars of methanol. 3. Ethanol series: 70, 80, 95% in plastic or glass Coplin jars stored at a cold temperature.
3. Methods 3.1. Probes Commercially available probes are prelabeled in combinatorial fashion and suspended in a hybridization solution.
3.2. Chromosome Preparation from Tissues 1. Using aseptic techniques in a tissue culture hood, finely mince the tissue using the blades in a sterile Petri dish. 2. Transfer the finely minced tissues into a vented-tissue culture flask containing sufficient media to cover the surface of the flask when placed down (usually 10–15 mL is sufficient). 3. Place the flask in the CO2 incubator and leave undisturbed for 24 h. 4. Check for growth using a light microscope. 5. When the desired growth or culture time has been achieved, add colcemid to the flask to a final concentration of 10 µg/mL for 2–3 h (see Note 1) in the CO2 incubator. 6. Transfer the media and any floating tissues or cells to a 15-mL conical tube (see Note 2). For non adherent cells, proceed to Step 10. 7. Add 10 mL of citrate saline to the flask and rinse the attached cells. Discard the citrate saline. 8. Add 10 mL of 1X trypsin to the flask. Monitor the release of adherent cells from the flask surface. Gently pipet the cells off the flask surface and transfer to a 15-mL conical tube. 9. Add 5 mL of fresh media to the 15 mL conical containing the detached cells (see Note 3). 10. Centrifuge the collected cells at 1500g for 10 min. 11. Pour or aspirate off the supernatant leaving approx 0.5–1 mL of solution. Gently resuspend the pelleted cells well by tapping the conical tube with fingers. 12. Add the prewarmed 0.075 M KCl solution in a drop-wise fashion for the first 1 mL, with mixing between drops (see Note 4). After the first mL has been added, add the remaining 14 mL of solution and invert gently. Place at 37°C for 10 min.
13. Add 5 drops of 3:1 methanol:acetic acid solution and invert (see Note 5). 14. Centrifuge at 1500g for 10 min. 15. Pour or aspirate off the supernatant and resuspend the pellet (see Note 6). Add fresh 3:1 methanol:acetic acid fixative with the first 1 mL added dropwise as before. Add the remaining 14 mL of fixative and invert gently. 16. Centrifuge at 1500g for 10 min. 17. Repeat the fixation Step 15. However, the first 1 mL does not need to be added in a dropwise fashion. Centrifuge and repeat for a total of 3 fixations. 18. The cell suspension may be stored in its pellet state under fixative at –20°C. 19. To prepare cytogenetic preparations, pour off the fixative and resuspend the pellet. Add sufficient fresh fixative so that the suspension is slightly translucent. 20. Using a 200-µL pipet, add 100 µL of suspension to clean glass slides (see Note 7). Allow the slides to dry and store at room temperature. Allow the slides to age for at least 2 d naturally, or place the slides at 37°C overnight.
3.3. Slide Pretreatment and Denaturation 1. Metaphase slides should be aged for at least 2 d at room temperature or placed at 37°C overnight before use. 2. Dehydrate the slides in an ethanol series (70, 80, 95%) for 5 min each. Allow the slides to air dry. 3. Add 15–20 µL of a 10% pepsin stock (see Note 8) to 50 mL of prewarmed 0.01 M HCl in a Coplin jar. Place the slides in the jar for 5 min (see Note 9) at 37°C. Meanwhile, prepare a 70% formamide/2X SSC solution in a Coplin jar and place at 75°C. 4. Remove the slides and place them in 1X PBS at room temperature for 5 min. 5. Incubate the slides in 1X PBS/MgCl2 at room temperature for 5 min. 6. To 50 mL of 1X PBS/MgCl2, add 1.5 mL of 37% formalin. Incubate the slides for 10 min in the formalin solution (see Note 10) at room temperature. 7. Incubate the slides in 1X PBS for 5 min at room temperature. 8. Pass the slides in a dehydration series as in Step 2. 9. When the slides have dried, check that the temperature of the formamide solution has reached 75°C (see Note 11). Denature the slides in the formamide solution for 2 min. 10. Immediately place the slides in 70% ethanol and proceed through the last dehydration series (see Note 12). Allow the slides to air dry.
3.4. Probe Denaturation 1. For each slide, use 10 µL of probe to cover a 22 × 22-mm coverslip. If the area to be probed is larger than this, more probe must be used. Place the appropriate amount of probe into an eppendorf tube. 2. Heat denature the probe at 75°C for 10 min either in a waterbath or PCR machine. 3. Place the probe at 37°C to preanneal for 1 h.
3.5. Hybridization 1. Take the preannealed probe from 37°C and carefully add to the denatured metaphase slide preparations. Since the probes are both directly and nondirectly labeled, work quickly and avoid extended exposure to light. 2. Carefully place a coverslip on the probe, avoiding bubbles. If bubbles do appear, gently push them to the slide be pressing down on the coverslip. 3. Ring the perimeter of the coverslip with rubber cement.
4. Place in a hybridization box (see Note 13) and place in a plastic bag (optional). Allow the slides to hybridize at 37°C for 48 h.
3.6. Post-Hybridization Washes and Detection 1. Preheat all the solutions in a 45°C waterbath. 2. Remove the slides from the hybridization box and carefully peel off the rubber cement. The coverslip may come away with the rubber cement or remain on the slide. Should the coverslip remain on the slide, proceed to place the slide in the first wash solution. 3. Wash the slides in 50% formamide/2X SSC, 3× for 5 min each. The coverslip should slide off in the first wash. Gently agitate the Coplin jar for a few seconds (see Note 14). 4. Wash the slides in 1X SSC, three times for 5 min each with gentle agitation. 5. Dip the slides in 0.01% Tween-20/4X SSC. Remove the slides and allow the excess solution to dip off, but do not allow the slides to dry. 6. Using Vial 2 from the SKY Kit provided by Applied Spectral Imaging, add 30 µL to 40 µL of blocking solution to the slides and coverslip. 7. Place the slides back in the hybridization box and incubate for 30 min at 37°C. 8. Carefully remove the coverslips and add 30 µL to 40 µL of detection reagent from vial 3 from the SKY Kit provided by Applied Spectral Imaging and coverslip. 9. Place the slides back in the hybridization box and incubate for approx 30 min at 37°C. 10. Carefully remove the coverslips and wash the slides in three washes of 0.01% Tween-20/ 4X SSC for 5 min each. Agitate gently. 11. Allow the excess solution to run off the slide and add 30 µL to 40 µL of detection reagent from vial 4 in the SKY Kit provided by Applied Spectral Imaging, and coverslip. 12. Place the slides back in the hybridization box and incubate for approx 30 min at 37°C. 13. Carefully remove the coverslips and wash the slides in three washes of 0.01% Tween-20/ 4X SSC for 5 min each. Agitate gently. 14. Rinse the slides in 2X SSC at room temperature. 15. Using 15 µL to 20 µL of the DAPI/Antifade mounting medium provided in vial 5, counterstain the sides and coverslip making sure that there are no bubbles. 16. The slides can now be viewed. The slides should be stored at –20°C.
3.7. Image Acquisition 1. Image acquisition and analysis should be carried out as soon as possible. Although the fluorescence can last for several months if stored at –20°C and exposed to as little light as possible, the signal intensity will diminish over time (see Notes 17–20). 2. Training for use of the system's acquisition and analysis is carried out at the time of installation of the system in the laboratory.
3.8. Hybridization of SKY Probes to Previously G-banded Slides: Slide Pretreatment 1. Remove any residual immersion oil from previously G-banded slides by washing in 2 washes of xylene for 5 min each at room temperature (see Note 15). 2. Destain the slides by soaking slides in methanol for 10–15 min, or until the slide has been thoroughly destained. 3. Once the slides have been destained, pass the slides through a rehydration series: 95, 80, and 70% ethanol for 5 min each. Allow the slides to air dry. 4. Continue the protocol outlined in Subheading 3.3. starting at Step 5. 5. In the case of previously banded slides, the denaturation time in 70% formamide/2X SSC
Table 1 Suggested G-Banding Steps Yielding Both Good Banding and Subsequent SKY Hybridization
Banding steps Trypsin (5% w/v stock) diluted 1/100 times Saline Saline Stain (Giemsa) Water Water Denaturing Time
Slide 3 d–1 mo
Slide >1 mo
In situ slide preparation 3 d–1 mo
In situ slide preparation >1 mo
10–20 s with agitation
Brief rinse Brief rinse 50 s Brief rinse Brief rinse 20–30 s
Brief rinse Brief rinse 1+ min Brief rinse Brief rinse 45 s-1 min
Brief rinse Brief rinse 1+ min Brief rinse Brief rinse 1 min-?
should be adjusted to reflect the properties of the slide (see Note 16, Table 1). A conservative denaturation time is 40 s. 6. All other steps, probe denaturation, hybridization and post-hybridization washes and detections are the same as outlined above.
4. Notes (Also see Table 2 for General Troubleshooting Tips) 1. If there is sufficient material, try different colcemid times to produce metaphase spreads that are a good length for cytogenetic analysis. Often times, different tissues and tumor types will behave differently with respect to their growth patterns. For slow growing cultures, an overnight treatment with colcemid may yield more metaphase spreads. This will require the colcemid concentration to be considerably reduced. Whereas for cultures which appear to be growing quickly, a shorter period of colcemid treatment, perhaps only 30 min, is sufficient to arrest enough cells in metaphase to produce spreads. In general it is advisable to give the culture a "half feed" one day before harvesting the cells, by removing half of the media from the culture and replacing it with fresh media. The sensitivity of the cells to colcemid is also a factor in obtaining good size chromosomes for analysis. It has been our experience that some tumors will have a very low tolerance for colcemid treatment, producing very tight and short chromosomes. This can be alleviated somewhat by reducing the final concentration of colcemid and increasing the incubation time, but this could sacrifice the number of cells arrested in metaphase. 2. Some cultures grow both as adherent and as nonadherent cells. To ensure that the entire tumor has been represented in the cytogenetic preparation, it is advisable to collect the cells that may be floating in the media. Once collected, they can be added to the rest of the cells which have been lifted off the culture flask using trypsin. 3. The use of fresh culturing media containing fetal calf serum when washing the collected cells helps to inactivate the trypsin. Since trypsin is a protease, prolonged exposure of the cells to the trypsin could rupture membranes and damage the DNA.
Table 2 Commonly Encountered SKY Difficulties
Weak Signal
Slide Age: optimal results have been obtained from slides not older than 2 mo in age. As the slides age, they become harder to denature. Conversely, very old preparations often have degraded DNA not adequate for FISH. Previously G-banded slides will have an even shorter lifespan and should be processed within 2 wk. Denaturation Time: As the slide ages, the chromosomes become harder to separate into single strands. Slides used within 1–2 wk of preparation should be denatured for 1.5–2 min. Slides that are older may require times that range from 2–3 min. Cytoplasmic Debris: The presence of cytoplasm may inhibit binding and contribute to background. A more aggressive protein pretreatment may be required. Excessive Slide Pretreatment: Excessive enzymatic treatment may damage the target DNA making it less efficient for hybridization with the probe.
Commercial Probes: Usually the company has properly processed the product with the necessary quality controls. Check that the probes were properly stored and used within the expiration date. Probe Concentration: The probe is usually in excess of the target DNA, however, make sure that sufficient probe has been added to adequately cover the area of interest on the slide.
Sealing of coverslip: It is critical that the coverslip is adequately sealed, preventing any moisture from entering the hybridized area and diluting the probe. Proper Temperature: Check that the temperature in the oven or hotplate unit is correct for hybridization or incubations. Incubation Times: Avoid taking shortcuts during incubation times with blocking reagents or detection reagents. Also be sure that the reagents do not dry up on the slide making washing more difficult.
Cytoplasmic Debris: This is the most common culprit causing background. Increase the incubation time during the protein digestion or maintain the same time but change the concentration. Bacterial/Yeast Contamination: Microorganisms that have been cultured along with the specimen may have also made its way onto the slide. Unfortunately, this may be unavoidable. Coverslips: If cells are to be grown in situ, use only glass coverslips. Plastic coverslips will cause autofluorescence. Residual Oils: Slides that have been previously visualized using immersion oil should be cleaned with xylene. Residual oils will prevent hybridization and cause background problems.
Fading Signals NA
Commercial Probes: This is usually not the cause for background, However, note the lot number for future reference.
Post-Hybridization Washes: Make sure that the correct temperature has been reached for the washes and incubations. Agitation during the washes can help to remove unbound probe and antibodies. Increasing the stringency of the washes by either increasing the temperature or altering the amount of SSC in the washes can also help. Avoid drying of the slide with any of the blocking or detection reagents.
Commercial Probes: Although these probes are supposed to be quality controlled, these too are under the same limitations of In-House probes. Take note of the lot number and expiry date of commercially made probes.
Antifade: Check that the DAPI/ Antifade solution is within its expiry date. Normally, the antifade is clear with a slight pink tinge. Antifade which has gone "off" will turn increasingly amber in colour. Expired antifade medium will cause rapid signal degradation and display a red glow when viewed under the microscope. (continued)
Table 2 (continued) Slide Poor Chromosome Morphology
Previously G-Banded Slides
Over-denaturation: The cause of poor chromosome morphology is usually caused by over-denaturation causing the DNA to be destroyed. This can be sample specific and/ or slide age related. Over-Processing: Over trypsinization for optimal banding can cause the DNA to become sensitive to subsequent denaturation. For this reason, denaturation times are greatly reduced. This will also have an affect on the quality of hybridization and signal strength.
Probe NA
Denaturation Temperature: Check that the temperature for denaturation is accurate. The final internal temperature of the Coplin jar should be 72°C. Add 1 degree for each slide that will be denatured in that jar. Avoid denaturing more than 5 slides in one jar at one time. Plastic Coplin jars will have a greater differential temperature between the bath and the internal temperature, as compared to a glass Coplin jar.
4. KCl has been traditionally used as the hypotonic solution used to swell the cells. Adding the first mL in a dropwise fashion to the cells prevents the sudden rush of water into the cells and bursting the contents into the supernatant. Gentle mixing between drops helps to ensure that the hypotonic solution is incorporated into the cell suspension. A gentle heat treatment at 37°C assists in swelling the cells more rapidly. If there is not a 37°C incubation, 30 min at room temperature will also adequately swell the cells. If the cells do not swell (see Note 5), increase the hypotonic incubation time in 5 min increments for subsequent harvesting of the same culture. 5. After the hypotonic swelling, the cells are very sensitive. Doing a "prefixation" with a few drops of methanol:acetic acid fixative helps to harden the cell membranes for subsequent centrifugation and fixations. The addition of the fixative also lyses any red blood cells that may be present. After the centrifugation, the pellet size should have doubled. This is an indication that the hypotonic treatment was successful. 6. Once the cells have been pelleted, the supernatant can be removed. This contains any ruptured membranes and cytoplasmic material. The pelleted cells should be gently resuspended with gentle flicking of the bottom of the conical tube. The addition of fixative in a dropwise solution helps to slowly introduce the fixative to the still swollen and sensitive cells. 7. There are many ways to prepare metaphase slides. Some laboratories use disposable 1-mL bulb pipets, glass pipets or pipetmans for adding the fixed cells to the slide. The use of a 200 µL pipetman can help to control the amount of suspension used, particularly if there are few cells. The cells are generally added to a slide that is tilted to an approx 45° angle. The slide may be dry or wet with either water or fixative. These different methods of slide making are based on trial and error. The relative humidity in the room as well as the season will influence the success of slide making. If the air is too dry, the use of a humidifier or steam generated by a boiling kettle or water on a hotplate can help to increase the relative humidity. If the surrounding air is too humid, a few seconds on a hotplate, which has been warmed to the touch, can facilitate proper drying. The slides should always be assessed by phase contrast microscopy to determine whether the current slide making technique is appropriate. To ensure successful SKY, the slides should have minimal cytoplasmic debris around the metaphases and chromosomes that are not too long or are overlapping. Adjust the cell density as required. In general, the chromosomes should appear dark grey. The banding patterns should be slightly noticeable. The slides can be stored at room temperature in a slide box. They should be used within the first 2 wk, but can be used as early as the next day. As the slides begin to age, they will first become more difficult to denature (see Note 9) then proceed to degrade making the DNA useless. 8. Pepsin is mildest of the proteases used for slide pretreatments. A 10% (w/v) pepsin stock should be made and aliquoted. They can be stored at –20°C almost indefinitely. The aliqouted pepsin should be a one use aliquot. Because each new batch of pepsin is different, the amount used to achieve the cleanest slides may vary. 9. A conservative approach to controlling the extent of protein digestion is to use the same amount of pepsin but increase the incubation time. In contrast, the increase in amount of pepsin used requires more strict timing, making the former method more flexible and forgiving. Gentle agitation can also facilitate the loosening of cytoplasmic debris. The extent of digestion can be viewed by phase contrast microscopy after the treatment, but before the formalin fixation step (Subheading 3.3., Step 6). 10. The use of formalin helps to maintain the chromosome morphology. This also makes the DNA a little bit more resistant to denaturation. Although the denaturation time of 2 min is sufficient to denature the DNA to single strands, the formalin treatment can be reduced in
Bayani and Squire time for slides that are much older (>2 mo). If the slides are old, reduce the formalin treatment to 5 min. For previously G-banded slides (Subheading 3.8.), the formalin fixation also helps to maintain the chromosome morphology which may have been harshly treated by the banding steps including trypsin digestion and heat treatment for artificial aging. Formamide is used in the denaturing solution because it has the ability to reduce the melting temperature of DNA. Ensure that the formamide solution has reached the proper internal temperature by measuring it with a thermometer. The solution inside plastic Coplin jars tend to be 3–4°C lower than the waterbath temperature, thus the temperature of the bath should be increased. Glass Coplin jars tend conduct the heat much better from the water to the solution inside the jar. As a rule of thumb, the temperature of the bath should be increased 1°C for each slide that will be placed for denaturation, since the temperature will drop with addition of each slide. Thus for a glass Coplin jar, where 5 slides will be added for denaturation, the waterbath temperature should be set at about 78–79°C so that the temperature of the solution is about 74–75°C. Two minutes is a standard time for slide denaturation. However, adjustments in the time should be made based on the quality and age of the slide. For much fresher slide preparations (ie., 1–3 d old), the DNA may not have had enough time to be properly aged. Although the formalin fixation helps to achieve this, the DNA may still be delicate. Reducing the time to 90 s may be sufficient. One can determine whether the slides were over denatured upon visual inspection after hybridization. The chromosomes will appear puffy with a visible "skeleton" running down the axis of each chromosome or chromatid, or ghost-like chromosomes with defined borders, but pale staining interiors. Over-denatured chromosomes will not pick up the DAPI counterstain as well as well denatured slides, often showing very brightly staining centromeres only. There may also be very little to no hybridization of the probe to the target DNA because the over-denaturation has damaged the DNA. Target slides that have been under-denatured will show more intact chromosomes with patchy hybridization. The chromosomes will pick up the DAPI staining well indicating that the DNA has not been over-processed and damaged. Denaturation of the slides is the most critical step when carrying out FISH based assays. Once the slides have been denatured, they must immediately be placed in 70% ethanol to keep them in their denatured state. The ethanol can be cold or at room temperature. While it is not required to have the ethanol replaced after each step, the 70% ethanol should be replaced after each experiment. The other ethanols (80 and 95%) can be topped up and replenished after every other experiment. If they are not stored at –20°C, they can be stored on the benchtop at room temperature, provided that they are tightly sealed to prevent evaporation. Any light proof container can be used as a hybridization box. A black video cassette box is a good container for hybridization. Although the box does not need to be dampened, it has been our experience that the hybridization kinetics seems to be better when there is a damp (not soaking wet) piece of paper towel or gauze lining the bottom of the box. Be sure to use clean distilled water since any bacteria that may be present can make its way onto the slide and pick up the antibodies, causing unnecessary background. The hybridization container can also be wrapped in a plastic bag to prevent the box from drying out. This is optional. All post-hybridization washes should be carried out with some gentle agitation. This helps to loosen any unbound probes or antibodies from the slide making it a much cleaner preparation. Ensure that all the reagents are free from bacteria, which can pick up the
antibodies. Should there be high background upon UV microscopy, one should consider more stringent washing conditions: either adding an extra wash for each step with more vigorous agitation, or adjusting the solutions. The concentration of Tween-20 for example could be increased from 0.01% to 0.2%. Background also appears when the slides have been allowed to dry during the washing and antibody incubation steps. Previously G-banded slides are often the only source of material left in clinical cytogenetics laboratories. Their slide pre-treatment and storage also make them difficult to be used for subsequent FISH-based analysis. However, a few steps can be done to increase the chances of success when using previously banded slides. Table 1 also outlines some of the guidelines for preparing G-banded slides, which will be used for SKY analysis. After G-banding analysis, the slides should be treated with xylene or some other agent that removes any residual emersion oil. The oil can quickly degrade the DNA. If the slides were coverslipped and sealed, the mounting media may also have degraded the DNA. This may be unavoidable, but try to avoid further DNA damage by adjusting protease treatments (which may be eliminated entirely since G-banding already requires a trypsin treatment), denaturing times and formalin fixations as described above. Adjust the denaturation time when denaturing previously G-banded slides. The DNA has already undergone some harsh treatment during the banding process, including a trypsin treatment to remove cytoplasm and enhance banding by stripping away some of the DNA associated proteins, and high heat treatment to allow for better contrast of the banding with the stain. Together with exposure to emersion oil, the target DNA is more likely to be in a more fragile state. To compensate for this, decrease the denaturing time to 40 s. It might also be useful to test out a slide from another source that was made and processed in the same fashion, before using the actual test slide. This will give an idea as to how well the assay will work and how much more processing the slide can handle. Try to image metaphase spreads that do not include a nucleus. While the chromosomes often fluoresce as brightly or more brightly than surrounding nuclei, smaller micronuclei tend to have very intense fluorescence that will change the intensity of the metaphase of interest by automatically adjusting the contrast during image acquisition. Try to avoid "bright spots" during image acquisition. For the same reasons described above, extraneous bright spots from conjugated antibodies that failed to be washed off can also reduce the intensity of the metaphase of interest. If possible, capture metaphases with few overlaps. This may be unavoidable when there are few metaphases, or the entire suspension consists of long chromosomes. The overlapping of chromosomes causes the false detection of "translocations" owing to the combinations of fluorochromes at the site of crossing which may correspond to one of the combinations in the spectral library. To save space on the hard drive as well as reducing the acquisition time, only select the metaphase of interest to be captured rather than including a lot of "dead space" surrounding the metaphase.
References 1. Speicher, M. R., Gwyn Ballard, S., and Ward, D. C. (1996) Karyotyping human chromosomes by combinatorial multi-fluor FISH. Nat. Genet. 12, 368–375. 2. Schrock, E., du Manoir, S., Veldman, T., et al. (1996) Multicolor spectral karyotyping of human chromosomes [see comments]. Science 273, 494–497. 3. Malik, Z., Dishi, M., and Garini, Y. (1996) Fourier transform multipixel spectroscopy and spectral imaging of protoporphyrin in single melanoma cells. Photochem. Photobiol. 63, 608–614.
4. Bell, R. (1972) Introductory Fourier Transform Spectroscopy. Academic Press, London. 5. Telenius, H., Pelmear, A. H., Tunnacliffe, A., et al. (1992) Cytogenetic analysis by chromosome painting using DOP-PCR amplified flow-sorted chromosomes. Genes Chromosomes Cancer 4, 257–263. 6. Fan, Y. S., Siu, V. M., Jung, J. H., and Xu, J. (2000) Sensitivity of multiple color spectral karyotyping in detecting small interchromosomal rearrangements. Genet. Test 4, 9–14. 7. Heim, S. and Mitelman, F. (1992) Cytogenetic analysis in the diagnosis of acute leukemia. Cancer 70, 1701–1709. 8. Heim, S. and Mitelman, F. (1995) Cancer Cytogenetics, 2 ed. Wiley-Liss, Inc., New York 9. Johansson, B., Mertens, F., and Mitelman, F. (1993) Cytogenetic deletion maps of hematologic neoplasms: circumstantial evidence for tumor suppressor loci. Genes Chromosomes Cancer 8, 205–218. 10. Markovic, V., Bouman, D., Bayani, J., Al-Maghrabi, J., Kamel-Reid, S., and Squire, J. (2000) Lack of BCR/ABL Reciprocal Fusion in Varian Ph Translocations: Use of Double Fusion Signal FISH and Spectral Karyotyping. Leukemia 14, 1157–1160. 11. Rowley, J. D., Reshmi, S., Carlson, K., and Roulston, D. (1999) Spectral karyotype analysis of T-cell acute leukemia. Blood 93, 2038–2042. 12. Rowley, J. D. (2000) Molecular genetics in acute leukemia. Leukemia 14, 513–517. 13. Hilgenfeld, E., Padilla-Nash, H., Schrock, E., Ried, T. (1999) Analysis of B-cell neoplasias by spectral karyotyping (SKY). Curr. Top. Microbiol. Immunol. 246, 169–174. 14. Gray, S. G., Kytola, S., Lui, W. O., Larsson, C., and Ekstrom, T. J. (2000) Modulating IGFBP-3 expression by trichostatin A: potential therapeutic role in the treatment of hepatocellular carcinoma. Int. J. Mol. Med. 5, 33–41. 15. Ghadimi, B. M., Schrock, E., Walker, R. L., et al. (1999) Specific chromosomal aberrations and amplification of the AIB1 nuclear receptor coactivator gene in pancreatic carcinomas. Am. J. Pathol. 154, 525–536. 16. Ghadimi, B. M., Sackett, D. L., Difilippantonio, M. J., et al. (2000) Centrosome amplification and instability occurs exclusively in aneuploid, but not in diploid colorectal cancer cell lines, and correlates with numerical chromosomal aberrations. Genes Chromosomes Cancer 27, 183–190. 17. Saunders, W. S., Shuster, M., Huang, X., et al. (2000) Chromosomal instability and cytoskeletal defects in oral cancer cells. Proc. Natl. Acad. Sci. USA 97, 303–308. 18. Beheshti, B., Karaskova, J., Park, P., Squire, J., and Beatty, B. (2000) Identification of a high frequency of chromosomal rearrangements in the centromeric regions of prostate cancer cell lines by sequential Giemsa-banding and spectral karyotyping. Mol. Diagn. 5, 23–32. 19. Luk, C., Tsao, M., Bayani, J., Shepherd, F., and Squire, J. A. (2001) Molecular cytogenetic analysis of non-small cell lung carcinoma by spectral karyotyping and comparative genomic hybridization. Cancer Genet. Cytogenet. 125, 87–99. 20. Macoska, J., Beheshti, B., Rhim, J., et al. (2000) Genetic Characterization of Immortalized Human Prostate Epithelial Cell Cultures: Evidence for Structural Rearrangements of Chromosome 8 and i(8q) Chromosome Formation in Malignant-Derived Cells. Cancer Gen. Cyto. 120, 50–57. 21. Carlotti Jr, C. G., Drake, J. M., Hladky, J., Teshima, I., Becker, L. E., and Rutka, J. T. (1999) Primary Ewing's sarcoma of the skull in children. utility Of molecular diagnostics, surgery and adjuvant therapies [In Process Citation]. Pediatr. Neurosurg. 31, 307–315. 22. Cohen, I. J., Issakov, J., Avigad, S., et al. (1997) Synovial sarcoma of bone delineated by spectral karyotyping [letter]. Lancet 350, 1679–1680.
23. Joyama, S., Ueda, T., Shimizu, K., et al. (1999) Chromosome rearrangement at 17q25 and xp11.2 in alveolar soft-part sarcoma: A case report and review of the literature. Cancer 86, 1246–1250. 24. Pandita, A., Zielenska, M., Thorner, P., et al. (1999) Application of comaparative genomic hybridization, spectral karyotyping, and microarray analysis in the identification of subtype-specific patterns of genomic changes in rhabdomyosarcoma. Neoplasia 1, 262–275. 25. Safar, A., Nelson, M., Neff, J. R., et al. (2000) Recurrent anomalies of 6q25 in chondromyxoid fibroma [In Process Citation]. Hum. Pathol. 31, 306–311. 26. Zielenska, M., Zhang, Z. M., Ng, K., et al. (2001) Acquisition of secondary structural chromosomal changes in pediatric ewing sarcoma is a probable prognostic factor for tumor response and clinical outcome. Cancer 91, 2156–2164. 27. Barnard, M., Bayani, J., Grant, R., Teshima, I., Thorner, P., and Squire, J. (2000) Use of multicolor spectral karyotyping in genetic analysis of pleuropulmonary blastoma. Pediatr. Dev. Pathol. 3, 479–486. 28. Bigner, S. H. and Schrock, E. (1997) Molecular cytogenetics of brain tumors. J. Neuropathol. Exp. Neurol. 56, 1173–1181. 29. Bayani, J., Zielenska, M., Marrano, P., et al. (2000) Molecular Cytogenetic Analysis of Medulloblastomas and Primitive Neuroectodermal Tumours Using Conventional Banding, Comparative Genomic Hybridization and Spectral Karyotyping. J. Neurosurg. 93, 437–448. 30. Huang, B., Ning, Y., Lamb, A. N., et al. (1998) Identification of an unusual marker chromosome by spectral karyotyping. Am. J. Med. Genet. 80, 368–372. 31. De Krijger, R. R., Mooy, C. M., Van Hemel, J. O., et al. (1999) CHARGE associationrelated ocular pathology in a newborn with partial trisomy 19q and partial monosomy 21q, from a maternal translocation (19;21) (q13.1;q22.3). Pediatr. Dev. Pathol. 2, 577–581. 32. Morelli, S. H., Deubler, D. A., Brothman, L. J., Carey, J. C., and Brothman, A. R. (1999) Partial trisomy 17p detected by spectral karyotyping. Clin. Genet. 55, 372–375. 33. Krapp, M., Baschat, A. A., Gembruch, U., Gloeckner, K., Schwinger, E., and Reusche, E. (1999) Tuberous sclerosis with intracardiac rhabdomyoma in a fetus with trisomy 21: case report and review of literature. Prenat. Diagn. 19, 610–613. 34. Peschka, B., Leygraaf, J., et al. (1999) Analysis of a de novo complex chromosome rearrangement involving chromosomes 4, 11, 12 and 13 and eight breakpoints by conventional cytogenetic, fluorescence in situ hybridization and spectral karyotyping. Prenat. Diagn. 19, 1143–1149. 35. Haddad, B. R., Schrock, E., Meck, J., et al. (1998) Identification of de novo chromosomal markers and derivatives by spectral karyotyping. Hum. Genet. 103, 619–625. 36. Ning, Y., Laundon, C. H., Schrock, E., Buchanan, P., and Ried, T. (1999) Prenatal diagnosis of a mosaic extra structurally abnormal chromosome by spectral karyotyping. Prenat. Diagn. 19, 480–482. 37. Marquez, C., Cohen, J., and Munne, S. (1998) Chromosome identification in human oocytes and polar bodies by spectral karyotyping. Cytogenet. Cell. Genet. 81, 254–258. 38. Barlow, C., Hirotsune, S., Paylor, R., et al. (1996) Atm-deficient mice: a paradigm of ataxia telangiectasia. Cell 86, 159–171. 39. Coleman, A. E., Forest, S. T., McNeil, N., Kovalchuk, A. L., Ried, T., and Janz, S. (1999) Cytogenetic analysis of the bipotential murine pre-B cell lymphoma, P388, and its derivative macrophage-like tumor, P388D1, using SKY and CGH. Leukemia 13, 1592–1600. 40. Coleman, A. E., Ried, T., and Janz, S. (1999) Recurrent non-reciprocal translocations of chromosome 5 in primary T(12;15)-positive BALB/c plasmacytomas. Curr. Top. Microbiol. Immunol. 246, 175–180.
41. Coleman, A. E., Schrock, E., Weaver, Z., et al. (1997) Previously hidden chromosome aberrations in T(12;15)-positive BALB/c plasmacytomas uncovered by multicolor spectral karyotyping. Cancer Res. 57, 4585–4592. 42. Hardt, T., Himmelbauer, H., Mann, W., Ropers, H., and Haaf, T. (1999) Towards identification of individual homologous chromosomes: comparative genomic hybridization and spectral karyotyping discriminate between paternal and maternal euchromatin in Mus musculus x M. spretus interspecific hybrids. Cytogenet. Cell. Genet. 86, 187–193. 43. Liyanage, M., Coleman, A., du Manoir, S., et al. (1996) Multicolour spectral karyotyping of mouse chromosomes. Nat. Genet. 14, 312–315. 44. McCormack, S. J., Weaver, Z., Deming, S., et al. (1998) Myc/p53 interactions in transgenic mouse mammary development, tumorigenesis and chromosomal instability. Oncogene 16, 2755–2766. 45. Shen, S. X., Weaver, Z., Xu, X., et al. (1998) A targeted disruption of the murine Brca1 gene causes gamma-irradiation hypersensitivity and genetic instability. Oncogene 17, 3115–3124. 46. Weaver, Z. A., McCormack, S. J., Liyanage, M., et al. (1999) A recurring pattern of chromosomal aberrations in mammary gland tumors of MMTV-cmyc transgenic mice. Genes Chromosomes Cancer 25, 251–260. 47. Wiener, F., Kuschak, T. I., Ohno, S., and Mai, S. (1999) Deregulated expression of c-Myc in a translocation-negative plasmacytoma on extrachromosomal elements that carry IgH and myc genes. Proc. Natl. Acad. Sci. USA 96, 13,967–13,972. 48. Ding, H., Roncari, L., Shannon, P., et al. (2001) Astrocyte-specific expression of activated p21-ras results in malignant astrocytoma formation in a transgenic mouse model of human gliomas. Cancer Res. 61, 3826–3836. 49. Mak, T. W., Hakem, A., McPherson, J. P., et al. (2000) Brcal required for T cell lineage development but not TCR loci rearrangement. Nat. Immunol. 1, 77–82. 50. Lefebvre, L., Dionne, N., Karaskova, J., Squire, J. A., and Nagy, A. (2001) Selection for transgene homozygosity in embryonic stem cells results in extensive loss of heterozygosity. Nat. Genet. 27, 257–258.
M-FISH: Methods and Applications
8 Multicolor FISH Syed M. Jalal and Mark E. Law 1. Introduction Chromosome "painting" by fluorescent labeled probes for each human chromosome has been available since the late 1980s. The DNA or RNA radioactive isotopes have been in use since 1969 as nucleic acid probes (1,2). The introduction of fluorescent labeled probes by Bauman et al. (1980) presented an attractive alternative for chromosomal in situ hybridization (3). Based on unique DNA sequences specific to individual chromosomes, painting probes were generated for each human chromosome (4,5). Pinkel et al. (1988) used in situ hybridization of 120 fluorescent DNA probes (FISH) along the entire length of chromosome 4 to generate a specific painting probe for this chromosome (6). By the early 1990s, whole chromosome painting probes (wcp) were commercially available for each human chromosome in two colors (green and orange). Jalal et al. presented the characteristics of the direct labeled wcps for every chromosome and their utility in clinical practice (7). The ability to resolve chromosomal anomalies was greatly enhanced when wcps became available as a complement to chromosome analysis by banding techniques. It was indeed exciting that by 1996, it became possible to "paint" the entire human genome simultaneously so that each chromosome fluoresced in a unique and distinct color (8). As is customary for wcps and multicolor FISH (M-FISH) methods, the highly repetitive DNA sequences (COT-1 DNA) are suppressed by excess unlabeled complementary DNA. The combinatorial labeling of five fluorophores makes it possible to assign a specific fluor combination and thus, a unique spectral signature to each human chromosome. The chromosomal regions that are rich in repetitive DNA sequences (constitutive heterochromatin) and acrocentric chromosome short arms are not labeled by these strategies. Schröck et al. (8) point out that for spectral karyotyping, all the information from emitted light is used by Fourier spectroscopy and charged coupled device imaging. The spectral signature for each chromosome is then converted to display as classification colors with the help of imaging software (8). Multicolor From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
Jalal and Law
spectral karyotyping (SKY) has been used as a diagnostic or research tool for over 300 cases (9). During 1996 also, another option to SKY was proposed to monitor each human chromosome in a unique and specific fluorescent color (10). This method also used combinatorial labeling based on five fluorophores (spectral intervals of 350–770 nm) to generate a unique label for each chromosome with a background staining of DAPI (4'-6-diamidino-2-phenylindole). Rather than spectroscopy, M-FISH utilizes a series of filters with defined emission spectra (see Note 1). Coupled with imaging software, the procedure generates unique and distinct fluorescent images for each chromosome. M-FISH has been called multicolor FISH, multifluor FISH, or multiplex FISH, but we prefer the term multicolor FISH. An advantage of M-FISH is that the standard FISH imaging systems can be relatively easily adapted for M-FISH analysis. More than 70 US laboratories have some type of computer image analysis system (11). Eils et al. have proposed strategies for optimization of probe labels, filter sets, and image analysis for M-FISH (12). Law and Jalal have also provided the practical guidelines for set up and analysis by M-FISH (13). M-FISH has been successfully utilized for identification of markers and derivative chromosomes for congenital disorders (14–16). It has also been used in clinical practice for identification of multiple chromosomal abnormalities in complex karyotypes more recently. M-FISH has been useful diagnostically for the detection of critical chromosome rearrangements in hematologic disorders (17).
1.1. Clinical Application of M-FISH M-FISH has been successfully utilized both for constitutional abnormalities in congenital disorders and acquired chromosome anomalies in hematologic diseases (see Note 2). In particular, M-FISH can often identify unknown markers, derivative chromosomes, and can resolve complex karyotypes. M-FISH can also play a key role in the detection of critical (primary) chromosome anomalies in hematologic diseases, especially when the karyotype is complex or when the chromosome morphology is of poor quality. However, such an effort involving M-FISH often needs to be complemented with use of locus specific fluorescent DNA probes for detection of subtle anomalies. Another important question is whether M-FISH analysis of karyotypically normal samples of hematologic disorders can be worthwhile in the detection of structural abnormalities. Our experience and that of the Eastern Cooperative Oncology Group (personal communication–Dr. Dewald) is that it is generally not helpful. The only exceptions are where the anomaly is too subtle to be picked up by banded chromosome analysis [e.g., t(12;21)(p13;q21)] or when the chromosome morphology is of such poor quality that even relatively major structural anomalies cannot be ruled out.
1.1.1. Congenital Disorders One of the more labor intensive and challenging efforts in clinical cytogenetics is to provide a comprehensive identification of markers, derivative chromosomes, or to resolve a complex karyotype. It has been estimated that de novo structural rearrangements occur with a frequency from 0.70/1000 rising to 2.4/1000 among mentally retarded individuals (18). The prenatal frequency of de novo supernumerary markers
(including chromosome 15 bisatellited marker) is around 1/2500 (19). Deletions associated with defined phenotypic anomalies have been well documented for almost all major bands (20). Balanced reciprocal translocations occur with a frequency of about 1 in 600. The risk for unbalanced chromosome composition in the progeny of such balanced carriers vary widely from 50% to 1 µg of DNA (see Note 5).
2.5. Preparation of CGH Probes 1. Labeled patient DNA (200 ng) and labeled reference DNA (200 ng) from the nick translation reaction. 2. Human Cot-1 DNA (1 µg/µL) (Gibco-BRL; Life Technologies, Grand Island NY). 3. 3 M Sodium acetate: Dissolve 408.1 g of sodium acetate•3 H2O in 800 mL of H2O. Adjust the pH to 5.2 with glacial acetic acid. H2O to 1 L. 4. 100% Chilled ethanol. Store at –20°C and bring out just prior to use. 5. Cotton tipped applicators (Citmed, Citronelle AL). 6. Slide warmer set to ~ 42°C. 7. Metal block or PCR block that holds 1.5 mL microfuge tubes. Place block on slide warmer so that the block warms to approx 42°C. 8. Hybrisol VII hybridization mix (50% formamide, 2X sodium saline citrate) (Ventana Medical Systems, Inc., Tucson AZ).
2.6. Denaturation of Target Metaphase Slides 1. 2. 3. 4. 5.
Coplin jars 20X sodium saline citrate (SSC) (Q-Biogene, Carlsbad CA). Store at room temperature. 2X SSC solution: 50 mL 20X SSC, 450 mL distilled water. Store at room temperature. Deionized formamide (Q-Biogene, Carlsbad CA). Store at 4°C. Denaturation solution (pH 7): 70% formamide, 2X SSC. Can be made in large quantities (500 mL and 1 L) and stored at 4°C. Denaturation solution may also be reused up to 4 or 5× and stored at 4°C between use. 6. Waterbath set to 75 ± 1°C. 7. Slide warmer set to 40 ± 2°C. 8. Ethanol series (same as in Subheading 2.2., step 6): 70, 85, and 100% ethanol. Store at room temperature. May be reused for 1 wk if used on a daily basis. May be reused for up to 4 wk if used only once or twice a week.
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CGH in Clinical Cytogenetics
9. Chilled ethanol series: 70%, 85% and 100% ethanol. Store at –20°C. May be reused for 1 week if used on a daily basis. May be reused for up to 4 weeks if used only 1× or 2× a wk.
2.7. Probe Denaturation 1. Waterbath set to 75 ± 1°C.
2.8. Hybridization Slide warmer set to 40 ± 2°C. Incubator set to 37°C. 22 × 22 mm glass coverslips. Rubber cement. Syringe: (1, 3, 5, or 10cc; chose size according to the number of slides you will be preparing) carefully discard needle. 6. Humid chamber: Most empty pipet containers may be utilized by placing a paper towel in the lower section under the rack and saturating the paper towel with water. 1. 2. 3. 4. 5.
2.9. Post-Hybridization Wash 1. 20X Sodium saline citrate (SSC) (Q-Biogene, Carlsbad CA). Store at room temperature. 2. 4X SSC Solution: 100 mL 20X SSC, 400 mL distilled water. Store at room temperature. 3. 4X SSC/0.1% Triton X-100 solution: 100 mL 20X SSC, 0.5 mL Triton X-100, 399.5 mL distilled water. Store at room temperature. 4. 2X SSC Solution: 50 mL 20X SSC, 450 mL distilled water. Store at room temperature. 5. Distilled water. 6. Waterbath set to 75 ± 1°C. 7. Waterbath set to 39°C. 8. Coplin jars. 9. Antifade Mounting Medium (Vectashield, H-1000) (Vector Laboratories, Burlingame, CA). 10. DAPI stock solution (1.5 µg/mL) (Vectashield with DAPI, H-1200) (Vector Laboratories, Burlingame, CA). 11. DAPI counterstain (0.5 µg/mL): Dilute DAPI stock solution with the Vectashield antifade mounting medium as follows: 400 µL DAPI stock solution; 800 µL anti-fade mounting medium. 12. 24 × 60 mm glass coverslips.
3. Methods 3.1. Normal Male Peripheral Blood Culture 1. Add 500–650 µL of whole fresh blood from a karyotypically normal male to 10 mL of starting medium. 2. Incubate at 37°C for ~72 h (3 d). 3. Add 200 µL of thymidine solution and gently mix. 4. Incubate at 37°C for 14–18 h (Overnight). 5. Centrifuge at ~155g for 10 min. 6. Discard supernatant and add 10 mL 1X PBS. Invert to mix. 7. Centrifuge at ~155g for 10 min. 8. Discard supernatant and add 10 mL of continuing medium. Invert gently to mix. 9. Incubate at 37°C for 4–5 h. 10. Add 6–7 drops of colcemid solution. Invert to mix.
Levy and Hirschhorn
11. Incubate in a 37°C water bath for 20 min. 12. Centrifuge at ~170g for 10 min. 13. Remove supernatant, leaving about 0.5 mL. Tap each tube several times to resuspend cells. Do this thoroughly to avoid clumping. Add 0.5 mL 75 mM KCl (which has been prewarmed to 37°C) quickly and tap tube to mix. Add 4.5 mL more KCl. 14. Incubate in a 37°C waterbath for 15 min. 15. Slowly add 1 mL of fresh fixative to each tube from the bottom up with a pasteur pipet. Invert gently to mix. 16. Centrifuge at ~170g for 10 min. 17. Remove supernatant except for about 0.5 mL. 18. Add fresh fixative drop-wise while mixing the tube. Add a total of 5 mL fixative. 19. Incubate at room temperature for 10 min. 20. Centrifuge at ~170g for 10 min. 21. Remove all of the supernatant except for about 0.5 mL. Flick pellet. 22. Add fresh fixative drop-wise while mixing the tube. Add a total of 5 mL fixative. 23. Repeat steps 20–22 two–three more times as necessary. 24. Remove supernatant. 25. Dilute pellet with appropriate amount of fix. The solution should be turbid and slightly cloudy (i.e., if a large pellet is obtained, add ~ 1–1.5 mL of fix. Add < 1 mL of fix if smaller pellet is obtained (see Note 6). 26. Drop slides as detailed in Subheading 3.2.
3.2. Preparation of Normal Male Target Metaphase Spreads 1. Prepare a closed environment with a relative humidity of approximately 55% (can range from 50–60% humidity) and a temperature of about 24–26.5°C. 2. Hold a Pasteur pipet about 2–4 in above the glass slide and let a single drop of the cell suspension fall onto the left hand side of the slide. Repeat quickly and let the second single drop fall on the right hand side of the slide (see Note 7). 3. Before all the fixative evaporates, immerse the slide into a Coplin jar containing fresh fixative for 1–3 s. Remove the slide from the Coplin jar and allow it to air dry in the closed humid/temperature environment described in step 1 above. 4. Check quality of the slides under light microscope (see Note 8). 5. Leave slides overnight at room temperature and then perform a further postfixation step by immersing the slides in a 1% formaldehyde solution for 5–10 min at 4°C. 6. Dehydrate slides by running them through an ethanol series, 2 min in each of 70, 85, and 100% ethanol. 7. Allow slides to air dry at room temperature or gently blow air (from laboratory air flow) over slides to dry quickly. 8. Store slides at room temperature for 2–4 wk. 9. Perform a test CGH analysis on one of the slides using either a normal reference vs normal specimen or using a specimen with a known chromosomal imbalance (see Note 9).
3.3. Isolation of High Molecular Weight DNA from Patient and Normal Samples DNA should be extracted according to the manufacturer's instructions. Alternatively, DNA may be extracted using standard methods (10) or any reliable DNA extraction kit.
Fig. 3. Electrophoresis gel (1% agarose) of Nick-translation products which have been titrated using varying concentrations of DNase. (Lane 1): 100 bp DNA ladder. (Lanes 5 and 8) show fragment sizes that would suitable for preparation of CGH probes.
3.4. Probe Labeling by Nick Translation 1. Fluorescein-12-dUTP is the fluorochrome used to label patient DNA, and Texas Red®-5dUTP is the fluorochrome used to label the reference DNA. 2. Prepare a 15°C waterbath, or add small amounts of ice to an ice bucket filled with tap water until the temperature reaches 15°C. 3. Set another waterbath to 72°C. 4. Add the following to a 1.5-mL microfuge tube (keep all reagents chilled on ice): 1 µg patient or reference DNA; 5 µL 10X reaction buffer mix; 5 µL dNTP mix; 1 µL fluorochrome-dUTP (1 mM); 1 µL DNase (0.01–0.1 U/µL); 2.5 µL DNA Pol I (10 U/µL). 5. Total volume made up to 50 µL with H2O. 6. Spin the tubes briefly to collect the reagents at the bottom. 7. Incubate for 60 min in 15°C waterbath. 8. Stop reaction with a 10 min incubation at 72°C. 9. Run a 1% agarose gel to check the fragment sizes. The optimal fragment sizes for CGH are from 300–2000 bp (Fig. 3). If the fragment sizes are too long, further incubation at 15°C with DNase I can be done. 10. Reaction can be scaled up for nick translation of larger samples.
3.5. Preparation of CGH Probes Add the following to a 1.5 mL microfuge tube: 1. 200 ng of labeled normal (reference) DNA from nick-translation reaction (10 µL) (see Note 10). 2. 200 ng of labeled patient DNA from nick translation reaction (10 µL). 3. 20–30 µg of Cot-1 DNA (20–30 µL) (see Note 11). 4. Add 1/10th vol of 3 M sodium acetate (4–5 µL).
Add 150 µL (>2 vol) of 100% ice cold ethanol. Place at –80°C for 40–60 min. Centrifuge for 40 min at 29,000g (or highest speed on centrifuge) at 4°C. Remove ethanol by gently pouring off. Wipe remaining ethanol with a sterile cotton tipped applicator (do not touch pellet). Place microfuge tube on metal block which is on the slide warmer (set to 42°C) to aid the evaporation of remaining ethanol. This should take approx 2–3 min. 11. Resuspend pellet in 10 µL of Hybrisol VII hybridization mix by pipeting up and down and vortexing for about 1 min. 12. The CGH probe can now be used immediately or may be stored at –20°C protected from light until needed.
5. 6. 7. 8. 9. 10.
3.6. Denaturation of Target Metaphase Slides 1. Pour approx 50 mL of the denaturation solution into a Coplin jar and place Coplin jar in a waterbath set to 75–76°C. Prewarm the denaturation solution to a temperature of ~73 ± 2°C (see Note 12). 2. Take required number of target metaphase slides out from the –20°C freezer and run the slides through the room temperature ethanol series (70, 85, and 100%), 2 min in each. 3. Allow slides to dry (5 min) or gently blow air (from laboratory air flow) over slides to dry. 4. Prewarm slides on a 37–40°C slide warmer for ~30 s. 5. Denature slides by immersing them in the denaturation solution (at 73 ± 1°C) for 2.5–5 min (see Note 13). 6. Quickly place slides in ice cold 70% alcohol for 3 min and then continue dehydrating the slides in the 85 and 100% ethanol series for 3 min each. 7. Allow slides to dry (5 min) or gently blow air (from laboratory air flow) over slides to dry.
3.7. Probe Denaturation 1. While running the target metaphase slides through the ethanol series, place the microfuge tube with the CGH probe in a water bath set to 75°C ± 1 and denature the probe for 10 min.
3.8. Hybridization 1. Fill a syringe (needle already discarded) with rubber cement. 2. Prewarm slides at about 37–42°C for ~1 min on slide warmer. 3. While slides are on the slide warmer, place each denatured CGH probe onto a single hybridization area (see Note 10) of the denatured slide and cover each area with a 22 × 22 mm glass coverslip. 4. Seal the glass coverslip by squeezing rubber cement from the syringe along the edges of the coverslip. 5. Incubate the slides at 37°C in a humid chamber for 2–3 d.
3.9. Post-Hybridization Washing 1. Pour approx 50 mL of the 2X SSC solution into a Coplin jar and prewarm the solution to 72 ± 2°C (waterbath should be set to about 75°C). 2. Pour approx 50 mL of the 4X SSC solution in to a Coplin jar and prewarm the solution to 37°C (waterbath should be set to about 39°C). 3. Pour approx 50 mL of the 4X SSC/0.1% TritonX solution into a Coplin jar and prewarm the solution to 37°C (waterbath should be set to about 39°C). 4. Pour approx 50 mL of the 2X SSC solution into a Coplin jar and leave at room temperature. 5. Pour approx 50 mL of distilled H2O into a Coplin jar and leave at room temperature.
6. Remove rubber cement from glass slide. 7. Gently remove the coverslip (without scratching slides). 8. Place the slides in the 2X SSC solution at 72 ± 2°C, agitate the slides for ~ 2 and then leave in the solution for 5 min. 9. Transfer the slides to the 4X SSC solution at 37°C and leave for 5 min. 10. Transfer the slides to the 4X SSC/0.1% Triton X solution at 37°C and leave for 5 min. 11. Transfer the slides back to the 4X SSC solution at 37°C and leave for 5 min. (Can use the same solution as in step 9). 12. Transfer the slides to the 2X SSC solution at room temperature for 5 min. 13. Transfer the slides to the H2O at room temperature and leave for 5 min. 14. Remove the slides from the H2O and allow slides to air dry at room temperature in the dark or gently blow air (from laboratory air flow) over slides to dry quickly. 15. Apply 10 µL DAPI counterstain to the target area of the slide. 16. Apply coverslip. 17. Leave slides in dark for 5–10 min and then proceed with CGH capturing and analysis. 18. Capture at least 10 of each autosome and 7 of each sex chromosome.
4. Notes 1. A male reference is chosen so that both the X and Y chromosome are represented on the normal target metaphase spreads. 2. If the initial cytogenetic workup of the patient was performed by another laboratory, then blood from the patient should be drawn into a sodium heparin tube so that DNA can be extracted and a peripheral blood culture can also be set up for FISH confirmation if required. In such cases, obtaining more than 3 mL of blood would be optimum. When the patient is an infant, < 3 mL of blood is often obtained and in these cases, you may only have enough blood for DNA extraction (CGH analysis). 3. Large quantities of male and female reference DNA may be extracted and stored at –20°C until needed. 4. With each fresh batch of DNase, try a range of concentrations from 0.0–0.1 U/µL and see which gives the best fragment sizes on an agarose gel. This concentration generally remains optimum. 5. A stock of labeled reference DNA may be generated by labeling more than 1 µg of DNA at a time. Store stock solution at –20°C. 6. A test slide should be prepared to examine the mitotic index and assess if the suspension needs to be diluted with fixative or concentrated by centrifugation and resuspension in a lower volume of fixative. 7. Dropping in two areas on the slide allows for two independent CGH hybridizations to occur on a single slide. Make sure that both drops are well separated. 8. When preparing the target metaphase slides, the goals are: (1) obtain metaphases that are evenly spread, relatively straight and have minimal overlaps, (2) minimize the amount of cytoplasmic debris on the slide and over the chromosomes, and (3) obtain chromosomes that appear greyish (not too black and/or "shiny" nor too light or "ghostly") under phase microscopy. 9. The quality of the target metaphase slides appears to be a key factor in the CGH procedure. Each batch of slides should be tested and suitable batches should be stored at –20°C. Begin test CGH analysis at about 2 wk after dropping slides and once satisfactory results are obtained, store slides at –20°C. Generally, the quality tends to hold true for the entire batch, i.e., if a particular batch does not give satisfactory result either keep these slides for other purposes such as FISH or discard. Laboratories that are proficient in making
Levy and Hirschhorn metaphase slides should first try their regular protocol for preparation of metaphase slides. In many cases, their protocol will provide metaphases suitable for CGH analysis if they fit the criteria mentioned in Note 8. When preparing CGH probes, consider preparing two separate probes, one where the reference is sex matched to the patient and the other where the reference is sex mismatched to the patient. The sex matched probe is important as it will reveal imbalances involving the sex chromosomes. If each probe is used on each of the two hybridization areas of a single slide (see Note 7), then the sex mismatched probe will serve as an internal control as color ratio differences are expected along the entire length of the sex chromosomes. Use ~ 20 µg Cot-1 DNA for marker cases and 30 µg for all other cases. As most marker chromosomes contain centromeric material, in some cases, using less Cot-1 DNA improves the detection. Denaturation solution should be prewarmed for at least 30 min. Solution can be microwaved at full power for about 20 s to speed up the prewarming period. Determine the optimal denaturation time for each batch of slides. Suitable slides will show both good hybridization and good inverse DAPI bands across a wider range of denaturation times. Try an initial denaturation time of 3.5–4 min.
References 1. Bryndorf, T., Kirchhoff, M., Rose, H., Maahr, J., Gerdes, T., Karhu, R., et al. (1995) Comparative genomic hybridization in clinical cytogenetics. Am. J. Hum. Genet. 57, 1211–1220. 2. Levy, B., Gershin, I. F., Desnick, R. J., Babu, A., Gelb, B. D., Hirschhorn, K., et al. (1997) Characterization of a de novo unbalanced chromosome rearrangement by comparative genomic hybridization and fluorescence in situ hybridization. Cytogenet. Cell Genet. 76, 68–71. 3. Levy, B., Dunn, T. M., Kaffe, S., Kardon, N., and Hirschhorn, K. (1998) Clinical applications of comparative genomic hybridization. Genet. Med. 1, 4–12. 4. Levy, B., Papenhausen, P. R., Tepperberg, J. H., Dunn, T. M., Fallet, S., Magid, M. S., et al. (2000) Prenatal molecular cytogenetic diagnosis of partial tetrasomy 10p due to neocentromere formation in an inversion duplication analphoid marker chromosome. Cytogenet. Cell Genet. 91, 165–170. 5. Gardner, R. J. M. and Sutherland, G. R., eds. (1996) Chromosome Abnormalities and Genetic Counseling. Oxford University Press, New York. 6. Kallioniemi, A., Kallioniemi, O. P., Sudar, D., Rutovitz, D., Gray, J. W., Waldman, F., et al. (1992) Comparative genomic hybridization for molecular cytogenetic analysis of solid tumors. Science 258, 818–821. 7. du Manoir, S., Speicher, M. R., Joos, S., Schröck, E., Popp, S., Dohner, H., et al. (1993) Detection of complete and partial chromosome gains and losses by comparative genomic in situ hybridization. Hum. Genet. 90, 590–610. 8. Kallioniemi, O. P., Kallioniemi, A., Sudar, D., Rutovitz, D., Gray, J. W., Waldman, F., et al. (1993) Comparative genomic hybridization: a rapid new method for detecting and mapping DNA amplification in tumors. Semin. Cancer Biol. 4, 41–46. 9. Kallioniemi, O. P., Kallioniemi, A., Piper, J., Isola, J., Waldman, F. M., Gray, J. W., et al. (1994) Optimizing comparative genomic hybridization for analysis of DNA sequence copy number changes in solid tumors. Genes Chromosomes Cancer. 10, 231–243. 10. Piper, J., Rutkowitz, D., Sudar, D., Kallioniemi, A., Kallioniemi, O. P., Waldman, F . M., et al. (1995) Computer image analysis of comparative genomic hybridization. Cytometry 19, 10–26. 11. Sambrook, J., Fritsch, E. F., and Maniatis, T., eds. (1989) Molecular Cloning: A Laboratory Manual. Vol. 1–3. Cold Spring Harbour Laboratory Press, Cold Spring Harbour, New York.
Cross Species CGH
10 Color Banding Vicki L. Hopwood, Christi J. Hada, and Armand B. Glassman 1. Introduction 1.1. History 1.1.1. Banding Techniques In the early 1970s, a number of chromosome banding techniques were developed which produced reproducible transverse bands of different lengths along human chromosomes. These techniques included Q-banding, a fluorescent banding technique discovered by Caspersson in 1969; G-banding, proposed in 1971 by both Sumner and Seabright; and R-banding, introduced by Dutrillaux and Lejeune in 1971 (1–4). Today conventional G-banding induced by either pretreatment with hot salt solutions or proteolytic enzymes has remained the gold standard in chromosome identification. While G-banding has remained the gold standard in clinical cytogenetics, morphologic and technical difficulties can prevent chromosome identification when the chromosomes are too short to detect small aberrations, when the chromosome morphology is poor, when karyotypes contain marker chromosomes, or chromosomes that have arisen from complex multiple rearrangements.
1.1.2. Fluorescent In Situ Hybridization The fluorescent in situ hybridization (FISH) technique, developed in 1986, in which colored DNA probes hybridize to various chromosome centromeres, was the beginning of the development of a number of subsequent FISH techniques that attempt to delineate chromosome abnormalities unresolved by conventional cytogenetics (5). In 1988, DNA painting probes were developed by fluorescence activated bivariate chromosome flow sorting (FACS). From the flow sorted chromosomes, DNA libraries from single chromosomes were created via degenerate oligonucleotide primed PCR (DOP-PCR). These whole chromosome painting probes have proven useful in verifying chromosome translocations that were suspected by G-banding (6,7).
10_Hopwood_133-142F[7.10.2]
Hopwood, Hada, and Glassman
1.1.3. Multiplex FISH By the end of the 1980s, multiple color FISH was being developed by using either combinatorial or ratio labeling of DNA probes with different fluorochromes to create multiple unique color combinations (8–10). In the early 1990s, up to 7 different color combinations were being used to simultaneously color individual whole chromosomes. This soon led to the idea that subregional probes for different regions of chromosomes could be used to create a type of chromosome bar code in multiple colors to allow simultaneous analysis of multiple chromosome regions in a single hybridization experiment (11–13). In 1996, two different research groups discovered that combinatorial labeling with 5 different fluorochromes (Cy3, Cy3.5, Cy5, Cy5.5, and FITC) could produce enough color combinations to color all 24 human chromosomes a uniquely different color (14,15).
1.1.4. Color Banding Using Human DNA Probes In 1997, a group from Cambridge University in England successfully introduced a color banding technique that uniquely labeled all of the human chromosomes (16). A banding resolution of 110 distinct color bands per haploid set was achieved by labeling 2 sets of subregional DNA probes with either red or green fluorescence. These probes were then hybridized to human metaphase spreads prepared by conventional cytogenetic airdried technique and counterstained with DAPI (4,6 diamidino-2phenylino-2-phenylindole). This division of the DNA probes into two different color labeled sets allowed a four color banding pattern to be discerned along the length of the chromosomes. Red and green for unique DNA fragments found in only one set but not the other, yellow, when DNA fragments existed in both sets in equal amounts and blue when no DNA probe existed in either set. The subregional DNA probes were created from Alu/polymerase chain reaction products produced from fragment somatic cell hybrids (human /rodent) that contained over 300 regions of the human genome (17). The Alu-PCR in this experiment caused specific amplification of human DNA but failed to amplify rodent DNA owing to the fact that Alu repeats occur only in primate DNA.
1.1.5. Color Banding Using Primate DNA Probes This same research team from Cambridge, England developed color banding using cross-species comparative genomic hybridization. This team, which included Malclom A. Ferguson-Smith, Johannes Wienberg, and Stefan Muller, termed this technique "cross species color banding" because they utilized DNA probes derived from bivariate fluorescence activated chromosome flow sorted (FACS) gibbon chromosomes (Hylobates concolor and Hylobates syndactylus) to produce color banding on human chromosomes (18). These gibbon DNA probes were uniquely labeled with FITC, Cy3 and Cy5 using a combinatorial labeling technique that resulted in 7 different color bands. Gibbons belong to the family of great apes. Gibbon DNA and human DNA have ~98% sequence homology. Color banding is achieved owing to this extensive sequence homology and the evolutionary chromosomal rearrangements that occurred during the phyletic evolution of humans from great apes. These evolutionary rearrangements provide unique color bands on different chromosomes when hybridized to
human DNA. In this paper, approx 100 bands were identified. Each chromosome, with the exception of chromosomes 15, 18, 21, 22, and the sex chromosomes, showed at least two and as many as six different colored subregions. Prior to this discovery, human chromosome painting probes were being used to study phyletic evolution in great apes, gibbons and Old World monkeys (19–24). This was the first time that higher primate DNA was hybridized to human chromosomes to produce a unique and specific color banding pattern. Utilizing the multiplex FISH techniques, these investigators were able to produce this color cross-species banding in a single hybridization experiment utilizing a fluorescence microscope with a quad band pass filter and a digital imaging system.
1.2. Applications of Color Banding 1.2.1. Cancer Cytogenetics In cancer cytogenetics, G-banding is still the gold standard. It is simple and robust. GTG Banding is the technique of choice for initial screening of karyotypic abnormalities. Chromosomes in cancer cells however, often present with very complex karyotypes or chromosomes with less than optimal morphology. Characterization of chromosomal breakpoints is emerging as an important area for cancer diagnosis and prognosis. Cross species color banding can identify marker chromosomes and redefine interpretations of ISCN bands involved in complex rearrangements. To date, 25 hematological malignancies and 13 solid tumors have been analyzed with the commercially available probe kit RxFISH (Rainbow cross-species FISH) (25–31). In all cases, color banding either confirmed or identified complex chromosome changes previously unidentifiable by conventional cytogenetics. Utilization of cross-species color banding can directly impact both the rate at which cytogenetic data is accumulated, as well as impact the accuracy of the breakpoints reported in the literature. Common chromosome breakpoints have been associated with the location of tumor suppressor genes, oncogenes, and other genes that play a role in cell growth, drug resistance, and apoptotic pathways. These common chromosome breakpoints, when well characterized, can play a role in patient diagnosis and prognosis and therefore have the potential to impact patient treatment.
1.2.2. Constitutional and Prenatal Cytogenetics There have been two reports in the literature of RxFISH being used to study constitutional chromosomal rearrangements. Four cases total were analyzed with color banding technique, including a case of partial duplication of 4q and a deletion of 4p in a 32 wk-old fetus (32). GAG banding was performed on fetal cord blood and an unbalanced karyotype was observed. The karyotype showed additional material of unknown origin on 4p. With color banding it could be determined that this was a case of partial trisomy 4q26-qter and monosomy 4p16. Deletion of the Wolf-Hirschhorn critical region was confirmed by use of a LSI Wolf-Hirschhorn probe (Vysis). Muller et al. utilized the following constitutional abnormalities: a translocation t(1;2)(q37;q42.3), a pericentric inversion inv(2)(p23q13), and a pericentric inversion inv(6)(p25q22) to illustrate the utility of their cross species color banding technique (18).
1.3. Strategies in Color Banding–Benefits and Limitations 1.3.1. Benefits Cross species color banding has been shown to be a rapid and easy way to detect chromosomal aberrations that can not be identified by G-banding alone (25–32). This technique is especially useful when GTG banding does not provide sufficient clues to enable followup by use of single whole chromosome painting probes. In addition, color banding can detect intrachromosomal abnormalities such as inversions, duplication, and small deletions that can not be detected by other multiplex FISH techniques such as MFISH and SKY. All referenced authors extol the benefits of this technique when used in combination with G-banding and other FISH detection systems.
1.3.2. Limitations Color banding resolution is only approx 100 bands or less. This number of bands provides some differentiation of chromosomes but is inadequate for small translocations, deletions or inversions. In addition, translocations are nondetectable by this technique if they involve regions painted a similar color.
2. Materials 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28.
Slides prepared by conventional cytogenetic methods. 10 µL RxFISH probe (Applied Imaging, Santa Clara, CA), store at –20°C. Formamide, molecular biology grade, 50 and 70% in 2X SSC, pH 7.5. Ethanol, denatured HPLC grade, 70, 85, and 100%. Methanol, absolute. Glacial acetic acid. 20X SSC (Saline sodium citrate), pH 7.0. 2X SSC, pH 7.0. HCl (2 N). Tween-20. Rabbit antiFITC antibodies (DAKO, V0403). FITC labeled goat anti-rabbit IgG antibodies (Vector, FI-1000). DAPI (4,6-Diamidino-2-phenylindole), (Vysis, 32-804831). Glass coverslips (22 × 22 mm). Glass Coplin jars (50 mL). Microscope slides. Humidified chamber at 37°C. Purified water (distilled, deionized). Rubber cement. Phase microscope. Waterbath set at 37, 45, 65, and 72°C. Oven set at 37°C. Oven set at 60–65°C with metal slide tray. Micropipetors and tips. pH meter. Microcentrifuge and microcentrifuge tubes. Freezer, –20°C. RxFISH CytoVision System (Applied Imaging, Santa Clara, CA).
29. Fluorescence microscope with automated filter wheel with a Quad filter block. 30. Cooled charge-coupled device video camera.
3. Methods 3.1. Slide Preparation and Aging 1. Prepare cytogenetic cell suspensions using the methanol/acetic acid fixation method. 2. Prepare microscope slides by placing a drop of cell suspension onto the slide and allowing the slide to dry at the proper temperature (25°C) and humidity (45–50%) required for chromosome spreading. 3. Using a phase microscope, monitor quality of slides and mark area of slide containing well spread metaphases, or those metaphases of interest. 4. Age slides prepared the same day in 60°C oven for 2 h or age 1-d-old slides stored overnight at room temperature in a 60°C oven for 1 h. Following aging, bring the slide to room temperature before proceeding with the next step of the RxFISH procedure. 5. Dehydrate slides in a 70, 85, and 100% ethanol series for 2 min each at room temperature and allow to airdry.
3.2. Preparation of Solutions for Denaturation and Hybridization Steps 1. 2. 3. 4.
Prepare 70% ethanol and place in –20°C freezer. Prepare 50 mL of 70% formamide/2X SSC, pH 7.5 and place in 72°C waterbath. Prepare 70, 85, and 100% ethanol and store at room temperature. Prepare humidified chamber and prewarm in 37°C oven.
3.3. Probe Denaturation 1. Warm tube containing RxFISH probe in a 37°C waterbath for 5 min. 2. Gently mix and then briefly centrifuge the tube. 3. Using a sterile pipet tip, transfer 10 µL of probe solution for each slide to be hybridized to a 0.5 mL microcentrifuge tube and cap the tube. 4. Return the unused portion of the RxFISH probe to –20°C. 5. Denature the aliquoted RxFISH probe by incubating in a 65°C waterbath for 10 min. 6. Following denaturation store probe in a 37°C waterbath for a minimum of 10 min and no longer than 2 h before being used.
3.4. Slide Denaturation 1. Confirm that the internal temperature of the 70% formamide/2X SSC solution is at the desired temperature of 72°C (see Notes 1 and 2). 2. Denature no more than 4 slides by incubation in the 70% formamide/2X SSC solution for 1.5 min (see Note 3). 3. Immediately quench the denatured slide in –20°C 70% ethanol (see Note 4). 4. Dehydrate slides in a 70, 85, and 100% ethanol series for 2 min each at room temperature and allow to air dry.
3.5. Hybridization Procedure 1. Reduce ambient lighting in order not to photo bleach RxFISH probe (see Note 5). 2. Pipet 10 µL of the denatured probe mixture onto the area of the slide that was marked for hybridization because it contains well spread metaphases or those metaphases of interest. 3. Slowly add 25 × 25 mm coverslip to avoid air bubbles.
4. Allow the probe solution to spread to the edges of the coverslip. Tap gently to remove any air bubbles avoiding any movement of the coverslip. 5. Seal the coverslip to the slide with rubber cement. 6. Incubate the slide in a humidified chamber for 48 h at 37°C (see Note 6).
3.6. Preparation of Solutions for Posthybridization Steps 1. Prepare 150 mL 2X SSC, pH 7.0. Dispense into three Coplin jars and place in waterbath set at 45°C (see Note 7). 2. Prepare 100 mL of 50% formamide/0.5X SSC, pH 7.0, dispense into two Coplin jars and place in 45°C waterbath. 3. Dispense 50 mL of 4X Tween solution, pH 7.5 (500 mL 4X SSC and 0.25 mL Tween 20 stock) in a Coplin jar and place in 45°C waterbath.
3.7. Posthybridization Wash 1. Carefully remove the rubber cement from coversliped slide(s) with forceps and float the coverslip off by incubating the slide in the first Coplin jar of 2X SSC at 45°C for 5 min (see Notes 8–10). 2. Wash the slide(s) for 5 min at 45°C in a Coplin jar containing 50% formamide/0.5X SSC. Transfer slide to second Coplin jar containing this same solution and repeat wash for another 5 min. 3. Wash slide(s) for 5 min at 45°C in a Coplin jar containing 2X SSC. Repeat this wash in the third Coplin jar containing this solution for an additional 5 min. 4. Transfer the slide to the Coplin jar containing the 4X Tween solution and incubate at 45°C for 10 min.
3.8. Antibody Detection Steps (Optional) 1. During the second formamide wash step in Subheading 3.7., centrifuge the two antibody tubes for FITC detection at 14,000g for 10 min at room temperature. Use only the supernatants from these tubes in the following steps. 2. To microcentrifuge tube add 1 µL of rabbit antiFITC antibody and 199 µL of 4X Tween for each slide to be processed. Gently mix the dilution. Incubate in the dark at room temperature for 10 min. 3. Drain excess fluid from the slide(s). 4. Add 200 µL rabbit antiFITC antibody, 1:200 dilution to each slide and incubate for 30 min in a humid chamber kept at 37°C. 5. Lower the temperature of the waterbath from 45 to 42°C. Prewarm a 50 mL Coplin jar of 4X Tween. Also prewarm an additional 250 mL of 45X Tween for a total of 6 additional washes. 6. Check that the waterbath and 4X Tween solutions are at 42°C. Remove coverslip from slide(s). Wash the slide for 5 min. Decant the solution and refill with fresh prewarmed 4X Tween, wash again for 5 min. Repeat this step once. 7. During these wash steps, in another microcentrifuge tube add 2 µL of FITC-labeled goat anti-rabbit IgG antibody and 198 µL of 4X Tween for each slide to be processes. Gently mix the dilution. Incubate in the dark at room temperature for 10 min. 8. Drain excess fluid from the slide. 9. Add 200 µL FITC-labeled goat anti-rabbit IgG antibody, 1:100 dilution to each slide and incubate for 30 min in a humid chamber kept at 37°C. 10. Check that the waterbath and 4X Tween solutions are at 42°C. Wash 3× at 42°C for 5 min each.
3.9. DAPI Counterstain 1. Mount the slide with 10 µL of the DAPI counterstain and antifade solution using a 22 × 22 mm coverslip (see Note 11).
3.10. Image Capture and Analysis 1. Turn on computer, select RxFISH software under the research menu. When activated, select the capture screen. Set the filter wheel in the proper order before beginning image capture. The probe is captured in layers of raw images that are combined for a final image. Rx-Cy5 is captured first followed by Rx-Cy3, Rx-FITC, and lastly Rx-DAPI. 2. Scan for metaphases using FITC. FITC has a less tendency to fade the signal, which should stay bright throughout all analysis. When you have found a metaphase, focus the metaphase using a ×100 oil objective. Select Rx-Cy5. 3. Rx-Cy5 is undetectable by the naked eye. Rely on the computer image for detail. When the exposure setting is 5 s a faint white image on a black background should be detectable. Focus slowly and in increments, as there is a time delay between the camera and the software. Adjust the bright and black until you have a good contrast (~90% accuracy). These settings will be slightly different for each individual image. 4. Hit the "Live" button and the filter wheel will automatically turn to the next fluorochrome on the list. For the other fluorochromes an exposure of 2 s seems to work best most of the time. Once a good image with a clear banding pattern has been achieved, click on the "Capture" button. 5. After completing captures for all four fluorochromes, select the box marked RxFISH Image Capture. Within the box select, batch complete. Keep all images; never delete them even when prompted. These images are often useful during analysis. 6. Activate the analysis menu. Choose the cell you wish to analyze (highlight the probe cell image). Select "Load cell" and multicolored banded chromosomes can be observed (see Note 12). In the Analysis Customize menu, the RxFISH image can also be displayed as an inverted DAPI image, which can help in chromosome identification. The Analysis Profile tool is used to display individual intensity profile of the chromosomes. 7. The chromosome must be separated using the Analysis commands. Once separation has been completed the Classifier and Auto commands are used to generate the karyotype of the cell.
4. Notes 1. The denaturation step is very critical to the procedure. Temperature and times are dependent upon the type and age of the sample. Each user should determine the appropriate temperature and time based on their particular need. Acceptable results can be obtained using a temperature range of 70–75°C and a time range of 1.5–2 min. 2. The internal temperature of the solutions in each Coplin jar throughout the procedure must be checked prior to each use. Often the temperature of the solutions in the Coplin jar will be one or more degrees below that of the water in the waterbath itself. 3. Each room temperature slide that is added to the 72°C formamide lowers the temperature of the 70% formamide/2X SSC by 0.5–1°C. If more than 4 slides are added per run, the temperature of the formamide/2X SSC will be insufficient for denaturation to occur. 4. If more than 4 slides are to be processed, both the denaturation temperature of the 70% formamide/2X SSC and the first Coplin jar of 70% ethanol must be allowed to return to their initial temperature, 72°C and –20°C respectively.
5. The Cy5 fluorochrome approaches the infrared wavelength range, which is very sensitive to being excited by white light. Accordingly, during image capture, this is the first fluorochrome to be exposed to light since it is the first to fade. 6. Slides may be hybridized for 12–96 h in a moist chamber at 37°C. Never hybridize probe for less than 12 h as signal intensity is greatly diminished. Forty-eight hour hybridization times provide slides with consistently strong signals. This is essential for successful image capture. Reduction in hybridization times should be based on each laboratory's experience. 7. To ensure quality results, discard solutions made at the end of each day. The solutions used in the denaturation steps should not be saved for use during the post-hybridization wash steps. 8. Posthybridization wash steps should be done in dim light to prevent photo bleaching of direct labeled fluorochromes (Cy5 and Cy3). 9. The slide should not be allowed to dry completely during any post-hybridization step. 10. If the cover slip fails to come off the slide, place the slide back into the 2X SSC for an additional 5 min and then check the coverslip again. 11. Store slides a –20°C and in the dark until they are ready to be imaged. 12. If the colors are pastel and not bright, recapture images on a darker setting (less exposure). When focusing images before capture, keep the exposure times lower as there will be less of a delay. There is a chip in the camera that gathers light for the exposure time and then sends the information to the computer, this is why there is a delay. The DAPI image should not be too dark. The DAPI image provides the background for the other colors. If the DAPI image is not bright enough, the chromosomes will look ragged. For this reason as well, it is essential that the DAPI image be in good focus.
References 1. Caspersson, T., Zech, L., and Johansson, C. (1970) Differential binding of alkylating fluorochromes in human chromosomes. Exp. Cell Res. 60, 315–319. 2. Sumner, A. T., Evans, H. J., and Buckland, R. A. (1971) New technique for distinguishing between human chromosomes. Nature New Biol. 232, 31–32. 3. Seabright M. (1971) A rapid banding technique for human chromosomes. Lancet 11, 971–972. 4. Dutrillaux, B. and Lejeune, J. (1971) A new technic of analysis of the human karyotype. Comptes Rendus Hebdomadaires des Seances de l Academie des Sciences—D: Sciences Naturelles 272, 2638–2640. 5. Pinkel, D., Straume, T., and Gray, J. W. (1986) Cytogenetic analysis using quantitative high-sensitivity, fluorescence hybridization. Proc. Natl. Acad. Sci. USA 83, 2934–2938. 6. Pinkel, D., Landegent, J., Collins, C., et al. (1988) Fluorescence in situ hybridization with human chromosome specific libraries: Detection of trisomy 21 and translocation of chromosome 4. Proc. Natl. Acad. Sci. USA 85, 9138–9142. 7. Lichter, P., Cremer, T., Borden, J., Manuelidis, L., and Ward, D. C. (1988) Delineation of individual human chromosomes in metaphase and interphase cells by in situ suppression hybridization using recombinant DNA libraries. Hum. Genet. 80, 224–234. 8. Nederlof, P. M., Robinson, D., Abunesha, R., et al. (1989) Three color fluorescence in situ hybridization for the simultaneous detection of multiple nucleic acid sequences. Cytometry 10, 20–27. 9. Nederlof, P. M., Van der Flier, S., Wiegant, J., et al. (1990) Multiple fluorescence in situ hybridization. Cytometry 11, 126–131. 10. Nederlof, P. M., van der Fleier, S., Wiegant, J., et al. (1992) Fluorescence ratio measurements of double-labeled probes for multiple in situ hybridization by digital imaging microscopy. Cytometry 13, 839–845.
11. Lengauer, C., Green, E. D., and Cremer, T. (1992) Fluorescence in situ hybridization of YAC clones after Alu-PCR amplification. Genomics 13, 826–828. 12. Lengauer, C., Speicher, M. R., Popp, S., et al. (1993) Chromosomal bar codes produced by multicolor fluorescence in situ hybridization with multiple YAC clones and whole chromosome painting probes. Hum. Mol. Genet. 2, 505–512. 13. Ried, T., Baldini, A., Rand, T. C., and Ward, D. C. (1992) Simultaneous visualization of seven different DNA probes by in situ hybridization using combinatorial fluorescence and digital imaging microscopy. Proc. Natl. Acad. Sci. USA 89, 1388–1392. 14. Schrock, E., du Manoir, S., Valman, T., et al. (1996) Multicolor spectral karyotyping of human chromosomes. Science 273, 494–497. 15. Speicher, M. R., Ballard, G. S., and Ward, D.C (1996) Karyotyping human chromosomes by combinatorial multifluor FISH. Nat. Genet. 12, 368–375. 16. Muller, S., Rocchi, M., Ferguson-Smith, M. A. and Wienberg, J. (1997) Toward a multicolor chromosome bar code for the entire human karyotype by fluorescence in situ hybridization. Hum. Genet. 100, 271–278. 17. Antonacci, R., Marzella, R., Finelli, P., Lonoce, A. and Forabosco, A. (1995) A panel of subchromosomal painting libraries representing over 300 regions of the human genome. Cytogenet. Cell Genet. 68, 25–32. 18. Muller, S., O'Brien, P. C., Ferguson-Smith, M. A., and Weinberg, J. (1998) Cross-species color segmenting: A novel tool in human karyotype analysis. Cytometry 33, 445–452. 19. Wienberg, J., Jauch, A., Stanyon, R., and Cremer, T. (1990) Molecular cytotaxonomy of primates by chromosomal in situ suppression hybridization. Genomics 8, 347–350. 20. Jauch, A., Wienberg, J., Stanyon, R., et al. (1992) Reconstruction of genomic rearragements in great apes and gibbons by chromosome painting. Proc. Natl. Acad. Sci. USA 89, 8611–8615. 21. Wienberg, J., Stanyon, R., Jauch, A., and Cremer, T. (1992) Homologies in human and Macaca fuscata chromosomes revealed by in situ suppression hybridization with human chromosome specific DNA libraries. Chromosoma 101, 265–270. 22. Koehler, U., Arnold, N., Wienberg, J., Tofanelli, A. and Stanyon, R. (1995) Genomic reorganization in the concolor gibbon (Hylobates concolor) revealed by chromosome painting. Genomics 30, 287–292. 23. Kohler, U., Bigoni, F., Wienberg, J. and Stanyon, R. (1995) Genomic reorganization and disrupted chromosomal synteny in the Siamang (Hylobates syndactylus) revealed by fluorescence in situ hybridization. Am. J. Phys. Anthropol. 97, 37–47. 24. Wienberg, J. and Stanyon, R. (1997) Comparative painting of mammalian chromosomes. Curr. Opin. Genet. Develop. 7, 784–791. 25. Teixera, M., Micci, F., Dietrich, C., and Heim, S. (1999) Cross-species color banding characterization of chromosomal rearrangements in leukemias with incomplete G-band karyotypes. Gene Chromosom. Cancer 26, 13–19. 26. Micci, F., Teixeira, M. R., Dietrich, C. U., Saeter, G., Bjerkehagen, B. and Heim, S. (1999) Combined RxFISH/G-banding allows refined karyotyping of solid tumors. Hum. Genet. 104, 370–375. 27. Harrison, C. J., Gibbons, B., Yang, F., et al. (2000) Multiplex fluorescence in situ hybridization and cross species color banding of a case of chronic myeloid leukemia in blastic crisis with a complex Philadelphia translocation. Cancer Genet. Cytogenet. 116, 105–110. 28. Teixeria, M. R., Micci, F., Dietrich, C. U., and Heim, S. (2000) Detailed genome-wide screening for inter- and intrachromosomal abnormalities by sequential G-banding and RxFISH color banding of the same metaphase cells. Cancer Genet. Cytogen. 119, 94–101.
29. Espinet, B., Sole, F., Salido, M., et al. (2000) Application of cross-species color banding (RxFISH) in the study of T-prolymphocytic leukemia. Haematologica 85, 607–612. 30. Koo, S. H., Kwon, K. C., Park, J. W., Lee, Y. E., and Kim, J. W. (2000) Characterization of chromosomal breakpoints in an ALL patient using cross-species color banding. Cancer Genet. Cytogenet. 119, 118–120. 31. Zhao, L., Hayes, K., and Glassman, A. (2000) Enhanced detection of chromosomal abnormalities with the use of RxFISH multicolor banding technique. Cancer Genet. Cytogenet. 118, 108–111. 32. Petek, E., Wagner, K., Steiner, H., Schaffer, H., and Kroisel, P. M. (2000) Prenatal diagnosis of partial trisomy 4q26-qter and monosomy for the Wolf-Hirschhorn critical region in a fetus with split hand malformation. Prenatal. Diagnosis 20, 349–352.
Multicolor Fiber FISH
11 Multicolor Fiber FISH Jaennelle Kraan, Anne R. M. von Bergh, Karin Kleiverda, Jan-Willem Vaandrager, Ekaterina S. Jordanova, Anton K. Raap, Philip M. Kluin, and Ed Schuuring 1. Introduction Various genetic abnormalities can be observed in many human diseases. They vary from numerical chromosomal aberrations, deletions, and amplification of specific regions to chromosomal translocations and insertions. In the past decade, numerous fluorescence in situ hybridization (FISH) methods have been developed for the detection of these abnormalities. FISH to interphase nuclei is one of the methods that is widely used to detect numerical chromosomal abnormalities, DNA amplification, and structural abnormalities ranging in size from approximately 10–1000 kilobases. Interphase cytogenetics requires a priori knowledge regarding the DNA sequences involved in the aberration. Particularly for the diagnostic detection of structural abnormalities such as chromosomal translocation breakpoints, the interphase method is highly dependent on the availability of appropriate breakpoint flanking probes. More recently, a set of high resolution FISH methods have been developed that collectively are referred to as Fiber FISH. The basis of Fiber FISH is to release DNA-molecules from the nucleus and to fix the stretched DNA in a (near) linear fashion onto a glass slide. The DNA fibers are hybridized with a set of probes labeled with different fluorochromes that cover the entire region of interest resulting in a characteristic string of FISH signals that have the attributes of a multicolor barcode (Fig. 1A, B). Barcodes up to 1000 kb can be generated, but a length of approx 300 kb is used in practice. When larger regions are targeted, artificial breakage of the target DNA may complicate interpretation of results. With its high and wide ranging resolution (1–1000 kb) as well as its color barcoding capacity, Fiber FISH has proven to be well suited as an adjunct physical mapping tool and for analysis of length polymorphisms as well as a valuable tool in molecular pathological research to pinpoint regions of chromosome (DNA) rearrangements at a much larger genomic scope than PCR, Southern blotting, and interphase-FISH. From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
Kraan et al.
Fig. 1. (A) Fiber FISH to map a breakpoint in the ETV6 (12p13) gene, present in a t(9;12)(q34;p13). The normal 300 kb barcode consists of seven cosmid probes as illustrated in the superimposed cosmid map. The upper fiber, representing the normal allele, shows hybridization of the normal barcode pattern. The second and third fiber show the complementary patterns representing the breakpoint products. The breakpoint in these leukemic cells was mapped within the middle cosmid (arrow). (B) Simultaneous hybridization of two specific barcodes for the involved genes in a 200 kb insertion. The upper fiber shows the normal barcode of one gene (MLL on 11q23), whereas the bottom fiber shows the normal barcode of the partner gene (AF4 on 4q21). The junction of both loci in the tumor DNA is visualized in the middle fiber. In this case, a part of the barcode of the MLL gene is inserted into the barcode of the AF4 gene (20). Note that a simple single color barcode may also enable exact mapping of breakpoints. (C) Fiber preparation stained with propidium iodide. If nuclei are present on the slide as red bright balls, as shown in this picture, the cell lysis has been insufficient. (D) Fiber preparation stained with propidium iodide. If the slide looks cloudy and bright crystals are present, as shown in this picture, the amount of cells is too high. (E) Fiber preparation stained
In this chapter, we will briefly summarize the development of Fiber FISH, describe some of its applications and present a detailed Fiber FISH protocol we have used over the last few years in our Lab.
1.1. The Development of Fiber FISH To prepare linear stretches of DNA released from the nucleus, various methods have been described (reviewed in 1) and published under different names including high resolution FISH, molecular combing, DNA fiber FISH, halo FISH and DIRVISH (2–7). All are based on the release of most of the DNA contents of cells on microscope object slides and linearizing DNA. In most methods, nuclei are prepared from fresh cells, frozen cells or frozen tissues and put on glass slides before release of the DNA (1). Other methods used isolated genomic DNA prepared in agarose blocks or in solution (2). For linearization of genomic DNA, most methods rely on mechanical or gravitational force. Wiegant et al. (4) used the halo method to release the DNA from nucleus. This method was originally used in the early sixties to visualize DNA strands with electromicroscopy. Using this approach, the DNA was released and combined with a histone extraction step, using a concentrated salt solution, and a DNA unwinding step, involving induction of single strand breaks by a combination of the DNA intercalator propidium iodide and UV radiation. The Fiber FISH method described in this chapter is based on this DNA halo technique. Following stretching and immobilization of (nuclear) DNA fibers, they are used as targets of multiple probes for the region of interest labeled with different haptens/ fluorochromes. It is estimated that DNA fragments in size up to approx 2–4 kb will hybridize as a single signal. Genomic probes cloned in large insert vectors as cosmids, PACs, and BACs in general have a complexity of 30–150 kb, and thus a single probe will be visible as numerous beads-on-a-string (Fig. 1A, B, F). The total length of the signals (i.e., the collection of beads-on-a-string) corresponds well with the real size (or complexity) of the probe (within the limits of the standard deviation of approx 1–2 kb) so that the genomic distance approximates the physical distance (3 kb = 1 µm). Because of the typical linear beads-on-a-string signal of the probe, this pattern can easily be discriminated from all other single background signals in the preparation that are due to aspecific hybridization (Fig. 1F). This enables the use of low stringency hybridization and washing conditions in Fiber FISH and is an important advantage over interphase-FISH especially if different probes are combined in a single experiment. Moreover, by using a set of different probes that cover a certain region and that are alternatively fluorescently labeled (red or green), probe contigs appear as multicolored, barcode like patterns in red, green, yellow (the overlap of clones labeled in green and red) and small gaps remaining dark when hybridized on linear DNA molecules
(continued) with propidium iodide. In this picture, the cells are sufficiently lysed and the cells are evenly distributed along the slide. DNA halos are present as comet like structures. (F) Fiber FISH preparation hybridized with a 250 kb two color (green and red) cosmid barcode. Observed with a double or triple filter, it is very easy to distinguish between the beads-on-a-string fiber signals and single background signals.
(Fig. 1A, B, F). Each contig, i.e., each barcode, will be unique for a certain region. The availability of such multicolored barcodes allows a rapid visual identification for physical mapping of new probes and for the analysis of DNA rearrangements in patient specimens.
1.2. Some Applications for Fiber FISH Fiber FISH finds application in physical mapping of DNA clones. Novel clones can be rapidly analyzed for size, position, and orientation when compared to already fully characterized clones in the region of interest (5,8). Such an approach has been used in genome projects. Fiber FISH was also used to map the genomic structure of a gene by hybridization of a cDNA clone in combination with genomic probes that covers all presumed exons and introns (9). This analysis illustrated that fragments as small as 500 bp can be detected. With a Fiber FISH barcode, various genetic abnormalities such as deletions, insertions, length polymorphisms, and translocations can be mapped physically in clinical specimens conveniently if they occur within the barcode. For instance, Florijn et al., (5) were the first to map two Duchenne dystrophy deletion breakpoints with Fiber FISH with an accuracy of 1–2 kb. We have applied our Fiber FISH protocol on a subset of B-cell lymphomas that had down-regulated expression of certain HLA-genes on chromosome 6p21.3 (10). Apart from confirming several length polymorphisms, this analysis revealed homozygous deletions in size ranging from 50–150 kb. This study enabled us to rapidly narrow down the size of the deleted region. With a set of probes that covers the constant region of the immunoglobulin heavy chain locus, numerous polymorphisms as well as somatic class switch recombination events were observed (11). In cases of DNA amplification, Fiber FISH permitted the determination of the number of amplicons, the orientation of each amplified fragment within the cluster, the size of each amplicon, the variation among different cells and also copy numbers of moderately repeated sequences (12). Fiber FISH has also been used to investigate viral insertions in the mammalian genome (13). Using Fiber FISH with contigs that cover the breakpoint regions in mantle cell lymphomas with t(11;14), follicular lymphomas with t(14;18) and ALL/AML with MLL-breaks on 11q23, the location of the breakpoints could be determined with an accuracy of few kilobases (14–16). At this stage, Fiber FISH is not used as a routine diagnostic assay to detect genetic aberrations in clinical specimens, because it is relatively time consuming and generally can only be applied to fresh or frozen cells or tissues. Also, the success rate (i.e., the number of cases from which sufficient fibers are obtained to draw reliable conclusions) is not 100% and depends on many experimental conditions. This implies that some experiments have to be repeated or that the conditions have to be adapted to the specific cellular material. Nevertheless, in our experience, Fiber FISH as a research tool, has provided essential contributions to the design of optimal probe-sets to detect all abnormalities by interphase-FISH (reviewed in ref. 17). The Fiber FISH analysis of the t(11;14) and t(14;18) translocations characteristic for mantle cell and follicular lymphoma respectively may serve as illustrative examples. The mapping of many breakpoints by Fiber FISH showed that they are scattered over large 350–500 kb regions, a size that can not be accommodated by conventional methods such as PCR and Southern blotting. Fiber FISH mapping clearly defined the maximum size of the
breakpoint regions. The Fiber FISH analysis also revealed a considerable number of cases (approx 20%) with uncommon complex, mono-allelic breakpoints. These included mono-allelic double breakpoints 3' and 5' of cyclin D1 at 11q13 or BCL2 at 18q21, either or not in combination with an insertion into the IgH-locus (18) or a small deletion in the UTR of cyclin D1 (19). Based on these data, we designed probe sets flanking all possible breakpoints and use these sets in our routine diagnostic setting for the detection of translocations using interphase FISH (14,15).
2. Materials 2.1. Preparation of DNA Fibers Using the Halo Method 1. 2. 3. 4.
5. 6. 7. 8. 9. 10. 11. 12.
Cultured cell suspension or 45 µM sections of frozen soft tissues/tumors or isolated PBL. PBS: 8 g NaCl, 0.29 g KCl, 1.449 g Na2HPO4, 0.249 g KH2PO4/L. Microfuge. Halo-solutions: a. Halo 1: 0.5% NP-40, 25 mM Tris-HCl, pH 8.0, 10 mM MgCl2, 0.5 mM CaCl2. b. Halo 2: 25 mM Tris-HCl pH 8.0, 0.2 mM MgCl2, 2 M NaCl. c. Halo 3: as Halo 2, with 4 mg/100 mL propidium iodide. d. Halo 4: 25 mM Tris-HCl pH8.0, 0.2 mM MgCl2, 0.2 M NaCl. e. Halo 5: 25 mM Tris-HCl pH8.0, 0.2 mM MgCl2. 20% bovine serum albumine (A9647 from Sigma, St. Louis, MO) in PBS; dissolve 2 g of BSA in 10 mL of sterile PBS, store in small portions at –20°C. Camag UV Cabinet II, low pressure mercury tube (8 W), 256 nm UV lamp. 10% SDS in ultrapure water; dilute to 0.05% (or 0.1%) in ultrapure water. Ethanol/ether 1:1. Glass microscope slides ca 76 × 26 mm with frosted edge, cleaned by dipping in a mixture of ethanol/diethylether 1:1 and wiped with a non-woven tissue (see Note 1). Glass plate, thickness 5 mm, on crunched ice. Fetal calf serum (FCS). Fluorescence microscope equipped with a PL Fluotar ×16 objective and a PL Fluotar ×100, objective and filters for viewing Texas Red/PI and fluorescein isothiocyanate (FITC).
2.2. Probe Labeling 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
Probe DNA (see Note 2). 10X Nicking buffer: 0.5 M Tris-HCl pH 7.8, 50 mM MgCl2, 0.5 mg BSA/mL. Nucleotide mixture (0.5 mM dGTP, 0.5 mM dATP, 0.5 mM dCTP, 0.1 mM dTTP). 100 mM Bio-16-dUTP (Roche Diagnostics, Basel) or 100 mM Dig-11-dUTP (Roche Diagnostics). 100 mM DTT. Sterile ultrapure water. DNase I grade II, Roche Diagnostics 104159, 1 mg/mL. DNA-polymerase I (M502A, 10 U/µL from Promega, Madison, WI). Yeast RNA (10 µg/µL Sigma R 6750). SS-DNA (salmon sperm DNA, 10 µg/µL Sigma D7290). 3 M NaAc pH 5.3–5.9. Ethanol absolute. Waterbath at 16°C. Centrifuge 13000 rpm at 4°C.
15. Hybridization mixture, for 1 mL: 300 µL deionized formamide, 100 µL 0.5 M sodium phosphate buffer pH 7.0, 100 µL 20X SSC, 500 µL ultrapure water, 100 mg dextransulphate; dissolve for 3 h at 70°C.
2.3. Hybridization 1. Slide warmer. 2. Labeled cosmid/PAC/P1/BAC/YAC probe. 3. Cot-1 DNA (Life Technologies, Gaithesburg, MD), ethanol precipitated and dissolved in hybridization mixture in a concentration of 3 µg/mL. 4. Denaturing mixture, for 1 mL: 700 µL deionized formamide, 100 µL 0.5 M sodium phosphate buffer pH 7.0, 100 µL 20X SSC, 100 µL ultrapure water. 5. Hybridization mixture. 6. Ethanol absolute. 7. 24 × 60 mm glass coverslips. 8. 24 × 24 mm glass coverslips.
2.4. Posthybridization and Immunodetection 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
2X SSC. Waterbath at 37°C. Coplin jar 100 mL. TNT: 0.1 mM Tris-HCl, pH 7.5, 0.15 M NaCl, 0.05% Tween-20. TNB: 0.5% Boehringer blocking reagent in 0.1 mM Tris-HCl, pH7.5, 0.15 M NaCl. Texas Red-labeled streptavidin (Vector Laboratories, Burlingame, CA) 1.0 mg/mL. Mouse anti-digoxigenin (Sigma) 4.0 mg/mL. Goat biotinylated anti-streptavidin (Vector) 0.5 mg/mL. Rabbit anti-mouse-Ig-FITC (Sigma) 15.3 mg/mL. Goat anti-rabbit-FITC (Vector) 1.5 mg/mL. Antifade mounting medium (Vectashield, Vector). 24 × 60 mm coverslips.
3. Methods 3.1. Preparing Slides with DNA Fibers Most types of cells are suitable for fiber FISH, as long as the cells have not been fixated or dried and the nuclei are intact. Frozen tissue samples or pelleted cells can be used as long as the tissue can be suspended to a cell suspension. Cells which have a lot of cytoplasm often need more rigorous treatment to lyse. Always start with the most gentle method and increase SDS-treatment if lysis is insufficient. Prior to beginning, place on ice: 1. Each Halo-solution and 0.05% SDS in ultrapure water in 100-mL beakers and two 100-mL beakers containing ultrapure water. 2. A tube containing 20% BSA and a tube containing PBS. 3. A glass plate (5 mm thickness).
3.1.1. Preparing a Cell Suspension From cultured cells, peripheral blood cells, or other cell suspensions: 1. Centrifuge 1 mL of cell suspension or trypsinized cells (approx 10,000–100,000 cells) in an Eppendorf tube for a few seconds in a microcentrifuge.
2. Remove supernatant. 3. Resuspend cells in 200 µL PBS (4°C). From frozen tissues: 1. 2. 3. 4. 5. 6.
Cut one or a few frozen sections of 45 µm (see Note 3). Place in an eppendorf tube on dry ice. Keep on dry ice until use. Thaw section for ± 30 s. Add ± 500 µL PBS (4°C). Suspend section by pipetting up and down vigorously.
3.1.2. Preparing DNA Fiber Slides 1. Pipet 20 µL of cells in a tube, adjust the volume with PBS (4°C) to 47,5 µL and add 2,5 µL 20% BSA/PBS and mix the suspension well. 2. Pipet the suspension onto a slide and evenly spread over the whole slide using a pipet tip. 3. Place the slide on an ice cold glass plate for 2 min. 4. Drain excess of fluid by placing the slide vertically (frosted edge upwards) onto a tissue for 40 s. 5. Blowdry very gently using compressed air until the edges are starting to dry (see Note 4). (For easily lysing cells like peripheral blood cells or cultured cells steps 6–9 can be omitted). 6. Dip slide gently vertically in Halo 1 for 30 s. 7. Remove slide slowly from solution in 3 s, drain excess of fluid on a tissue for 7 s (see step 4). 8. Dip slide gently vertically in Halo 2 for 30 s. 9. Remove slide slowly from solution in 3 s, drain excess of fluid on a tissue for 7 s (see step 4). 10. Dip slide gently vertically in Halo 3 for 45 s. 11. Remove slide slowly from solution in 3 s, drain excess of fluid on a tissue for 7 s (see step 4). 12. Clean the backside of the slide with a piece of tissue. 13. Place the slide horizontally on the ice cold glass plate. 14. Place the still wet slide under the UV lamp at a distance of 1–10 cm (see Note 5). 15. Irradiate immediately for 1–10 min at 254 nm (see Note 5). 16. Place slide vertically onto a tissue for 10 s (see step 4). 17. Dip the slide gently vertically for 30 s in Halo 4. 18. Remove slide slowly from solution in 3 s, drain excess of fluid on a tissue for 7 s (see step 4). 19. Dip the slide gently vertically for 30 s in Halo 5. 20. Remove slide slowly from solution in 3 s, drain excess of fluid onto a tissue for 7 s (see step 4). 21. Repeat for 2 washes in ultrapure water. 22. Leave slide to dry vertically in a rack at room temperature for few minutes. 23. Examine the slide under a fluorescent microscope with ×16 objective and TRITC-filter (see Note 6) and examine whether (a) the cells are properly lysed (Fig. 1C) (see Note 7); (b) the amount of cells is sufficient (Fig. 1D) (see Note 8); (c) the number of comet like structures (representative for fibers) on the slide is sufficient (Fig. 1E) (see Note 8). 24. Leave slides to dry overnight at room temperature before proceeding with hybridization; long term storage of slides is possible at –20°C in a closed container.
3.2. Probe Labeling 1. Mix in a tube: 5 µL 10X nicking buffer, 5 µL 0.1 M DTT, 4 µL nucleotide mixture, 0.5 µL of labeled nucleotide, 1 µg of DNA and adjust volume with ultrapure water to 44 µL. 2. Place on ice and add 1 µL DNA-polymerase.
150 3. 4. 5. 6. 7. 8. 9. 10. 11.
Kraan et al. Dilute DNase I stock solution 1:500 /1:1000/ 1:2000 in ice cold ultrapure water. Add 5 µL of diluted DNase I. Incubate for 2 h at 16°C. Place on melting ice and take an aliquot of 5 µL, test fragment length on a 2% agarose gel (see Note 9). Add 20 µg ss-DNA and 20 µg yeast RNA. Precipitate with 0.1 vol 3 M NaAc and 2.5 volume ethanol absolute –20°C. Leave for 30 min on melting ice. Spin in a microcentrifuge at full speed for 30 min, remove ethanol and air dry pellet. Resuspend probe in hybridization mixture in a concentration of 30–60 ng/µL, dissolve for 30 min at 37°C, store in the dark (at 4°C or –20°C).
3.3. Hybridization 1. Bake the slides with fibers on a slide warmer of 80°C for 2 h (see Note 10). 2. Prepare probe mixture: 3 ng/µL of labeled cosmid/PAC/P1 probe of each probe, cot-1 DNA in a 50-fold excess per probe, add up to 10 µL with hybridization mixture. 3. Denature probe mixture for 8 min at 80°C. 4. Quench on melting ice for 2 min. 5. Mix, spin down briefly in a microcentrifuge. 6. Pre-anneal probe mixture for 30 min in a 37°C waterbath. 7. Apply 120 µL of Denaturing mixture (70% deionized formamide/2X SSC/50 mM sodiumphosphate) on a 24 × 60 mm coverslip. 8. Invert the slide with the fiber side onto the cover slip allowing denaturing mixture to spread. 9. Turn the glass slide back with coverslip up and put the slide on a slide warmer of 80°C for exactly 3 min. 10. Remove coverslips gently by tilting the glass slide and let the coverslip slide off. 11. Wash for 2 min in 2X SSC on ice (4°C). 12. Wash for 5 min in 70% ethanol (–20°C). 13. Dehydrate slide in 90 and 100% ethanol at RT. 14. Leave to air dry vertically in a rack. 15. Put 10 µL probe mixture on slide. 16. Cover with a 24 × 24 mm coverslip. 17. Hybridize upside down overnight at 37°C in a moist chamber.
3.4. Posthybridization and Immunodetection Prewarm 400 mL 2X SSC to 37°C in waterbath: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Soak coverslip off in 2X SSC for 5 min at 37°C in a Coplin jar (see Note 11). Wash 3× for 5 min in 2X SSC at 37°C. Wash for 5 min in TNT. Add 120 µL of TNB onto a coverslip 24 × 60 mm and invert slide onto it. Incubate upside down for 20 min at 37°C in a moist chamber. Prepare a 1:1000 mouse antidigoxigenin antibody and 1:100 Texas Red-labeled streptavidin mixture in TNB; 120 µL per slide. Soak coverslip off in TNT. Apply antibody mixture to a 24 × 60 mm coverslip, invert slide onto it. Incubate upside down for 30 min at 37°C in a moist chamber. Soak coverslip off in TNT. Wash 3× 5 min in TNT.
12. Prepare a rabbit 1:1000 antimouse-Ig-FITC and 1:100 goat biotinylated-antistrepavidin antibody mixture in TNB; 120 µL per slide. 13. Apply antibody mixture to a 24 × 60 mm coverslip, invert slide onto it. 14. Incubate upside down for 30 min at 37°C in a moist chamber. 15. Prepare a 1:100 goat antirabbit FITC antibody and 1:200 Texas Red-labeled streptavidin mixture in TNB; 120 µL per slide. 16. Soak coverslip off in TNT. 17. Wash 3× 5 min in TNT. 18. Apply antibody mixture to a 24 × 60 mm coverslip, invert slide onto it. 19. Incubate upside down for 30 min at 37°C in a moist chamber. 20. Soak coverslip off in TNT. 21. Wash 3× 5 min in TNT. 22. Dehydrate in a series of 70–90–100% ethanol. 23. Allow to air dry. 24. Apply 10 µL antifade medium to slide and cover with 24 × 60 mm coverslip.
3.5. Signal Viewing and Interpretation The amount of background on the slide is very high due to the large probe fragments. However, the background is very easy to distinguish from the beads-on-a-string fibers (Fig. 1E). FISH signals are analyzed according to Vaandrager et al. (11). Known distances between probes and/or probe lengths (e.g., obtained by restriction mapping or in case of large probes by pulsed field gel electophoresis) provide internal length references (see e.g. in ref. 14). Differences in degree of DNA condensation on individual glass slides can be eliminated by computer-aided stretching or compressing of the digital images and normalization to the total length of the barcode. In case of the presence of abnormal barcodes, e.g., derived from breaks, the hybridization efficiency can be verified by the presence of normal barcode signals from normal alleles. The total amount of fibers that is needed to map a breakpoint depends on the amount of tumor cells in the initial cell suspension. However, in general, measurement of five of each normal and abnormal barcode residues will be sufficient for accurate mapping of breakpoints (14).
4. Notes 1. Although many slide surfaces have appeared to be suitable for Fiber FISH, in our experience, a special coating is not required. 2. It is adviced to use column cleaned probe DNA for nick translation since DNase I is very sensitive to contamination of small amounts of phenol, salt or RNA. 3. It is possible to cut several sections and store them in –70°C for up to two months. How many sections are required for a single experiment depends on the specific conditions used to lyse the cells, as more rigorous lysing will detach more cells from the slide. 4. Keep slide horizontal and rainbow like patterns will occur. 5. The UV radiation nicks the DNA. Too much irradiation will result in small DNA-fragments that will detach, whereas, too little irradiation will give an inefficient hybridization with just a few signals. It is therefore important to initially verify the proper UV dose frequently and each time the lamps are replaced by applying a series of irradiation times varying from 1–10 min and by varying the distance from the slide to the UV-lamp between 1–10 cm. A Strata-Linker might also be used. Be aware to use appropriate eye- and skinprotection at all times against UV irradiation.
6. Do not cover slide and do not use oil. 7. There should be comet like structures present (Fig. 1E). If nuclei are still present as red bright balls, the lysis is insufficient (Fig. 1C). In that case one should perform the following protocol: dip slide gently vertically in 0.05% SDS for 10–30 s, drain excess of fluid, dip slide in Halo 1 for 10 s, proceed with step 10. However, use of SDS usually decreases the amount of cells that remain on the slide. In that case, one should also apply more cells or try to dry the slide more. The drier the slide, the more difficult lysis will be, so be careful not to dry too much. 8. The amount of fibers is sufficient when you see comet like structures all over the field, and when they are neatly arranged (Fig. 1E). If it is a cloudy view and you see bright crystals, the amount of cells is too high and should be decreased (Fig. 1D). If the slide is completely black (except for dirt), check the cell suspension after step 3 for presence of cells. If there are easily visible cells in the suspension, they probably were removed during the lysis step. Skip step 5 and blow dry the slide in step 6 drier, i.e., dry the upper part completely but leave the lower part still quite wet and proceed with Halo 3. If lysis after the above steps is still insufficient, the last resort is to spin down the cell suspension, remove supernatant, resuspend cells in 50–100 µL FCS and freeze overnight at –70°C. Thaw rapidly and start with Subheading 3.1.1. 9. Probes are labeled with biotin and/or digoxygenin. Ideal sizes for probe fragments are in between 400–800 bp. This is achieved by changing the amount of DNase I from standard nick translation protocols. Check fragment lengths on a 2% agarose-gel, and test on germline fibers. After labeling, probes are precipitated and dissolved in hybridization mixture, thus allowing more probes to be mixed without altering hybridization conditions. 10. Slides can be used after overnight drying at room temperature, or after storage at –20°C. 11. Do not remove coverslip at any time by any force; soak coverslip off in a Coplin jar.
Acknowledgment We are grateful to Berna Beverloo for providing the contig of cosmid probes for the EVT6 region and the cells with the ETV6-breakpoint. The work was in part financially supported by grants of the Dutch Cancer Society NKB-UL-99-1997 and NKBKUN-99-1912 and of the IRS/J.A. Cohen Institute IRS6.3.4. References 1. Heng, H. H. and Tsui, L. C. (1998) High resolution free chromatin/DNA fiber fluorescent in situ hybridization. J. Chromatogr. A 806, 219–229. 2. Bensimon, A., Simon, A., Chiffaudel, A., Croquette, V., Heslot, F., and Bensimon, D. (1994) Alignment and sensitive detection of DNA by a moving interface. Science 265, 2096–2098. 3. Heiskanen, M., Kallioniemi, O., and Palotie, A. (1996) Fiber-FISH: experiences and a refined protocol Genet. Anal. 12, 179–184. multicolor DNA fiber fluorescence in situ hybridization. Blood 88, 1177–1182. 4. Wiegant, J., Kalle, W., Mullenders, L., et al. (1992) High-resolution in situ hybridization using DNA halo preparations. Hum. Mol. Genet. 1, 587–591. 5. Florijn, R. J., Bonden, L. A., Vrolijk, H., et al. (1995) High-resolution DNA Fiber-FISH for genomic DNA mapping and colour bar- coding of large genes. Hum. Mol. Genet. 4, 831–836.
6. Heng, H. H., Squire, J., and Tsui, L. C. (1992) High-resolution mapping of mammalian genes by in situ hybridization to free chromatin. Proc. Natl. Acad. Sci. USA 89, 9509–9513. 7. Parra, I. and Windle, B. (1993) High resolution visual mapping of stretched DNA by fluorescent hybridization. Nat. Genet. 5, 17–21. 8. Inazawa, J., Ariyama, T., Tokino, T., Tanigami, A., Nakamura, Y., and Abe, T. (1994) High resolution ordering of DNA markers by multi-color fluorescent in situ hybridization of prophase chromosomes. Cytogenet. Cell Genet. 65, 130–135. 9. Florijn, R. J., van de Rijke, F. M., Vrolijk, H., et al. (1996) Exon mapping by fiber-FISH or LR-PCR. Genomics 15, 277–282. 10. Riemersma, S. A., Jordanova, E. S., Schop, R. F., et al. (2000) Extensive genetic alterations of the HLA region, including homozygous deletions of HLA class II genes in B-cell lymphomas arising in immune- privileged sites. Blood 96, 3569–3577. 11. Vaandrager, J. W., Schuuring, E., Kluin-Nelemans, H. C., et al. (1998) DNA fiber fluorescence in situ hybridization analysis of immunoglobulin class switching in B-cell neoplasia: aberrant CH gene rearrangements in follicle center-cell lymphoma. Blood 92, 2871–2878. 12. Shiels, C., Coutelle, C., and Huxley, C. (1997) Analysis of ribosomal and alphoid repetitive DNA by fiber-FISH. Cytogenet. Cell Genet. 76, 20–22. 13. Lestou, V. S., Strehl, S., Lion, T., Gadner, H., and Ambros, P. F. (1996) High-resolution FISH of the entire integrated Epstein-Barr virus genome on extended human DNA. Cytogenet. Cell Genet. 74, 211–217. 14. Vaandrager, J. W., Schuuring, E., Zwikstra, E., et al. (1996) Direct visualization of dispersed 11q13 chromosomal translocations in mantle cell lymphoma by genome for highresolution studies. Blood 88, 1172–1182. 15. Vaandrager, J. W., Schuuring, E., Raap, T., Philippo, K., Kleiverda, K., and Kluin, P. (2000) Interphase FISH detection of BCL2 rearrangement in follicular lymphoma using breakpoint-flanking probes. Genes Chromosomes. Cancer 27, 85–94. 16. Von Bergh, A., Emanuel, B., Zelderen-Bhola, S., et al. (2000) A DNA probe combination for improved detection of MLL/11q23 breakpoints by double-color interphase-FISH in acute leukemias. Genes Chromosomes Cancer 28, 14–22. 17. Kluin, Ph. M., Vaandrager, J. W., van Krieken, J. H. J. M., and Schuuring, E. (1996) Chromosomal markers in lymphoma diagnosis. Curr. Diagn. Pathol. 3, 187–199. 18. Vaandrager, J. W., Schuuring, E., Philippo, K., and Kluin, P. M. (2000) V(D)J recombinasemediated transposition of the BCL2 gene to the IGH locus in follicular lymphoma. Blood 96, 1947–1952. 19. De Boer, C. J., Vaandrager, J. W., v. Krieken, J. H. J. M., Holmes, Z., Kluin Ph. M., and Schuuring, E. (1997) Visualization of mono-allelic chromosomal aberrations 3' and 5' of the cyclin D1 gene in mantle cell lymphoma using DNA fiber fluorescence in situ hybridization. Oncogene 15, 1599–1603. 20. Von Bergh, A., Gargallo, P., De Prijck, B., et al. (2001) Cryptic t(4;11) encoding MLL-AF4 due to insertion of 5' MLL sequences in chromosome 4. Leukemia 15, 595–600.
Multi-Telomere FISH
12 Multi-Telomere FISH Samantha J. L. Knight and Jonathan Flint 1. Introduction The standard investigation for suspected chromosomal rearrangements in patients is cytogenetic analysis at a 400–550 band resolution, yet this cannot routinely detect rearrangements smaller than 5 Megabases (Mb), and much larger abnormalities escape notice if they occur in regions where the banding pattern is not distinctive. In the future, this problem will largely be solved by the use of high resolution micro-arrays that will allow the entire genome to be investigated for submicroscopic chromosomal rearrangements. However, until this technology becomes routine, the only way of achieving increased reliability and resolution is to focus on specific chromosomal regions such as the ends of chromosomes (telomeres). Screening telomeres for rearrangements has a number of attractions. First, the majority of translocations involve chromosome ends and therefore an assay that targets telomeres will detect these with 100% sensitivity regardless of size. Second, the regions adjacent to telomeres are gene-rich, so rearrangements involving such regions are more likely to have phenotypic consequences than rearrangements in many other parts of the genome (1). Finally, rearrangements involving telomeres are emerging as an important cause of human genetic diseases (2–7). For example, Wolf-Hirschhorn syndrome (chromosome 4p), Cri du Chat syndrome (chromosome 5p), Miller-Dieker syndrome (chromosome 17p), and alpha-thalassaemia with mental retardation (ATR-16, chromosome 16p) are all known to be caused by the unbalanced products of subtelomeric translocations. Until recently, testing for rearrangements involving telomeres has proved problematical both owing to the complexity of the sequence structure of chromosome ends (8–13) and the technical problem of designing a highly sensitive and specific telomere assay which would also be financially acceptable. Both difficulties have now been addressed and multi-telomere FISH assays that use telomere specific probes for the detection of cryptic rearrangements are available. The assay outlined in this chapter is the Chromoprobe Multiprobe®-T System (Cytocell Ltd) and involves the use of From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
Knight and Flint
a microscope slide that is divided into 24 squares and a Multiprobe® device, which is essentially a coverslip with 24 raised square bosses (14). This arrangement allows up to 24 dual hybridizations (48 in total) to be performed, so all telomeres can be investigated on a single microscope slide. An overview of the procedure is shown in Fig. 1. In brief, each assay involves adding a drop of fixed chromosome suspension from the patient sample onto each square of the slide. To each square of the device, the appropriately labeled telomere probes are added. The slide and the device are then sandwiched together. The probe and chromosomal DNA are denatured simultaneously on a hotplate and hybridization allowed to proceed overnight. Following hybridization, a series of wash steps are performed and the resulting slides are analyzed by fluorescence microscopy. The numbers of signals specific to each telomere probe are counted and any anomalies indicating possible rearrangements are investigated. Further investigation may be achieved either by using individual telomere specific clones, which are commercially available ready labeled, or alternatively, by acquiring a glycerol set of telomere-specific clones and preparing and labeling the DNA "in-house." The Chromoprobe Multiprobe®-T System is widely used for the detection of cryptic subtelomeric rearrangements in individuals with idiopathic mental retardation. The probes within the current system are mainly PACs from the 2nd Generation set of telomere clones (see Table 1[b]). However, the original Multiprobe® system used the 1st Generation set of telomere clones that consisted mainly of cosmids with a few PACs and P1s (see Table 1[a]). It was using these 1st Generation clones that Knight et al. showed that subtelomeric rearrangements are an important cause of mental retardation, occurring in 7.4% individuals with moderate to severe developmental delay and dysmorphic features, and in about half of those presenting with a positive family history (25). These findings have since been confirmed in numerous case reports (26–34) and in larger studies where researchers have been able to divide their patients according to the degree of mental disability (35–43). There are other large studies which present frequencies of subtelomeric anomalies varying from 2.2–9%, but in these cases the selection criteria were more diverse (44–48). In an attempt to identify a more refined subset of individuals in whom subtelomeric rearrangements might be occurring, de Vries et al. assessed clinical variables for a number of developmentally delayed individuals and normal controls whose samples had been tested for telomeric integrity (49). The results indicated that prenatal onset of growth retardation and a positive family history for developmental delay are good indicators for the presence of subtelomeric anomalies. These clinical criteria, in addition to features suggestive of a chromosomal phenotype, were included in a five item clinical checklist that de Vries et al. predicted would improve the diagnostic pick up rate of subtelomeric rearrangements among the developmentally delayed (49). Although the Chromoprobe Multiprobe®-T System was originally used in the study of developmental delay, providing new diagnoses in affected individuals, it is now also proving invaluable for other clinical applications (50). For example, there are an increasing number of reports where the study of telomere integrity has allowed the full resolution of patients' karyotypes (51–54). In such cases, diagnostic laboratories had previously discovered an abnormal karyotype, but further submicroscopic rearrangements could not be ruled
Fig. 1. Overview of the Chromprobe Multiprobe®-T Assay.
Table 1(a) 1st Generation Telomere Clones Telomere 1p 1p 1q 1q 2p 2p 2q 2q 3p 3q 4p 4q 5p 5q 6p 6q 7p 7q 7q 8p 8q 8q 8q 9p 9q 10p 10q 11p 11p 11q 11q 12p 12q 12q 13q 13q 14q 14q 15q 16p 16p 16q 17p
Clone ID CEB108d GS-13-P11 112N326Q6 2123.2a1 GS-68-13 2052f6 210-E14 2112b2 B47a2,AT-B47b2 B35c1 B31 cT55 84c11 B22a4 GS-36-12 2158e3 109a64 3 2000a5d GS-63-M14 2205a2 129A5 2053b3 34-H2 2241c1 2189b6 2136a1 2209a2 146C2 161D7 2072c1 GS-90-15 GS-221-K18 2196b2 85-A10 2002e1 60-H4 2006a1 GS-154-PI GS-119-L6 cGG4 D3b1 2111b1
Availabilitya ATCC Incyte ICRF ATCC Incyte ATCC DuPont/Incyte ATCC ATCC ATCC ATCC ATCC ATCC ATCC Incyte ATCC ATCC OA ATCC Incyte ATCC LANL ATCC Incyte ATCC ATCC ATCC ATCC LLNL LLNL ATCC Incyte Incyte ATCC DuPont ATCC DuPont ATCC Incyte Incyte ATCC ATCC ATCC
Clone Typeb Cosmid (16) PAC Cosmid Cosmid (14) PAC Cosmid PI Cosmid Cosmid (14) Cosmid Cosmid (17) Cosmid (18) Cosmid Cosmid PAC Cosmid Cosmid Cosmid (19) Cosmid PAC Cosmid Cosmid Cosmid PAC Cosmid (14) Cosmid Cosmid (14) Cosmid Cosmid Cosmid Cosmid PAC PAC Cosmid PI Cosmid PI Cosmid PAC PAC Cosmid Cosmid Cosmid (14) (continued)
Table 1(a) (continued) Telomere 17q 17q 18p 18q 18q 19p 19q 20p 20p 20q 21q 21q 22q 22q XpYp XqYq
Clone ID 111D9 B37c1 GS-52-M11 127B6 2050a6 F20643 F21283d THY7 2005a4 GS-204-A16 2H14 C9a1 106G1220 N85A3 CY29 C8.2/1d
Availabilitya LYNL ATCC Incyte LYNL ATCC LYNL LYNL OA ATCC Incyte DuPont/Incyte ATCC ICRF ATCC/ICRF ATCC ATCC
Clone Typeb Cosmid Cosmid PI Cosmid Cosmid Cosmid Cosmid Cosmid Cosmid PAC (14) PI Cosmid Cosmid (20) Cosmid (21) Cosmid (22) Cosmid (23)
aClones are available from ATCC (American Type Culture Collection), Incyte (http://www.incyte.com), ICRF (Imperial Cancer Research Fund MPI for Molecular Genetics reference library database), Du Pont (Du pont Merck Pharmaceutical Company Human Foreskin Fibroblast P1 Library 1), LANL (Los Alamos Naional Library), LLNL (Laurence Livermore National Library). RGI (Research Genetics Inc), Bacpac website (http://bacpac.med.buffalo.edu/human/overview.html), from the originating author ('OA') or, for research purposes and for registered users only, from the Human Genome Mapping Project Resource Centre (http://www.hgmp.mrc.ac.uk). bAll clones except those referenced separately are attributed to the National Institutes of Health and Institute of Molecular Medicine Collaboration (15) cAll clones are attributed to Knight and Lese et al. (24) dClones used in Cytocell Ltd's Chromoprobe Multiprobe®-T System.
out because of the insufficient resolution of standard karyotyping. Multi-telomere FISH is also being used in this way for the characterization of the often complex karyotypes found in hematological malignancies (55–58). A further application is in providing new diagnoses in spontaneous recurrent miscarriages and infertility (26,59). Telomere specific probes also find use in the investigation of rearrangements when there are already clues regarding the possible involvement of particular telomeric regions. For example, in selected cases, individual telomere specific probes have proved informative for testing cleavage stage embryos for preimplantation diagnosis (60–62). A major aim of the Multiprobe® telomere assay is to improve diagnostic capabilities so that families can be better informed, genetic counselling made as accurate as possible and therapeutic and preventative strategies advanced. Currently, there at least five other strategies that may also be employed for the study of telomere integrity (1) the telomere chip (63), (2) a comparative genome hybridization approach (64), (3) scanning short tandem repeat polymorphisms (65–67), (4) locus copy number measurement by hybridization with amplifiable probes (68,69) and (5) multiplex or multicolor
Table 1(b) 2nd Generation Telomere Clones Telomere 1p 1p 1q 1q 2p 2p 2q 2q 3p 3p 3q 3q 4p 4p 4q 4q 5p 5p 5q 6p 6p 6q 7p 7q 8p 8p 8q 8q 9p 9p 9q 9q 10p 10p 10q 10q 11p 11p 11q 11q 12p 12p 12q
Clone ID GS-62-L8 GS-232-B23d GS-160-H23 GS-167-K11 GS-892-G20d GS-8-L3 GS-1011-O17d RG-172-113 GS-1186-B18d RG-228-K22 GS-196-F4d GS-56-H22 GS-36-P21d GS-118-B13 GS-963-K6d GS-31-J3 GS-189-N21d GS-24-H17 GS-240-G13d GS-62-I11d GS-196-I5 GS-57-H24d GS-164-D18 GS-3K-23 GS-580-L5d GS-77-L23 GS-489-D14d GS-261-I1 GS-43-N6d RG-41-L13 GS-112-N13d GS-135-I17 GS-306-F7d GS-23-B11 GS-137-E24d GS-261-B16 GS-908-H22d GS-44-H16 GS-770-G7d GS-26-N8 GS-496-A11d GS-8-M16 GS-124-K20
Availabilitya
Clone Typec
Incyte Incyte Incyte Incyte Incyte Incyte Incyte RGI Incyte RGI Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte
PAC BAC PAC BAC PAC BAC PAC BAC PAC BAC PAC BAC PAC BAC PAC BAC PAC PAC PAC PAC BAC PAC PAC PAC PAC BAC PAC BAC PAC BAC PAC BAC PAC BAC PAC BAC PAC PAC PAC PAC PAC BAC BAC (continued)
Table 1(b) (continued) Telomere
Clone ID
12q 13q 13q 14q 14q 15q 15q 16p 16p 16q 16q 17p 17p 17q 17q 18p 18p 18q 18q 19p 19p 19q 19q 20p 20p 20q 21q 21q 22q 22q XpYp XpYp XqYq Xq
GS-221-K18d GS-163-C9d GS-1-L16 GS-820-M16d GS-200-D12 GS-124-05d GS-154-P1d GS-121-I4d RG-191-K2 GS-240-G10d GS-191-P24 GS-202-L17d GS-68-F18 GS-362-K4d GS-50-C4 GS-52-M11 GS-74-G18d GS-964-M9d GS-75-F20 GS-546-C1d RG-129-F16 GS-48-O23 GS-325-I23 GS-1061-L1d GS-82-O2 GS-81-F12d GS-63-H24d GS-2-H14b GS-99-K24d CTD-3018-K24d GS-98-C4 RPCI-11-839-D20d GS-225-F6 GS-202-M24
Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte RGI Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte RGI Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte Incyte BacPac Incyte Incyte
PAC PAC PAC PAC BAC PAC PAC PAC BAC PAC PAC PAC BAC PAC BAC PI BAC PAC BAC PAC BAC PAC BAC PAC PAC PAC PI PAC PAC BAC PAC BAC BAC PAC
FISH (M-TEL) (70–72). Two approaches for assessing all possible human telomeres are commercially available – the Chromoprobe Multiprobe®-T System of Cytocell Ltd and the ToTel Vysion Multicolor FISH Probe Panel of Vysis Inc. Of these, the Chromoprobe Multiprobe®-T System is used widely in clinical diagnostic laboratories. In this chapter we give a detailed account of the methodology involved in this assay and troubleshoot problems that are commonly encountered. We also present the materials and methodology necessary to prepare and use a complete set of indirectlylabeled telomere FISH probes "in house."
2. Materials 2.1. Preparing Fixed Chromosome Suspensions 1. 1–5 mL peripheral blood sample or 25 mL healthy, dividing lymphoblastoid cell line (see Note 1). 2. Access to class II tissue culture hood (e.g., BioMAT-2, Envair Ltd., Rossendale, UK). 3. 25 cm3 and 75 cm3 tissue culture flasks (Corning Inc., New York, USA). 4. Nunctubes (Gibco-BRL, Paisley, UK). 5. RPMI 1640 Media: with NaHCO3, without Glutamine (Sigma, Poole, UK). 6. Penicillin (500 IU/mL)/Streptomycin (–5000 UG/mL) (Gibco-BRL, Paisley, UK). 7. L-glutamine : 200 mM (Gibco-BRL, Paisley, UK). 8. Foetal calf serum (FCS) (Globepharm). 9. M form phytohaemagglutinin (PHA) (Gibco-BRL, Paisley, UK). 10. Thymidine (Sigma, Poole, UK). 11. KaryoMax colcemid® solution 10 mg/mL (Gibco-BRL, Paisley, UK). 12. Potassium chloride (KCl) (Sigma, Poole, UK). 13. Methanol, AnaLaR Grade (BDH Laboratory Supplies, Poole, UK). 14. Glacial acetic acid (BDH Laboratory Supplies, Poole, UK).
2.2. Hybridization and Post-Hybridization Processing Using Chromoprobe Multiprobe®-T System (Cytocell Ltd.) 1. 2. 3. 4.
5. 6. 7. 8. 9. 10. 11. 12. 13.
Phase contrast microscope (e.g., Olympus BX40, Olympus Optical Co. Ltd., UK). Plastic or glass Coplin jars (Raymond Lamb Inc., Eastbourne, UK). Two heating blocks with flat surface (e.g., Cytocell Hotplate, Cytocell Ltd., Adderbury, UK). CCD microscope equipped with Pinkel filter wheel containing DAPI, Texas Red, FITC, dual and triple bandpass filters (e.g., Olympus BX60, Olympus Optical Co. Ltd., UK). Fluorescence grade microscope lens immersion oil (Carl Zeiss Ltd., Welwyn Garden City, UK). Fixed chromosome suspension Super premium microscope slides (BDH Laboratory Supplies, Poole, UK). Chromoprobe Multiprobe®-T System Kit (Cytocell Ltd). Fixative (3:1 methanol(AnalaR): glacial acetic acid). 20X SSC: 3 M sodium chloride (Sigma, Poole, UK), 0.3 M tri-sodium citrate (Sigma, Poole, UK). Wash solution I: 0.4X SSC Wash solution II: 2X SSC + 0.05% Tween 20 (BDH Laboratory Supplies, Poole, UK). Nail varnish (available from many high street stores).
2.3. Extraction of Telomere Clone DNA 1. Orbital shaking incubator (e.g., G24, New Brunswick Scientific Co. Inc., Edison, NJ). 2. Vacuum microcentrifuge (e.g., DNA Speed Vac DNA120, Savant Instruments Inc., Farmingdale, USA). 3. Glycerol stocks or stabs of telomere clones (see Table 1 for availability). 4. Ampicillin (Sigma, Poole, UK). 5. Kanamycin (Sigma, Poole, UK). 6. Chloramphenicol (Sigma, Poole, UK). 7. LB agar plates: 1% w/v NaCl (Sigma, Poole, UK), 1% w/v Bactotryptone (Difco Labs, Michigan, USA), 0.5% w/v Bactoyeast extract (Difco Labs, Michigan, USA), 1.5% w/v
8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
Bactoagar (Difco Labs, Michigan, USA) and appropriate antibiotic (ampicillin at 50 µg/mL, chloramphenicol at 12.5 µg/mL or kanamycin at 35 µg/mL). 2X TY Broth: 1.6% w/v Bactotryptone (Difco Labs, Michigan, USA). 1% w/v Bactoyeast extract (Difco Labs, Michigan, USA), 0.5% w/v NaCl (Sigma, Poole, UK). Glycerol (Sigma, Poole, UK). 250 mL centrifuge tubes with orange screw caps (Corning Incorporated, New York, USA). Cell resuspension solution: 1% glucose (filter-sterilized), 10 mM EDTA, 25 mM TrisHCl, pH 7.4. Cell lysis solution: 0.2M NaOH (Sigma, Poole, UK), 1% sodium dodecyl suphate (SDS) (USB). Neutralizing solution: 3M potassium acetate (Sigma, Poole, UK), 11.5% v/v glacial acetic acid, AnalaR Grade (BDH Laboratory Supplies, Poole, UK). Plastic funnels (BDH Laboratory Supplies, Poole, UK). Mesh (Hybaid Ltd., Ashford, UK). Isopropanol, AnaLar Grade (BDH Laboratory Supplies, Poole, UK). Ethanol, AnaLar Grade (BDH Laboratory Supplies, Poole, UK). TE Buffer 10 mM Tris-HCl, pH 8.0 (Sigma, Poole, UK), 1 mM EDTA (Sigma, Poole, UK).
2.4. Indirect Labeling of Telomere Clone DNAs by Nick-Translation 1. 1 mM Biotin-16-dUTP (Roche, Lewes, UK). 2. 1 mM Digoxigenin-11-dUTP (Roche, Lewes, UK). 3. 10X dNTP mix: 0.5 mM each of dATP, dGTP, dCTP; 0.1 mM dTTP (100 mM stocks from Roche, Lewes, UK). 4. 10X nick translation buffer: 0.5M Tris-HCl, pH 7.5, 50 mM MgCl2, 0.5 mg/mL nucleasefree bovine serum albumin (BSA), fraction V (Sigma, Poole, UK). 5. 100 mM dithiothrietol (Sigma, Poole, UK). 6. 2.5 ng/µL DNAse I (Amersham Life Sciences Ltd., Little Chalfont, UK). 7. 10,000 U/mL DNA polymerase I (New England Biolabs, Hitchin, UK). 8. SELECT™-B spin columns packed with Sephadex G50 (5 Prime→3 Prime Inc., Arapahoe Boulder, USA). 9. Salmon sperm DNA (2 mg/mL stock sonicated to 200–500 bp). 10. 1 mg/mL human COT-1 DNA (GibcoBRL, Paisley, UK). 11. Formamide (Fluka). 12. Hybridization solution: 65% formamide, 1X SSC, 10% dextran sulfate MW 500,000 (BDH Laboratory Supplies, Poole, UK).
2.5. Hybridization of Indirectly Labeled Probes and Post- Hybridization Processing 1. 2. 3. 4. 5. 6. 7. 8. 9.
Super premium microscope slides (BDH Laboratory Supplies, Poole, UK). 22 mm × 22 mm glass coverslips (BDH Laboratory Supplies, Poole, UK). Light proof plastic slide box (Raymond Lamb Inc., Eastbourne, UK). 22 mm × 64 mm coverslips manually cut from Parafilm (American National Cam. USA). Wash solution I: 0.4X SSC Wash solution II: 2X SSC + 0.05% Tween-20 (BDH Laboratory Supplies, Poole, UK). ST buffer: 4X SSC +0.05% Tween-20 (BDH Laboratory Supplies, Poole, UK). BSA fraction V (Sigma, Poole, UK). Blocking solution: 3% w/v BSA in ST buffer, filter-sterilized through 0.45 µm filter (see Note 2).
10. Antibody suspension 1 for dual detection: 1 mL blocking solution + 18 µL mouse antidigoxin fluorescein isothiocyanate (FITC) (Sigma, Poole, UK) + 0.65 µL avidin Texas Red (Vector Laboratories, Peterborough, UK) (see Note 3). 11. Antibody suspension 1 for digoxigenin detection only: 1 mL blocking solution + 18 µL Mouse anti-digoxin fluorescein isothiocyanate (FITC) (Sigma, Poole, UK). 12. Antibody suspension 1 for biotin detection only: 1 mL blocking solution + 0.65 µL avidin Texas Red (Vector Laboratories, Peterborough, UK). 13. Antibody suspension 2 for dual detection: 1 mL blocking solution + 1.7 µL rabbit antimouse FITC (Sigma, Poole, UK) + 7.5 µL biotin anti-avidin (Vector Laboratories, Peterborough, UK). 14. Antibody suspension 2 for digoxigenin detection only: 1 mL blocking solution + 1.7 µL rabbit anti-mouse FITC (Sigma, Poole, UK). 15. Antibody suspension 2 for biotin detection only: 1 mL blocking solution + 7.5 µL biotin anti-avidin (Vector Laboratories, Peterborough, UK). 16. Antibody suspension 3 for dual detection: 1 mL blocking solution + 1.7 µL goat antirabbit FITC (Sigma, Poole, UK) + 0.65 µL avidin Texas Red (Vector Laboratories, Peterborough, UK). 17. Antibody suspension 3 for digoxigenin detection only: 1 mL blocking solution + l.7 µL goat anti-rabbit FITC (Sigma, Poole, UK). 18. Antibody suspension 3 for biotin detection only: 1 mL blocking solution + 0.65 µL avidin Texas Red (Vector Laboratories, Peterborough, UK). 19. Vectashield mounting medium: (Vector Laboratories, Peterborough, UK) containing 1.5 µg/mL 4',6-diamidino-2-phenylindole (DAPI). 20. Nail varnish (available from many high street stores).
3. Method 3.1. Preparing Fixed Metaphase Chromosome Suspensions 3.1.1. From Peripheral Blood 1. Equilibrate RPMI-1640, FCS, L-glutamine and penicillin/streptomycin to 37°C in a waterbath (see Note 4). 2. In a Class II tissue culture hood, use sterile technique and make complete medium by adding 100 mL FCS, 5 mL L-glutamine and 5 mL penicillin/streptomycin to the 500 mL bottle of RPMI-1640. 3. To duplicate Nunc tubes, add 0.25 mL peripheral blood, 5 mL complete medium, and add PHA to a final concentration of 2%. 4. Place in a 37°C incubator for 72 h. 5. Add 100 µL of 15 mg/mL thymidine to each culture and mix gently. 6. Place in a 37°C incubator for 16–18 h. 7. Centrifuge cultures at 180g for 5 min. 8. Pour off supernatant and resuspend cell pellet in 5 mL complete medium. 9. Centrifuge at 180g for 5 min. 10. Pour off supernatant and resuspend cell pellet in 5 mL complete medium. 11. Place in a 37°C incubator for 5 h. 12. Add 100 µL of 10 µg/mL KaryoMax colcemid 13. Place in a 37°C incubator for 10 min. 14. Centrifuge at 180g for 5 min. 15. Pour off the supernatant and resuspend the cell pellet in 7 mL 0.075M KCl prewarmed to 37°C.
Multi-Telomere FISH 16. 17. 18. 19.
Incubate at 37°C for 15 min. Centrifuge at 180g for 5 min. Discard supernatant. Rest tube on a vortex set at medium speed and fix the cells by the careful, dropwise addition of precooled 3:1 methanol: acetic acid (fixative). When the solution turns brown, the fixative may be added more rapidly until a total of 5 mL have been added. Centrifuge at 180g for 5 min and discard supernatant. Add 5 mL cold fixative. Centrifuge at 180g for 5 min and discard supernatant. Add 5 mL cold fixative. Centrifuge at 180g for 5 min and discard supernatant Resuspend pellet in 3 mL fixative. Store at –20°C until ready to use.
3.1.2. From Lymphoblastoid Cell Lines 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
Grow cells until they are proliferating well in a vol of 50 mL complete medium. 18–24 h prior to harvesting, remove old medium and replace with fresh medium. When ready to harvest, transfer 20 mL of healthy proliferating cells to a 50 mL Falcon tube. Add 200 µL of 10 µg/mL KaryoMax colcemid and mix gently. Place in a 37°C incubator for 50–60 min (see Note 5). Centrifuge at 180g for 5 min. Pour off the supernatant and resuspend the cell pellet in 7 mL 0.075M KCl prewarmed to 37°C. Incubate at 37°C for 20 min (see Note 6). Centrifuge at 180g for 5 min and discard supernatant. Rest the tube on vortex set at medium speed and fix cells by the dropwise addition of 2 mL precooled fixative. Add a further 13 mL cold fixative. Centrifuge at 180g for 5 min and discard supernatant. Add 15 mL cold fixative. Centrifuge at 180g for 5 min and discard supernatant. Add 15 mL cold fixative. Centrifuge at 180g for 5 min and discard supernatant Resuspend pellet in 1 mL fixative. Store at –20°C until ready to use.
3.2. Hybridization and Post-Hybridization Processing Using Cytocell Ltd Chromoprobe Multiprobe®-T System (see Note 7) 3.2.1. Optimize Concentration of Fixed Chromosome Suspension 1. Gently apply 2 µL of the suspension to the surface of a clean, Super Premium Microscope slide. 2. Allow the drop to dry and view by phase-contrast microscopy using a ×10 objective. 3. Ideally there should be a mitotic index of ≥5% (see Note 8) and individual metaphases should be well defined with minimal overlapping chromosomes (see Fig. 2a). 4. If the cell density is too high, dilute the suspension with cold fresh fixative until the desired concentration is achieved. 5. If the concentration is too low, pellet the cells at 160g for 5 min. Pour off the supernatant and resuspend the pellet with increasing volumes of fresh fixative until the desired concentration is achieved.
3.2.2. Prepare the Multiprobe®-T Microscope Slide 1. Soak the slide in 100% methanol for 2 min. 2. Polish dry with a clean soft tissue 3. Pipet 2 µL of optimized fixed chromosome suspension onto each square of the Multiprobe®-T slide in four discrete sets of pipetting following the order: (A) Square 1, 19, 5, X, 17, 3, 21, and 7. Allow to dry. (B) Square 2, 20, 6, Y, 18, 4, 22, and 8. Allow to dry. (C) Square 9, 11, 13, and 15. Allow to dry. (D) Square 10, 12, 14, and 16. Allow to dry. 4. Examine each spot under phase-contrast to ensure that no squares have been missed and that all squares have an acceptable number of metaphases for analysis (see Note 9).
3.2.3. Hybridization Procedure 1. Preheat one heating block to 37°C and one to 75°C (see Note 10). 2. Place the Chromoprobe Multiprobe® Hybridization Chamber in a 37°C waterbath to equilibrate. 3. Mix the hybridization solution (provided in kit) by repeated pipetting. 4. Transfer 60 µL to a fresh Eppendorf tube and prewarm to 37°C in a heating block, incubator or waterbath. 5. Prewarm the Multiprobe® device, probe side up (i.e., raised bossed surfaces up and labeled surface down). Do not touch the bossed surfaces. 6. Prepare one Coplin jar containing 2X SSC and three Coplin jars containing the series 70, 85, and 100% Ethanol respectively. 7. Wash preprepared, spotted template slide for 2 min in 2X SSC and then dehydrate for 2 min in each of 70, 85, and 100% Ethanol. 8. Airdry the slide and place spotted side up on a 37°C heating block. 9. Meanwhile, use a P10 micropipet to add 2 µL of prewarmed hybridization solution to each raised square/boss of the Multiprobe® device (keep on 37°C heating block). 10. Carefully invert the template slide (so that spots are now facing downwards) and bring into contact with the Multiprobe® device with the appropriate squares matching i.e., so that square 1 is located over the top right hand square of the Multiprobe® device, which is marked with a yellow spot. 11. Gently lift the slide/Multiprobe® device and invert so that the slide is now beneath the device (see Note 11). 12. Place on a 37°C heating block for 10 min. 13. Keeping the slide/Multiprobe® device arrangement flat, carefully transfer to the surface of a 75°C heating block. 14. Denature for 1–3 min depending on the age of the fixed chromosome suspension (see Note 12). Fig. 2. (a) An example of a metaphase spread that is of acceptable quality for hybridization. (b) A normal hybridization pattern shown by the 3p3q telomere specific PACs. (c) The bloated appearance of chromosomes which have been overdenatured. In this case, the del 7p result remains clear. (d) The speckled appearance is typical of excess antibody – a similar appearance may arise through insufficient washing. (e) The 2p2q polymorphism – in this case the arrowed 2q signal is barely visible. (f) The crosshybridization of the 12p cosmid to the subtelomeric regions of 6p and 20q. (g) and (h) hybridization patterns on squares 4 and 11 of the same microscope slide revealing a clinically significant unbalanced translocation (4p monosomy and 11p trisomy) in an individual with developmental delay. In all hybridization examples, the p-arm signals are shown in red and the q-arm signals in green.
15. Immediately transfer the slide/Multiprobe® device to the prewarmed Chromoprobe Multiprobe® Hybridization Chamber (or light-proof plastic slide box), replace the lid and leave overnight with the lid of the waterbath off.
3.2.4. Post-Hybridization Washing and Mounting 1. Add wash solution I to a clean Coplin jar and equilibrate in a 72°C waterbath. Then, adjust to pH 7.0. 2. Add wash solution II to a clean Coplin jar and stand at room temperature (20–25°C). 3. Retrieve the slide/Multiprobe® device from the hybridization chamber. 4. Carefully remove the Multiprobe® device from the template slide and immediately place the slide in solution I for 2 min. Using forceps, agitate the slide gently up and down. 5. Transfer to solution II for 30 s. 6. Drain excess wash solution by holding the long edge of the slide against tissue for 10–20 s. Do not allow the slide surface to dry. 7. Add 20 µL DAPI-Antifade solution (provided in kit) to both ends of a large (24 × 60 mm) coverslip (also provided in kit) and gently lower the hybridized area of the slide onto the prepared coverslip. 8. Inspect the mounted area and coax out any air bubbles by gentle pressure with blunt ended forceps. 9. Place a paper towel over the slide and coverslip and apply gentle pressure to remove any excess mounting medium. 10. Seal by brushing a thin layer of nail varnish around the rim of the coverslip. 11. Leave in a dark box or cupboard for at least 10 min prior to viewing.
3.2.5. Viewing the Hybridized Slide by Fluorescence Microscopy 1. Place the slide on the microscope stage (see Note 13). 2. Using the ×10 objective and DAPI filter wheel, focus on Square 1 and identify metaphase chromosomes of a single cell. 3. Add a drop of mineral oil to the square and switch to the oil immersion objective (×100). 4. Identify the selected metaphase chromosomes and switch to the triple band pass filter wheel (DAPI, FITC, and Texas Red). 5. Score the p-arm (green) and q-arm (red) telomere signals and note the chromosomal location. A normal result for Square 1 is two green signals and two red signals on the p-arm and q-arm telomeres of chromosome 1 (see Note 14). 6. Confirm the results using FITC and Texas Red filters individually. 7. Repeat steps 2–6 until 5 unambiguous results from 5 different metaphases on the square have been scored. 8. Repeat steps 2–7 for every square of the slide. 9. Note the results. Any abnormal results or unsatisfactory hybridizations for certain telomere probes indicate those probes for which repeat hybridizations should be carried out on the sample (see Note 15). 10. Confirm abnormalities on a fresh sample from the test patient and where possible, also analyze samples from each parent. This will determine whether the abnormality is a true anomaly (and if so, whether it is de novo or familial in origin), or whether it might be a benign polymorphic variant (see Note 16).
3.3. Extraction of Telomere Clone DNA (see Note 17) 1. Make LB plates containing the correct antibiotic (ampicillin at 50 µg/mL, kanamycin at 30 µg/mL or chloramphenicol at 12.5 µg/mL).
2. Remove required glycerols from –70°C freezer and place in a container of dry ice (see Note 18). 3. Streak desired glycerols onto plates and place in a 37°C bacterial incubator overnight. 4. Add 100 mL 2X TY media to a 250 mL centrifuge tube. Add appropriate antibiotic as outlined in step 1. 5. Innoculate the medium with a single colony from the plate and grow overnight at 37°C in a shaking incubator. 6. Make glycerol stocks by removing 700 µL from the overnight culture and adding 300 µL 100% glycerol. Mix well, split between two Eppendorf tubes, label and store at –70°C 7. Pellet the remaining bacteria by centrifugation at 350g for 15 min. 8. Pour off supernatant and invert tubes on paper towels to allow excess supernatant to drain. 9. Resuspend the pellet in 30 mL cold Cell Resuspension Solution. Mix vigorously and pipet up and down to ensure that all lumps are removed. 10. Add 30 mL of cell lysis solution. Gently invert tubes once to mix. 11. Leave standing at room temperature for 5 min (no longer) 12. Immediately add 30 mL of cold Neutralizing solution. Invert gently to mix. 13. Place on ice for 15 min–invert gently every 5 min. 14. Centrifuge at 4000g at 4°C for 40 min. 15. Label a fresh 250 mL-tube and place a plastic funnel in the top. 16. Cut a circle of hybridization mesh, cut a slit to the center and fit into funnel. 17. Carefully pour centrifuged sample through the mesh and funnel into the 250-mL tube. Ensure that no flocculent material passes through the mesh. 18. Remove the funnel and mesh and wash with water and ethanol for subsequent use. 19. Precipitate the DNA by adding 0.7 vol 100% isopropanol. 20. Mix well and centrifuge at 4000g for 40 min 21. Pour off supernatant and add 25 mL 70% ethanol. 22. Vortex and centrifuge at 4000g for 10 min. 23. Pour off supernatant and drain excess by inversion on paper towel. 24. Resuspend pellet in 1 mL TE buffer (pH 8.0) (see Note 19). 25. Check the extracted DNA by running 5 µL on a 0.9% minigel alongside a λHindIII marker. Intact, cosmid DNA should remain in a high molecular weight position. 26. Measure the concentration of the extracted DNA (e.g., using fluorometer). 27. Store the extracted DNA at –20°C
3.4. Indirect Labeling of Telomere Clone DNAs by Nick-Translation (see Notes 20 and 21) 1. Place an Eppendorf tube on ice and add: 1.0 µg probe DNA, 1.2 µL biotin-16-dUTP (e.g., for p-arm probes) or digoxigenin-11-dUTP (e.g., for q-arm probes), 5.0 µL 10X dNTP mix, 5.0 µL 10X nick translation buffer, 5.0 µL DTT (100 mM), 4.0 µL DNAse (2.5 ng/µL) (see Note 22), 1.0 µL DNA Polymerase I (10,000 U/µL), x µL dH2O to give total reaction vol of 50 µL. 2. Vortex briefly and microfuge on "touch" setting to eliminate air bubbles. 3. Transfer to 15°C waterbath for 90 min. 4. Pause the reaction by placing the tube on ice. 5. Remove 5 µL and run on 2% w/v agarose gel with a PhiX174 size standard. 6. A smear of fragments from 50–500 bp is optimal for hybridization. If larger than this, add a further 1 µL DNAse to the reaction and incubate at 15°C for an additional 30 min.
7. When the probe is the correct size, remove unincorporated nucleotides by passing the through a SELECT™-B spin column prepacked with Sephadex™ G-50. 8. Add 25 µL salmon sperm (scale up accordingly if more than 1 µg DNA was labeled). 9. Add dH2O to give a final probe concentration of 10 ng/µL (take into account the amount of DNA removed for checking). 10. Note the volume of the 10 ng/µL probe mix. 11. Add the appropriate amount of COT-1 DNA per 1 µL of probe mix (calculate the amount to be added based on the probe and its original insert size [see Note 23]). 12. Calculate the volume of probe/COT-1 mix containing 120 ng probe and aliquot this volume into Eppendorf tubes. 13. Dry down the aliquots by centrifugation in a speedyvac (do not overdry). 14. To create chromosome specific p-arm and q-arm telomere hybridization mixes, resuspend each pellet in 38 µL hybridization solution and mix solutions together to give a total vol of 76 µL. 15. To create individual telomere-specific mixes (i.e., p-arm or q-arm probes only), resuspend each pellet in 76 µL hybridization solution. 16. Mix well and store at –20°C.
3.5. Hybridization of Indirect Labeled Probes and Post-Hybridization Processing (see Note 20) 3.5.1. Hybridization 1. Switch on heating block and preheat to 75°C. 2. Transfer 18 µL probe hybridization solution to a clean Eppendorf tube and prewarm to 37°C in a waterbath or heating block. 3. Optimize concentration of test fixed cell suspension as described in Subheading 3.2.1. 4. Soak super premium microscope slide in 100% methanol for 2 min. 5. Polish dry with clean soft tissue. 6. Drop ~10–20 µL of optimized fixed chromosome suspension onto the center of the slide. 7. Allow to dry and check quality by phase-contrast microscopy using ×10 objective. 8. Label the frosted end of the slide with the experiment details and mark boundaries of the chromosome spot on the reverse side of the slide using a diamond cutter. 9. Prepare one Coplin jar containing 2X SSC and three Coplin jars containing the ethanol series 70, 85, and 100% respectively. 10. Wash preprepared template slide (spotted with test fixed cell suspension) for 2 min in 2X SSC and then dehydrate for 2 min in each of 70, 85, and 100% ethanol. 11. Air dry slide and place chromosome spotted side up on a 37°C heating block. 12. Mix the prewarmed hybridization solution by gentle repeated pipeting (avoid bubbles). 13. Pipet hybridization solution onto the central region of the slide demarcated by the diamond cutter. 14. Carefully lower a 22 × 22 mm coverslip over the hybridization solution. Coax out any air bubbles by gentle pressure with blunt ended forceps. 15. Carefully transfer the slide (coverslip uppermost) to surface of the 75°C heating block. 16. Allow to denature for 1–3 min depending on the age of the fixed chromosome suspension (see Notes 12 and 24). 17. Immediately transfer to an empty light-proof plastic slide container, replace the lid and place in a 37°C waterbath with the lid off overnight.
3.5.2. Post-Hybridization Washing, Antibody Detection, and Mounting 1. Prepare blocking solution and antibody suspensions 1–3 (see Note 25). 2. Vortex antibody suspensions well and microcentrifuge at top speed for 10 min. Keep in the dark and if necessary, equilibrate to room temperature prior to use. 3. Add wash solution I to a clean Coplin jar and equilibrate in a 72°C waterbath. Then, adjust the pH to pH 7.0. 4. Add wash solution II to a clean Coplin jar and stand at room temperature (20–25°C). 5. Meanwhile, place a piece of tissue moistened with water in the bottom of one end of a light proof plastic box (e.g., an empty slide box). 6. Using scissors, cut 4 pieces of ~22 × 64 mm parafilm for each slide being processed. 7. Remove the slide from light-proof box in the waterbath and jerk sharply over tissue paper to remove the coverslip. 8. Immediately place the slide in solution I for 2 min. Using forceps, agitate slide gently up and down. 9. Transfer to solution II for 30 s. 10. Drain excess wash solution by holding the long edge of the slide against tissue for 10–20 s. Do not allow the slide surface to dry. 11. Place the slide in the prepared light-proof plastic box in a raised position (e.g., with each end resting on a cocktail stick or on the inside platforms of the box). Quickly pipet 300 µL blocking solution over the slide and cover with a parafilm coverslip. Avoid air bubbles. 12. Put the lid on the box and place in a 37°C oven for 40–50 min. 13. During the incubation period, prewarm 1.5 L of ST solution to 37°C. 14. Following incubation, remove the parafilm coverslip from the slide and place the slide in a glass slide holder containing prewarmed ST solution. 15. Place on a shaking platform for 3 min. Keep in the dark by placing an inverted light-proof container (e.g., a cardboard box) over the top. 16. Remove the slide and drain the excess wash solution as in step 10. 17. Place the slide in the light-proof plastic box as before and immediately add ~80 µL antibody suspension 1 to the hybridized area. 18. Avoiding air bubbles, carefully overlay parafilm coverslip. 19. Put the lid on the box and place in a 37°C incubator for 10 min. 20. Remove the parafilm coverslip and immediately transfer the slide to a glass slide holder containing prewarmed ST solution. 21. Agitate on shaking platform as before for 3 min. 22. Pour off the solution and replace with fresh prewarmed ST solution. 23. Repeat steps 21 and 22 a further 2×. 24. After the third wash, remove the slide and drain the excess wash solution as described in step 10. 25. Place the slide in the light-proof plastic box as before and immediately add ~80 µL appropriate antibody suspension 2 to the hybridized area 26. Avoiding air bubbles, carefully overlay a parafilm coverslip. 27. Put the lid on the box and place in 37°C incubator for 10 min. 28. Remove the parafilm and wash the slide 3× each for 3 min in fresh prewarmed ST solution. 29. Remove the slide and drain excess wash solution as in step 10. 30. Place the slide in the light-proof plastic box as before and immediately add ~80 µL appropriate antibody suspension 3 to the hybridized area. 31. Put the lid on the box and place in a 37°C incubator for 10 min.
32. Remove the parafilm coverslip and perform a final 3 washes each for 3 min in fresh prewarmed ST solution. 33. During the final wash, add ~25 µL DAPI in Vectashield to a 22 × 22 mm coverslip resting on a paper towel. 34. Remove the slide and drain the excess wash solution as in step 10. 35. Gently lower the hybridized area of the slide onto the prepared coverslip. 36. Place a paper towel over the slide and coverslip and apply gentle pressure to remove any excess mounting medium. 37. Inspect the mounted area and coax out any air bubbles by gentle pressure with blunt ended forceps. 38. Seal by brushing a thin layer of nail varnish around the rim of the coverslip. 39. Place in the dark and allow to dry before viewing by fluorescence microscopy as described in Subheading 3.2.5.
4. Notes 1. For optimal chromosome preparations, peripheral blood samples should be collected in lithium-heparin tubes, the samples should be transported at room temperature and cultured as soon as possible. The quality of the fixed cell suspensions deteriorates markedly with time. 2. Blocking solution can be made in bulk and stored in filter-sterilized aliquots at 4°C for up to 6 mo. 3. 1-mL aliquots of antibody suspensions can be stored in light-proof containers at 4°C for up to 1 mo. 4. To avoid contamination, tissue culture media always should be placed in a designated waterbath reserved for tissue culture work. 5. Colcemid prevents spindle formation and so arrests the chromosomes in the metaphase stage of the cell cycle. The amount of time the cells are left in the colcemid solution affects the morphology of the chromosomes. If they are left for too short a period of time, the chromosomes may be long, but the resulting MI may not be sufficient. However, if the cells are left for too long, they appear shorter and sub-optimal for analysis. 6. Under-incubation of cells in hypotonic solution will fail to burst open the cell whereas, over-incubation will lead to excessive bursting. 7. Although the Chromoprobe Multiprobe® System Kit contains probes and reagents which have been quality-controlled by Cytocell Ltd., it is advisable to confirm optimal performance of the kit by carrying out an initial test hybridization using a good quality normal control chromosome suspension prior to proceeding with valuable study samples. 8. Although the ideal MI is ≥5%, this may not be achievable owing to problems, such as the age of the sample or it's origin (e.g., leukaemic samples often have a suboptimal MI). In these circumstances, one should aim for approx 5 metaphases in the central region of the chromosome spread. In particularly difficult cases where the MI is very low and there is limited sample, it may be more feasible to opt for a multicolor FISH technique such as M-TEL (71). 9. If there are not enough metaphases on only a few squares then it is possible to respot some suspension over the original spot on these squares. 10. For the 37°C heating block it is sufficient to invert a standard tube-holding heating block so that the flat surface is uppermost. However, the 75°C hotplate must be a solid block with even surface temperature. 11. The best technique is to first lift the slide/Multiprobe arrangement upwards holding only the etched end of the slide between the forefinger and thumb of one hand. Then, gently
hold the arrangement between the thumb and forefinger of the other hand (do not squeeze) and invert. The arrangement can then be transported safely held flat in the palm of the hand or a tray. It is important to get the denaturating step right. If the chromosomes are denatured for too long, then the chromosomes become bloated and there may be tracking of the probe signal along the chromosome arm (see Fig. 2c). Conversely, if the denaturation time is not enough, then the morphology will be retained, but there will be little if any hybridization. In general, the longer the cell suspension has been kept at –20°C, the longer the chromosomes require to become denatured. For example, a cell suspension prepared and hybridized on the same day may need only 45 s to denature whereas, a sample over a year old may need more than 3 min. On average, samples that are 1–3 mo old require about 1 min 15 s denaturing time at 75°C. Some microscopes have stages that make it difficult to view the extreme ends of the slides. In these situations, turning the slide around 180° should alleviate the problem. Before attempting to score any results it is important to be familiar with certain characteristics associated with some of the telomere clones so that misinterpretation can be avoided. It is entirely normal for some of the clones to detect polymorphisms – these clones hybridize only to their cognate telomeres, but if a polymorphism is present, they hybridize only partially or not at all to one of the chromosome homologues. It is also characteristic for some clones to exhibit crosshybridization – these clones hybridize to other telomeres in addition to their cognate telomeres (24). Examples of a normal 3p3q hybridization pattern, the 2q polymorphism, the crosshybridization of 12p and a clinically significant unbalanced telomeric rearrangement are shown in Fig. 2. A list of known polymorphisms and crosshybridization patterns associated with the 1st and 2nd Generation telomere clones are listed in Table 2. When repeat hybridizations are necessary one must decide whether the use of a whole new Multiprobe® slide and device is justified. The alternative to this is either to (1) purchase ready labeled individual telomere probes (e.g., from Cytocell Ltd., Appligene Oncor or Vysis Inc.) or (2) to obtain a set of telomere clone glycerols and prepare one's own stocks of DNA and labeled probes for hybridization. The latter can be very cost-effective: once the initial preparation of the clones has been achieved, bulk stores of labeled, optimized probes will be stable at –20°C at least 2 yr. A list of the 1st and 2nd generation telomere-specific clones and where glycerol stocks or stabs may be obtained is given in Table 1. The telomere clones in the Chromoprobe Multiprobe ®-T System Kit are indicated. Unusual results may reflect true subtelomeric rearrangements or benign polymorphisms and misinterpretation must be avoided. See Table 2 for a list of polymorphisms and crosshybridization patterns known to be associated with the 1st and 2nd Generation telomere specific clones and Fig. 2 for FISH examples. It is not necessary to prepare DNA from telomere clones if the Chromoprobe Multiprobe®-T System Kit (Cytocell Ltd., UK) or any other commercially available kit (e.g., ToTel Vysion Multicolor FISH Probe Panel from Vysis Inc.) is being used. However, it may be desirable to obtain and process a complete set of telomere clones, especially when small numbers of repeat hybridizations are required. A list of the 1st and 2nd generation telomerespecific clones and where glycerol stocks or stabs may be obtained is given in Table 1. The telomere clones in the Chromoprobe Multiprobe®-T System Kit are indicated. If dry ice is not available, glycerols can be kept on ice for a limited period, but repeated access in this manner will reduce the viability of the glycerol stock. If the pellet does not resuspend quickly, it may be left at 4°C overnight.
Table 2 Cross Hybridization and Polymorphisms of 1st and 2nd Generation Telomere Clonesa 1st Generation Clones Telomere
2nd Generation Clones Clone
210-E14 CY29
2q 9p
GS-1011-O17 GS-43-N6
Cross-hybridizations:
5p with acrocentric p-arms 5q with acroncentric centromeres 8p with 1p 11p with 17p 12p with 6p and 20q (both faint)
84c11 GS-90-I5 2205a2 2209a2 GS-90-I5
8p with 1p and 3q (both faint) 9q with 109p and 16p, 18p, XqYq (faint) 11p with 17p 11q with 12q (interstitial) 12p with 6p and 20q (both faint) 12p with 6p and 20q (both faint) 15q with 1q and 15q (both interstitial) 17p with 17q (two interstitial sites) 17q with 1p and 6q (both faint) 20q with 6p (faint) 22q with 2q (interstitial)
GS-580-L5 GS-112-N13 GS-908-H22 GS-770-G7 GS-496-A11 GS-8-M16 GS-124-O5 GS-202-L17 GS-362-K4 GS-81-F12 GS-99-K24
aAdapted
from knight, S. J. L. and Flint, J., J. Med. Genet. 2000, 37, 401–409. With permission from the BMJ Publishing Group.
2q XpYp
Polymorphisms:
20. This section is not applicable if the Chromoprobe Multiprobe®-T System Kit (Cytocell Ltd., Adderbury, UK) or any other commercially available kit is being used. 21. As indirectly labeled probes keep well for approx 2 yr, it may be desirable to increase the amounts labeled and increase the labeling reaction volume accordingly. 22. The exact concentration of DNAse varies between batches and the amount of DNase may vary between different DNA templates. Ideally, with each new batch, the amount of DNAse needed should be optimized for each template and the optimal period of incubation noted so that the same conditions can be applied for future labelings of the template DNA. 23. The exact amount of COT-1 used should be optimized for each batch of probe made. The amount of COT-1 to be added primarily depends on the Alu content of the probe. For the telomere clones, the standard amount of COT-1 to add to labeled cosmids with insert sizes of 30–40 kb is 625 ng for every 1 µL of probe mix. For PACs and small BACs with insert sizes of ~100 kb, 1 µg COT-1 should be added. For larger BACs up to 3 µg COT-1 may be required. Notable exceptions include the the chromosome 19 clones such as F20643 and 20283 which require up to 10 µg COT-1 per 1 µL of probe mix). 24. If a hotplate is not available, the chromosomes may be denatured in 70% formamide/ 0.1 mM EDTA in 2X SSC at 70°C for 5 min followed by three washes in 2X SSC at 4°C and subsequent dehydration through an ethanol series. The probe mixture is denatured separately at 95°C for 5 min prior to adding to the slide. 25. Make antibody suspensions 1–3 appropriately, according to whether single or dual detection is required. The antibody concentration is extremely important. If the concentration of the antibody is too low there may be little or no hybridization. Conversely, if it is too high there may be a very "speckled" background making it impossible to identify the cognate signals (see Fig. 2[d]). As there can be some variation between batches it is advisable to optimize the dilution of each new batch of antibody by hybridizing reliable control probes to good quality control chromosome suspensions prior to proceeding with valuable study samples.
References 1. Saccone, S., De Sario, A., Della Valle, G., and Bernardi, G. (1992) The highest gene concentrations in the human genome are in telomeric bands of metaphase chromosomes. Proc. Natl. Acad. Sci. USA 89, 4913–4917. 2. Altherr, M. R., Bengtsson, U., Elder, F. F. B., et al. (1991) Molecular Confirmation Of Wolf-Hirschhorn Syndrome With a Subtle Translocation Of Chromosome-4. Am. J. Hum. Genet. 49, 1235–1242. 3. Kuwano, A., Ledbetter, S. A., Dobyns, W. B., Emanuel, B. S., and Ledbetter, D. H. (1991) Detection of deletions and cryptic translocations in Miller-Dieker syndrome by in situ hybridization. Am. J. Hum. Genet. 49, 707–714. 4. Lamb, J., Harris, P. C., Wilkie, A. O. M., Wood, W. G., Dauwerse, J. G., and Higgs, D. R. (1993) De novo truncation of chromosome 16p and healing with (TTAGGG)n in the α-thalassemia/mental retardation syndrome (ATR-16). Am. J. Hum. Genet. 52, 668–676. 5. Overhauser, J., Bengtsson, U., McMahon, J., et al. (1989) Prenatal diagnosis and carrier detection of a cryptic translocation by using DNA markers from the short arm of chromosome 5. Am. J. Hum. Genet. 45, 296–303. 6. Wilkie, A. O. M., Lamb, J., Harris, P. C., Finney, R. D., and Higgs, D. R. (1990) A truncated chromosome 16 associated with α-thalassaemia is stablised by the addition of telomeric repeats (TTAGGG)n. Nature. 346, 868–871.
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25. Knight, S. J., Regan, R., Nicod, A., et al. (1999) Subtle chromosomal rearrangements in children with unexplained mental retardation. Lancet 354, 1676–1681. 26. Brackley, K. J., Kilby, M. D., Morton, J., Whittle, M. J., Knight, S. J., and Flint, J. (1999) A case of recurrent congenital fetal anomalies associated with a familial subtelomeric translocation. Prenat. Diagn. 19, 570–574. 27. de Vries, B. B., Bitner-Glindzicz, M., Knight, S. J., et al. (2000) A boy with a submicroscopic 22qter deletion, general overgrowth and features suggestive of FG syndrome. Clin. Genet. 58, 483–487. 28. Warburton, P., Mohammed S., and Ogilvie, C. M. (2000) Detection of submicroscopic subtelomeric chromosome translocations: a new case study. Am. J. Med. Genet. 6, 51–55. 29. Bacino, C. A., Kashork, C. D., Davino, N. A., and Shaffer, L. G. (2000) Detection of a cryptic translocation in a family with mental retardation using FISH and telomere regionspecific probes. Am. J. Med. Genet. 92, 250–255. 30. Praphanphoj, V., Goodman, B. K., Thomas, G. H., and Raymond, G. V. (2000) Cryptic subtelomeric translocations in the 22q13 deletion syndrome. J. Med. Genet. 37, 58–61. 31. Knight-Jones, E., Knight, S., Heussler, H., Regan, R., Flint, J., and Martin, K. (2000) Neurodevelopmental profile of a new dysmorphic syndrome associated with submicroscopic partial deletion of 1p36.3. Dev. Med. Child Neurol. 4, 2201–2206. 32. Kleefstra, T., van de Zande, G., Merkx, G., Mieloo, H., Hoovers, J. M., and Smeets, D. (2000) Identification of an unbalanced cryptic translocation between the chromosomes 8 and 13 in two sisters with mild mental retardation accompanied by mild dysmorphic features. Eur. J. Hum. Genet. 8, 637–640. 33. Vogels, A., Devriendt, K., Vermeesch, J. R., et al. (2000) Cryptic translocation t(5;18) in familial mental retardation. Ann. Genet. 43, 117–123. 34. de Vries, B. B. A., Knight, S. J. L., Homfray, T., Smithson, S. F., Flint, J., and Winter, R. M. (2001) Submicroscopic subtelomeric 1qter deletions: a recognisable phenotype? J Med Genet. 38, 175–178. 35. Viot, G., Gosset, P., Fert, S., et al. (1999) Cryptic subtelomeric rearrangements detected by FISH in mentally retarded and dysmorphic patients. Am. J. Hum. Genet. 63, Supplement: A10. 36. Slavotinek, A., Rosenberg, M., Knight, S., et al. (1999) Screening for submicroscopic chromosome rearrangements in children with idiopathic mental retardation using microsatellite markers for the chromosome telomeres. J. Med. Genet. 36, 405–411. 37. Rossi, E., Piccini, F., Zollino, M., et al. (2001) Cryptic telomeric rearrangements in subjects with chromosomal phenotype and mental retardation. J. Med. Genet. 38, 417–420. 38. Anderlid, B., Annerén, G., Blennow, E., and Nordenskjöld, M. (1998) Subtelomeric rearrangements detected by FISH in patients with idiopathic mental retardation. Am. J. Hum. Genet. 65, Suppl: A67. 39. Riegel, M., Baumer, A., Jamar, M., et al. (2001) Submicropic terminal deletions and duplications in retarded patient with unclassified malformation syndromes. Hum. Genet. 109, 286–294. 40. Colleaux, L., Rio, M., Heuertz, S., et al. (2001) A Novel automated strategy for screening cryptic telomeric rearrangements in children with idiopathic mental retardation. Eur. J. Hum. Genet. 9, 319–327. 41. Fan, Y. S., Zhang, Y., Speevak, M., Farrell, S., Jung, H. J., and Siu, V. M. (2001) Detection of submicroscopic aberrations in patients with unexplained mental retardation by fluorescence in situ hybridization using multiple subtelomeric probes. Genet. Med. 3, 416–421. 42. Clarkson, B., Pavenski, K., Dupuis, L., et al. (2002) Detecting rearrangements in children using subtelomeric FISH and SKY. Am. J. Med. Genet. 107, 267–274.
43. Baker, E., Hinton, L., Callen, D. F., et al. (2002) Study of 250 childrren with idiopathic mental retardation reveals nine cryptic and diverse subtelomeric chromosome anomalies. Am. J. Med. Genet. 107, 285–293. 44. Lamb, A. N., Lytle, C. H., Aylsworth, A. S., et al. (1998) Low proportion of subtelomeric rearrangements in a population of patients with mental retardation and dysmorphic features. Am. J. Hum. Genet. 65, Suppl: A169. 45. Vorsanova, S. G., Koloti, D., Sharonin, V. O., Soloviev, V., and Yurov, Y. B. (1998) FISH analysis of microaberrations at telomeric and subtelomeric regions in chromosomes of children with mental retardation. Am. J. Hum. Genet. 65, Suppl: A154. 46. Joyce, C. A., Hart, H. H., Fisher, A. M., and Browne, C. E. (1999) Use of subtelomeric FISH probes to detect abnormalities in patients with idiopathic mental retardation and characterize rearrangements at the limit of cytogenetic resolution. J. Med. Genet. 36, Suppl: S16. 47. Ballif, B. C., Kashork, C. D., and Shaffer, L. G. (2000) The promise and pitfalls of telomere region-specific probes. Am. J. Hum. Genet. 67, 1356–1359. 48. Anderlid B-M, Schoumans, J., Annerén, G., et al. (2002) Subtelomeric rearrangements detected in patients with idiopathic mental retardation. Am. J. Med. Genet. 107, 275–284. 49. de Vries, B. B., White, S. M., Knight, S. J., et al. (2001) Clinical studies on submicroscopic subtelomeric rearrangements: a checklist. J. Med. Genet. 38, 145–150. 50. Knight, S. J. and Flint, J. (2000) Perfect endings: a review of subtelomeric probes and their use in clinical diagnosis. J. Med. Genet. 37, 401–409. 51. Joyce, C. A., Dennis, N. R., Cooper, S., and Browne, C. E. (2001) Subtelomeric rearrangements: results from a study of selected and unselected probands with idiopathic mental retardation and control individuals by using high-resolution G-binding and FISH. Hum. Genet. 109, 440–451. 52. Horsley, S. W., Knight, S. J. L., Nixon, J., et al. (1998) Del(18p) shown to be a cryptic translocation using a multiprobe FISH assay for subtelomeric chromosome rearrangements. J. Med. Genet. 35, 722–726. 53. Brkanac, Z., Cody, J. D., Leach, R. J., and DuPont, B. R. (1998) Identification of cryptic rearrangements in patients with 18q-deletion syndrome. Am. J. Hum. Genet. 62, 1500–1506. 54. Benzacken, B., Monier-Gavelle, F., Pierre Siffroi, J., Agbo, P., Chalvon, A., and Philippe Wolf, J. (2001) Acrocentric chromosome polymorphisms: beware of cryptic translocations. Prenat. Diagn. 21, 96–98. 55. Tosi, S., Scherer, S. W., Giudici, G., Czepulkowski, B., Biondi, A., and Kearney, L. (1999) Delineation of multiple deleted regions in 7q in myeloid disorders. Gene. Chromosom. Canc. 25, 384–392. 56. Tosi, S., Giudici, G., Rambaldi, A., et al. (1999) Characterization of the human myeloid leukemia-derived cell line GF-D8 by multiplex fluorescence in situ hybridization, subtelomeric probes, and comparative genomic hybridization. Gene. Chromosom. Canc. 24, 213–221. 57. Jaju, R. J., Haas, O. A., Neat, M., et al. (1999) A new recurrent translocation, t(5;11)(q35;p15.5), associated with del(5q) in childhood acute myeloid leukemia. Blood 94, 773–780. 58. Foot, N., Neat, M. J., Kearney L et al. (1999) Multiple FISH technology to clarify abnormal leukaemic karyotypes. J. Med. Genet. 36, S38. 59. Wakui, K., Tanemura, M., Suzumori, K., Hidaka, E., Ishikawa, M., Kubota, T., et al. (1999) Clinical applications of two-color telomeric fluorescence in situ hybridization for prenatal diagnosis: identification of chromosomal translocation in five families with recurrent miscarriages or a child with multiple congenital anomalies. J. Hum. Genet. 44, 85–90.
60. Scriven, P. N., Handyside, A. H., and Ogilvie, C. M. (1998) Chromosome translocations: segregation modes and strategies for preimplantation genetic diagnosis. Prenat. Diagn. 18, 1437–1449. 61. Handyside, A. H., Scriven, P. N., and Ogilvie, C. M. (1998) The future of preimplantation genetic diagnosis. Hum. Reprod. 13 Suppl 4, 249–255. 62. Mackie-Ogilvie, C., Harrison, R. H., Handyside, A. H., and Scriven, P. N. (1999) The use of subtelomeric probes in preimplantation genetic diagnosis. J. Med. Genet. 36, Supplement: S15. 63. Lese, C. M., Zhang, X., Pinkel, D., et al. (1999) Comparative genomic hybridization arrays: Towards a "telomere chip." Am. J. Hum. Genet. 65, 41. 64. Ghaffari, S. R., Boyd, E., Tolmie, J. L., Crow, Y. J., Trainer, A. H., and Connor, J. M. (1998) A new strategy for cryptic telomeric translocation screening in patients with idiopathic mental retardation. J. Med. Genet. 35, 225–233. 65. Rosenberg, M. J., Vaske, D., Killoran, C. E., et al. (2000) Detection of chromosomal aberrations by a whole-genome microsatellite screen. Am. J. Hum. Genet. 66, 419–427. 66. Borgione, E., Giudice, M. L., Galesi, O., et al. (2001) How microsatellite analysis can be exploited for subtelomeric chromosomal rearrangement analysis in mental retardation. J. Med. Genet. 38, E1. 67. Rosenberg, M. J., Killoran, C. Dziadzio, L., et al. (2001) Scanning for telomeric deletions and duplications and uniparental disomy using genetic markers in 120 children with malformations. Hum. Genet. 109, 311–318. 68. Armour, J. A., Sismani, C., Patsalis, P. C., and Cross, G. (2000) Measurement of locus copy number by hybridisation with amplifiable probes. Nucl. Acids Res. 28, 605–609. 69. Sismani, C., Armour, J. A., Flint, J., Girgallia, C., Regan, R., and Patsalis, P. C. (2001) Screening for subtelomeric chromosome abnormalities in children with idiopathic mental retardation using the multiprobe telomere FISH and the new MAPH telomeric assays. Eur. J. Hum. Genet. 9, 527–532. 70. Granzow, M., Popp, S., Keller, M., et al. (2000) Multiplex FISH telomere integrity assay identifies an unbalanced cryptic translocation der(5)t(3;5)(q27;p15.3) in a family with three mentally retarded individuals. Hum. Genet. 107, 51–57. 71. Brown, J., Saracoglu, K., Uhrig, S., Speicher, M. R., Eils, R., and Kearney, L. (2001) Subtelomeric chromosome rearrangements are detected using an innovative 12-color FISH assay (M-TEL). Nat. Med. 7, 497–501. 72. Brown, J., Horsley, S. W., Jung, C., et al. (2000) Identification of a subtle t(16;19)(p13.3;p13.3) in an infant with multiple congenital abnormalities using a 12–colour multiplex FISH telomere assay, M-TEL. Eur. J. Hum. Genet. 8, 903–910.
Screening Cryptic Telomeric Rearrangements
13 Fluorescence Genotyping for Screening Cryptic Telomeric Rearrangements Laurence Colleaux, Solange Heuertz, Florence Molinari, and Marlene Rio 1. Introduction Mental retardation (MR), defined as an intelligence quotient (IQ) less than 70, represents the most frequent serious handicap in children and young adults. Moderate to severe MR (IQ18 weeks). We use the method described above for all slides of all specimens prepared for interphase FISH analysis. 20. Do not denature or wash more than 3 slides at one time per Coplin jar. 21. Stringency of temperature and buffer concentration is important for denaturation. The temperature of the denaturation solution must be 73 ± 1°C, and should be verified immediately before each use. Verify that the pH of the denaturation solution is between 7.0–8.0 before each use, as well. 22. Timing of the last ethanol wash, removing the slide to the slide-warmer, and applying the probe mix is very important for successful hybridization. If the timing of the hybridization is such that the slide is ready more than 2 min before the probe is ready, the slide should remain in the jar of 100% ethanol. 23. Hybridized slides can be stored with coverslips at –20°C, in the dark. Under these conditions, the slides can be stored for up to 12 mo without significant loss in fluorescence signal intensity.
References 1. Johnson, M. P. and Miller, O. J. (1992) Cytogenetics. in: Reproductive Risks and Prenatal Diagnosis, (Evans, M. I., ed.), Appelton and Lange, Norwalk, CT. pp. 237–250. 2. Evans, M. I., Bottoms, S. F., Carlucci, T., Grant, J., Belsky, R. L., Solyom, A. E., et al. (1988) Determinants of altered anxiety after abnormal maternal serum alpha-fetoprotein screening. Am. J. Obstet. Gynecol. 159, 1501–1504.
16_Feldman_219-242F[7.10.2]
Feldman, Aviram-Goldring, and Evans
3. Caccia, N., Johnson, J. M., Robinson, G. E., and Barna, T. (1991) Impact of prenatal testing on maternal-fetal bonding: chorionic villus sampling versus amniocentesis. Am. J. Obstet. Gynecol. 165, 1122–1125. 4. Sjogren, B. and Uddenberg, N. (1990) Prenatal diagnosis for psychological reasons: comparison with other indications, advanced maternal age and known genetic risk. Prenat. Diagn. 10, 111–120. 5. Marteau, T. M., Cook, R., Kidd, J., Michie, S., Johnston, M., Slack, J., et al. (1992) The psychological effects of false-positive results in prenatal screening for fetal abnormality: a prospective study. Prenat. Diagn. 12, 205–214. 6. Goel, V., Glazier, R., Summers, A., and Holzapfel, S. (1998) Psychological outcomes following maternal serum screening: a cohort study. Can. Med. Assoc. J. 159, 651–656. 7. Pergament, E., Chen, P. X., Thangavelu, M., and Fiddler, M. (2000) The clinical application of interphase FISH in prenatal diagnosis. Prenat. Diagn. 20, 215–220. 8. Evans, M. I., Ebrahim, S. A., Berry, S. M., Holzgreve, W., Isada, N. B., Quintero, R. A., et al. (1994) Fluorescent in situ hybridization utilization for high-risk prenatal diagnosis: a trade-off among speed, expense, and inherent limitations of chromosome-specific probes. Am. J. Obstet. Gynecol. 171, 1055–1057. 9. Cremer, T., Landegent, J., Bruckner, A., Scholl, H. P., Schardin, M., Hager, H. D., et al. (1986) Detection of chromosome aberrations in the human interphase nucleus by visualization of specific target DNAs with radioactive and non-radioactive in situ hybridization techniques: diagnosis of trisomy 18 with probe L1.84. Hum. Genet. 74, 346–352. 10. Landegent, J. E., Jansen in de Wal, N., Dirks, R. W., Baao, F., and Van-der Ploeg, M. (1987) Use of whole cosmid cloned genomic sequences for chromosomal localization by non-radioactive in situ hybridization. Hum. Genet. 77, 366–370. 11. Julien, C., Bazin, A., Guyot, B., Forestier, F., and Daffos, F. (1986) Rapid prenatal diagnosis of Down's syndrome with in-situ hybridisation of fluorescent DNA probes. Lancet. 2, 863–864. 12. Pinkel, D., Straume, T., and Gray, J. W. (1986) Cytogenetic analysis using quantitative, high-sensitivity, fluorescence hybridization. Proc. Natl. Acad. Sci. USA 83, 2934–2938. 13. Cremer, T., Lichter, P., Borden, J., Ward, D. C., and Manuelidis, L. (1988) Detection of chromosome aberrations in metaphase and interphase tumor cells by in situ hybridization using chromosome-specific library probes. Hum. Genet. 80, 235–246. 14. Guyot, B., Bazin, A., Sole, Y., Julien, C., Daffos, F., and Forestier, F. (1988) Prenatal diagnosis with biotinylated chromosome specific probes. Prenat. Diagn. 8, 485–493. 15. Lichter, P., Cremer, T., Tang, C. J., Watkins, P. C., Manuelidis, L., and Ward, D. C. (1988) Rapid detection of human chromosome 21 aberrations by in situ hybridization. Proc. Natl. Acad. Sci. USA 85, 9664–9668. 16. Lichter, P., Cremer, T., Borden, J., Manuelidis, L., and Ward, D. C. (1988) Delineation of individual human chromosomes in metaphase and interphase cells by in situ suppression hybridization using recombinant DNA libraries. Hum. Genet. 80, 224–234. 17. Pinkel, D., Landegent, J., Collins, C., Fuscoe, J., Segraves, R., Lucas, J., et al. (1988) Fluorescence in situ hybridization with human chromosome-specific libraries: detection of trisomy 21 and translocations of chromosome 4. Proc. Natl. Acad. Sci. USA 85, 9138–9142. 18. Robinson, A., Bender, B. G., Linden, M. G., and Salbenblatt, J. A. (1990) Sex chromosome aneuploidy: the Denver Prospective Study. Birth Defects. 26, 59–115. 19. Jacobs, P. A., Melville, M., Ratcliffe, S., Keay, A. J., and Syme, J. (1974) A cytogenetic survey of 11,680 newborn infants. Ann. Hum. Genet. 37, 359–376. 20. Ratcliffe, S. G., Stewart, A. L., Melville, M. M., Jacobs, P. A., and Keay, A. J. (1970) Chromosome studies on 3500 newborn male infants. Lancet. 1, 121–122.
Prenatal Aneuploidy Detection by FISH
21. Klinger, K. W., Dackowski, W., Leverone, B., Locke, P., Nass, S. G., Lerner, T., et al. (1990) Prenatal detection of aneuploidy of 21, 18, 13, X or Y by interphase in situ hybridization. Am. J. Hum. Genet. 47Suppl, A224. 22. Yu, L. C., Bryndorf, T., Christensen, B., Segraves, R., Kuo, W. L., Pinkel, D., et al. (1990) Enumeration of specific chromosomes in uncultured fetal cells using fluorescence in situ hybridization (FISH). Am. J. Hum. Genet. 47Suppl, A287. 23. Kuo, W. L., Tenjin, H., Segraves, R., Pinkel, D., Golbus, M. S., and Gray, J. (1991) Detection of aneuploidy involving chromosomes 13, 18, or 21, by fluorescence in situ hybridization (FISH) to interphase and metaphase amniocytes. Am. J. Hum. Genet. 49, 112–119. 24. Sawa, R., Hayashi, Z., Tanaka, T., Onda, T., Hoshi, K., Fukada, Y., et al. (2001) Rapid detection of chromosome aneuploidies by prenatal interphase FISH (fluorescence in situ hybridization) and its clinical utility in Japan. J. Obstet. Gynaecol. Res. 27, 41–47. 25. Lewin, P., Kleinfinger, P., Bazin, A., Mossafa, H., and Szpiro-Tapia, S. (2000) Defining the efficiency of fluorescence in situ hybridization on uncultured amniocytes on a retrospective cohort of 27,407 prenatal diagnoses. Prenat. Diagn. 20, 1–6. 26. Morris, A., Boyd, E., Dhanjal, S., Lowther, G. W., Aitken, D. A., Young, J., et al. (1999) Two years' prospective experience using fluorescence in situ hybridization on uncultured amniotic fluid cells for rapid prenatal diagnosis of common chromosomal aneuploidies. Prenat. Diagn. 19, 546–551. 27. Eiben, B., Trawicki, W., Hammans, W., Goebel, R., Pruggmayer, M., and Epplen, J. T. (1999) Rapid prenatal diagnosis of aneuploidies in uncultured amniocytes by fluorescence in situ hybridization. Evaluation of >3,000 cases. Fetal. Diagn. Ther. 14, 193–197. 28. Aviram-Goldring, A., Daniely, M., Dorf, H., Chaki, R., Goldman, B., and Barkai, G. (1999) Use of interphase fluorescence in situ hybridization in third trimester fetuses with anomalies and growth retardation. Am. J. Med. Genet. 87, 203–206. 29. Thilaganathan, B., Sairam, S., Ballard, T., Peterson, C., and Meredith, R. (2000) Effectiveness of prenatal chromosomal analysis using multicolor fluorescent in situ hybridisation. Br. J. Obstet. Gynaecol. 107, 262–266. 30. Cheong Leung, W., Chitayat, D., Seaward, G., Windrim, R., Ryan, G., Barrett, J., et al. (2001) Role of amniotic fluid interphase fluorescence in situ hybridization (FISH) analysis in patient management. Prenat. Diagn. 21, 327–332. 31. Ulmer, R., Pfeiffer, R. A., Kollert, A., and Beinder, E. (2000) Diagnosis of aneuploidy with fluorescence in situ hybridization (FISH); value in pregnancies with increased risk for chromosome aberrations. Z. Geburtshilfe. Neonatol. 204, 1–7. 32. Bryndorf, T., Lundsteen, C., Lamb, A., Christensen, B., and Philip, J. (2000) Rapid prenatal diagnosis of chromosome aneuploidies by interphase fluorescence in situ hybridization: a one-year clinical experience with high-risk and urgent fetal and postnatal samples. Acta Obstet. Gynecol. Scand. 79, 8–14. 33. Ben Khalifa, M., Mercier, S., Tachdjian, G., and Baldi, M. (1999) Diagnostic prenatal des aneuploidies chromosomiques majeures. La Gynecologie 42, 60–61. 34. Cremer, A. F., Jansen in de Wal, N., Wiegant, J., Dirks, R. W., Weisbeek, P., van der Ploeg, M., et al. (1987) Non-radioactive in situ hybridization. A comparison of several immunocytochemical detection systems using reflection-contrast and electron microscopy. Histochemistry 86, 609–615. 35. Lichter, P., Jauch, A., Cremer, T., and Ward, D. C. (1990) Detection of Down syndrome by in situ hybridization with chromosome 21 specific DNA probes. Prog. Clin. Biol. Res. 360, 69–78. 36. Nederlof, P. M., Van der Flier, S., Wiegant, J., Raap, A. K., Tanke, H. J., Ploem, J. S., et al. (1990) Multiple fluorescence in situ hybridization. Cytometry 11, 126–131.
37. Klinger, K., Landes, G., Shook, D., Harvey, R., Lopez, L., Locke, P., et al. (1992) Rapid detection of chromosome aneuploidies in uncultured amniocytes by using fluorescence in situ hybridization (FISH). Am. J. Hum. Genet. 51, 55–65. 38. Ward, B. E., Gersen, S. L., Carelli, M. P., McGuire, N. M., Dackowski, W. R., Weinstein, M., et al. (1993) Rapid prenatal diagnosis of chromosomal aneuploidies by fluorescence in situ hybridization: clinical experience with 4500 specimens. Am. J. Hum. Genet. 52, 854–865. 39. Ledbetter, D. H. (1992) The 'colorizing' of cytogenetics: is it ready for prime time? Hum. Mol. Genet. 1, 297–299. 40. American College of Medical Genetics (1993) Prenatal interphase fluorescence in situ hybridization (FISH) policy statement. Am. J. Hum. Genet. 53, 526–527. 41. Ward, B. E., Gersen, S. L., Theve, R., Wright, M., and Carelli, M. P. (1999) Rapid prenatal diagnosis of chromosomal aneuploidies by fluorescence in situ hybridization: clinical experience on 10,000 specimens, in: Introduction to Fluorescence in situ Hybridization: Principles and Clinical Applications, (Andreeff M. and Pinkel D., eds.), Wiley-Liss, Inc., New York, NY. pp. 409–428. 42. Bryndorf, T., Christensen, B., Vad, M., Parner, J., Brocks, V., and Philip, J. (1997) Prenatal detection of chromosome aneuploidies by fluorescence in situ hybridization: experience with 2000 uncultured amniotic fluid samples in a prospective preclinical trial. Prenat. Diagn. 17, 333–341. 43. Bryndorf, T., Christensen, B., Vad, M., Parner, J., Carelli, M. P., Ward, B. E., et al. (1996) Prenatal detection of chromosome aneuploidies in uncultured chorionic villus samples by FISH. Am. J. Hum. Genet. 59, 918–926. 44. Bryndorf, T., Christensen, B., Xiang, Y., Philip, J., Yokobata, K., Bui, N., et al. (1994) Fluorescence in situ hybridization with a chromosome 21-specific cosmid contig: 1-day detection of trisomy 21 in uncultured mesenchymal chorionic villus cells. Prenat. Diagn. 14, 87–96. 45. Strovel, J. W., Lee, K. D., Punzalan, C., and Schwartz, S. (1992) Prenatal diagnosis by direct analysis of uncultured amniotic fluid and chorionic villus cells using interphase fluorescence in situ hybridization (FISH). Am. J. Hum. Genet. 51, A12. 46. Verlinsky, Y., Ginsberg, N., Chmura, M., Freidine, M., White, M., Strom, C., et al. (1995) Cross-hybridization of the chromosome 13/21 alpha satellite DNA probe to chromosome 22 in the prenatal screening of common chromosomal aneuploidies by FISH. Prenat. Diagn. 15, 831–834. 47. Lapidot-Lifson, Y., Lebo, R. V., Flandermeyer, R. R., Chung, J. H., and Golbus, M. S. (1996) Rapid aneuploid diagnosis of high-risk fetuses by fluorescence in situ hybridization. Am. J. Obstet. Gynecol. 174, 886–890. 48. Mercier, S. and Bresson, J. L. (1995) Prenatal diagnosis of chromosomal aneuploidies by fluorescence in situ hybridization on uncultured amniotic cells: experience with 630 samples. Ann. Genet. 38, 151–157. 49. D'Alton, M. E., Malone, F. D., Chelmow, D., Ward, B. E., and Bianchi, D. W. (1997) Defining the role of fluorescence in situ hybridization on uncultured amniocytes for prenatal diagnosis of aneuploidies. Am. J. Obstet. Gynecol. 176, 769–774. 50. Cacheux, V., Tachdjian, G., Druart, L., Oury, J. F., Serero, S., Blot, P., et al. (1994) Evaluation of X, Y, 18, and 13/21 alpha satellite DNA probes for interphase cytogenetic analysis of uncultured amniocytes by fluorescence in situ hybridization. Prenat. Diagn. 14, 79–86. 51. Tepperberg, J., Pettenati, M. J., Rao, P. N., Lese, C. M., Rita, D., Wyandt, H., et al. (2001) Prenatal diagnosis using interphase fluorescence in situ hybridization (FISH): 2-year multicenter retrospective study and review of the literature. Prenat. Diagn. 21, 293–301.
52. American College of Medical Genetics, and American Society of Human Genetics (2000) Technical and clinical assessment of fluorescence in situ hybridization: an ACMG/ASHG position statement. I. Technical considerations. Test and Technology Transfer Committee. Genet. Med. 2, 356–361. 53. Cai, L. S., Lim, A. S., and Tan, A. (1999) Rapid one-day fluorescence in situ hybridisation in prenatal diagnosis using uncultured amniocytes and chorionic villi. Ann. Acad. Med. Singapore 28, 502–507. 54. Evans, M. I., Klinger, K. W., Isada, N. B., Shook, D., Holzgreve, W., McGuire, N., et al. (1992) Rapid prenatal diagnosis by fluorescent in situ hybridization of chorionic villi: an adjunct to long-term culture and karyotype. Am. J. Obstet. Gynecol. 167, 1522–1525. 55. Fiddler, M., Frederickson, M. C., Xien Chen, P., and Pergament, E. (2001) Assessment of fetal status in multiple gestation pregnancies using interphase FISH. Prenat. Diagn. 21, 196–199. 56. Philip, J., Bryndorf, T., and Christensen, B. (1994) Prenatal aneuploidy detection in interphase cells by fluorescence in situ hybridization (FISH). Prenat. Diagn. 14, 1203–1215. 57. Saura, R., Roux, D., Maugey-Laulon, B., Taine, L., Wen, Z. Q., Vergnaud, A., et al. (1998) False-negative results of trisomy 21 on direct analysis on chorionic villus sampling. Prenat. Diagn. 18, 866–867. 58. Thein, A. T., Abdel-Fattah, S. A., Kyle, P. M., and Soothill, P. W. (2000) An assessment of the use of interphase FISH with chromosome specific probes as an alternative to cytogenetics in prenatal diagnosis. Prenat. Diagn. 20, 275–280. 59. Feldman, B., Ebrahim, S. A., Hazan, S. L., Gyi, K., Johnson, M. P., Johnson, A., et al. (2000) Routine prenatal diagnosis of aneuploidy by FISH studies in high-risk pregnancies. Am. J. Med. Genet. 90, 233–238. 60. Isada, N. B., Hume, R. F., Jr., Reichler, A., Johnson, M. P., Klinger, K. W., Evans, M. I., et al. (1994) Fluorescent in situ hybridization and second-trimester sonographic anomalies: uses and limitations. Fetal. Diagn. Ther. 9, 367–370. 61. Spathas, D. H., Divane, A., Maniatis, G. M., Ferguson-Smith, M. E., and FergusonSmith, M. A. (1994) Prenatal detection of trisomy 21 in uncultured amniocytes by fluorescence in situ hybridization: a prospective study. Prenat. Diagn. 14, 1049–1054. 62. Cooper, M. L., Redman, J. B., Mensing, D. E., and Cheung, S. W. (1998) Prenatal detection of chromosome aneuploidies in uncultured amniocytes by FISH: Advantages and limitations. Am. J. Hum. Genet. 63, A161. 63. Jalal, S. M., Law, M. E., Carlson, R. O., and Dewald, G. W. (1998) Prenatal detection of aneuploidy by directly labeled multicolored probes and interphase fluorescence in situ hybridization. Mayo Clin. Proc. 73, 132–137. 64. Verlinsky, Y., Ginsberg, N., Chmura, M., White, M., Strom, C., and Kuliev, A. (1998) Detection of translocations involving the Y-chromosome in prospective prenatal screening of common chromosomal aneuploidies by FISH. Prenat. Diagn. 18, 390–392. 65. Eiben, B., Trawicki, W., Hammans, W., and Epplen, J. T. (1999) False-negative finding in rapid interphase FISH analysis of uncultured amniotic cells. Prenat. Diagn. 19, 892–893. 66. Estabrooks, L. L., Sapeta, M., Lytle, C., Challinor, P., Dietrich-Cook, H., Crenshaw, D., et al. (1999) Prenatal interphase FISH using the AneuVysion probe set in over 10,000 samples. Am. J. Hum. Genet. 65(Suppl), A162. 67. Meyer, L. M., Ramin, K. D., Ramsey, P. S., Ogburn, P. L., and Jalal, S. M. (2000) Fluoresent in situ hybridization technique for the rapid detection of chromosomal abnormalities. Obstet. Gynecol. 95, S64. 68. Bink, K., Pauer, H. U., and Bartels, I. (2000) Interphase FISH test as a rapid test for trisomies in amniotic fluid—results of a prospective study. Z. Geburtshilfe. Neonatol. 204, 8–13.
69. Robertson, S., Jackle, B., Cathey, L., Merant, L., Pittman, A., and Pattenati, M. J. (1998) Prenatal interphase aneuploidy detection in uncultured amniocytes using fluorescence in situ hybridization (FISH). J. Assoc. Genet. Tech. 24, 151. 70. Evans, M. I., Henry, G. P., Miller, W. A., Bui, T. H., Snidjers, R. J., Wapner, R. J., et al. (1999) International, collaborative assessment of 146,000 prenatal karyotypes: expected limitations if only chromosome-specific probes and fluorescent in-situ hybridization are used. Hum. Reprod. 14, 1213–1216. 71. Feldman, B., Ebrahim, S. A., Gyi, K., Flore, L. A., and Evans, M. I. (2000) Rapid confirmation of previously detected prenatal mosaicism by fluorescence in situ hybridization in interphase uncultured amniocytes. Genet Test. 4, 61–63. 72. American College of Medical Genetics (1999) Interphase/nuclear fluorescence in situ hybridization (nuc ish). in: Standards and guidelines for clinical genetics laboratories. 2nd ed. 73. Hsu, L. Y. F. (1992) Prenatal diagnosis of chromosomal abnormalities through amniocentesis, in: Genetic disorders and the fetus: diagnosis, prevention and treatmen (Milunsky, A., ed.), Johns Hopkins University Press, Baltimore, ML. pp. 190–210. 74. Winsor, E. J., Silver, M. P., Theve, R., Wright, M., and Ward, B. E. (1996) Maternal cell contamination in uncultured amniotic fluid. Prenat. Diagn. 16, 49–54. 75. Christensen, B., Bryndorf, T., Philip, J., Xiang, X., and Hansen, W. (1993) Prenatal diagnosis by in situ hybridisation on uncultured amniocytes: Reduced sensitivity and potential risk of misdiagnosis in blood stained samples. Prenat. Diagn. 13, 581–587. 76. Rebello, M. T., Abas, A., Nicolaides, K., and Coleman, D. V. (1994) Maternal contamination of amniotic fluid demonstrated by DNA analysis. Prenat. Diagn. 14, 109–112. 77. Benn, P. A. and Hsu, L. Y. (1983) Maternal cell contamination of amniotic fluid cell cultures: results of a U. S. nationwide survey. Am. J. Med. Genet. 15, 297–305. 78. Nuss, S., Brebaum, D., and Grond-Ginsbach, C. (1994) Maternal cell contamination in amniotic fluid samples as a consequence of the sampling technique. Hum. Genet. 93, 121–124. 79. Moskowitz, J., Ward, B. E., and Weinstein, M. (1993) Optimized amniocentesis methods enhance performance of fluorescence in situ hybridization (FISH) for prenatal diagnosis. Am. J. Obstet. Gynecol. 168, 394. 80. Estabrooks, L. L., Hanna, J. S., and Lamb, A. N. (1999) Overwhelming maternal cell contamination in amniotic fluid samples from patients with oligohydramnios can lead to false prenatal interphase FISH results. Prenat. Diagn. 19, 179–181. 81. Winsor, E. J., Dyack, S., Wood-Burgess, E. M., and Ryan, G. (1999) Risk of false-positive prenatal diagnosis using interphase FISH testing: hybridization of alpha-satellite X probe to chromosome 19. Prenat. Diagn. 19, 832–836. 82. Thangavelu, M., Chen, P. X., and Pergament, E. (1998) Hybridization of chromosome 18 alpha-satellite DNA probe to chromosome 22. Prenat. Diagn. 18, 922–925. 83. Tardy, E. P. and Toth, A. (1997) Cross-hybridization of the chromosome 13/21 alpha satellite DNA to chromosome 22 or a rare polymorphism? Prenat. Diagn. 17, 487–488. 84. Thangavelu, M., Chen, P. X., and Pergament, E. (1998) Cross-hybridization of the chromosome13/21 alpha-satellite DNA probe to chromosome 22. Prenat. Diagn. 18, 831–834. 85. Weier, H. U. and Gray, J. W. (1992) A degenerate alpha satellite probe, detecting a centromeric deletion on chromosome 21 in an apparently normal human male, shows limitations of the use of satellite DNA probes for interphase ploidy analysis. Anal. Cell. Pathol. 4, 81–86. 86. Seres-Santamaria, A., Catala, V., Cuatrecasas, E., and Villanueva, R. (1993) Fluorescent in-situ hybridisation and Down's syndrome. Lancet. 341, 1544. 87. Mizunoe, T., and Young, S. R. (1992) Low fluorescence alpha satellite region yields negative result. Prenat. Diagn. 12, 549–550.
88. Bossuyt, P. J., Van Tienen, M. N., De Gruyter, L., Smets, V., Dumon, J., and Wauters, J. G. (1995) Incidence of low-fluorescence alpha satellite region on chromosome 21 escaping detection of aneuploidy at interphase by FISH. Cytogenet. Cell. Genet. 68, 203–206. 89. Verma, R. S. and Luke, S. (1992) Variations in alphoid DNA sequences escape detection of aneuploidy at interphase by FISH technique. Genomics. 14, 113–116.
FISH on Fetal Cells in Maternal Blood
17 Prenatal Diagnosis of Chromosomal Abnormalities Using Maternal Blood Farideh Z. Bischoff, Dianne X. Dang, Dorothy E. Lewis, and Joe Leigh Simpson 1. Introduction Fetal chromosomal aneuploidies can be detected by fluorescent in situ hybridization (FISH) analysis of intact fetal cells circulating in maternal blood. Given the low number of circulating fetal cells (1 in 104 to 106 maternal cells) at any given time during pregnancy and given that no fetal-specific markers can unambiguously distinguish maternal from fetal cells, success in fetal cell analysis relies on hybridization and detection efficiency of probes in cells recovered following some formal enrichment. Consequently, many different protocols have been developed using one or more techniques to enrich and improve purity of fetal cells for subsequent FISH. FISH analysis is complicated by enrichment not being 100 percent efficient, yielding heterogeneous mixtures of cell types that require different FISH conditions for optimal signal detection. In addition, certain methods used during enrichment, namely fixation and storage of cells, can adversely affect the quality of cells recovered for FISH analysis. The focus of this chapter will be to highlight variables that impact FISH analysis of fetal cells recovered from maternal blood. Detailed description of the methods developed at Baylor College of Medicine is provided. Recovery of fetal cells for DNA analysis using PCR techniques will not be reviewed; however, several recent reviews are recommended (1–3).
1.1. Application of FISH on Fetal Cells in Maternal Blood In the United States, offering prenatal cytogenetic diagnosis is considered "standard of care" of pregnant women 35 yr or older at the time of delivery. Fetal cells are thus obtained invasively using techniques such as chorionic villus sampling or amniocentesis. The threshold for these procedures has long been 35 yr of age, a largely arbitrary figure taking into account the relative risk of the most common autosomal aneuploidy (trisomy 21) and the likelihood of a miscarriage secondary to the procedure. From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
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Despite the accuracy and safety of chorionic villus sampling and amniocentesis, there has been relatively little impact on the incidence of trisomy 21 because 80% of newborn infants with Down syndrome are born to women below the age of 35 (4,5). Moreover, only about half of U.S. gravidas over age 35 undergo an invasive prenatal diagnostic procedure. For this reason, women under age 35 yr must be offered maternal serum analyte screening, which may or may not lead to invasive procedure. This noninvasive method detects about 65% in the overall general population, but fewer in younger women (6–8). Application of FISH to detect fetal chromosomal abnormalities (mainly aneuploidy) using maternal blood offers an alternative noninvasive means of testing all pregnancies with the potential for a lower false-positive detection than the 5% accepted for maternal serum screening (9–12). Unlike other screening methods, fetal cells from maternal blood can also provide direct evaluation of fetal cells from an ongoing pregnancy, rendering genetic counseling less ambiguous for most couples.
1.1.1. Aneuploidy Detection Diagnosis of fetal aneuploidy, primarily trisomy 13, 18, and 21, has been accomplished by FISH (13–17). Early studies employed sequential or multi-color FISH, enabling detection of up to three chromosomes simultaneously (X, Y, and usually either 21 or 18). However, effective prenatal testing in the general population will require concurrent assessment of all the common aneuploidies: which involve chromosomes X, Y, 13, 18, and 21 (18). Thus, we have developed a five-color FISH protocol that enables simultaneous analysis of all five-chromosomes following a single hybridization reaction (19). Based on analysis of more than 300 maternal specimens, our FISH strategy yields >90% hybridization efficiency of all five probes with a very low false-positive detection rate of XY (4%) and autosomal aneuploid (95%, [19]). Although reduced hybridization efficiency theoretically might be influenced by probe (signal) size, we did not observe this among the control cells scored. Given that different cell types cannot be avoided after enrichment, it is important to use FISH methods that permit analysis of all cells, despite differences in signal quality (intensity and size). This will allow interpretation of each cell.
1.6. Strategies to Distinguish Fetal from Maternal Cells Accurate genetic diagnosis of rare fetal cells that exist in maternal blood depends on the ability of the observer to identify fetal cells in a background of maternal cells. Attempting to further reduce the number of nuclei to be analyzed by FISH, immunohistochemical staining techniques have been described for distinguishing fetal erythroblasts from maternal erythroblasts (76–83). Zheng et al. (76) described simultaneous immunohistochemical staining using a mouse anti-fetal hemoglobin antibody and FISH using a chromosome Y-probe. However, a fraction of maternal cells isolated also stained positive for HbF. Given that as many as 50% of circulating nucleated RBCs are fetal in origin and desirable for FISH (41), automated methods to scan and locate candidate cells based on morphology and staining for subsequent FISH would be attractive (75). Unfortunately, detection of the globin chains and/or morphology requires staining solutions that often contain preservatives capable of interfering with FISH.
2. Materials 2.1. Flow Sorting 2.1.1. General Reagents 1. Isolymph ficoll gradient (density 1.077) (Gallard Schlesinger, Carle Place, NY, cat. no. T1000). 2. 10X Phosphate buffered saline (PBS) solution: 137 mM NaCl, 27 mM KCl, 43 mM KH2PO4, 14 mM Na2HPO4·7H2O dissolved in deionized water, sterilize through 0.22 µm filter, and store at room temperature for up to 1 mo. 3. 1X PBS solution: Dilute 10X PBS in deionized water, sterilize through 0.22 µm filter, and store at 4°C. Solution must be warmed to room temperature prior to use. 4. PBS-EDTA (PBSE): Dissolve 0.0372 g of EDTA (reagent grade) in 100 mL of 1X PBS, sterilize through 0.22 µm filter, and store at 4°C. Solution must be warmed to room temperature prior to use. 5. Trypan Blue (0.4%) solution: Dissolve 0.4 g of Trypan Blue (Sigma, St. Louis, MO, cat. no. T0776) in 100 mL of deionized water, sterilize through 0.22 µm filter, and store at room temperature.
2.1.2. Depletion of CD3+ and CD13+ Maternal Cells 1. CD3 and CD13 antibodies both labeled with biotin (Biodesign International, Kennebunk, ME, cat. no. P01106B and P01150B, respectively). 2. Quantum/Streptavidin magnetic particles (Clemente Associates, Madison, CT, cat. no. SAB250). Store at 4°C.
3. Rare earth magnet (Clemente Associates, Madison, CT). 4. PBSE/2% FBS solution: Add 10 mL of heat inactivated FBS to 490 mL of PBSE, sterilize through 0.22 µm filter, and store at 4°C for up to 1 mo. Solution must be warmed to room temperature prior to use. 5. PBSE/5% FBS solution: Add 25 mL of heat inactivated fetal bovine serum (FBS) to 475 mL of PBSE, sterilize through 0.22 µm filter, and store at 4°C for up to 1 mo. Solution must be warmed to room temperature prior to use. 6. Prepare Quantum magnetic particles by calculating the particle amount needed for each sample, a final concentration of 5 µg of particles for 106 cells is needed. Add the desired amount of particles (should be in the range of 300–400 µL) to a 15 mL polypropylene conical tube. Dilute 1:100 with PBSE/5% FBS and mix well. Separate particles with magnet and carefully transfer particles using a pipet to a new 15-mL tube. Discard supernatant.
2.1.3. Cell Surface Staining for CD71 and CD45 1. Fluorescein isothyocyanate (FITC)-labeled CD71 mAb (Becton Dickinson, San Jose, CA, cat. no. 347513); phycoerythrin (PE)-labeled CD45 mAb (KC56-RD1) (Coulter Corp., Hialeah, FL, cat. no. 6603839) dilute to 0.1 mg/mL using PBSE/2% FBS and store at 4°C for up to 1 mo. 2. Paraformaldehyde (4%) solution: Add 4.0 g of paraformaldehyde (reagent grade) to 90 mL deionized water. To dissolve, adjust to pH 10.0. Once in solution, lower to pH 7.0. Add 10 mL of 10X PBS (for a final concentration of 4.0 g in 100 mL of 1X PBS), sterilize through 0.22 µm filter and store at 4°C. 3. Prepare 3% paraformaldehyde by diluting 4% paraformaldehyde 3:1 with 1X PBS and store at 4°C.
2.1.4. Flow Cytometry for Isolation of CD71+ and CD45– Cells 1. EPICS Model 753 (Coulter Corp.) - equipped with the Cicero High-Speed Sort System (Cytomation, Inc., Ft. Collins, CO). 2. An argon ion laser (Coherent, Inc., Palo Alto, CA). 3. 3X Quartz SortSense flow cell tip with 100 µm orifice diameter and Profile pickup lens (Coulter Corp.). 4. Optical filters include a 457–502-nm longpass laser blocking filter, a 550-nm longpass dichroic filter to transmit the FITC emission to a 525-nm bandpass and bend the PE emission to a 575-nm bandpass filter. 5. Isoton II sheath solution (Coulter Corp.). 6. Autoclave sterilized microcentrifuge tubes and clean silylated (positive charge) glass slides.
2.2. FISH 2.2.1 Cellular Fixation, DNA Dehydration and Denaturation 1. Carnoy's fixative: Standard (v/v) 3 parts methanol : 1 part acetic acid (100 mL) prepared fresh (within 30 min of use). 2. Ethanol solutions (70, 90, and 100%): Using 100% absolute ethanol, prepare 70 and 90% ethanol (v/v) with deionized water. Prepare two bottles of each (500 mL). Store one at room temperature and the other at –20°C. 3. 20X SSC solution: Premeasured powder (Oncor, Gaithersburg, MD, cat. no. S4073) dissolved in 1 L of deionized water. 4. 70% formamide/2X SSC denaturation solution: Prepare fresh prior to use in a 50 mL glass Coplin jar with lid by combining 28 mL formamide [Fisher Scientific (ultrapure
Bischoff et al. molecular biology grade) (Pittsburg, PA, cat. no. F84-1), 4 mL 20X SSC and 8 mL deionized water. To prevent cracking of glass Coplin jar, gradually prewarm this solution in a 43°C waterbath then transfer to a 70°C waterbath.
2.2.2 Five-Color FISH 1. Purchase direct fluorophore labeled chromosome specific probes. In comparing several manufacturer FISH probe products, we have found the specificity and quality of directlabeled probes (Vysis, Inc.; Downers Grove, IL) to be best for our application. These probes are of suitable size, which generate bright fluorescence signals that are visually distinct, enabling simultaneous analysis of chromosomes X, Y, 13, 18, and 21. Three alpha-satellite centromere-specific (CEP) and two locus-specific (LSI) probes are combined: CEP X SpectrumGreen™, CEP X SpectrumOrange™, CEP Y SpectrumAqua™, CEP 18 SpectrumAqua™, CEP 18 SpectrumOrange™, LSI 13 SpectrumGreen™, and LSI 21 SpectrumOrange™ (Vysis, Inc.). Probes must be protected from light and stored frozen at –20°C. Aliquoting is not necessary. 2. In optimizing our five-color FISH strategy, chromosomes X, Y, 13, 18, and 21 are efficiently detected as yellow, blue, green, pink, and red/orange fluorescent colors, respectively. Therefore, prior to preparing the five probe cocktail, combinatorial mixing of the CEP X and CEP 18 probes is necessary for generating two of the five fluorescent colors, yellow and pink, respectively. This is done by premixing equal amounts (premix only 5 µL of each probe at a time) of CEP X SpectrumGreen™ and CEP X SpectrumOrange™ to create a yellow fluorescence signal. Similarly, premix equal amounts of CEP 18 SpectrumAqua™ and CEP 18 SpectrumOrange™ to create a pink fluorescence signal. Store premixed probes at –20°C. 3. For a hybridization area of 22 × 22 mm per slide, prepare a 10 µL five probe cocktail in a sterile microcentrifuge tube by combining 0.5 µL of each LSI 13 and 21 probes, 0.3 µL of each CEP X (premixed), CEP 18 (premixed) and CEP Y probes, 1.0 µL deionized water, and 7.1 µL LSI™ probe buffer (provided with purchase of LSI probes). 4. Prior to performing FISH, prepare a 37°C humidity chamber by placing an empty plastic pipet tip rack in the center of a small plastic container with a tight fitting lid. Fill approx 10% of volume with water and store in 37°C incubator. 5. 2X SSC solution: Dilute 20X SSC in deionized water, adjust to pH 7.0. Store at room temperature for up to 6 mo. 6. 1X PBD solution: Dilute 10X PBDTM (Oncor, Gaithersburg, MD, cat. no. S1370-7) with deionized water. Store at 4°C for up to 6 mo. 7. DAPI (4',6-Diamidino-2-phenylindole) II counterstain in antifade solution (125 ng DAPI/mL) (Vysis, Inc., Downers Grove, IL, cat. no. 32-804831). 8. Slide boxes for storage of processed slides at 4°C.
2.2.3. Microscope Analysis 1. Axiophot or Axioskop fluorescent microscope equipped with camera and fluorescence objectives of ×40 and ×100 magnification (Carl Zeiss, Inc., Thornwood, NY). 2. Appropriate DAPI single bandpass filter [Omega Optical, Brattleboro, VT) and Aqua/ Green/Orange triple bandpass filter set (Vysis Inc., Downers Grove, IL). 3. High pressure light source, 100 W Hg lamp (Carl Zeiss, Inc., Thornwood, NY).
3. Methods 3.1. Blood Separation 1. Collect approx 30 mL of venous blood in sodium heparin vacutainers (see Note 2).
2. Transfer 15 mL of blood to a 50-mL polypropylene conical tube and add 15 mL of PBSE (final ratio is 1:1 blood:PBSE). A 30 mL blood sample is divided into two tubes. 3. Underlay each mixture of blood:PBSE with 10–15 mL Isolymph using a sterile syringe and Pasteur pipet. Tightly cap the tubes and centrifuge for 25 min at 1600-rpm (200g) with the brake off. 4. Remove tubes carefully. Using a vacuum and Pasteur pipet, carefully remove the top layer (plasma and platelets) and discard. Leave behind approx 1 cm of this layer. 5. With a 10-mL pipet, combine the mononuclear cell layer from the two tubes in a 50-mL polypropylene tube. Centrifuge for 10 min at 1600-rpm (200g) with the brake on. 6. Pour off the supernatant and resuspend the pellet in 50 mL of PBSE. Centrifuge for 5 min at 1200-rpm (100g). Pour off the supernatant and resuspend pellet in PBSE in a volume equal to the initial blood vol (30 mL) (see Note 3). Vortex for an even suspension of cells. 7. Transfer 50 µL of each cell suspension to a clean 5-mL polypropylene conical tube and add 50 µL of 0.2% Trypan blue. Place cells on hemacytometer for cell count. Resuspend cells at a concentration of 20 × 106 cells/mL in PBSE/2% FBS.
3.2. Quantum Magnetic Particle Depletion 1. Stain cells by mixing 1 µg of each CD3-biotin and CD13-biotin with 106 cells. Incubate on ice for 20 min. 2. Wash cell suspension twice with PBSE. Resuspend the cells in a 15 mL polypropylene tube at 10 × 106 cells/mL in PBSE/5% FBS. 3. Add appropriate amount of washed avidin magnetic particles (amount calculated in Subheading 2.1.2.). Incubate on ice for 15–20 min, swirling at 5 min intervals to ensure uniform suspension of particles and cells. 4. Place tube against magnet for 5 min. Carefully remove unbound cells with an automatic pipetter and dispense into a clean 15-mL tube. Repeat the magnetic separation with this second tube to ensure the removal of all magnetic particles. Dispense unbound cells into a third clean 15-mL tube. 5. Centrifuge the unbound cells and resuspend in 10–20 mL of PBSE for a postdepletion hemacytometer cell count as described in Subheading 3.1., step 7. Resuspend cells at a concentration of 20 × 106 cells/mL in PBSE/2% FBS.
3.3. Cell Surface Staining 1. Add 1 µg of CD71-FITC (half the amount suggested by manufacturer) and 10 µL of diluted CD45-PE (see Subheading 2.1.3.) per 1 × 106 cells. Incubate on ice for 20 min. 2. Wash cells with PBSE/2% FBS and resuspend in 3% paraformaldehyde at a concentration of 10 × 106 cells/mL. Incubate on ice for 60 min. 3. Wash cells twice with PBSE/2% FBS and resuspend in PBSE/2% FBS at a concentration of 10 × 106 cells/mL. 4. Store tubes at 4°C, keep dark until ready for sort.
3.4. Flow Sorting 1. Tune argon laser to 488-nm and operate at 50 mW. 2. Color compensation is 25–30% of FITC signal from the PE signal, 5% of PE signal from the FITC, and is monitored by using samples stained with the appropriate single- and dual- color fluorochromes. 3. Crystal drive frequency is increased to 30 kHz to create more and smaller droplets. Sheath pressure is at 12 psi. 4. Sorting is performed by using two-droplet deflection with the anticoincidence engaged.
Samples are suspended in a volume ranging from 0.2–2.0 mL of PBSE/2% FBS to create a flow rate of 1000–6000 cells/s, depending on the cell concentration after separation and depletion. 5. Forward-angle light scatter is collected as a linear signal, and all fluorescence emissions are collected on a four-decade logarithmic scale. A light scatter gate is set to eliminate debris and aggregates. Target cells are CD45–,CD71+.
3.5. Cell Collection 1. A silylated slide is set in the path of the sort stream for collecting the cells of interest. Slides are allowed to air dry completely. Dry slides are then incubated in fresh Carnoy's fixative twice for 15 min each to remove flow sorting Isoton II solution and to adhere cells to slide. Dry slides are stored at –20°C until FISH analysis. In place of a slide, a sterile microcentrifuge tube can be used for collecting cells in suspension. In this case, sorted cells are washed once in PBSE/2% FBS (62) to remove residual saline, then resuspended in 20–50 µL supernatant and stored at 4°C until FISH (see Note 4).
3.6. Five-Color FISH 1. Incubate slides in 2X SSC at room temperature for 5 min. 2. Dehydrate cellular DNA by incubating slides serially in 70, 90, and 100% ethanol, 2 min each, and air dry completely. 3. Denature cellular DNA by incubating slide in 70% formamide/2X SSC for 20 min. This denaturation time is based on 3% paraformaldehyde fixation. If less than 3% fixative was used, denaturation time can be lowered by 5–10 min. Also note, if more than one slide is to be denatured at a time, the temperature of the 70% formamide/2X SSC solution will decrease by 1°C for each additional slide. Therefore, increase the waterbath temperature accordingly. 4. During the 20 min denaturation time, begin preparing the five-probe cocktail and store on ice protected from light. 5. Immediately transfer slide to ice-cold (–20°C) 70% ethanol for 2 min followed by 2 min incubation in ice cold (–20°C) 90 and 100% ethanol. Air-dry slide completely. 6. Denature five-probe cocktail by incubating in a 70°C waterbath for 5 min. 7. Apply probe cocktail immediately to target area on slide, cover with a 22 × 22-mm glass coverslip and seal with rubber cement. 8. Place slide in 37°C humidity chamber and allow for overnight (16 h) hybridization. 9. Next morning, prewarm approx 40 mL 2X SSC in a glass Coplin jar with lid to 70°C in a waterbath. 10. Processing only one slide at a time, remove coverslip and rubber cement. Place slide in 2X SSC at 70°C for only 10 s. 11. Immediately transfer slide to 1X PBD for 1 min. 12. Apply 18 µL DAPI II counterstain to a 24 × 50-mm glass coverslip. Drain excess PBD from slide using a paper towel then place slide on top of coverslip/DAPI. Gently press out any large air bubbles. Protect from excess exposure to room light by placing slides in a slide box. 13. Allow DAPI to soak into cells for 10 min prior to viewing under fluorescence microscope. Once analysis is complete, slides are stored at 4°C in a slide box.
3.7. Microscope Analysis 1. Each chromosome is identified by a probe-specific color and each cell is analyzed for the presence of 0, 1, 2, 3 or more signals per probe. Although we have arbitrarily chosen to
score 3000 nuclei per hybridization reaction, on average only 1500 nuclei are available after flow sorting for FISH analysis (see Note 5). 2. Fetal male cells are identified by the presence of one signal each for the X (yellow signal) and the Y (blue signal) chromosomes (see Note 6). 3. Detection of fetal trisomy 13, 18, and 21 relies on scoring three distinct signals for the autosome involved. Consequently, close attention must be given to distinguish three signals from split-domain signals. Because chromosome condensation is variable in certain stages of interphase and that FISH probes are typically composed of several DNA fragments, non-fluorescent gaps will appear within a probe signal on either one or both homologs. Therefore, signals are considered to represent split-domains' when (1) the size and intensity of each of the two signals is less than that of the signal for the other homologue, and (2) the distance between the two signals is less than the diameter of either of the two signals (see Note 6).
3.8. FISH on MACS Cells There are some alterations in the FISH protocol when analysis is to be performed on MACS enriched cells from maternal blood (see Note 7).
4. Notes 1. Antibodies detected by fluorescence can affect FISH analysis when using multiple probes for aneuploidy detection. Using FITC-labeled antibody to stain for an abundant intracellular protein (i.e., gamma globin) will result in nuclei that are fluorescent all over. Thus, DNA probes labeled with fluorophores that emit in the green spectrum will be difficult to detect, limiting the number of chromosome specific probes available for FISH. Therefore, it is important to know prior to FISH those fluorophores used to label cells for FACS enrichment. 2. Temperature control of blood specimens prior to enrichment is important in maintaining suitable sample quality for subsequent separation enrichment and FISH. For overnight storage, specimens should be kept at room temperature. Extreme hot or cold temperature conditions will result in cell clumping or cell lysis, making enrichment inefficient. For shipping blood specimens, ice packs may be necessary during the summer months of the year. 3. Independent of type and density of gradient used to separate cells, it is important that the recovered cell layer be thoroughly washed to avoid cytoplasmic background and clumping of nuclei that would interfere with FISH analysis. 4. Specious particles in cytoplasma may exist, making nuclei appear to be engulfed in a haze or cloud. Probe hybridization is nearly zero. As in conventional cytogenetics, washes are inadequate and cell drying is not performed under controlled temperature and humidity conditions. To avoid this problem, cells sorted directly onto silylated slides must be allowed to dry slowly (30–60 min) on a 37°C warm plate followed by Carnoy's fixation. Following Carnoy's fixation, similar precautions need to be taken. Cytoplasmic particulate background can be especially problematic when humidity is low and rooms heated (i.e., winter). To overcome this, slides are allowed to dry slowly after Carnoy's fixation either flat or upright while placed within a small box to maintain the humidity level. Alternatively, cells collected (by FACS or MACS) in a plastic tube can be washed prior to placement on slides. To avoid cell loss, cells should not be cytocentrifuged or suspended in greater than 100–200 µL of volume for spreading onto slides.
5. Enrichment probably increases the relative frequency of fetal cells only 100 fold; thus, perhaps 1 fetal cell per 103 maternal cells exists rather than the 1 per 105 prior to enrichment. Depending on the separation and enrichment method used, the number of total cells recovered and the number of cells scanned will vary. Our group scores up to 3000 nuclei per specimen. If we fail to detect a single fetal cell after scoring 3000 nuclei, we find it unlikely that scoring additional cells will detect fetal cells. 6. Each observer should use a score sheet to record the interpretation of each cell at the time of analysis. As in clinical cytogenetics, cells are analyzed in a systematic manner from left/right and down. An experienced observer can analyze 3000 cells on one slide in 2–3 h when three probes are used or 3–5 h when five probes are used. In conventional prenatal cytogenetics, the diagnosis of fetal aneuploidy is dependent on detection in multiple colonies, but in fetal cell analysis, the detection of only one trisomic cell among enriched cells is considered sufficient as shown by correlation with subsequent fetal karyotype. Of course, this is possible only when hybridization efficiency is optimal and signals can be detected among all or most cells. 7. FISH on MACS cells is relatively easier to perform given that fixation using paraformaldehyde is either absent or done using low 1–2% concentration. After MACS, recovered nuclei should be evaluated under phase contrast. If nuclei are gray and flat, then denaturation time should be reduced considerably to 1–3 min using an 80°C oven (not formamide). If paraformaldehyde fixation is used, then denaturation time may need to be increased. If FISH signals are weak or absent, pretreatment using proteinase K or pepsin may be required.
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51. Elias, S., Lewis, D. E., Simpson, J. L., et al. (1996) Isolation of fetal nucleated red blood cells from maternal blood: persistence of cells from prior pregnancy is unlikely to lead to false positive results. J. Soc. Gynecol. Invest. 3, 359A. 52. Jansen, M. W., Brandenburg, H., Wildschut, H. I., et al. (1997) The effect of chorionic villus sampling on the number of fetal cells isolated from maternal blood and on maternal serum alpha-fetoprotein levels. Prenat. Diagn. 17, 953–959. 53. Samura, O., Sekizawa, A., Zhen, D. K., Falco, V. M., and Bianchi, D. W. (2000) Comparison of fetal cell recovery from maternal blood using a high-density gradient for the initial separation step: 1.090 versus 1.119 g/mL. Prenat. Diagn. 20, 281–286. 54. Sekizawa, A., Farina, A., Zhen, D. K., et al. (1999) Improvement of fetal cell recovery from maternal blood: suitable density gradient for FACS separation. Fetal Diagn. Ther. 14, 229–233. 55. Troeger, C., Holzgreve, W., and Hahn, S. (1999) A comparison of different density gradients and antibodies for enrichment of fetal erythroblasts by MACS. Prenat. Diagn. 19, 521–526. 56. Ganshirt-Ahlert, D., Burschyk, M., Garritsen, H. S. P., et al. (1992) Magnetic cell sorting and the transferrin receptor as potential means of prenatal diagnosis from maternal blood. Am. J. Obstet. Gynecol. 166, 1350–1355. 57. Busch, J., Huber, P., Pfluger, E., et al. (1994) Enrichment of retal cells from maternal blood by high gradient magnetic cell sorting (double MACS) for PCR-based genetic analysis. Prenat. Diagn. 14, 1129–1140. 58. Steele, C. D., Wapner, R. J., Smith, J. B., et al. (1996) Prenatal diagnosis using fetal cells isolated from maternal blood: a review. Clin. Obstet. Gynecol. 39, 801–813. 59. Wachtel, S. S., Sammons, D., Manley, M., et al. (1996) Fetal cells in maternal blood: recovery by charge flow separation. Hum. Genet. 98, 162–166. 60. Price, J. O., Elias, S., Wachtel, S. S., et al. (1991) Prenatal diagnosis using fetal cells from maternal blood by multi-parameter flow cytometry. Am. J. Obstet. Gynecol. 165, 1731–1737. 61. Sohda, S., Arinami, T., Hamada, H., Nakauchi, H., Hamaguchi, H., and Kubo, T. (1997) The proportion of fetal nucleated red blood cells in maternal blood: estimation by FACS analysis. Prenat. Diagn. 17, 743–752. 62. Lewis, D. E., Schober, W., Murrell, S., et al. (1996) Rare event selection of fetal nucleated erythrocytes in maternal blood by flow cytometry. Cytometry 23, 218–227. 63. Wang, J. Y., Zhen, D. K., Falco, V. M., et al. (2000) Fetal nucleated erythrocyte recovery: fluorescence activated cell sorting-based positive selection using anti-gamma globin versus magnetic activated cell sorting using anti-CD45 depletion and anti-gamma globin positive selection. Cytometry 39, 224–230. 64. Zheng, Y. L., DeMaria, M. A., Zhen, D. K., et al. (1995) Flow sorting of fetal erythroblasts using intracytoplasmic anti-fetal hemoglobin: Preliminary observations on maternal samples. Prenat. Diagn. 15, 897–905. 65. Serlachius, M., Von Koskull, H., Wessman, M., and Schroder, J. (2000) The use of transferrin for enrichment of fetal cells from maternal blood. Prenat. Diagn. 20, 407–410. 66. DeMaria, M. A., Zheng, Y. L., Zhen, D. K., et al. (1996) Improved fetal nucleated erythrocyte sorting purity using intracellular antifetal hemoglobin and Hoechst 33342. Cytometry 25, 37–45. 67. Latham, S. E., Suskin, H. A., Petropoulos, A. et al. (1996) A monoclonal antibody to human placental lactogen hormone facilities isolation of fetal cells from maternal in a model system. Prenat. Diagn. 16, 813–821.
68. Hengstschlager, M. and Bernaschek, G. (1997) Fetal cells in the peripheral blood of pregnant women express thymidine kinase: a new marker for detection. FEBS. Lett. 404, 299–302. 69. Zheng, Y. L., Zhen, D. K., DeMaria, M. A., et al. (1997) Search for the optimal fetal cell antibody: results of immunophenotyping studies using flow cytometry. Hum. Genet. 100, 35–42. 70. Valerio, D., Aiello, R., and Altieri, V. (1997) Isolation of fetal erythroid cells from maternal blood based on expression of erythropoietin receptors. Mol. Hum. Reprod. 3, 451–455. 71. Bigbee, W. L. and Grant, S. G. (1994) Use of allele-specific glycophorin A antibodies to enumerate fetal erythroid cells in maternal circulation. Ann. NY. Acad. Sci. 731, 128–132. 72. Murrell-Bussell, S., Nguyen, D., Schober, W. D., et al. (1998) Optimized fixation and storage conditions for FISH analysis of single-cell suspensions. J. Histochem. Cytochem. 46, 971–974. 73. Tanke, H. J., Oosterwijk, J. C., Mesker, W. E., et al. (1996) Detection of 'rare event' fetal erythroblasts in maternal blood using automated microscopy. Early. Hum. Dev. 47 Suppl, S89–S93. 74. Oosterwijk, J. C., Knepfle, C. F., Mesker, W. E., et al. (1998) Strategies for rare-event detection: an approach for automated fetal cell detection in maternal blood. Am. J. Hum. Genet. 63, 1783–1792. 75. Bischoff, F. Z., Marquez-Do, D., Nguyen, D. D., et al. (2000) Semi-automated screening of nucleated red blood cells for prenatal diagnosis using fetal cells in maternal blood. J. Soc. Gynecol. Investig. 7 Suppl, 180A. 76. Zheng, Y. L. Carter, N. P., Price, C. M., et al. (1993) Prenatal diagnosis from maternal blood: Simultaneous immunophenotyping and FISH of fetal nucleated erythrocytes isolated by negative magnetic cell sorting. J. Med. Genet. 30, 1051–1056. 77. Zheng, Y. L., Zhen, D. K., Farina, A., et al. (1999) Fetal cell identifiers: results of microscope slide-based immunocytochemical studies as a function of gestational age and abnormality. Am. J. Obstet. Gynecol. 180, 1234–1239. 78. Oosterwijk, J. C., Mesker, W. E., and Ouwerkerk, M. C. (1996) Detection of fetal erythroblasts in maternal blood by one-step gradient enrichment and immunocytochemical recognition. Early. Hum. Dev. 47 (suppl), 595–597. 79. Mesker, W. E., Ouwerkerk-van Velzen, M. C., Oosterwijk, J. C., et al. (1998) Two-colour immunocytochemical staining of gamma (gamma) and epsilon (epsilon) type haemoglobin in fetal red cells. Prenat. Diagn. 18, 1131–1137. 80. Oosterwijk, J. C., Mesker, W. E., Ouwerkerk-van Velzen, M. C., et al. (1998) Fetal cell detection in maternal blood: a study in 236 samples using erythroblast morphology, DAB and HbF staining, and FISH analysis. Cytometry 32, 178–185. 81. Oosterwijk, J. C., Mesker, W. E., Ouwerkerk-van Velzen, M. C., et al. (1998) Development of a preparation and staining method for fetal erythroblasts in maternal blood:simultaneous immunocytochemical staining and FISH analysis. Cytometry 32, 170–177. 82. Mavrou, A., Colialexi, A., Tsangaris, G. T., et al. (1998) Fetal cells in maternal blood: isolation by magnetic cell sorting and confirmation by immunophenotyping and FISH. In Vivo 12, 195–200. 83. Oosterwijk, J. C., Mesker, W. E., Ouwerkerkerk-vanVelzen, M. C., et al. (1998) Development of a preparation and staining method for fetal erythroblasts in maternal blood: Simultaneous immunocytochemical staining and FISH analysis. Cytometry 32, 170–177.
PGD for Aneuploidies by FISH
18 Preimplantation FISH Diagnosis of Aneuploidies Yury Verlinsky, Jeanine Cieslak, and Anver Kuliev 1. Introduction Preimplantation genetic diagnosis (PGD) has been introduced as a principally new approach to the prevention of genetic disorders, avoiding prenatal diagnosis and potential termination of pregnancy (1,2). It is based on the genetic testing of oocytes or embryos, with the purpose of establishing an unaffected pregnancy, rather than performing fetal diagnosis after at risk patients become pregnant, facing a risk for pregnancy termination if the fetus is affected. Although PGD was originally introduced for pre-existing genetic disorders (3,4), its application appears to be of special relevance for sporadic conditions, such as chromosomal abnormalities, which contribute significantly to pregnancy loss and infertility. PGD has presently been performed in more than 3000 clinical cycles worldwide, resulting in 700 clinical pregnancies and births of approximately 600 unaffected children (5). At least three quarters of these clinical cycles were done for the age related aneuploidies by the method of fluorescent in situ hybridization (FISH) analysis, described in detail previously in an Atlas of Preimplantation Genetic Diagnosis (6), and briefly summarized in the present chapter.
1.1. Approaches to Preimplantation Genetic Diagnosis PGD is currently performed by two major approaches, which involves the testing of either blastomeres biopsied from the cleaving embryos, or polar bodies removed from matured and fertilized oocytes. Blastomere biopsy can be done as early as the 6–8-cell stage and allows testing for both maternally and paternally derived genetic abnormalities (3,6). First and second polar body (PB1 and PB2) removal, on the other hand, allows testing exclusively for maternally derived abnormalities (4,6). Each of the two approaches has advantages and disadvantages, and are applied depending on the clinical circumstances. For example, despite a reduction in embryo cell number, which may have an influence on the embryo viability, blastomere biopsy is the method of choice for paternally derived dominant conditions and translocations, as well as for From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
18_Verlinsky_259-274F[7.10.2]
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gender determination and HLA typing. On the other hand, removal of PB1 and PB2, naturally extruded from oocytes in the process of maturation and fertilization, respectively, should not have any effect on the embryo viability, however provides no information on gender and paternal mutations. PB1 and PB2 genetic analysis is of great value for testing of the autosomal recessive conditions and the maternally derived dominant mutations and translocations. It is also a method of choice for specific diagnosis of X-linked diseases, avoiding the discard of 50% male fetuses currently seen in blastomere based gender determination. Finally, because over 90% of chromosomal errors originate from maternal meiosis, the PB approach may be of special value for PGD of aneuploidies. This approach is also of importance due to a relatively high rate of mosaicism at the cleavage stage, which is recognized as the major limitation of the blastomere based PGD for chromosomal disorders (see below).
1.2. Preimplantation FISH Diagnosis PGD for the age related aneuploidies is currently done by FISH analysis, using commercially available chromosome specific probes (Vysis, Downers Groves, IL). It was first applied in 1991 for gender determination using DNA probes specific either for the X or Y chromosome (7). Since testing for only one of the sex chromosomes could lead to misdiagnosis of gender due to a possible failure of hybridization, a dual FISH was introduced, involving the simultaneous detection of X and Y, each in different color (8). Further, the dual FISH analysis was combined with a ploidy assessment to improve the accuracy, by adding a centromeric probe specific for chromosome-18 (9,10). Testing was then extended to up to five autosomes, including chromosomes 13, 16, 21, and 22 (11,12), although it is currently possible to analyze up to a dozen chromosomes, using additional rounds of rehybridization (12,13). The overall experience of preimplantation FISH analysis currently involves more than 2000 clinical cycles, resulting in an improved pregnancy rate in poor prognosis IVF patients (5). Approximately half of these cycles were performed by FISH analysis of blastomeres and half by FISH analysis of PB1 and PB2, resulting in hundreds of unaffected pregnancies and healthy children born at the present time. The follow up confirmation studies of the preselected abnormal embryos, and the babies born following the procedure, demonstrated an acceptable accuracy of the FISH analysis, which is described below. Examples of normal and abnormal FISH patterns in PB1, PB2 and blastomeres are presented in Fig. 1.
1.2.1. FISH Analysis in Blastomeres The reliability of the FISH technique for aneuploidy detection in blastomeres has been extensively studied (14–17). By comparing the FISH results in the cleaving embryos to morphological abnormalities and maternal age, it was established that the observed chromosomal abnormalities were not related to the limitations of the FISH technique, but were due to the embryo variables (14,15). However, a high rate of mosaicism was observed at the cleavage stage (15–17), which was particularly high in slow embryos exhibiting an arrested development. An overall 12% mosaicism rate was shown to be a common feature in cleaving embryos (18), which represents a major limitation of the FISH analysis of aneuploidies performed at this stage. This may affect
Fig. 1. Normal pattern of FISH signals and abnormalities detected by five-color probe in the first and second polar bodies and blastomeres. (A) Normal paired signals for chromosomes 13, 16, 18, 21, and 22 in the first polar body (a total of ten signals), and one signal for the same chromosomes in the second polar body (a total of 5 signals; on the bottom left corner). (B) Normal blastomere nucleus, two signals for each pair of chromosomes studied (a total of ten signals. (C) Extra signal for chromosome 18 in the first polar body (shown by three arrows) and a normal pattern of signals for other chromosomes in the first and all five chromosomes in the second polar body (one signal for chromosome 18 in the second polar body is shown by one arrow). The extra signal for chromosome 18 in the first polar body indicates a lack of one of the chromosome 18 in the corresponding oocyte, which will lead to monosomy 18 in the resulting embryo, following the extrusion of this one chromatid to the second polar body. (D) Three signals for chromosome 21 in blastomere nucleus and metaphase chromosomes (shown by three arrows) indicating trisomy 21 in the embryo. All other chromosomes probed showed a normal signal pattern (a total of 11 signals instead of 10). (E) Missing signals for chromosomes 13 and 18 in the second polar body (a total of three signals instead of the expected 5; bottom left corner). (F) Double trisomy 13 and 18 in the resulting embryo, orignating from the oocyte shown in (E). The embryo is mosaic for trisomy 18, evident by the presence of three signals for chromosome 18 in the cell on the left (three arrows, showing only chromosome 18 in this nucleus) and five signals for this chromosome 13 and 18 in the cell on the right (five arrows showing only signals for chromosomes 13 and 18), instead of the expected six signals for the chromosomes 13 and 18 in this double trisomy embryo.
a diagnostic accuracy only partially, because the abnormal cell detection from a mosaic embryo will not lead to transfer. An average clinically relevant proportion of mosaicism has been calculated to be in the range 5% (19). Mosaicism at the cleavage stage is shown in Fig. 1F. It has recently been shown that mosaicism will also present diagnostic problems at the blastocyst stage (20) despite the initial prediction that the abnormal cells are deviated mainly to trophectoderm.
1.2.2. FISH Analysis of the First Polar Body PB1 is the by product of the first meiotic division, extruded during maturation of oocyte. The first attempt to use FISH analysis for testing PB1 was undertaken in 1994 (21–23). In this work, 130 unfertilized M-II oocytes were tested simultaneously with their PB1 using X-chromosome and chromosome 18 specific probes. It was demonstrated that PB1 FISH data allows an exact prediction of the chromosome set in the corresponding oocytes (21,23). Each chromosome in PB1 was represented by double dots (signals), corresponding to two chromatids in each univalent (Fig. 1A). The data suggested that the number of signals (chromatids) in PB1 reliably predicts the corresponding number of signals (chromatids) in the MII oocytes, thereby providing an excellent tool for the genetic pre-selection of oocytes. It was also of interest, that in addition to a normal distribution of signals in PB1 and the corresponding MII oocytes, meiotic errors were also detected, confirming the accuracy of PB1 diagnosis for predicting the genotype of the corresponding oocyte. For example, in one PB1, four signals for chromosome 18 were detected, perfectly in accordance with the lack of the chromosome 18 signals in the corresponding MII oocyte (chromosome 18 nondisjunction). This suggested that the chromosomal complements of the oocyte could be inferred from the testing of PB1, which can be removed following its extrusion from the mature oocyte with no potential influence on the embryo viability. Another interesting phenomenon was the observation of chromatid mal-segregation as a possible cause of chromosomal aneuploidy in the resulting mature oocytes (see an example of extrachromatid signal in Fig. 1C). In four oocytes, instead of the expected two signals, three were found in the MII oocytes, which perfectly corresponded to a single signal in the corresponding PB1. Similar results were reported by another group, confirming diagnostic significance of the PB1 FISH analysis for predicting the genotype of the preimplantation embryo (24).
1.2.3. FISH Analysis of the Second Polar Body PB2 is the by product of the second meiotic division, extruded following fertilization of oocyte. The need for FISH analysis of PB2 for PGD of aneuploidies was first proposed in 1995, when it was demonstrated that PB1 testing alone does not allow predicting the resulting genotype of the oocyte (22). It was shown that in contrast to the paired dots in PB1, each chromosome in PB2 was represented by a single dot (see left upper panel in Fig. 1A), so the lack of or addition of a signal for a particular chromosome provided evidence of a second meiotic division error. Although only 19 of 55 oocytes in this first study were tested by both PB1 and PB2, evidence for a possible error in both PB1 and PB2 was presented. This data suggested that some
oocytes selected as normal, based on the PB1 FISH analysis, could still appear to be abnormal following non-disjunction in the second meiotic division (Fig. 1E). Therefore, FISH analysis for both PB1 and PB2 has become the basic requirement for PGD of aneuploidies, which allows detection of errors in both the first and second meiotic divisions. Currently, more than 5000 oocytes have been analyzed by FISH analysis, showing the accuracy and reliability of PB1 and PB2 testing for predicting the karyotype of the embryo, resulting from the corresponding oocyte. The data demonstrated 50% aneuploidy rate in oocytes from IVF patients of advanced maternal age (25–27), resulting from the errors in both the first and second meiotic divisions, in contrast to the previously believed concept that aneuploidies mainly originate from meiosis I (28).
2. Materials 2.1. Preparation of PB1 and PB2 and Blastomeres, Following their Removal from Oocytes and Embryos 2.1.1. Preparation of PB1 and PB2 Microscope slides (25 × 75 × 1 mm) (Fisher Healthcare, Houston, Texas). Culture flask (50 mL) (Fisher Healthcare, Houston, Texas). 5 3/4" Pasteur pipets. Mouthpiece with tubing to hold micropipette (Sigma, St. Louis, MO, Cat. no. A-5177). Carbide marker for engraving glass (Fisher Healthcare, Cat. no. 13-378). Lead pencil and permanent marker. Rubber bulb for blow drying. Glacial acetic acid *. Methanol *. HPLC grade H2O (Mallinckrodt Baker Inc., Paris, Kentucky). Stereomicroscope. Inverted microscope with phase contrast optics, ×10 and ×20 objectives (Olympus CK 40, Olympus America Inc., Melville, NY). 13. Microtorch (Blazer Corporation, New York, NY). 14. Micropipets (1–5 µL) (Drummond Scientific, Broomall, Penn.). 15. Hanging drop slide (engrave a circle in the bottom center using a carbide marker) Fisher Healthcare, Cat. no. 12-560. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
2.1.2. Preparation of Blastomeres The items 1–13 under Subheading 2.1.1. and the following additional materials are needed: 1. 2. 3. 4. 5.
Micropipets (25–50 µL) (Drummond Scientific). 35 × 10 mm Petri dishes (Falcon) (Fisher Healthcare, Cat. no. 08-757-100A). Bovine serum albumin (BSA) (Sigma, Cat. no. A-3311). Sodium citrate. Hypotonic solution containing 6 mg/mL of BSA and 1% sodium citrate is dissolved in HPLC H2O, filtered through a 0.2 µm filter and stored at 5°C.
*Store previously opened bottles at 5°C to reduce water absorption from the atmosphere.
2.2. Pretreatment 1. 2. 3. 4. 5. 6. 7. 8.
Graduated cylinders and serological pipets. Coplin jars (8). Pepsin (Vysis, Downers Grove, Il, Cat. no. 30-801265). Hydrochloric acid (2N). Magnesium chloride. Phosphate buffered saline (Irvine Scientific, Santa Ana, CA). Neutral buffered formalin (10%) (w/v 4% Formaldehyde) (VWR, Chicago, Il Cat. no. 3239). 20X SSC Solution: Dissolving 175.3 g of sodium chloride and 88.2 g sodium citrate in 1 L of HPLC H2O and adjusting pH to 5.3. pH adjustments are made using a HCl (1 N) solution. Filtered through a 0.45 µm pore filtration unit, and stored at room temperature for up to 6 mo. 2X SSC Solution: Adding 100 mL of 20X SSC to 900 mL of HPLC grade water and pH to 7.0–7.5; filtered and stored at room temperature for up to 6 mo, with working solution to be changed weekly. 1% Formaldehyde: Combining 30 mL of buffered neutral formalin (10%), 90 mL of 1X PBS and 0.54 g MgCl. This 1% formaldehyde solution can be stored at 5°C and the working solution changed weekly. 0.5 mg/mL Pepsin solution: Combining 25 mg of pepsin per 50 mL of 0.01 N HCl. Fresh pepsin solution is prepared every 1–2 wk and maintained at 37°C. Ethanol series: (70, 85, 100%): Diluting ethyl alcohol with HPLC grade water. Methanol.
2.3. Application of Probes, Denaturation and Hybridization 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Slide warmer (capable of consistent temperature, i.e., 68–73°C). Air incubator (set at 37°C). Microcentrifuge. Vortex. Calibrated thermometers (for slide warmer, incubator and waterbath). Micropipetors (2–20 µL, 20–200 µL) and appropriate sterile tips. Glass dishes with removable tray (Fisher Healthcare, Cat. no. 08-812). Coverslips (22 × 30 mm) (Corning) (Fisher Healthcare, Cat. no. 12-531A). Microcentrifuge tubes. Forceps (fine tip). Parafilm (Fisher Healthcare, Cat. no. 13-374-10). Directly labeled probes commonly used for PGD of aneuploidies Vysis: Chromosome 13 Locus Specific Identifier (LSI) # 32-192018 Spectrum green; Chromosome 18 Centromeric Enumeration Probe (CEP) Cat. no. 32-131018 Spectrum aqua; Chromosome 21 Locus Specific Identifier (LSI) Cat. no. 32-190002 Spectrum orange; X & Y Centromeric Enumeration Probe Cat. no. 32-131051 Green X, Orange Y; MultiVysion PGT Chromosomes X, Y, 13, 18, and 21 Cat. no. 32-131080; MultiVysion PB Panel, Chromosomes 13, 16, 18, 21, and 22 Cat. no. 32-131085.
2.4. Washing and Counterstain Application 1. 2. 3. 4.
Sodium chloride. Sodium citrate. HPLC grade H2O (see Subheading 2.1.1). NP-40 (Vysis, Cat. no. 32-804818).
PGD for Aneuploidies by FISH 5. 6. 7. 8. 9. 10. 11.
Sodium hydroxide solution (1 N). Hydrochloric acid (1 N). Water bath (capable of maintaining temperatures up to 100°C). pH meter and standards. Vectashield antifade mounting medium (Vector Labs, Cat. no. H-1000 ). DAPI counterstain (Sigma, Cat. no. D1388). 0.4X SSC/0.3% NP-40: combine 20 mL 20X SSC, pH 5.3, 977 mL HPLC grade water and 3 mL NP-40. Mix thoroughly until NP-40 is dissolved. Adjust pH to 7.0– 7.5 with NaOH. Add water to bring the final vol to 1 L, and filter through a 0.2 µm pore filtration unit. Store unused solution at room temperature for up to 6 mo. 2X SSC/0.1% NP-40: 100 mL 20X SSC, pH 5.3, 899 mL HPLC grade water and 1 mL of NP-40. Mix thoroughly and measure pH at room temperature. Adjust pH to 7.0–7.5 with NaOH. Add water to bring the final vol to 1 L, and filter through a 0.2 µm pore filtration unit. Store unused solution at room temperature for up to 6 mo. Discard used solutions at the end of each day. 0.7X SSC/0.3% NP-40: 35 mL 20X SSC. pH 5.3, 962 mL HPLC grade water and 3 mL NP-40. Mix thoroughly until NP-40 is dissolved. Adjust pH to 7.0–7.5 with NaOH. Add water to bring the final vol to 1 L. DAPI stock solution: Prepare a stock solution of DAPI counterstain (1 mg/mL) in HPLC H2O. DAPI working solution: The working solution (0.5 µg/mL) is prepared by adding 50 µL of DAPI stock solution to 100 mL of HPLC H2O. Store at –20°C. DAPI /antifade: DAPI working solution is combined with Vectashield antifade mounting medium, 1: 1, and stored at –20°C until needed.
2.5. Signal Evaluation 1. Microscope (Microphot FXA - Nikon) with epifluorescence attachment. 2. Single bandpass filters (Chroma Tech.) for all fluorophores: DAPI (blue), FITC (green), TRITC (red), AQUA (aqua), F15 (gold), and F6 (blue). 3. Dual - bandpass FITC/TRITC (red and green), Aqua /Blue and triple-bandpass DAPI/ FITC/TRITC (red, green, and blue) filters are also recommended. 4. Photographic equipment: 35-mm camera loaded with P400 Kodak Ektachrome film or a CCD camera, filter wheel and computer with imaging software (Quips Imaging Workstation, Applied Imaging, Santa Clara, CA). 5. Immersion oil (fluorescence) (Cargille Laboratories, Ins, Cedar Grove, NJ, Cat. no. 16212).
3. Methods 3.1. Preparation of PB1 and PB2 and Blastomeres for FISH Analysis, Following Their Removal from Oocytes and Embryos 3.1.1. Preparation of PB1 and PB2 1. Prepare fresh fixative (methanol and glacial acetic acid, 3:1) in a 50 mL culture flask and store in the freezer until needed. 2. Pull micropipettes over the flame of the microtorch to obtain an attenuated tip with an inner diameter of approximately 50 µm. A larger diameter may lead to a potential PB loss. 3. Clean again, already precleaned glass slides using fixative to remove any grease or dirt, which may be on the slide. This is achieved by dropping a few drops of fixative and wiping with a lint free tissue.
4. Fill the hanging drop slide with HPLC H2O using a pasteur pipet. 5. After oocytes/zygotes have been manipulated and PB removal has been accomplished, the PB(s) can be found in the micromanipulation dish in a 20 µL drop of culture medium under oil (6) using an inverted microscope with phase contrast optics (×10 and ×20 objectives). 6. Once located, using the micropipet, a small amount of water is aspirated to insure proper control of fluid in and out of the pipet. 7. After aspiration of a small amount of water, the PB is aspirated into the pipet and brought to the hanging drop slide containing water. The PB is released from the pipet by blowing gently until it is visualized in the center circle of the hanging drop slide. Do not allow the polar body to settle and stick to the glass surface of the hanging drop slide. 8. Once rinsed in the water, the PB is aspirated again into the pipet. Any oil surrounding the pipet usually is removed by going through the water. The PB is transferred to a clean slide and a drop of water containing the PB is released from the pipet by gently blowing. 9. After partial evaporation of the water, the PB will swell and begin to flatten out onto the slide. Prior to complete drying of the water, a drop of fixative is placed on top of the PB from the same micropipet to obtain spreading of the chromatin. 10. Prior to complete drying, another drop of fixative is placed on top of the polar body and repeated if necessary until the cytoplasm dissolves. Careful attention is paid to observe this process and to thoroughly remove all cytoplasm (see Notes 1 and 5). 11. The location of the chromatin is defined by encircling using the carbide marker, taking care to lightly engrave the glass to avoid interference from glass fragments. A second heavier circle is engraved on the bottom of the slide to easily locate the smaller circle and thus the chromatin at the time of analysis. 12. The slide is marked with the patient's name and the corresponding oocyte number, along with pertinent information such as the number of pieces of chromatin. 13. Additional drops of fixative are added to the slide and blown dry using a rubber bulb. 14. Slides can be stored at room temperature overnight before hybridization or if hybridized immediately, a pretreatment method is recommended. Results can be obtained well within a reasonable time frame for embryo transfer. 15. Using a permanent marker, the area in which the PB chromatin is enclosed is marked from the back of the slide. This determines the area in which the probe is to be placed.
3.1.2. Preparation of Blastomeres 1. Prepare fresh fixative (methanol and glacial acetic acid, 3:1) in a 50 mL culture flask and store in the freezer until needed. 2. Engrave a circle in the bottom of a 35 × 10 mm Petri dish and add 3 mL of hypotonic solution. The circle allows easy location of blastomeres. 3. Using a microtorch, 25–50 µL micropipets are pulled to obtain an attenuated tip approximately 70 µm in diameter. 4. Aspirate a small amount of hypotonic solution into the pipet. 5. The blastomere contained in a microdrop of culture medium is located using a stereomicroscope. The size of the pipet opening is checked prior to picking up the blastomere to insure it is larger than the blastomere. Gently aspirate the blastomere into the pipet and transfer it to the Petri dish containing hypotonic solution. 6. After 3–5 min, the blastomere is aspirated into the pipet and transferred to a microscope slide with a small amount of hypotonic solution. 7. Under the control of the inverted microscope with phase contrast optics, the blastomere is constantly observed until drying is almost complete. Just prior to crystallization of the
hypotonic solution, the fixative is aspirated into the pipet and dropped onto the blastomere. While constantly observing the cell, just before drying occurs, fixative is dropped again. This is done several times until the cytoplasm has dissolved with only the nucleus remaining. Complete removal of the cytoplasm is essential to hybridization (see Note 1). 8. Using the carbide marker, the nucleus is encircled for easy location after hybridization. 9. After recording pertinent information on the frosted area of the slide, several drops of fixative are added to the slide and blown dry using a rubber bulb. 10. The slides are pretreated. Just prior to probe application, the exact location of the nucleus is indicated on the bottom of the slide using a permanent marker. This defines the area in which to apply the probe.
3.2. Pretreatment 1. 2. 3. 4. 5. 6. 7.
Incubate slides 10 min in 2X SSC, pH 7.0–7.5, at 37°C. Fix slides for 5 min in 1% formaldehyde at ambient temperature. Wash slides 5 min in 1X PBS, pH 7.0–7.5, at ambient temperature. Incubate slides 5 min in 0.5 mg/mL pepsin in 0.01 N HCI at 37°C. Wash 5 min in 1X PBS at ambient temperature. Drain slides and wipe the back of the slides to remove excess PBS. Immerse slides sequentially in 70, 85, and 100% ethanol at ambient temperature for one minute, air dry and proceed with hybridization. 8. For the purpose of rehybridization, prior to pretreatment, coverslips are removed from the slides and the slides are placed in methanol for 5 min to insure fixation of the chromatin to the slide.
3.3. Probe Application, Hybridization and Wash 3.3.1. Probe Mixtures Probe mixtures are prepared according to the manufacturer specifications. 1. Prepare a 3 color probe mixture by first centrifuging, then vortexing each of the probes of interest and 1 vial of LSI hybridization buffer for 10 s. For 10 µL of working probe, i.e., chromosomes 13, 18 and 21, add 1 µL of each probe to 7 µL of LSI hybridization buffer in a small microcentrifuge tube. Vortex and centrifuge to mix. 2. For a single chromosome probe mixture, add 1 µL of probe and 2 µL of HPLC H 2O to 7 µL of hybridization buffer. For an X & Y CEP probe mixture, vortex and centrifuge the probe and 1 vial of CEP hybridization buffer. For 10 µL of working probe, add 1 µL of X and Y probe to 7 µL of CEP hybridization buffer and then add 2 µL of HPLC H2O. Vortex and centrifuge for 10 s. 3. MultiVysion 5 color probe mixtures are ready to use. Centrifuge and vortex prior to probe application. All working probe mixtures can be stored at –20°C for several months according to the manufacturers expiration date.
3.3.2. Hybridization Procedure 1. Prior to probe application, 22 × 30 mm coverslips are cut into 8 × 8 mm squares using a carbide marker and stored in a glass Petri with lid. 2. Parafilm is cut into approximately 22 × 22 mm squares and stored in a Petri dish. 3. A humidification chamber for hybridization is prepared by placing a paper towel moistened with sterile filtered water into a glass (staining) dish and the slide rack is placed inside and covered. The humidification chamber is warmed in an air incubator at 37°C prior to the application of the working probe.
4. The working probe is removed from the freezer, centrifuged for 10 s, and mixed by vortexing. 5. Using a micropipetor, 2 µL of working probe is applied to the marked area in which the chromatin is located. Immediately after application of the probe, an 8 × 8 mm coverslip is placed on top using forceps. Avoid air bubbles, which interfere with hybridization. If any air bubbles should appear, depress the coverslip lightly using forceps. 6. Coverslips can be sealed using rubber cement or parafilm. When applying parafilm, insure adhesion to the slide by pressing down around the coverslip (see Note 2). 7. The slides are placed on the slide warmer at 69°C for 8 min for simultaneous denaturation of both probe and specimen nucleic acids. Afterward, they are removed from the slide warmer and quickly transferred to the humidification chamber, which is placed in a 37°C air incubator for hybridization to occur (see Notes 3 and 4).
3.3.3. Washing Procedures The following two wash protocols save time, do not require formamide and are routinely used in our laboratory. 3.3.3.1. RAPID WASH I This wash is used for 1–3 color probe mixtures and MultiVysion PGT—Chromosomes 13, 18, 21, X, Y 1. Fill a Coplin jar with 0.4X SSC/0.3% NP-40, pH 7.4, and place in a 73°C waterbath. Using a calibrated thermometer, check the temperature of the solution inside the jar before adding slides for the wash procedure. The solution temperature should be 73 ± 1°C. 2. Fill a second Coplin jar with 2X SSC/0.1% NP-40, pH 7.4, and place at room temperature. 3. Place slide(s) in the 0.4X SSC/0.3% NP-40 immediately after removing the coverslip. When all the slides are in the jar (maximum of 4) incubate for 5 min. 4. After 5 min, remove the slide(s) from the wash solution and place in the Coplin jar, containing 2X SSC/0.1% NP-40 at room temperature. Incubate for l min. 5. Remove the slide(s) from the wash solution, dip slides in a Coplin containing HPLC grade water and place vertically to drain on a paper towel in a dark area (such as a drawer).
3.3.3.2. RAPID WASH II This wash is used for MultiVysion PB panel probe—Chromosomes 13, 16, 18, 21, and 22. 1. Fill a Coplin jar with 0.7X SSC/0.3% NP-40, pH 7.4, and place in a 73°C waterbath. Using a calibrated thermometer, check the temperature of the solution inside the jar before adding slides for the wash procedure. The solution temperature should be 73 ± 1°C. 2. Fill a second Coplin jar with 2X SSC/0.1% NP-40, pH 7.4, and place at room temperature. 3. Place slide(s) in the 0.7X SSC/0.3% NP-40 immediately after removing the coverslip. When all the slides are in the jar (maximum of 4) incubate for 7 min. 4. After 7 min remove the slide(s) from the wash solution and place in the Coplin jar, containing 2X SSC/0.1% NP-40 at room temperature. Incubate for 1 min. 5. Remove the slide(s) from the wash solution, dip slides in a Coplin containing HPLC grade water and place vertically to drain on a paper towel in a dark area (such as a drawer).
3.3.4. DAPI Counterstain 1. Apply approx 10 µL to each slide and covered with a 22 × 30 mm coverslip. 2. Slides are blotted using a paper towel or paper blotter to evenly spread and remove excess medium from the slide. (For hybridizations using MultiVysion 5–color probe mixtures, Vectashield antifade mounting medium is applied without DAPI).
3.4. Signal Evaluation 1. Signals are determined under ×600 magnification using fluorescence immersion oil. Fluorophores are readily photobleached by exposure to light. To limit this degradation, handle all solutions containing fluorophores in reduced light. This includes all steps involved in handling the hybridized slide. Carry out all steps, which do not require light for manipulation (incubation periods, washes, etc.) in the dark (see Note 2). 2. Fluorescence microscopy is accomplished using a 100 W mercury lamp. Although the manufacturer recommends no more than 200 h of use, hybridization signals begin to appear dim after 175 h, creating potential for misdiagnosis. Replacement bulbs must be on hand. 3. For the MultiVysion PGT probe, chromosome X is seen in blue, chromosome Y is seen in gold, chromosome 13 is seen in red, chromosome 18 is seen in aqua and chromosome 21 is seen in green (see Notes 7 and 8). 4. For the MultiVysion PB Panel probe: chromosome 13 is seen in red, chromosome 16 is seen in aqua, chromosome 18 is seen in violet blue, chromosome 21 is seen in green and chromosome 22 is seen in gold (Fig. 1) (see Notes 7 and 8). 5. Visualization of signals is performed using the appropriate single band pass filters for the probe fluorophores (red, green, blue, gold, aqua and DAPI). Dual or triple band pass filters are useful in distinguishing signals from nonspecific fluorescence or bleed through usually seen with centromeric enumeration probes, which hybridize to alphoid repeat sequences resulting in large bright signals (see Note 7). 6. When determining the number of signals present, consider the size and intensity of each signal especially when in close proximity to one another. Chromosomes 13, 21, and 22 are identified using locus specific identifier DNA probes that contain specific sequences homologous to the chromosomes of interest as well as unlabeled blocking DNA to suppress common sequences. These result in smaller round signals when compared to signals from centromeric enumeration probes which hybridize to a greater number of alpha repeat sequences identifying chromosomes 16,18, X, and Y (see Notes 6 and 7). 7. Signals for different chromosomes which are within close proximity of one another to the point of overlapping, are distinguished from nonspecific hybridization by close examination using both single and dual bandpass filters. Upon imaging, the overlapping portion of the signals may appear yellow or even white because of the fluorophore combination (see Notes 7 and 8). Use of an imaging system is highly recommended when using probe mixtures containing greater than 3 colors. 8. PB1 contains two chromatids for each chromosome, so the signals for each chromosome are paired, at least 1 domain apart and of equal size (see Fig. 1A, C, E). However, if chromatids are in close proximity of one another, the signals may appear as one fluorescent strip (see Fig. 1E for chromosome 16 signals in PB1), representative of two chromatids (see Notes 6 and 9). 9. PB2 contains single chromatids for each chromosome, therefore, resulting in one fluorescent signal for each chromosome tested (see Fig. 1A, C, E).
10. Two, single dot signals for each chromosome studied are normally observed in each blastomere nucleus (see Fig. 1B, D, F). However, signals can appear as double dots depending upon the stage of the cell cycle, degree of chromatin condensation and overspreading. After replication, a signal may appear as paired dots < 1 domain apart or as a strip consisting of two interconnected dots. These signals are counted as one signal according to standard criteria (see Notes 7 and 8). 11. If signals are of equal size and intensity and are 2 domains apart they are counted as two separate signals. However, proximity of two separate signals may be even closer than two domains in highly condensed nuclei and must be considered in order to avoid a misdiagnosis. Size and intensity of the signals of the individual nuclei as well as additional nuclei on the same slide must be taken into consideration when distinguishing nonspecific fluorescence from actual signals. Hybridization spots of lower intensity, smaller in size or with a flat, nonfluorescing appearance are not counted (see Notes 6 and 7).
4. Notes 1. Prior to performing FISH, it is imperative that chromatin of blastomeres and PB1 and PB2 is completely isolated, free of cytoplasm, and thoroughly affixed to the microscope slide. Therefore, prior to applying fluorescent probes, slides with fixed PB or blastomeres are pretreated to maintain chromatin morphology and remove any residual cytoplasm. Residual cytoplasm poses the greatest interference to the formation of new specific hybrids during the reannealing of nucleic acids and appears as nonspecific fluorescence, making diagnosis difficult. This is an important step to overcome. Inadequate isolation of the chromatin and presence of cellular debris may result in nonspecific fluorescence after hybridization, rendering interpretation of signals difficult or even impossible. 2. Standardization and quality control monitoring of all steps involved in the FISH process, including fixation, is crucial to signal quality and interpretation. A lymphocyte control slide must be run with every assay to insure specificity. 3. Hybridization can vary from 2 h (CEP and LSI probes) to 16 h (whole chromosome paints and subtelomeric probes) depending upon the probe mixture used. Hybridization with MultiVysion probes, in which DAPI counterstain is not used, should not exceed 3 h. This is due to the strong background intensity of the chromatin that may occur with aqua labeled placental DNA present in the probe mixture. The recommended hybridization time for MultiVysion probes is 2 h for blastomeres and should not exceed 3 h for polar bodies. 4. The Hybrite (Vysis) can be used instead of a slide warmer and incubator oven for the simultaneous denaturing and hybridization of nucleic acids (maximum of 12 slides). A program is edited for a melting temperature of 69°C for 8 min followed by hybridization at 37°C for 3–16 h. A few milliliters of water are placed in each trough along the slide warmer for humidity, especially important for overnight hybridizations. Slides are placed on the Hybrite slide warmer after the probe is applied and covered with a coverslip and parafilm. The cover is closed and the program is started. Slides are left undisturbed until the hybridization period is over. A slide thermometer should be used to insure proper function, i.e., accurate melting temperature, prior to initiating a program. 5. Inadequate PB1 fixation in which residual cytoplasm is present may result in hybridization failure due to the inability of probe nucleic acids to access nucleic acids in the fixed specimen. If new hybrids should form, signals may appear faint and /or pulverized with multiple dots. This is often seen with excessively degenerate 1st polar bodies. Inadequate fixation of the chromatin along with cellular debris may result in nonspecific fluorescence after hybridization rendering interpretation of signals difficult or even impossible.
6. Diffuse or multiple dot signals (pulverization) may be seen from time to time involving one probe or all probes, regardless of procedure standardization, making interpretation complex. This is usually a result of chromatin degradation. The quality of both PB1 and PB2 signals must be taken into consideration, particularly when diffuse or split signals are present. 7. Nonspecific hybridization will fluoresce on two or more single band pass filters at the same, exact location and usually appears dull. Occasionally, bleed through of extremely bright signals can be seen with filters not intended for the specific fluorophore. They are seen as dull, flat fluorescing areas distinguishable from specific signals. This is often seen with probes that target alpha satellite repeat sequences, which generally result in diffuse bright signals. 8. Intense nonspecific hybridization is also ruled out by examination with the appropriate single and dual bandpass filters. Blastomere nuclei without hybridization signals, which are free of cytoplasm and located on the same slide with other nuclei in which signals are visible, are considered abnormal. Under these conditions, the absence of signals cannot be attributed to hybridization failure. This is not uncommon, especially if variation in size between nuclei is evident or if nuclei are fragmented. 9. In evaluating fluorescent signals in PB1, removed following fertilization assessment, e.g., 24 h after retrieval, signals representing each chromatid may be located further apart as separation of the chromatids occurs with aging. These pre-divided signals are considered normal, making signal number even easier to ascertain (see the chromosome 22 gold signals in PB1 in Figure 1A, and also the chromosome 18 signals in PB1 in Fig. 1E). 10. A high accuracy and reliability of preimplantation FISH diagnosis for aneuploidies, using blastomeres and PB1 and PB2 were demonstrated by confirmation studies of the whole embryos which were predicted abnormal and by the follow-up cytogenetic testing of outcomes of more than 500 clinical pregnancies yielded from approx 2000 PGD cycles (5).
References 1. Verlinsky, Y. and Kuliev, A. M. (eds.) (1993) Preimplantation diagnosis of genetic diseases: A new technique in assisted reproduction. Wiley-Liss, New York. 2. Edwards, R. G. (ed.) (1993) Preconception and Preimplantation Diagnosis of Genetic Diseases. Cambridge University Press, Cambridge. 3. Handyside, A. H., Kontogiani, E. H., Hardy, K., and Winston, R. M. L. (1990) Pregnancies from biopsied human preimplantation embryos sexed by Y-specific DNA amplification. Nature 344, 768–770. 4. Verlinsky, Y., Ginsberg, N., Lifchez, A., et al. (1990) Analysis of the first polar body: preconception genetic diagnosis. Hum. Reprod. 5, 826–829. 5. International Working Group on Preimplantation Genetics. (2001) Preimplantation Genetic Diagnosis: Experience of Three Thousand Clinical Cycles. Report of the 11thAnnual Meeting of International Working Group on Preimplantation Genetics, in Association with 10th International Congress of Human Genetics, Vienna, May 15, 2001. Reprod. BioMed. Online 3 (in press). 6. Verlinsky, Y. and Kuliev, A. (2000) Atlas of Preimplantation Genetic Diagnosis. Parthenon, London, N. Y. 7. Griffin, D. K., Handyside, A. H., Penketh, R. J. A., Winston, R. M. L., and Delhanty, J. D. A. (1991) Fluorescent in-situ hybridization to interphase nuclei of human preimplantation embryos with X and Y chromosome specific probes. Hum. Reprod. 6, 101–105.
8. Griffin, D. K., Wilton L. J., Handyside, A. H., Winston, R. M. L., and Delhanty, J. D. A. (1992) Dual fluorescent in-situ hybridization for the simultaneous detection of X and Y chromosome specific probes for the sexing of human preimplantation embryonic nuclei. Hum. Genet. 89, 18–22. 9. Schrurs, B. M., Winston, R. M. L., and Handyside, A. H. (1993) Preimplantation diagnosis of aneuploidy using fluorescent in-situ hybridization: Evaluation using a chromosome 18-specific probe. Hum. Reprod. 8, 296–301. 10. Munne, S., Weier, H. U. G., Stein, J., Grifo, J., and Cohen, J. (1993) A fast and efficient method for simultaneous X and Y in-situ hybridization of human blastomeres. J. Assisted Reprod. Genet. 10, 82–90. 11. Munne, S., Lee, A., Rozenwaks, Z., Grifo, J., and Cohen, J. (1993) Diagnosis of major chromosome aneuploidies in human preimplantation embryos. Hum. Reprod. 8, 2185–2191. 12. Munne, S., Magli, M. C., Bahce, M., Fung, J., Legator, M., and Morison, L. (1998) Preimplantation diagnosis of the aneuploidies most commonly found in spontaneous abortions and live births: XY, 13, 14, 15, 16, 18, 21, 22. Prenat. Diagn. 18, 459–1466 13. Bahce, M., Cohen, J., and Munné, S. (1999) Preimplantation genetic diagnosis of aneuploidy: Were we looking at the wrong chromosomes? J. Assist. Reprod. Genet. 16, 154–159. 14. Munné, S., Alikani, M., Tomkin, G., Grifo, J., and Cohen, J. (1995) Embryo morphology, developmental rates and maternal age are correlated with chromosome abnormalities. Fertil. Steril. 64, 382–391. 15. Munné, S., Weier, H. U. G., Grifo, J., and Cohen, J. (1994) Chromosome mosaicism in human embryos. Biol. Reprod. 51, 373–379. 16. Delhanty, J. D. A., Griffin, D. K., and Handyside, A. H. (1993) Detection of aneuploidy and chromosomal mosaicism in human embryos during preimplantation sex determination by fluorescent in situ hybridisation (FISH). Hum. Molec. Genet. 2, 1183–1185. 17. Harper, J. C., Coonen, E., Handyside, A. H., Winston, R. M. L., Hopman A. H. N., and Delhanty, J. D. A. (1994) Mosaicism of autosomes and sex chromosomes in morphologically normal monospermic preimplantation human embryos. Pren. Diagn. 15, 41–49. 18. International Working Group on Preimplantation Genetics. (1997) Current Status of Preimplantation Diagnosis. J. Assist. Reprod. Genet. 14, 72–75. 19. International Working Group on Preimplantation Genetics (2001) 10th Anniversary of Preimplantation Genetic Diagnosis. J. Assist. Reprod. Genet. 18, 66–72. 20. Evsikov, S. and Verlinsky, Y. (1998) Mosaicism in inner cell mass of human blastocysts. Hum. Reprod. 13, 3151–3155 21. Dyban, A., Fredine, M., Severova, E., et al. (994) Detection of aneuploidy in human oocytes and corresponding first polar bodies using FISH. 7th International Conference on Early Prenatal Diagnosis. Jerusalem, Israel, May 22–27 (Abstract #97). 22. Verlinsky, Y., Cieslak, J., Freidine, M., et al. (1995) Pregnancies following pre-conception diagnosis of commom aneuploidies by fluorescent in-situ hybridization. Hum. Reprod. 10, 1923–1927. 23. Dyban, A., Fredine, M., Severova, E., Cieslak, J., and Verlinsky, Y. (1996) Detection of aneuploidy in human oocytes and corresponding first polar bodies by FISH. J. Assist. Reprod. Genet. 13, 72–77. 24. Munné, S., Daily, T., Sultan, K. M., Grifo, J., and Cohen, J. (1995) The use of first polar bodies for preimplantation diagnosis of aneuploidy. Hum. Reprod. 10, 1014–1120. 25. Verlinsky, Y., Cieslak, J., Ivakhnenko, V., Lifchez, A., Strom, C., and Kuliev, A. (1966) Birth of healthy children after preimplantation diagnosis of common aneuploidies by polar body FISH analysis. Fertil. Steril. 66, 126–129.
26. Verlinsky, Y., Cieslak, J., Ivakhnenko, V., Evsikov, S., Strom, C., and Kuliev, A. (1998) Pre-Pregnancy Genetic Testing For Age-Related Aneuploidies by Polar Body Analysis. Genet. Testing 1, 231–235. 27. Verlinsky, Y., Cieslak, J., Ivakhnenko, V., et al. (1999) Prevention of Age-Related Aneuploidies by Polar Body Analysis. J. Assist. Reprod. Genet. 16, 165–235. 28. Verlinsky, Y., Cieslak, and J., Kuliev, A. (2001) High Frequency of Meiosis II Aneuploidies in IVF Patients of Advanced Maternal Age. Reprod. Technol. 10, (in press).
Microdeletion Syndromes
19 Microdeletion Syndromes Characteristics and Diagnosis Stuart Schwartz and Michael D. Graf 1. Introduction Schmickel first defined the Contiguous Gene syndromes in 1986. These are syndromes that involve the deletion of a contiguous stretch of DNA, including multiple genes, on a chromosome. They are also referred to as microdeletion syndromes or segmental aneusomy. These syndromes are clinically recognized with distinct physical, behavioral, and mental characteristics and often involve some individual features that can be inherited in a Mendelian fashion (i.e., lissencephaly, heart defects, etc.). No other type of cytogenetic abnormality has benefited more from the introduction of fluorescence in situ hybridization (FISH) than these syndromes. While some of the abnormalities can be detected cytogenetically, FISH has added dramatically to the detection of these disorders and should be used whenever possible to confirm the deletions (Table 1). 2. Common Microdeletion Syndromes 2.1. Smith-Magenis Syndrome Smith-Magenis syndrome (SMS), with an estimated incidence of 1 in 25,000 births, is caused by a deletion at 17p11.2. This deletion causes a consistent pattern of physical features, developmental delay, and behavior problems. The physical features include a distinctive face including brachycephaly, prominent forehead, synophrys, epicanthal folds, broad nasal bridge, ear anomalies, and prognathism. In addition, there is often brachydactyly, peripheral neuropathy, a deep, hoarse voice, and decreased sensitivity to pain. Individuals with SMS have varying degrees of mental retardation (MR) and there is often speech delay. Perhaps the most recognizable features of SMS are the sleep disturbances (difficulty falling and staying asleep) and behavioral problems. Commonly observed behavior problems include head-banging, wrist-biting, autoamplexation (self-hugging), onychotillomania (pulling out of one's fingernails or toenails), and polyembolokoilamania (inserting objects into body orifices) (1). From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
19_Schwartz_275-290F[7.10.2]
Table 1 Microdeletion Syndromes Syndrome
Phenotypic features
FISH probesa
15q11-q13
Commercial (SNRPN)
Hypotonia, Microcephaly, Ataxic Gait, Inappropriate Laughter, Seizures, Hypopigmentation, Mental Retardation
Commercial (D15S10)
Miller-Dieker Syndrome
Type I Lissencephaly, Dysmorphic Facies
17p13.3
Commercial (D17S379)
Velo-Cardio Facial Syndrome (Del-22q)
Abnormal Facies, Cleft Palate, Thymic Hypoplasia, Hypocalcemia, Heart Defect (Conotruncal Defect)
22q11
Commercial (TUPLE1)
Langer-Giedion Syndrome
Trichorhinophalangeal Syndrome (Sparse Hair, Bulbous nose, Cone-shaped Phalangeal epiphyses), Multiple Exostoses, Mental Retardation
AWTA (WAGR)
Aniridia, Wilms Tumor, Genitourinary Dysplasia, Mental Retardation
11p13
Smith-Magenis Syndrome
Dysmorphic Facial Features, Behavioral Abnormalities, Self Destructive Behavior, Peripheral Neuropathy, Mental Retardation
17p11.2 (FLII, TOP3, SHMT1)
Schwartz and Graf
Hypotonia, Hyperphagia, Obesity, Short Stature, Small Hands and Feet, Hypopigmentation, Mental Retardation
7q11.23
Commercial (ELN)
Rubinstein-Taybi Syndromeb
Dysmorphic Facial Features, Broad Thumbs and First Toes, Mental Retardation
Alpha-Thalassemia and Mental Retardation (ATR-16)
Dysmorphic Facial Features, Alpha-Thalassemia, Mental Retardation
Alagille Syndromeb
Dysmorphic Facial Features, Chronic Cholestasis, Vertebral Arch Defects, Pulmonic Stenosis
20p11.23-p12.2
Greig-Cephalopolysyndactyly Syndromeb
Craniosynostosis, Polysyndactyly, Mental Retardation
Albrights Hereditary Osteodystrophy-Like Syndrome
Short stocky build, Abnormal Facies, Brachymetaphalangism, Seizures, Developmental Delay
1p36 Deletion Syndrome
Hypotonia, Developmental Delay, Growth Abnormalities, Craniofacial Dysmorphism, Minor Cardiac Malformations
Xp22.3 Deletion
X-Linked Ichthyosis, Mental Retardation, Epilepsy, Ocular Albinism, Kallman Syndrome
Xp22.3
Xp21 Deletion
Muscular Dystrophy, Glycerol Kinase Deficiency, Congenital Adrenal Hypoplasia, Mental Retardation
Saethre—Chotzen Syndromeb
Saethre-Chotzen Syndrome, Learning Difficulties
7p21.1
Dysmorphic Facial Features, Infantile Hypercalcemia, Congenital Heart Disease, Gregarious Personality, Premature Aging of the Skin, Mental Retardation
Table 1 (continued) Syndrome
Unilateral Cryptorchidism, Idiopathic Infertility
Commercial (PCR Primers)
van der Woude Syndrome
Cleft Lip With or Without Cleft Palate; Bilateral Lip Pits; Hypodontia
1q32–1q41
Diamond-Blackfan Anemia
Red Blood Cell Hypoplasia, Macrocephalia, Hypotonia and Psychomotor Retardation
19q13.2
NF1 Microdeletion Syndromeb
Neurofibromatosis, Early Age Onset of Cutaneous Neurofibromas, Facial Dysmorphism, Learning Disabilities, Mental Retardation
Distal 22q Microdeletion
Hypotonia, Severe Language Delay, Mild Facial Dysmorphism
22q13–22qter
Commercial (D22S39, ARSA)
17p11.2 Duplication
Charcot-Marie-Tooth (CMT) Disease, Developmental Delay
Commercial (FLII, TOP 3, SHMT1)
Cat-Eye Syndrome
Coloboma, Choanal Atresia, Learning Disabilities, Mental Retardation
Dicenteric (15)
Seizures, Autism, Mental Retardation, Mild Facial Dysmorphism
15q11–15q13
aFISH bThe
probes are available either from Commercial Companies or through Investigators/Published Articles. occurrences of these syndromes are primarily owing to mutations, not chromosomal deletions.
Y Chromosome Deletion
The critical region of SMS is estimated to contain about 5 Mb of DNA that usually allows cytogenetic detection of the deletion. However, some patients may have smaller deletions and FISH is often necessary to confirm small cytogenetic deletions.
2.2. Miller-Dieker Syndrome Miller-Dieker syndrome (MDS), a rare contiguous gene deletion, is caused by a deletion at 17p13.3. The phenotype of MDS consists of type I lissencephaly, mental retardation and characteristic facies including, prominent forehead, bitemporal hollowing, microcephaly, short nose with upturned naries, protuberant upper lip, thin vermilion border, and small jaw (2). A few cases of MDS are autosomal recessive, but most have a deletion at 17p13.3. Studies have delineated a gene responsible for the lissencephaly (LS1) seen in this syndrome, while deletions of other putative genes are suspected to cause the dysmorphic features in the syndrome. This deletion can occur by a number of mechanisms including recombination of a parental balanced translocation or inversion of chromosome 17, a ring chromosome 17, or by a de novo deletion. Approximately 50% of these deletions can be detected by routine cytogenetics, but FISH with an MDS probe localized to 17p13.3 can detect or confirm whether the critical region for MDS is deleted. Additionally, some cases of isolated lissencephaly can be detected with this probe.
2.3. Prader-Willi Syndrome and Angelman Syndrome Prader-Willi syndrome (PWS) and Angelman syndrome (AS) each have incidences of about 1 in 10,000–15,000 births and are caused by alterations at the region of 15q11– q13. The majority of cases (70%) of both PWS and AS are caused by a deletion of that region. The other causes not discussed in detail here are uniparental disomy (UPD), imprinting mutations, and, in the case of AS, gene mutations. PWS and AS exhibit genetic imprinting, meaning that the phenotype is determined by parental origin of the abnormal chromosome 15. If the deletion is on the chromosome 15 inherited from the mother, AS will be the result, whereas a paternally inherited deletion will cause PWS. The clinical phenotypes of these two conditions are quite distinct. PWS consists of severe hypotonia in infancy, developmental delay, hypogonadism, short stature, and mental retardation. Beginning in early childhood, severe hyperphagia (over eating) leading to obesity may be one of the most distinctive behaviors, although there can also be temper tantrums, stubbornness, and obsessive-compulsive behaviors. There is also a typical facial appearance, especially in childhood, consisting of almond-shaped eyes, narrow bifrontal diameter, narrow nasal bridge, and a down-turned mouth with a thin upper lip. The characteristic features of AS include milder hypotonia, early seizures, developmental delay, delayed or absent speech, ataxia, and severe mental retardation. Typical behaviors include periods of inappropriate laughter, hand-flapping, tongue-thrusting, sleep abnormalities, hyperactivity, and aggressiveness. Common physical features include a large, wide mouth, widely spaced teeth, a prominent pointy chin, scoliosis, contractures, and hypopigmentation (3). High-resolution chromosome analysis will often detect PWS/AS deletions, but FISH with a SNRPN probe is often needed to confirm cytogenetic findings or to detect
submicroscopic deletions. However, FISH can not determine the parental origin of the chromosomes so further molecular analysis (methylation analysis or uniparental disomy studies) is required to determine whether the deletion will lead to PWS or AS.
2.4. Velocardiofacial Syndrome and DiGeorge Syndrome Velocardiofacial syndrome (VCF) and DiGeorge syndrome are both caused by a deletion at 22q11. They are syndromes with overlapping clinical features and recent literature has suggested using the general nomenclature of 22q11 Deletion syndrome when describing the condition. This may be the most common microdeletion syndrome, with an estimated incidence of 1 in 4000 births. Clinical features of the 22q11 Deletion syndrome are extremely variable, but can include hypernasal speech, learning disabilities, hypocalcemic seizures, and hypoplastic thymus leading to T-cell abnormalities. The typical physical features of the 22q11 Deletion include long, tapered fingers, cleft palate, prominent nose with squared nasal root, and microcephaly. In the more serious cases (DiGeorge syndrome), there are abnormalities in the third and fourth brachial arches leading to both thymic hypoplasia and parathyroid hypoplasia. Congenital heart disease is commonly associated with this deletion (85% of patients), most often a conotruncal defect. Therefore, it is suggested that if certain structural defects are found prenatally, FISH for the 22q deletion is warranted. Only about 20–30% of the 22q11 deletions are detected by routine cytogenetics. It is necessary to utilize FISH to document a deletion. Most commonly a commercially available TUPLE1 probe is used to detect the deletion (4).
2.5. Williams Syndrome Williams syndrome is caused by a deletion of the q11.23 region of chromosome 7, which includes the elastin gene. Williams syndrome is a developmental disorder involving both the central nervous system and vascular connective tissue. Its physical features often include prominent lips, epicanthal folds, blue eyes with a stellate pattern of the iris, anteverted nares, long philtrum, renal and dentition abnormalities, and premature aging of the skin. There is commonly a heart defect, most often supravalvular aortic stenosis (5–8). Infants with Williams syndrome are often colicky and have hypercalcemia. Children with this syndrome have gregarious personalities as they are often outgoing, loquacious, and very friendly. Persons with Williams syndrome are usually moderately mentally retarded and can have some behavior problems. This disorder is not detectable by routine or high-resolution chromosome analysis. FISH using a DNA probe of the elastin gene will detect the deletion.
3. Less Common Microdeletion Syndromes 3.1. Langer-Giedion Syndrome Langer-Giedion syndrome (tricho-rhino-phalangeal syndrome type II–TRPS II) is a contiguous gene syndrome involving the deletion of at least two genes (TRPS I and EXT I) that are responsible for autosomal dominant disorders (TRPS I and multiple exostoses). The Langer-Giedion syndrome includes phenotypic features seen in both of these autosomal dominant syndromes. The phenotypic findings consists of developmental delay/mental retardation, sparse hair, bulbous nose, cone shaped phalangeal
epiphyses (all seen in TRPS I), and multiple cartilaginous exostoses. Mapping studies have suggested that the developmental delay/mental retardation is caused by genes outside of the TRPS I gene. Thus, the microdeletion of the TRPS I, EXTI, and MR genes, localized to 8q24.1, is responsible for the resultant phenotype (9). In many cases, this deletion can be detected by routine or high-resolution analysis. While no commercially available probes are available, cosmid, phage, PAC, and YAC probes are available for deletion detection by FISH, as well as microsatellite markers within the deleted region (10).
3.2. Rubinstein-Taybi Syndrome Rubinstein-Taybi syndrome (RTS) is an autosomal dominant disorder, which has been localized to 16p13.3. In some cases this disorder has been due to a deletion of the RTS gene in this region. Rubinstein-Taybi syndrome consists of a number of phenotypic features including growth and mental retardation, broad thumb and halluces, short stature, and a typical facies (beaked nose, prominent columella, hypoplastic maxilla, and down-slanted palpebral fissures). Molecular analysis has demonstrated that this syndrome is due to disruption of the CREB binding protein (CBP), due to point mutation or chromosomal rearrangement (including deletions, translocations and inversions). The CBP gene codes for a large nuclear protein that is involved in transcriptional regulation, chromatin remodeling, and the integration of several different transduction pathways (11–13). This deletion is usually not detectable by either routine or high-resolution chromosomal analysis. Initial studies utilizing the cosmid RT1, which includes the CREB binding protein, had suggested that up to 25% of RTS patients had a chromosomal syndrome; however more recent studies have suggested that a lower figure (8–12%) is more likely. A work by Petrij et al. has indicated a group of 5 cosmid probes (rather than just RT1) should be used for complete FISH analysis (12).
3.3. Aniridia Wilms Tumor Association Aniridia Wilms Tumor Association (AWTA), also referred to as the Wilms tumor, Aniridia, Genitourinary dysplasia and Retardation syndrome (WAGR) is due to a deletion in the short arm of chromosome 11 (11p13). Children with this deletion present with aniridia (absence of iris) and mental retardation. Some of the individuals with this deletion and an XY karyotype will have sex reversal and be phenotypic females. A portion of the individuals with deletions will also have a Wilms tumor, a kidney tumor that is the most common childhood tumor. Due to the common association of the various features, any child with a deletion, without a Wilms tumor at ascertainment, must be monitored for this cancer. Genes for aniridia (AN2), Wilms tumor (WT1) and sex reversal have all been identified in this region (14). This deletion can usually be detected with routine or high-resolution cytogenetic analysis. A series of cosmid probes are available that can be used for FISH confirmation of deletions in this region (15).
3.4. Alpha-Thalassemia and Mental Retardation Syndrome (ATR-16) Alpha-Thalassemia and Mental Retardation syndrome (ATR-16) is a rare disorder that is owing to the deletion in 16p13.3 in the telomeric region of the short arm. The
loss of the two alpha-hemoglobin genes in this region results in the individuals being a carrier for alpha-thalassemia, while loss of other contiguous genes is responsible for the minor dysmorphic features and mental retardation (16). If the other parent is a carrier, they could have alpha thalassemia or Hemoglobin H. A recent study by Pfiefer et al. has indicated that the SOX8 gene, which codes for a 446 amino acid protein expressed strongly in the brain, is deleted in an ATR-16 patient and is a good candidate gene contributing for the mental retardation in these patients (17). This syndrome is rarely initially detected by high-resolution chromosome analysis. Rather, it is usually ascertained by phenotypic findings and confirmed by FISH or molecular analysis.
3.5. Alagille Syndrome Alagille syndrome is a genetic disorder localized to 20p11.23–20p12.2. Mild dysmorphic facial features, chronic cholestasis (associated with intrahepatic bile duct paucity), cardiovascular anomalies, ocular anomalies, and minor skeletal malformations, characterize this condition. The Jagged 1 (JAG1) gene has been identified as the gene responsible for Alagille syndrome. This gene encodes a ligand in the Notch signaling pathway and is believed to be involved in cell fate determination. Approximately 70% of the identified cases of Alagille syndrome are thought to be owing to a JAG 1 mutation, which includes protein truncation, splicing, and missense mutations. Whole gene deletions can also cause Alagille syndrome. However, these are infrequent, as they account for only approx 6% of the cases (18,19). Approximately 95% of the cases of Alagille syndrome have a cardiac defect. Most involve right-sided defects, which can range from mild peripheral pulmonic stenosis to the severe forms of Tetralogy of Fallot. Recent studies have shown that individuals with isolated heart defects (e.g. Tetralogy of Fallot) can have mutations in the JAG1 gene (20). The finding of a deletion associated with Alagille syndrome is an infrequent event, but most can be detected by routine cytogenetics or high-resolution chromosomal analysis. A contig consisting of YACs and BACs is available for FISH analysis.
3.6. Greig-Cephalopolysyndactyly Syndrome Greig-Cephalopolysyndactyly syndrome is an autosomal dominant disorder, which has in some cases been associated with a deletion in 7p13. This syndrome has been characterized by craniosynostosis and polysyndactyly. It has been shown to be owing to point mutations and translocations involving the zinc finger gene GLI3. Further analysis has revealed that while mutations of GLI3 results in Greig-Cephalopolysyndactyly syndrome, mutations in this gene may lead to Pallister-Hall syndrome or post-axial polydactyly type A. Patients with Greig-Cephalopolysyndactyly resulting from a deletion of the GLI3 gene and contiguous region demonstrate significant developmental retardation and mental retardation, in addition to the phenotypic findings (polysyndactyly, bifid thumb, peculiar skull shape, hip dislocation, and advanced bone age) (21,22). Most of the deletions that have been detected in association with this contiguous gene have been detected by utilizing standard cytogenetics. For more detailed analysis, both investigator developed FISH probes and molecular markers are available.
3.7. Albright Hereditary Osteodystrophy-Like Phenotype Albright hereditary osteodystrophy-like phenotype is a reported syndrome in patients with a subtle deletion in the telomeric region of the long arm of chromosome 2 (2q37–2qter). The features seen in this syndrome includes a short stocky build, abnormal facies (including a round face, sparse hair, deep set eyes, bulbous nose, thin vermilion border), brachymetaphalangism, seizures, and developmental delay. Behavior findings include periods of hyperkinesis and aggressive behavior. Although a number of these patients have been reported, no candidate gene region has been implicated to date (23,24). A number of patients have been ascertained and identified using both routine cytogenetic analysis and high-resolution studies. Several YACs and BACs are available for a more detailed molecular analysis of this region.
3.8. 1p36.3 Deletion Syndrome A microdeletion syndrome involving a deletion of the 1p36.3 had been reported with increasing frequency over the past several years and appears to have increasing important in genetics. Phenotypic features seen in these patients include: hypotonia, developmental delay and mental retardation, growth abnormalities (growth retardation, microcephaly, obesity), craniofacial dysmorphism (large anterior fontanelle, prominent forehead, deep set eyes, flat nasal bridge, midfacial hypoplasia, ear asymmetry, pointed chin, orofacial clefting), and minor cardiac malformations (25). A neurodevelopmental profile has been suggested for this syndrome in which severe learning disability, motor delay with hypotonia, markedly delayed visual maturation, and postural asymmetry together with epilepsy is seen (26). In some instances, patients with this deletion have been ascertained because of a suspicion of Prader-Willi syndrome, while many have been referred because of the hypotonia. Shapira et al. have studied a group of 14 patients, using both FISH and DNA polymorphisms and have found that there is no uniform region of deletion and the cases contain a spectrum of different deletion sizes (27). Many of these patients have been detected by routine and high-resolution cytogenetics because of the distinctive double dark band seen in 1p36. Also, as the phenotype is so broad, it is difficult to specifically look for a deletion by FISH in a specific subgroup of patients. However, several patients have been reported in which 1p36.3 deletions have been detected using a subtelomeric probe kit. Several groups have utilized a repetitive probe (1DZ2) in 1p36.3 to confirm deletions. As indicated above, this region has been studied with a series of BACs, which are available for FISH analysis (27).
3.9. Xp22.3 Deletion The Xp22.3 syndrome is a classical contiguous gene deletion syndrome that is seen in males. It involves the deletion of several genes in the pseudoautosomal region of the X chromosome, each resulting in a specific phenotype. This syndrome involves the deletion of genes resulting in X-linked ichthyosis, mental retardation, epilepsy, ocular albinism, and Kallman syndrome. In some cases this will also involve short stature
owing to chondrodysplasia punctata. The patients may be ascertained because of any of the above phenotypes and subsequently determined to have a deletion covering several genes (28,29). This deletion is usually detectable by standard cytogenetics analysis as it can encompass several megabases of DNA. However, some smaller deletions can exist, which can be detected by FISH using commercial probes for X-linked ichthyosis (STS) or Kallman syndrome (KAL) (28,29).
3.10. Xp21 Deletion Similar to the above-mentioned Xp22.3, the contiguous gene deletion involving Xp21 is also seen in males. This contiguous gene deletion syndrome also involves the deletion of specific genes, in this case in Xp21, each again resulting a specific phenotype. Most of these patients are males ascertained due to the presence of Duchenne muscular dystrophy. However, they have additional phenotypic findings that may include: Aland Island eye disease, adrenal hypoplasia, glycerol kinase deficiency, retinitis pigmentosa, and ornithine transcarbamylase deficiency. The exact phenotype again depends on the precise breakpoint and which genes are deleted (30,31). While some of these patients have been detected cytogenetically, many of the deletions are submicroscopic and must be delineated using FISH probes and microsatellite markers localized to this region.
3.11. Saethre-Chotzen Syndrome Saethre-Chotzen syndrome is an autosomal dominant craniosynostosis disorder that is relatively common. This syndrome is characterized by brachydactyly, soft tissue syndactyly and mildly dysmorphic facial features (ptosis, facial asymmetry, and prominent ear crura). Molecular analysis has revealed that a mutation in the coding region of the TWIST gene (which encodes a basic helix-loop-helix transcription factor) accounts for a number of these cases. Approximately 80% of the cases of this syndrome result from an abnormality in the TWIST gene. Gripp et al. have suggested that up to 37% of the cases might be due to large deletions (32). Cases, which involve a deletion of more than just the TWIST gene, also have developmental delay. This gene has been localized to 7p21.1 (32). This is not a syndrome that can usually be detected with routine or high-resolution cytogenetic analysis, with the exception of translocations. However several probes for FISH are available to determine whether a deletion is present and the extent of that deletion. It is important to differentiate whether the underlying cause is a mutation or deletion, due to the association of developmental delay with deletions.
3.12. Van der Woude Syndrome Van der Woude syndrome is a highly penetrant autosomal dominant form of syndromic cleft lip and palate. It is estimated that it accounts for approx 2% of all cleft lip and palate cases. Phenotypic features associated with this syndrome include: cleft lip with or without cleft palate, bilateral lip pits, and hypodontia. Patients with this syndrome have normal intelligence, however, those patients with a deletion have developmental delay. The gene for this syndrome has not been identified, but has been
localized to a 1.6 cM region in the 1q31–1q41 region. This is also the region that has been implicated in the deletion cases (34,35). There have only been a few cases with this syndrome identified as having a deletion. Those which have a deletion, have been detected by routine chromosome analysis. A 4.4 Mb YAC contig through the critical region has been constructed, with both BACs and PACs available for a more thorough analysis (35).
3.13. Diamond-Blackfan Anemia Diamond-Blackfan anemia is a rare constitutional blood disorder in which there is pure red-cell aplasia in the neonatal period or in infancy. Both its etiology and pathogenesis are unknown. Linkage analysis has localized this disorder to a 4.1 cM region at 19q13.2. Analysis of over 50 individuals with this syndrome has revealed that in some cases, a small microdeletion is associated with this anemia. These patients, in addition to the red blood cell hypoplasia, had other phenotypic findings including macrocephaly, hypotonia, and psychomotor retardation. These additional findings in microdeletion patients suggest that this is a contiguous gene deletion. Analysis of the microdeletion patients has reduced the critical region for this syndrome to about 1 Mb (36,37). The initially detected deletion patients identified with this syndrome were ascertained using standard or high resolution chromosomal analysis. Subsequent to this, a number of investigators have utilized FISH to better characterize the deletions (37).
3.14. Neurofibromatosis Neurofibromatosis is a well characterized autosomal disorder in which patients have café-au-lait spots and neurofibromas. It is a syndrome that has considerable variable expressivity. Molecular analysis has shown a variety of mutations associated with the syndrome. However, more recent studies have indicated that approx 5–10% of these patients have a deletion of 17q11.2, which includes the NF1 gene rather than a mutation. In addition to the typical findings seen in neurofibromatosis, the microdeletion patients have other findings such as earlier onset of cutaneous neurofibromas, facial dysmorphism, and learning disabilities/mental retardation. The addition of these findings to neurofibromatosis classifies the deletion as a contiguous gene syndrome. Similar to that seen in other microdeletion syndromes (Prader-Willi syndrome, Angelman syndrome, Velo-cardio-facial syndrome and Williams syndrome), specific repetitive/paralogous segments flank the deletion and are responsible for unequal meiotic crossingover leading to the consistent microdeletion (38,39). These deletions are not readily detectable by cytogenetic analysis alone. A variety of FISH probes, including a detailed YAC map, are available for a more detailed analysis (39).
3.15. Distal 22q Deletion The utilization of subtelomeric probes will yield the detection of microdeletions not previously seen. One such terminal deletion that has been characterized by a number of groups is of the subtelomeric region of the long arm of chromosome 22. These patients present with hypotonia, severe language delay, and mild facial dysmorphism. Precise phenotypic characterization of these deletions have been difficult as many of these
result from reciprocal translocations and contain not only a deletion, but in many cases a duplication (40,41). These patients are essentially only ascertained using FISH with a subtelomeric 22q probe (D22S39; ARSA). Several of these cases have been ascertained serendipitously using the VCF probe, and although that probe is present, the D22S39 probe that is used as a control probe is deleted, confirming this distal deletion.
3.16. Y Chromosome Deletions One recent microdeletion that has been identified involves a deletion in the long arm of the Y chromosome (Yq13). This is not a contiguous gene deletion, but rather a microdeletion involving DNA important in male fertility. Thus, these men will normally present with only infertility. Deletions have been detected in three different regions of the long arm of the Y chromosome; the AZFa, AZFb, or AZFc regions. While there are many varied reported frequencies for this deletion, it is estimated that 2–4% of patients with severely impaired spermatogenesis will have a microdeletion in this region. A smaller frequency of males with less severe defects will also have a deletion in this region (42,43). This microdeletion can not be detected by cytogenetic or FISH analysis. These deletions will only be detected using PCR analysis of markers within the three regions (42,43).
4. Microduplication Syndromes Theoretically for many interstitial microdeletions, a reciprocal microduplication syndrome should exist. This does not seem to be true for the vast majority of these cases, however. They may occur, but the clinical phenotype may be too mild to lead to cytogenetic analysis or it is possible that they are cytogenetically too subtle to permit a diagnosis. In this review, three well documented microduplication syndromes (two of which involve supernumerary chromosomes) will be presented. All three of these syndromes are well established and delineated in the literature.
4.1. 17p11.2 Duplications The 17p11.2 duplication is thought to be the homologous reciprocal recombination of the Smith-Magenis deletion, with a de novo duplication of the region deleted in Smith-Magenis. The clinical phenotype seen in this syndrome is considerably milder than that associated with the deletion of the same region. These patients can have Charcot-Marie-Tooth disease type 1A , along with developmental delay (44,45). These patients are difficult to diagnose with either standard or high resolution cytogenetics. They can, however, be easily identified using FISH. The same commercial probes used to identify the Smith-Magenis deletion (FLII, TOP3, SHMT1) can also be used to determine the presence of a duplication. In addition, detailed genomic maps of this region have been constructed, indicating the availability of other FISH probes or microsatellite markers.
4.2. Cat-eye Syndrome Cat-eye syndrome (CES) is a disorder with a variable phenotype of multiple anomalies. Some of these findings include: downward slanting palpebral fissures, micro-
pthalmia, congenital heart defect, urinary tract anomalies, and skeletal anomalies. All of these features may be seen simultaneously in only 1/3 of the cases, however both anal atresia and ocular colobomas must be present to make a clinical diagnosis. Mild to moderate mental retardation is seen in about 1/3 of the cases. Cytogenetically, this syndrome is characterized by the presence of a supernumerary bi-satellited dicentric chromosome derived from chromosome 22 (46,47). The supernumerary marker chromosome is easily identified by routine cytogenetics. Nevertheless, not all dicentric chromosomes derived from chromosome 22 will be associated with the Cat-eye syndrome phenotype. The critical region for this syndrome, localized to 22q11.2, must be present. This area has been heavily studied and a number of probes are available to confirm this region's presence. It should be noted that the probes for VCF (i.e., TUPLE1) are distal to this region and are not appropriate to use to delineate the CES syndrome (47).
4.3. Dicentric (15) Syndrome The dicentric chromosome 15, better known as an inv dup(15), is also a supernumerary dicentric chromosome. This is the most common structurally abnormal supernumerary chromosome seen cytogenetically. It has a variable phenotype and usually only mild facial dysmorphism is seen. Most often this syndrome is associated with seizures, autism, and mental retardation. Similar to the above mentioned syndrome (CES), this chromosome is bisatellited and dicentric and can involve breaks in at least four different areas in 15q. The abnormal phenotype is believed to only be associated with those cases in which the Prader-Willi/Angelman syndrome (PWS/AS) critical region in 15q is present. In those cases where the breakpoint is proximal to this critical region, the individual will have a normal phenotype (except for where uniparental disomy occurs) (48,49). Again, this marker is routinely ascertained with standard cytogenetic analysis. However, no phenotype will be present with the absence of the PWS/AS critical region. The presence of this region cannot be done by cytogenetic analysis, but must be examined with FISH. Utilization of a probe used to diagnoses the deletion in Prader-Willi syndrome (i.e., SNRPN) must be used. Both a number of commercial and noncommercial probes are available for these studies (49).
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21. Kalff-Suske, M., Wild, A., Topp, J., Wessling, M., Jacobsen, E. M., Bornholt, D., et al. (1999) Point mutations throughout the GLI13 gene causing Grieg cephalopolysyndactyly syndrome. Hum. Mol. Genet. 8, 1769–1777. 22. Williams, P. G., Hersh, J. H., Yen, F. F., Barch, M. J., Kleinert, H. E., Kunz, J., et al. (1997) Greig cephalopolysyndactyly syndrome: altered phenotype of a microdeletion syndrome due to the presence of a cytogenetic abnormality. Clin. Genet. 52, 436–441. 23. Phelan, M. C., Rogers, R. C., Clarkson, K. B., Bowyer, F. P., Levine, M. A., Estabrooks, L. L., et al. (1995) Albright hereditary osteodystrophy and del(2) (q37.3) in four unrelated individuals. Am. J. Hum. Genet. 58, 1–7. 24. Wilson, L. C., Leverton, K., Oudi Luttikhuis, M. E., Oley, C. A., Flint, J., Wolstenholme, J., et al. (1995) Brachydactyly and mental retardation: an Albright hereditary osteodystrophylike syndrome localized to 2q37. Am. J. Hum. Genet. 56, 400–407. 25. Slavotinek, A., Shaffer, L. G., and Shapira, S. K. (1999) Monosomy 1p36. J. Med. Genet. 36, 657–663. 26. Knight-Jones, E., Knight, S., Heussler, H., Regan, R., Flint, J., and Martin, K. (2000) Neurodevelopmental profile of a new dysmorphic syndrome associated with submicroscopic partial deletion of 1p36.3. Dev. Med. Child. Neurol. 42, 201–206. 27. Shapira, S. K., McCaskill, C., Northrup, H., Sikes, A. S., Elder, F. F., Sutton, V. R., et al. (1997) Chromosome 1p36 deletions: the clinical phenotype and molecular characterization of a common newly delineated syndrome. Am. J. Hum. Genet. 61, 642–650. 28. Gohlke, B. C., Haug, K., Funkami, M., Friedl, W., Noeker, M., Rappold, G. A., et al. (2000) Interstitial deletion in Xp22.3 is associated with X linked ichthyosis, mental retardation, and epilepsy. J. Med. Genet. 37, 600–602. 29. Weissortel, R., Strom, T. M., Dorr, H. G., Rauch, A., and Meitinger, T. (1998) Analysis of an interstitial deletion in a patient with Kallmann syndrome, X-linked ichthyosis and mental retardation. Clin. Genet. 54, 45–51. 30. Fries, M. H., Lebo, R. V., Schonberg, S. A., Golabi, M., Seltzer, W. K., Gitelman, S. E., et al. (1993) Mental retardation locus in Xp21 chromosome microdeletion. Am. J. Hum. Genet. 46, 363–368. 31. Stuhrmann, M., Heilbronner, H., Reis, A., Wegner, R. D., Fischer, P., and Schmidtke, J. (1991) Characterisation of a Xp21 microdeletion syndrome in a 2-year-old boy with muscular dystrop, glycerol kinase deficiency and adrenal hypoplasia congenita. Hum. Genet. 86, 414–415. 32. Gripp, K. W., Zackai, E. H., and Stolle, C. A. (2000) Mutations in the human TWIST gene. Hum. Mutat. 15, 150–155. 33. Johnson, D., Horsley, S., Moloney, D. M., Oldridge, M., Twigg, S. R., Walsh, S., et al. (1998) A comprehensive screen for TWIST mutations in patients with craniosynostosis identifies a new microdeletion syndrome of chromosome band 7p21.1. Am. J. Hum. Genet. 63, 1282–1293. 34. Schutte, B. C., Bjork, B. C., Coppage, K. B., Malik, M. I., Gregory, S. G., Scott, D. J., et al. (2000) A preliminary gene map for the Van der Woude Syndrome critical region derived from 900 kb of genomic sequence at 1q32-q41. Genome Res. 10, 81–94. 35. Schutte, B. C., Basart, A. M., Watanabe, Y,. Laffin, J. J., Coppage, K., Bjork, B. C., et al. (1999) Microdeletions at chromosome bands 1q32–q41 as a cause of Van der Woude syndrome. Am. J. Hum. Genet. 84, 145–150. 36. Tentler, D., Gustavsson, P., Elinder, G., Eklof, O., Gordon, L., Mandel, A., et al. (2000) A microdeletion in 19q13.2 associated with mental retardation, skeletal malformations, and Diamond-Blackfan anaemia suggests a novel contiguous gene syndrome. J. Med. Genet. 37, 128–131.
37. Gustavsson, P., Garelli, E., Draptchinskaia, N., Ball, S., Willig, T. N., Tentler, D., et al. (1998), Identificatin of microdeletions spanning the Diamond-Blackfan anemia locus on 19q13 and evidence for genetic heterogeneity. Am. J. Hum. Genet. 63, 1388–1395. 38. Correa, C. L., Brems, H., Lazaro, C., Marynen, P., and Legius, E. (2000) Unequal Meiotic Crossover: A Frequent Cause of NF1 Microdeletions. Am. J. Hum. Genet. 66, 1969–1974. 39. Riva, P., Corrado, L., Natacci, F., Castorina, P., Wu, B. L., Schneider, G. H., et al. (2000) NF1 microdeletion syndrome: refined FISH characterization of sporadic and familial deletions with locus-specific probes. Am. J. Hum. Genet. 66, 100–109. 40. Praphanphoj, V., Goodman, .K., Thomas, G. H., and Raymond, G. V. (2000) Cryptic subtelomeric translocations in the 22q13 deletion syndrome. J. Med. Genet. 37, 58–61. 41. Precht, K. K., Lese, C. M., Spiro, R. P., Huttenlocher, P. R., Johnston, K. M., Baker, J. C., et al. (1998) Two 22q telomere deletions serendipitously detected by FISH. J. Med. Genet. 35, 939–942. 42. Maurer, B., Gromoll, J., Simoni, M., and Nieschlag, E. (2001) Prevalence of Y chromosome microdeletions in infertile men who consulted a tertiary care medical centre: the Munster experience. Andrologia 33, 27–33 43. Van Landuyt, L., Lissens, W., Stouffs, K., Tournaye, H., Liebaers, I., and Van Steirteghem, A. (2000) Validation of a simple Yq deletion screening programme in an ICSI candidate population. Mol. Hum. Reprod. 6, 291–297. 44. Potocki, L., Chen, K. S., Park, S. S., Osterholm, D. E., Withers, M. A., Kimonis, V., et al. (2000) Molecular mechanism for duplication 17p11.2- the homologous recombination reciprocal of the Smith-Magenis microdeletion. Eur. J. Hum. Genet. 8, 220–235. 45. Thomas, P. K., Marques, W., Jr., Davei, M. B., Sweeney, M. G., King R. H., Bradley J. L., et al. (1997) The phenotypic manifestations of chromosome 17p11.2 duplication. Brain 120 (Pt3), 465–478. 46. Berends, M. J., Tan-Sindhunata, G., Leegte, B., and van Essen, A. J. (2001) Phenotypic variability of Cat-Eye syndrome. Genet. Couns. 12, 23–34. 47. Johnson, A., Minoshima, S., Asakawa, S., Shimizu, N., Shizuya, H., Roe, B. A., et al. (1999) A 1.5–Mb contig within the cat eye syndrome critical region at human chromosome 22q11.2. Genomics 57, 306–309. 48. Wandstrat, A. E., Leana-Cox, J., Jenkins, L., and Schwartz, S. (1998) Molecular cytogenetic evidence for a common breakpoint in the largest inverted duplications of chromosome 15. Am. J. Hum. Genet. 62, 925–936 49. Leana-Cox, J., Jenkins, L., Palmer, C. G., Plattner, R., Sheppard, L., Flejter, W. L., et al. (1994) Molecular cytogenetic analysis of inv dup(15) chromosomes, using probes specific for the Prader-Willi/Angelman syndrome region: clinical implications. Am. J. Hum. Genet. 54, 748–756.
Molecular Cytogenetics in Reproductive Pathology
21 Molecular Cytogenetics in Reproductive Pathology Hélène Bruyère, Evica Rajcan-Separovic, and Dagmar K. Kalousek 1. Introduction Conventional cytogenetic analysis has contributed for the last 35 yr to establishing the etiology of spontaneous abortions (SAs), representing an important diagnostic aid for reproductive pathologists, geneticists, and physicians. There is however a problem in obtaining a cytogenetic result from 10–30% of abortion specimens owing to culture failure. In addition, growth of maternally-derived cells in culture can result in a false negative result. Nowadays, new molecular cytogenetic tools are available to get cytogenetic information in almost all cases of SA submitted to the Cytogenetics laboratory. Pregnancy loss is common in human reproduction, with over 50% of all conceptions and 15–20% of recognized pregnancies resulting in failure. The majority of the losses occurs early in gestation. Cytogenetic abnormalities represent the major etiology for reproductive failure, responsible for >70% of early losses (before 6 wk of gestation), around 50% of losses between 8–15 wk of gestation, and 5–10% of stillbirths (1). Nearly all these chromosomal defects happen de novo, as a result of either a meiotic or a postzygotic division error or due to an abnormal fertilization. The meiotic errors can occur in both maternal and paternal gametes, but are more frequently maternal in origin. One of the most common causes of pregnancy loss is chromosomal trisomy. It may be present in all cells of the developing embryo, or, in some cases, one of the three chromosome copies may be lost by anaphase lagging or non-disjunction (2) or chromosome demolition (3) at an early postzygotic cell division. This event, called "trisomy rescue", leads to chromosomal mosaicism, the coexistence of two cell lines in the conceptus, one disomic and the other trisomic. The trisomic cell line can be present in both the embryo and the placenta. This situation represents generalized mosaicism and can be detected in about 10% of spontaneous abortions when specifically looked for (4). Viable pregnancies with generalized mosaicism can be diagnosed by amniotic fluid analysis, but a subset may remain cryptic (5,6). If the trisomic cell line is limited From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
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Bruyère, Rajcan-Separovic, and Kalousek
to the placenta, this situation is called confined placental mosaicism (CPM) (7). At the time of chorionic villus sampling at 10–12 wk of gestation, about 1–2% of pregnancies present such a situation (8–11). Three types of CPM are defined, based on cell lineage involved: Type I: the trisomic cell line is confined to the trophoblast; Type II: the trisomic cell line is confined to the chorionic villus mesenchyme; Type III: the trisomic cell line is detected in both cell lineages. In utero fetal growth retardation and a poor perinatal outcome are commonly associated with CPM (12,13). Furthermore, when CPM is detected, the chromosomally normal fetus has a risk of one third of having uniparental disomy (the same parental origin for a given chromosome pair) for the chromosomal pair that is trisomic in the placenta. Uniparental disomy involving specific chromosomes (i.e., 7, 14, and 15) leads to an abnormal fetal phenotype (14,15).
1.1. Spontaneous Abortion Abortion is defined as the premature expulsion or removal of the conceptus from the uterus before it is viable. A gestational age of 20 wk of gestation or a fetal weight of 500 g are currently considered to be the lower limits of fetal viability. The main cause of SAs is chromosomal abnormality. Trisomies are found in 26% of pregnancy losses, triploidy and tetraploidy in 10% and sex chromosome monosomy in 9% (1). About 10% of the cases show mosaicism for aneuploidy (4). Less frequently, an unbalanced structural rearrangement is found (2%), or double trisomy (0.6–1.9%) (16–18). Therefore, over 50% of all SAs are chromosomally abnormal. Monosomy X represents the most common single chromosomal anomaly found in cytogenetically abnormal SAs. The most common trisomy is trisomy 16, which occurs in a third of the trisomic conceptuses. The frequency of other trisomies is summarized in Table 1. Histological and morphological examination is not helpful in distinguishing between chromosomally normal and abnormal abortion specimens (19). For that reason, cytogenetic testing is essential in order to establish the etiology of SA and provide genetic and reproductive counselling.
1.2. Stillbirth Stillbirth is defined as a fetus dying intrapartum or antepartum after 20 wk of gestation or having a weight over 500 g. This event occurs in about 0.4–4% of total births (20), with developing countries having the highest rates. Stillbirths in North America represents about 1% of births (21). Incidence of chromosomal aberrations in stillbirth is about 4% in non-macerated fetuses (1,22), and more than twice (9%) in macerated stillborns (22,23).
1.3. Limitations of Conventional Cytogenetic Testing Conventional cytogenetic studies of products of conception rely on obtaining viable tissues, establishing primary cultures, and harvesting metaphase chromosomes for analysis. Although the contribution of conventional cytogenetic testing to reproductive pathology has been immense, there are several limitations:
Table 1 Trisomy Frequency in First Trimester Trisomic Spontaneous Abortions, Arranged from Ref. (1) Trisomy
16 22 21 15 18 13 2 14 7 8 4 9 20 10 3 6 12 11 5 17
31.4 11.2 10 7.1 4.6 4.6 4.6 4 3.8 3.3 3.3 3 2.5 2 1.3 1.3 0.8 0.4 0.4 0.4
1. The major problem of cytogenetic analysis of tissues from products of conception is obtaining dividing cells. Cytogenetic testing on tissues from SA has a high rate of tissue culture failure (10–40%). Placenta has a very poor growth rate after 34 wk of gestation. Tissues of macerated stillbirth also fail to grow in more than half of the cases. 2. The selective growth of maternal decidua may lead to the cytogenetic diagnosis of a normal female karyotype not representative of the true fetal chromosome complement. 3. Cultural artifacts may occur in long-term cultures of chorionic stroma.
To avoid these problems, fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH), two recently developed molecular cytogenetic techniques, utilize uncultured cells and tissues to overcome the limitations of cell culture. They provide an alternative approach for cytogenetic analysis of products of conception and stillbirths.
2. Molecular Cytogenetic Techniques 2.1. Fluorescence In Situ Hybridization Fluorescence in situ hybridization (FISH) allows the detection of the presence (or absence) of a DNA sequence of interest directly on metaphases or interphasic nuclei. A probe (a DNA sequence complementary to the region of interest), labeled directly or
indirectly with a fluorochrome, is hybridized with the clinical material after denaturation of both the probe's and the specimen's DNAs. The fluorescent signal can then be visualized by a fluorescence microscope. This technique is now widely used in clinical cytogenetic laboratories.
2.1.1. Application A chromosome defect is usually strongly suspected when the pathological examination of a late abortion reveals a fetus with focal anomalies. Confirmation of a suspected chromosomal abnormality can be done by FISH. For example, the presence of a posterior cervical cystic hygroma is an indicator of a cytogenetic abnormality in 85% of cases, mostly monosomy X, but also trisomy 21 and 18 (24). Therefore, for this fetal defect, the use of probes for chromosomes 13, 18, 21, X and Y can provide definitive diagnosis. When a specific fetal defect is not present, the range of possible chromosome anomalies is wider. Although a complete chromosome scan is theoretically possible, the use of fluorescent probes for chromosomes 13, 15, 16, 18, 21, 22, X and Y allows the detection of the most common autosomal trisomies, as well as sex aneuploidies, triploidies and tetraploidies. This approach can potentially establish an etiology for more than 80% of chromosomally abnormal SAs (see Table 1). Weremowicz et al. (25) showed that it is a rapid and cost effective approach, avoiding the need to continue culture for 42% of the samples. In another study (26), FISH probes for chromosome 13, 15, 16, 18, 21, X and Y were selected according to ultrasound findings or autopsy results and applied to specimens that failed to grow in culture. This approach led to a result in 28 out of 30 cases, with an aneuploidy detected in 46% of the cases. The 2 cases with FISH failure represented severely macerated fetuses. In the case of pathological examination of stillbirth, FISH performed with probes for chromosomes 13, 18, 21, X, Y can reveal all types of aneuploidy usually compatible with late gestation (1). Such probes are now commercially available as kits of aneuploidy detection (Cytocell®, Adderbury, UK, Vysis®, Downers Grove, IL).
2.1.2. Limitations Valuable information is provided on the copy number of specific chromosomes corresponding to the probe used in the FISH assay. Most of the time, enumeration for a chromosome is done with a centromeric probe, as this kind of probe provides large signals that are easy to count. Unfortunately, it does not provide any information on the structure of the chromosome analyzed. When three signals are detected, the sample is assumed to be trisomic, whereas it also could be triploid or contain an unbalanced structural rearrangement. The simultaneous use of two or more probes allows one to distinguish between aneuploidy and polyploidy, which are far more common than unbalanced structural abnormalities. In addition, although several probes with different fluorescent dyes can be used in one or two experiments, FISH does not provide a screen for the entire genome, and only the most common trisomies can be tested for. The presence of chromosomal mosaicism with an abnormal cell line present in less than 10% of the cells cannot be established with confidence. To increase their efficiency in detecting mosaicism, cytogenetic laboratories providing clinical FISH analy-
ses need to establish cut-off values for the detection of a mosaic aneuploid cell line (27). The cut-off value varies according to the tissue, to the probe and potentially to the observer.
2.2. Comparative Genomic Hybridization The technique of CGH allows the entire genome to be screened for extra or missing chromosome material in a single hybridization (28). It involves the simultaneous hybridization of test and reference DNA, each labeled with a different fluorochrome, to normal target metaphase chromosomes. The fluorescence intensity ratio of the test and reference DNA is quantitated and analyzed by using a digital image analysis system. It reveals gains and losses of the test DNA relative to the reference DNA.
2.2.1. Application Recently, Daniely et al. (1998) used CGH to study 38 products of conceptions of undetermined etiology from couples experiencing recurrent spontaneous abortions (29). Eighteen cases were analyzed both cytogenetically and by CGH. Consistent results were found in 15 cases, while 2 partial unbalances were revealed by CGH only and one case of mosaicism for trisomy 16 was detected by routine cytogenetic analysis but missed by CGH. Twenty samples were analyzed by CGH only, with abnormal results in 12 cases. Ploidy level was not tested in this study (29). Lomax et al. (2000) (30) analyzed 301 spontaneous abortions from couples with RSA or advanced maternal age by both traditional cytogenetic analysis and CGH coupled with flow cytometry. Forty-eight of their cases failed to grow in culture, but 96% of these were successfully analyzed by CGH. Two-third of these specimens were cytogenetically abnormal. Out of 253 samples successfully analyzed by both methods, correlation of results was found in 235. The discrepant results were due to maternal contamination and tetraploidy in 14 cases. Hypertriploidy was identified cytogenetically in 3 cases, whereas CGH showed only aneuploidy. One case showed a gain for chromosome 18, whereas cytogenetics showed a tetraploid karyotype with an unbalanced rearrangement of chromosome 1. This case was interpreted as resulting from sample mislabeling. CGH has been also shown as a valuable technique for cytogenetic analysis of macerated stillbirth (31). Sixteen fetuses with a known karyotype, including 5 macerated fetuses, were successfully analyzed by CGH. Ten stillborn fetuses were also analyzed after tissue culture failure for conventional cytogenetics. Nine fetuses had normal results. The authors' did not provide any explanation for an abnormal CGH pattern with gains of both chromosome 17 telomeric regions, which were not confirmed by FISH with the chromosome 17 long arm telomeric probe. Several probes spanning a region may be needed in some cases to confirm an abnormal CGH result.
2.2.2. Limitations Comparative genomic hybridization detects chromosomal unbalance but does not allow the diagnosis of a change in the ploidy level. This is of more concern in cases of early spontaneous abortions, for which polyploidies represent 20% of the cytogenetically abnormal cases. However, it is much rarer in stillbirth. Therefore, another test should be added for the detection of polyploidy, whenever CGH shows balanced result.
Several options are possible: a) Flow cytometry, which has been used extensively for the quantitative determination of cellular DNA content of molar pregnancies. It is easy to perform, rapid, accurate and inexpensive (32). It has recently been successfully used in SA analysis (30,31). b) FISH analysis with probes for at least 2 different chromosomes. c) Microsatellites analysis, which also provides further insight into the parental origin of the extra haploid set of chromosomes. The limitation of this process is that the ploidy level cannot be established in cases with combined aneuploidy and polyploidy (e.g., 70,XXY,+2). As polyploidy is not associated with an increased recurrence risk, the genetic counselling based on the report of the aneuploidy only will not be affected. CGH allows the detection of unbalanced rearrangements over 10 Mb and has the same resolution as conventional cytogenetic analysis of cultured tissues from spontaneous abortions (300–350 bands). Although small rearrangements may be missed by CGH, it gives a more precise extent of the genomic unbalance. However, the exact nature of the rearrangement requires conventional cytogenetic analysis. Mosaicism may be missed by CGH testing when the unbalanced cell line is present in 5% for any given specimen, it is reasonable to suspect that the scorers applied different scoring criteria. It is important to determine the source of variation between the two scorers. This can be done when scorers examine a series of nuclei together and discuss the source of scoring discrepancies "nucleus-by-nucleus".
4.15. Clinical Evaluation Study It is useful to perform a clinical evaluation study before using the BCR/ABL FISH test in clinical practice. The clinical evaluation should attempt to test all the param-
Interphase FISH Studies of CML
eters of the new test that might be anticipated in clinical practice. Normal values need to be established as well as an abnormal reference range. Because these figures vary among laboratories depending upon experience and proficiency, it is important that they be determined for each laboratory independently. Before beginning the clinical evaluation study, the investigator should have completed efforts to standardize the pre-analytical, analytical and post-analytical factors including collection, transportation and preparation of specimens. In addition, the scoring criteria, analytical sensitivity, number of cells needed for a clinically pertinent power of testing sensitivity, and interpretation of results should be established. Furthermore, all safety issues should have been identified and addressed. The clinical evaluation study could be done in various ways and may involve any number of specimens, but from a statistical point of view, the more specimens the better. A reasonable study could be based on 20 or more normal specimens and up to 20 specimens from patients known to have CML. It is important to code the specimens so that they can be studied blindly. Two technologists should score each specimen independently, making sure to record the signal patterns of scorable cells and the number of cells that do not meet the scoring criteria. When the clinical evaluation is complete, calculate the normal cutoff using data from the normal specimens. The normal values can be calculated in several different ways. It is generally unacceptable to use the mean plus or minus two or three standard deviations, even though this is common in the literature. This statistical approach is unacceptable because it assumes the data fit a bell-shaped curve. For BCR/ABL fusion studies this is not the case for either patients who have 100% normal cells or patients with untreated CML who have >90% neoplastic cells. Although some statistical methods to calculate the normal cutoff are available (1,69), the following approach is relatively simple and should suffice for studies of CML using FISH. The number of cells that should be analyzed to achieve an expected power of testing sensitivity depends on the degree of confidence required, on the level of mosaicism to be excluded, and on the analytical sensitivity of the probe (70). The closer the analytical sensitivity of any probe approaches 100%, the more a relatively few anomalous signals in any number of observations might indicate the presence of a second cell line. The scoring process represents only 52% of the total effort to perform FISH studies (47). In our experience, and that of others, it is not difficult to score 500 nuclei, record the data, and capture two or three representative images in less than 20 min. Thus, little is gained by scoring fewer cells. Moreover, the high sensitivity of the newer FISH tests becomes particularly effective when 500 or more nuclei are examined. In one study, the analysis of 500 interphase nuclei was shown to approximate the sensitivity to detect both normal and abnormal cells by conventional cytogenetic studies on 25 metaphases (3). A good way to achieve an analytical sensitivity of FISH for BCR/ABL fusion to approach 100% for interphase nuclei is to score only those cells that meet the scoring criteria for normal or neoplastic signal patterns. The key to the success of this approach is defining strict scoring criteria and then consistently following them. Strict scoring criteria have been published for S-FISH and D-FISH (1,2).
Dewald
One method to establish the normal cutoff and the abnormal reference range is to study a series of normal and abnormal specimens in a random and blinded fashion. This series should include 20 or more samples that are pre-designated for use in the calculation of the normal cutoff. The number of false-positive nuclei should be determined for each of the predesignated normal specimens. This analysis predicts the maximum number of abnormal appearing nuclei that was encountered in any patient. The normal cut-off can then be established by using this number to calculate the upper bound of a one-sided 95% confidence interval analysis using the binomial distribution. Table 1 shows a series of cutoffs calculated using the binomial distribution formula for 200- or 500-nuclei samples showing from 0–15 nuclei with false-positive signal patterns. The abnormal reference range (percentage of cells with an abnormal pattern) can be calculated using data from specimens from untreated patients with CML. As part of the clinical evaluation study, it is useful to determine the proportion of cells that do not meet the scoring criteria in a series of specimens. This figure can be calculated using the same statistical method as for the normal values and used in future studies as a quality control parameter. Whenever the proportion of unscorable cells exceeds the expected range, the test may have experienced unexpected technical problems. The clinical sensitivity and clinical specificity can be calculated from the results of the clinical evaluation study. The clinical sensitivity refers to the percentage of correctly identified true positive specimens. The clinical specificity refers to the percentage of correctly identified true negative specimens. If the sample size is large enough, it may be useful to calculate the predictive value of the test. This is the percentage of true positive and true negative specimens that were correctly identified by the test. When significant procedural changes are contemplated, such as a change of probes or concentration of probes, it is important to perform equivalency tests to revalidate test performance. These studies should establish that the procedure change is equivalent or better than the old procedure. Depending upon the nature of the change in procedure, it may be necessary to revalidate. For less significant changes, for example, changes in lot numbers of the same probe, a series of side-by-side analyses and evaluation of standard controls may suffice.
4.16. Quality Control Studies with FISH The purpose of using controls in FISH studies is to assure that the procedure is working appropriately, to verify that the scoring criteria are applied consistently, to monitor technologists' competency, and to help interpret performance values. FISH studies with BCR and ABL use differently colored probes. The scoring criteria require analyzing only those cells that have an expected signal pattern. In this case, the scoring criteria should permit immediate detection of system or technical failure. For example, the inability to see both BCR and ABL signals should be an indication that the procedure is not working. It is useful to run a positive control that contains a known percentage of normal and Ph-positive nuclei. For quantitative FISH studies, the mixture of cells from positive and negative controls is particularly valuable because it represents a challenge that is similar to the test in clinical practice, i.e., quantifying normal and abnormal cells.
Table 1 Normal Cut-Off Using One-Sided 95% Confidence Interval for the Observed Number of False-Positive Cells out of 200 or 500 Cells Scored Based on the Binomial Distribution Cells scored
Falsepositive cells
Percent false-positive cells
Normal cutoff (%)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
1.5 2.5 3.0 4.0 4.5 5.0 6.0 6.5 7.0 7.5 8.5 9.5 10.0 10.5 11.5 12.0 0.6 1.0 1.2 1.6 1.8 2.0 2.4 2.6 2.8 3.2 3.4 3.6 3.8 4.2 4.4 4.6
Control specimens should be run with each specimen or batch of specimens. It is possible to make control specimens by using leftover cells obtained from patients with CML that were studied in clinical practice. Patients undergoing leukophoresis can also be a good source of control cells for CML. The performance of the test, reagents and technologists can be monitored by graphing data from the studies of the standard control specimens on a test-by-test basis over
time. This method is also useful to monitor the performance of new lots and to obtain performance verification of probes. Moreover, graphing data from standard controls is useful to evaluate the equivalency of methodological changes such as switching from an indirect-labeled probe to a direct-labeled probe. The graph should include a mean and standard deviation based on the results from the pilot study and clinical evaluation study. It is important to update the statistics whenever there are significant changes in the procedures, including new technologists. Any of the following results of the standard control can indicate testing problems: (1) the run is more than three standard deviations from the mean, (2) two consecutive values are more than two standard deviations from the mean, (3) four consecutive values are more than one standard deviation from the mean, or (4) ten consecutive values fall on one side of the mean (71). Any of these situations can indicate technical or personnel problems with the test and require an investigation to identify the source of the variation and for which appropriate corrective action should be taken. Minor corrective actions may include re-testing the sample or using an additional scorer. Major corrective actions may require changes in procedure, using new reagents or new controls, reassessment of the basic statistics of the control results, remedial training of personnel, or even complete revalidation of the test.
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27. Stock, W., Westbrook, C., Peterson, B., et al. (1997) Value of molecular monitoring during the treatment of chronic myeloid leukemia: A Cancer and Leukemia Group B study. J. Clin. Oncol. 15, 26. 28. Shtivelman, B., Lifshitz, R., Gale, R., and Canaani, E. (1983) Fused transcript of abl and bcr genes in chronic myelogenous leukaemia. Nature 315, 550. 29. Konopka, J., Watanabe, S., Singer, J., Collins, S., and Witte, O. (1985) Cell lines and clinical isolates derived from Ph-positive chronic myelogenous leukemia patients express C-abl proteins with a common structural alteration. Proc. Natl. Acad. Sci. USA 82, 1810. 30. Arnoldus, E., Wiegant, J., Noordermeer, I., et al. (1990) Detection of the Philadelphia chromosome in interphase nuclei. Cytogenet. Cell. Genet. 54, 108–111. 31. Tkachuk, D., Westbrook, C., Andreeff, M., et al. (1990) Detection of bcr-abl fusion in chronic myelogeneous leukemia by in situ hybridization. Science 250, 559–562. 32. Sinclair, P., Green, A., Grace, C., and Nacheva, E. (1997) Improved sensitivity of BCRABL detection: A triple-probe three-color fluorescence in situ hybridization system. Blood 90, 1395–1402. 33. Seong, D., Kantarjian, H., Ro, J., et al. (1995) Hypermetaphase fluorescence in situ hybridization for quantitative monitoring of Philadelphia chromosome-positive cells in patients with chronic myelogenous leukemia during treatment. Blood 86, 2343–2349. 34. Seong, C.-M., Giralt, S., Kantarjian, H., et al. (2000) Early detection of relapse by hypermetaphase fluorescence in situ hybridization after allogeneic bone marrow transplantation for chronic myeloid leukemia. J. Clin. Oncol. 18, 1831–1836. 35. Appelbaum, F., Clift, R., Radich, J., Anasetti, C., and Buckner, C. (1995) Bone marrow transplantation for chronic myelogenous leukemia. Semin. Oncol. 22, 405–411. 36. ICSG. (1994) Italian Cooperative Study Group on Chronic Myeloid Leukemia. Interferon alfa-2a as compared with conventional chemotherapy for the treatment of chronic myeloid leukemia. N. Engl. J. Med. 330, 820–825. 37. Talpaz, M., Kantarjian, H., Kurzrock, R., Trujillo, J., and Gutterman, J. (1991) Interferonalpha produces sustained cytogenetic responses in chronic myelogenous leukemia. Philadelphia chromosome-positive patients. Ann. Int. Med. 114, 532–538. 38. Kloke, O., Niederle, N., Qiu, J., et al. (1993) Impact of interferon alpha-induced cytogenetic improvement on survival in chronic myelogenous leukaemia. Br. J. Haematol. 83, 399–403. 39. Allan, N., Richards, S., and Shepherd, P. (1995) UK Medical Research Council randomised, multicentre trial of interferon-alpha n1 for chronic myeloid leukaemia: improved survival irrespective of cytogenetic response. Lancet 345, 1392–1397. 40. Silver, R. T., Woolf, S. H., Hehlmann, R., et al. (1999) An evidence-based analysis of the effect of busulfan, hydroxyurea, interferon, and allogeneic bone marrow transplantation in treating the chronic phase of chronic myeloid leukemia: developed for the American Society of Hematology. Blood 94, 1517–1536. 41. Thiesing, J., Ohno-Jones, S., Kolibaba, K., and Druker, B. (2000) Efficacy of STI571, an Abl tyrosine kinase inhibitor, in conjunction with other antileukemic agents against Bcr-Abl-positive cells. Blood 96, 3195–3199. 42. Druker, B. (1999) Status of BCR-ABL Tyrosine Kinase Inhibitors in CML, in Hematology (Schechter, G., ed.), American Society of Hematology, Washington D. C., pp. 160–171. 43. Laurent, E., Talpaz, M., Kantarjian, H., and Kurzrock, R. (2001) The BCR gene and Philadelphia chromosome-positibe leukemogenesis. Cancer Res. 61, 2343–2355. 44. Kobzev, Y., Domracheva, E., Zakharova, A., Khoroshko, N., Turkina, A., and Dewald, G. (1998) Fluorescence in situ hybridization studies of interphase nuclei for assessing
response to therapy in patients with chronic myeloid leukemia. Cancer Genet. Cytogenet. 106, 128–134. Nacheva, E., Holloway, T., Brown, K., Bloxham, D., and Green, A. (1993) Philadelphianegative chronic myeloid leukaemia: detection by FISH of BCR-ABL fusion gene localized either to chromosome 9 or chromosome 22. Br. J. Haematol. 87, 409–412. Dewald, G., Ketterling, R., Wyatt, W., and Stupca, P. (2002) Cytogenetic studies in neoplastic hematologic disorders, in Clinical Laboratory Medicine (McClatchey, K., ed.), Williams and Wilkens, Baltimore, pp. 658–685. Dewald, G., Stallard, R., Alsaadi, A., et al. (2000) A multi-center investigation with D-FISH BCR/ABL1 probes. Cancer Genet. Cytogenet. 116, 97–104. Dewald, G., Wyatt, W., and Silver, R. (1999) Atypical BCR and ABL D-FISH patterns in chronic myeloid leukemia and their possible role in therapy. Leuk Lymphoma 34, 481–491. Sinclair, P. B., Nacheva, E. P., Leversha, M., et al. (2000) Large deletions at the t(9;22) breakpoint are common and may identify a poor-prognosis subgroup of patients with chronic myeloid leukemia. Blood 95, 738–743. Le Gouill, S., Talmant, P., Milpied, N., et al. (2000) Fluorescence in situ hybridization on peripheral-blood specimens is a reliable method to evaluate cytogenetic response in chronic myeloid leukemia. J. Clin. Oncol. 18, 1533–1538. Sandberg, A. (1990) Chronic myelocytic leukemia, in The Chromosomes in Human Cancer and Leukemia (Sandberg, A. ed.), Elsevier, New York, pp. 458–520. Thaler, J., Gastl, G., Fluckinger, T., et al. (1996) Interferon alpha-2c therapy of patients with chronic myelogenous leukemia: long-term results of a multicenter phase-II study. Austrian Biological Response Modifier (BRM) Study Group. Ann. Hematol. 72, 349–355. Kantarjian, H., Smith, T., O'Brien, S., Beran, M., Pierce, S., and Talpaz, M. (1995) Prolonged survival in chronic myelogenous leukemia after cytogenetic response to interferonalpha therapy. Ann. Intern. Med. 122, 254. Hehlmann, R., Heimpel, H., Hasford, J., et al. (1994) Randomized comparison of interferonalpha with busulfan and hydroxyurea in chronic myelogenous leukemia. Blood 84, 4064–4077. ICSG. (1995) Italian Cooperative Study Group on Chronic Myeloid Leukemia. Chronic myeloid leukemia, BCR/ABL transcript, response to alpha-interferon and survival. Leukemia 9, 1648–1652. Cuneo, A., Bigoni, R., Emmanuel, B., et al. (1998) Fluorescence in situ hybridization for the detection and monitoring of the Ph-positive clone in chronic myelogenous leukemia: comparison with metaphase banding analysis. Leukemia 12, 1718–1723. Nolte, M., Werner, M., Ewig, M., et al. (1996) Fluorescence in situ hybridization (FISH) is a reliable diagnostic tool for detection of the 9;22 translocation. Leuk. Lymphoma. 22, 287–294. Muhlmann, J., Thaler, J., Hilbe, W., et al. (1998) Fluorescence in situ hybridization (FISH) on peripheral blood smears for monitoring Philadelphia chromosome-positive chronic myeloid leukemia (CML) during interferon treatment: a new strategy for remission assessment. Genes Chromosomes Cancer 21, 90–100. Lesser, M. L., Dewald, G. W., Sison, C. P., and Silver, R. T. (2000) Correlation of three methods of measuring cytogenetic response in chronic myeloid leukemia (CML). Canc. Genet. Cytogenet. In press. Mitelman, F. (1993) The cytogenetic scenario of chronic myeloid leukemia. Leuk. Lymphoma 11 Suppl, 11–15. Diez-Martin, J. L., Dewald, G. W. and Pierre, R. V. (1988) Possible cytogenetic distinction between lymphoid and myeloid blast crisis in chronic granulocytic leukemia. Am. J. Hematol. 27, 194–203.
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CISH and FISH in Pathology
23 Chromogenic In Situ Hybridization and FISH in Pathology Bae-Li Hsi, Sheng Xiao, and Jonathan A. Fletcher 1. Introduction Fluorescence in situ hybridization (FISH) technologies enable rapid detection of chromosome aberrations in all manner of tissues, including both fresh and archival specimens. These technologies have gained broad acceptance in the clinical cytogenetic and research communities. However, these same methods are used less frequently by noncytogenetic diagnostic pathology services. This is, in part, because FISH imaging equipment is not universally available to the diagnosticians (surgical pathologists) responsible for histological diagnoses. Therefore, it is gratifying that various improvements in ISH probes and detection protocols, particularly over the past five years, have enabled routine evaluation of enzymatic ISH by light microscopy. Virtually all malignant human tumors contain clonal chromosomal aberrations that are responsible, in part, for tumorigenic progression from nonneoplastic progenitor cell to cancer. These aberrations often affect genes involved in cellular proliferation, apoptosis, and invasiveness, and, in so doing, account for many clinicopathological properties that are hallmarks of the cancer diagnosis. Although conventional histological examination is the mainstay of surgical pathology, there are an increasing number of situations where cytogenetic markers provide critical diagnostic and prognostic information. In many cases, the cytogenetic aberrations are best interpreted in the context of histology. One well-known example is that of ERBB2 (HER2/NEU) gene amplification in breast carcinoma, wherein it is important to evaluate amplification specifically in the invasive components of the tumor (1). Therefore, there is need for detection strategies which enable interpretation of molecular cytogenetic assays in histological preparations. Ideally, such assays would be read on an ordinary light microscope, rather than requiring a fluorescence system (2–4). In that way, molecular cytogenetic assays could be adopted more widely by the surgical pathology community, very much akin to immunohistochemistry, and could function as "special stains" in relationship to the routine histological evaluation of a given case. From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
23_His_343-352F[7.10.2]
Hsi, Xiao, and Fletcher
The notion of interpreting DNA-based tests in conjunction with the standard histological appraisal is not new. However, there are very few pathology/histology laboratories which perform chromogenic in situ hybridization (CISH) for brightfield detection, and there are even fewer laboratories which use such methods for dualcolor detection of chromosomal translocations, amplifications, or deletions. The methods described herein enable reproducible FISH or CISH evaluation of various chromosomal aberrations in a wide range of pathology specimens, including paraffin sections, frozen materials, and cytopathology preparations. Importantly, these methods provide a mechanism whereby molecular cytogenetic evaluations can be routinely integrated in a standard histopathology or cytopathology work-up. Most histopathology assays are performed in interphase cells rather than in cytogenetic metaphase preparations. Therefore, unique sequence and other locus-specific probes, e.g., alpha satellite probes, are generally more relevant as histopathology/ cytopathology adjuncts than are metaphase-oriented molecular cytogenetic approaches such as comparative genomic hybridization and chromosomal painting. Notably, locus-specific ISH is equally applicable to cytogenetic or archival preparations. Almost any source of intact nuclei can be used, including: (1) histological sections; (2) touch preparations; (3) cytological preparations; (4) bone marrow smears; (5) nuclei disaggregated from thick, e.g., 25–50 micron, paraffin sections; (6) nuclei disaggregated from frozen specimens; and (7) cytogenetic preparations. As discussed above, a key advantage in using histological sections is that the tumor cells are studied in their native architecture.
1.1. Pros and Cons of FISH vs CISH FISH is more widely used for molecular cytogenetic analyses, particularly in cytogenetic laboratories, than is CISH. However, both methods have their distinct advantages and disadvantages. One substantial advantage of the FISH approach is that probe detection can be accomplished by direct detection. By contrast, chromogenic detection methods are indirect by definition, and CISH generally requires at least two additional steps beyond probe hybridization, prior to nuclear counterstaining. For example, a probe can be labeled with FITC or rhodamine, and thereby detected directly using the FISH method. The same probe might be labeled with biotin and then detected by sequential incubations with strepavidin-HRP and DAB, using the CISH method. Another advantage of FISH is that penetration of probes and detection reagents, to the target chromosomal regions, is accomplished more readily than with the larger detection proteins, e.g., alkaline phosphatase, customarily used in CISH detection. CISH, on the other hand, has several advantages that are of particular relevance in paraffin section applications. For example, paraffin section histological detail is generally better appreciated with brightfield, rather than fluorescence, counterstaining and viewing. This is in part because cellular and extracellular proteins can contribute to a dull, generalized, autofluorescence, which often obscures FISH signals in paraffin sections (see Note 1). Another factor is that large regions of the tissue section can be scanned rapidly after CISH counterstaining with conventional stains such as hematoxylin. Morphological detail is readily apparent using low-power objectives (×10 or ×20), and
the CISH probe signals themselves can be apparent even at such low magnification. Fluorescence probe signals and counterstains on the other hand, are generally only appreciated at substantially higher magnification. A further advantage of CISH is that the probe signals are not subject to rapid fading and the slides can therefore be archived.
1.2. FISH/CISH in Histological Paraffin Sections One advantage in performing FISH or CISH in paraffin sections is that paraffinembedded materials are readily available for virtually all pathology specimens. In addition, fixation and embedding methods can be standardized, leading to a very consistent platform for subsequent FISH or CISH detection. A unique advantage is that subtle differences in cellular morphology are often appreciated best when the cells are situated in their native architecture. It can be more difficult to identify different cell types once the individual nuclei have been extracted from paraffin sections. A disadvantage of histological paraffin sections (generally four–six micron) is that this thickness is less than the diameter of virtually all mammalian nuclei. Therefore, the nuclei are invariably incomplete, and evaluation of chromosomal deletions can be challenging. On the other hand, evaluation of gene amplifications or translocations is relatively straightforward (Fig. 1). Thicker sections can be used, in order to accomplish better representation of intact nuclei. However, overlapping nuclei are then more of a problem.
1.3 Alternate Pathology Applications: FISH/CISH in Disaggregated Nuclei, Touch Preparations, and Cytological Preparations The constraint of nuclear slicing, always an issue in thin paraffin sections, can be circumvented by any of several alternate approaches. The methods for these alternate approaches are beyond the scope of this chapter, but they are described in the literature and are summarized below (5,6). In general, all of these approaches enable evaluation of FISH or CISH probes in intact cells. However, they provide less information about cell type and tissue architecture compared to the paraffin section methods described herein. One approach involves disaggregating intact nuclei from thick (generally 25–50 micron) paraffin sections (7). This approach is particularly applicable when cells do not need to be evaluated in the context of their native architecture. However, in our experience, this method is less forgiving technically, compared to hybridization in thin paraffin sections. The enzymatic treatment required for release of nuclei can sometimes damage the nuclei, and this is compounded during subsequent slide denaturation steps. Therefore, a subset of specimens will evidence poor nuclear morphology and will have suboptimal FISH or CISH signals. Intact nuclei can also be disaggregated from fresh or frozen tissue specimens, and in general such applications are more foolproof than disaggregation from paraffin (6). FISH or CISH can also be performed after pressing either fresh or thawed (frozen) tissue against a glass slide (6). These touch imprints require enzymatic digestion before probe hybridization. Otherwise, the labeled probes would not readily access their target
Fig. 1. (A) Dual color CISH evaluation of chromosome 17 centromere (DAB) and ERBB2 (HER2/NEU) locus (Fast-Red) in breast cancer cell line, showing chromosome 17 aneusomy and high level ERBB2 amplification. (B) Combined immunohistochemical and CISH evaluation of ERBB2 (HER2/NEU) protein (Fast-Red) and genomic locus (DAB) in cell block of invasive breast cancer. Strong membrane-associated ERBB2 expression results from high-level genomic amplification. (C) High level MYCN (N-myc) genomic amplification in paraffin section of neuroblastoma. Heterogeneity of MYCN amplification is apparent, with neoplastic cells in the right hand part of the field being nonamplified. (D) Dual-color FISH in Burkitt lymphoma paraffin section, demonstrating MYC gene region rearrangement resulting from translocation of chromosome band 8q24. Closely-associated red-brown signal pairs represent the nonrearranged chromosome 8, whereas isolated red or brown signals (at top right) represent the translocation chromosomes.
chromosomal domains through the intact cell membranes and cytoplasm. An advantage of this approach is that nuclei are intact, and therefore evaluation of chromosomal deletions is straightforward. Disadvantages are that nuclear size and shape are altered by the requisite enzymatic treatment, and it can be difficult therefore to distinguish morphologically between different cell populations, e.g., neoplastic versus nonneoplastic cells. Cytological preparations have unique advantages for FISH or CISH purposes. Like touch preparations, they provide intact cells. However, "cytological" methods of preparation, including certain proprietary technologies such as the ThinPrep (Cytyc Corporation), are often highly standardized and very conducive to FISH/CISH applications (6).
2. Materials 2.1. Slide Treatment Before Hybridization 1. Four-micron thick paraffin sections, mounted on Superfrost/Plus microscope slides (Fisher Scientific, Pittsburgh, PA). 2. 60°C oven. 3. Microwave oven, Model JE1390GA (General Electric Co., Louisville, NY). 4. Slide Moat, Model 240000 (Boekel Scientific, Feasterville, PA). 5. Glass Coplin jars. 6. Tris-EDTA solution: 0.1 M Tris-HCl, 40 mM EDTA, pH 7.0. Dissolve 24.2 g Tris-base and 29.22 g EDTA in 1800 mL dH2O, adjust pH with 10 N NaOH to pH 7, and QS to 2 L. 7. Phosphate buffered saline (PBS): 137 mM NaCl, 2.7 mM KCl, 4.3 mM Na2HPO4, 1.4 mM KH2PO4. Dissolve 8 g NaCl, 0.2 g KCl, 1.44 g of Na2HPO4 and 0.24 g KH2PO4 in 900 mL of dH2O QS to 1 L. 8. Digest-All 3 (Zymed Laboratories, South San Francisco, CA). 9. 10% buffered formalin phosphate (Fisher Scientific Co., Fair Lawn, NJ). 10. Xylene. 11. 100, 85, and 70% ethanol.
2.2. Denaturation and Hybridization 1. Thermocycler with slide adapter, e.g., PTC-200/225 (MJ Research Inc., South San Francisco, CA). 2. 37°C humidified oven. 3. Plastic slide chamber. 4. Cover glass. 5. Rubber cement. 6. Biotin and/or Digoxigenin labeled DNA probes, e.g., Her2, C-Myc , N-Myc , (Zymed Laboratories).
2.3. Post-Hybridization Wash 1. 70–80°C waterbath. 2. Glass Coplin jars. 3. 20X SSC: Dissolve 175.3 g of NaCl and 88.2 g of sodium citrate in 800 mL H2O, QS to 1 L, and adjust pH to 7.0. 4. 2X SSC: Mix 50 mL 20X SSC with 450 mL H2O. 5. 0.5X SSC: Add 10 mL 2X SSC to 30 mL H2O. 6. PBS/T: Add 250 µL Tween-20 to 500 mL of PBS.
2.4. Detection 2.4.1. FISH 1. CAS-block (Zymed Laboratories). 2. Antibody dilution: Dissolve 10 g of lyophilized normal goat serum in 100 mL of CAS-block. 3. Strepavidin, Alexa-594 conjugate (Molecular Probes, Eugene, OR). Dilute at 1:500 in Antibody diluent. 4. Anti-digoxigenin-fluorescein, Fab-fragment (Roche Diagnostics Co., Indianapolis, IN). Dilute at 1:500 in Antibody diluent. 5. PBS/T. 6. DAPI mounting medium (Vector Laboratories, Burlingame, CA).
2.4.2. CISH 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
CAS-block (Zymed Laboratories). Antibody dilution: Dissolve 10 g of lyophilized normal goat serum in 100 mL of CAS-block. HRP-streptavidin (Zymed Laboratories). Prediluted, ready to use. Anti-digoxigenin-AP, Fab-fragment (Roche Diagnostics Co., Indianapolis, IN). Dilute at 1:500 in Antibody diluent. Anti-digoxigenin-fluorescein, Fab-fragment (Roche Diagnostics Co.). Dilute at 1:500 in Antibody diluent. Alkaline phosphatase anti-fluorescein (Vector Laboratories). Dilute at 1:500 in Antibody diluent. DAB Reagent Set (Zymed Laboratories). Prepared fresh according manufacturer's protocol. Fast Red Substrate Pack (Zymed laboratories). Prepared fresh according manufacturer's protocol. Ultracleaning filter units (0.45 µm) (Fisher Scientific). PBS/T. Gill's hematoxylin (Vector Laboratories). Glycerogel (DAKO Co., Carpinteria, CA).
3. Methods 3.1. Slide Treatment Before Hybridization 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Bake slides at 60°C overnight in an oven. Deparaffinize the slides in 3 changes of xylene, 15 min each. Dehydrate the slides in 100% ethanol, 3×, 2 min each, and air dry. Place Tris-EDTA solution in the microwave oven in a plastic Coplin jar or other microwave proof plastic slide container, then heat to 199°F using the temperature probe. Place the slides in the Tris-EDTA solution and continue the microwaving at 199°F for 15 min. Remove the slides and place them in the PBS. Blot excess PBS from the slides and then place slides in the humidified chamber of the Slide Moat (or other humidified incubator) at 37°C. Add 100–500 µL Digest-All 3 to the sections, and let digestion proceed for 1–30 min dependent on the tissue type and fixation (see Note 1). Stop the digestion by placing the slides in PBS. Fix the slides in 10% buffered formalin for 1 min, then rinse off the formalin by placing slides briefly in 40 mL PBS in a Coplin jar. Dehydrate the slides through 70, 85, and 100% ethanol, 2 min each, at room temperature. Air dry.
3.2. Denaturation and Hybridization 1. Add sufficient probe to the section, e.g., 10 µL for an area corresponding to a 22 × 22 mm cover slip. 2. Place coverslip over the section and seal edges with rubber cement. 3. Place the slides on the slide holder in a thermocycler and denature the slides for 3 min at 94°C. 4. Transfer the slides to a plastic slide chamber and place in a humidified incubator at 37°C overnight.
3.3. Post-Hybridization Wash 1. Set the waterbath temperature according to the number of slides per Coplin jar, 73°C for 1 slide, 74°C for 2 slides, 75°C for 3 slides, and 76°C for 4 slides. 2. Place glass Coplin jars containing 40 mL of 0.5X SSC in the waterbath and allow the Coplin jar SSC solution to equilibrate to the waterbath temperature. Coplin jars, and contents, should be no cooler than room temperature when placed in the waterbath. Otherwise, the jar may crack. Confirm final temperature using a thermometer. 3. Remove rubber cement and cover slips from the slides. 4. Wash the slides in the 0.5X SSC for 5 min. 5. Remove the slides and transfer to 40 mL PBS/T in a Coplin jar, at room temperature.
3.4. Detection 3.4.1. FISH 1. Remove excess PBS/T from the slides and place in a humidified plastic slide chamber. 2. Apply 100–500 µL CAS-block to the section and incubate for 10 min at room temperature. 3. Tap off CAS-block, then apply 100 to 500 µL of antibody diluent containing the fluorconjugated detection reagents, e.g., 1:500 dilutions of streptavidin-Alexa 594 and antidigoxigenin-fluorescein. Incubate for 30 min at room temperature. 4. Wash the slides 3× in 40 mL PBS/T, 2 min each wash, at room temperature. 5. Counterstain slides with DAPI mounting medium.
Remove excess PBS/T from the slides and place them in a humidified plastic slide chamber. Add CAS-block onto the section and incubate for 10 min at room temperature. Tap off CAS-block, then add HRP-streptavidin and incubate for 30 min at room temperature Wash the slides 3× in 40 mL PBS/T, 2 min each wash, at room temperature. Prepare the DAB substrate according to the manufacturer's instructions, remove the excess PBS/T from the slides and incubate the slide with DAB for 15 min. Wash the slides 3× in 40 mL PBS/T, 2 min each, at room temperature. Remove excess PBS/T from the slides, add antidigoxigenin-fluorescein (see Note 2) and incubate for 30 min at room temperature. Wash the slides 3× in 40 mL PBS/T, 2 min each, at room temperature. Remove excess PBS/T from the slides, add alkaline phosphatase anti-fluorescein and incubate for 30 min at room temperature. Wash the slides 3× in 40 mL PBS/T, 2 min each, at room temperature. Prepare the Fast Red substrate according to the manufacturer's instructions, then pass it through a 0.45 µm filter. Drain/tap excess PBS/T from the slides, then add Fast Red substrate to the section. Incubate for 30 min total with 2 changes of Fast Red substrate at 10 min intervals. This is
Hsi, Xiao, and Fletcher accomplished by tapping the Fast Red substrate from the slides every 10 min and replenishing with additional filtered substrate. Wash the slides in 40 mL dH2O at room temperature. Counterstain the slides with hematoxylin, being careful not to overstain (see Note 3). Gill's formula (without organic solvent–see Note 4) should be used in conjunction with Fast-Red. Wash the slides in running tap water for several minutes. Do not use ammonia citrate to intensify the blue of the hematoxylin. Heat the Glycerogel at 50–75°C in an oven or waterbath and add a drop to the section (without use of organic solvent) then cover it with cover slip. Remove excess glycerogel by gently pressing down on the cover slip, heat the slide on a hot plate (37–45°C) if the glycerogel has solidified.
4. Notes 1. Residual extracellular and cellular proteins can give rise to dull red-to-orange autofluorescence, which can obscure the probe FISH signals, particularly when the actual probe signals are of low intensity. Autofluorescence can often be minimized by increasing the enzymatic digestion time for the paraffin section. Inadequate tissue section digestion will also tend to impede probe access to the target chromosomal domains (resulting in weak "true" signals) and can increase nonspecific binding of the probe to nonchromosomal cellular components. Therefore, digestion time should generally be increased if cell morphology is excellent (based on the DAPI counterstain), and if the cells have scattered small nonspecific signals. A properly hybridized paraffin section should have wellpreserved cell morphology (although not necessarily perfect), readily apparent probe signals, and should be devoid of nonspecific signals. 2. The CISH detection protocol here stipulates amplification of the digoxigenin-labeled probe by sequential incubations with fluorescein anti-digoxigenin and alkaline phosphatase antifluorescein. However, digoxigenin-labeled probes can also be detected without the amplification step, in which case the fluorescein antidigoxigenin is replaced by alkaline phosphatase anti-digoxigenin. 3. The different colors in dual-color CISH (brown from DAB and red from Fast-Red, in this protocol) are less distinct from each other than is the case for fluorescein vs rhodamine in dual-color FISH. It can be particularly difficult to distinguish DAB from Fast-Red when the probe signals are very small. However, the color differences can often be appreciated by focusing up and down through the section. At certain focal points, the Fast-Red will be more or less refractile and the distinct red color will be apparent. It is also important that the hematoxylin counterstain be kept to the minimum needed to define the nuclear contours and tissue architecture. Therefore, the hematoxylin should be only a light blue. Otherwise, the hematoxylin will mask the DAB vs FastRed color differences. 4. Organic solvents cannot be used in mounting the cover slips after staining with FastRed. FISH and CISH slides are ordinarily kept at 4°C, although we have found that CISH slides can be kept at room temperature for approx several weeks. FISH signals fade partially after several months in storage, whereas CISH slides are stable for approx 2 yr. 5. The dual-color CISH protocol can be modified slightly for combined CISH and immunohistochemical staining (Fig. 1 ). In this case, one chromosomal target and one protein are detected by single color CISH and immunohistochemistry, respectively.
References 1. Ross, J. S. and Fletcher, J. A. (1998) The HER-2/neu oncogene in breast cancer: prognostic factor, predictive factor, and target for therapy. Stem Cells 16, 413–428. 2. Hopman, A. H., Claessen, S., and Speel, E. J. (1997) Multi-colour brightfield in situ hybridisation on tissue sections. Histochem. Cell Biol. 108, 291–298. 3. Speel, E. J., Ramaekers, F. C., and Hopman, A. H. (1995) Cytochemical detection systems for in situ hybridization, and the combination with immunocytochemistry, 'who is still afraid of red, green and blue?' Histochem. J. 27, 833–858. 4. Tanner, M., Gancberg, D., Di Leo, A., Larsimont, D., Rouas, G., Piccart, M. J., and Isola, J. (2000) Chromogenic in situ hybridization: a practical alternative for fluorescence in situ hybridization to detect HER-2/neu oncogene amplification in archival breast cancer samples. Am. J. Pathol.157, 1467–1472. 5. Davison, J. M., Morgan, T. W., Hsi, B. L., Xiao, S., and Fletcher, J. A. (1998) Subtracted, unique-sequence, in situ hybridization: experimental and diagnostic applications. Am. J. Pathol. 153, 1401–1409. 6. Xiao, S., Renshaw, A. A., Cibas, E. S., Hudson, T. J., and Fletcher, J. A. (1995) Novel fluorescence in situ hybridization approaches in solid tumors: Characterization of frozen specimens, touch preparations, and cytologic preparations. Am. J. Pathol.147, 896–904. 7. Schofield, D. E. and Fletcher, J. A. (1992) Trisomy 12 in pediatric granulosa-stromal cell tumors. Demonstration by a modified method of fluorescence in situ hybridization on paraffin-embedded material. Am. J. Pathol.141, 1265–1269.
FISH of HER2 in Breast Cancer
24 FISH Detection of HER2 Amplification in Breast Cancer Rosemary E. Mueller and Frances P. O'Malley 1. Introduction Gene amplification is frequently detected in human tumor cells and is thought to make an important contribution to tumorigenesis (1,2). Systematic scanning of the whole genome of tumor cells using comparative genomic hybridization has revealed that gene copy number changes occur concurrently in many areas of the genome in solid tumors (3). Detailed analysis of altered regions of DNA has revealed complex DNA rearrangements often involving multiple genes and spanning several megabases in solid tumors. Overlaid on gene rearrangements are frequent changes in chromosome ploidy (4–6). The analysis of amplified regions of DNA can lead to the identification of novel genes that contribute to tumorigenesis, but is complicated by the co-amplification of neighboring genes in these large, complex rearrangements. Many tumors show such a high degree of general DNA and chromosome rearrangement that some researchers argue the critical event in tumorigenesis is genomic instability (7–10) with gene amplification being a consequence.
1.1. Amplification of the HER2 Gene in Breast Cancer The HER2 gene was first identified in the DNA of chemically induced rat neuroblastomas (12), where it was designated "neu". The human equivalent of "neu" was independently cloned from a cDNA library and called "HER 2" (13) for its homology to the epidermal growth factor receptor. The gene was also cloned from genomic DNA and referred to as "c-erbB2" (14,15) for its relation to a viral gene responsible for avian erythroblastosis. Preclinical data has shown that HER2 gene amplification directly contributes to tumor cell growth through the function of its encoded protein called p185 or erbB2. The erbB2 protein is related to the epidermal growth factor receptor, sharing the common structure of a large glycosylated extracellular ligand binding domain, a single hydrophobic transmembrane domain, and a cytoplasmic domain that contains a tyrosine kinase catalytic domain, reviewed in (16). ErbB2 participates in a network of signaling when homodimerized or dimerized with other members of From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
Mueller and O'Malley
the erbB protein family (17). Activated erbB2 enhances signaling through the MAPK pathways, which transduce growth factor signals to mediate mesenchymal–epithelial interactions (18–21). ErbB2 signaling has been shown to affect morphogenic differentiation programs in murine breast epithelial cells (22,23) and to induce cell migration and invasion of extracellular matrix in vitro (24). HER2 gene amplification results in overexpression of the protein p185 and occurs in about one third of breast cancers (25–28). There remain unresolved issues with respect to the technical validation of methods of assessing HER2 alterations (11). With respect to clinical validation, an association between HER2 amplification and an adverse prognosis in lymph node positive (LNP) disease has been consistently demonstrated since this association was first reported by Slamon et al. (25–30) The data evaluating the prognostic significance of HER2 overexpression in lymph node negative (LNN) disease, particularly as assessed by immunohistochemistry, is controversial; some studies show a positive correlation with poor clinical outcome (31–40) whereas others show no association (41–51). For a review of immunohistochemical studies, see ref. (52). However, studies evaluating HER2 gene amplification in lymph node negative (LNN) disease have consistently shown an association between HER2 gene amplification and adverse prognosis. In a study by Press et al. (53), HER2 gene amplification was assessed by fluorescence in situ hybridization (FISH) in a series of 240 untreated LNN breast cancer patients. In these patients, the relative risks of early recurrence, any recurrence, and disease-related death were statistically significantly associated with HER2 amplification by FISH. A further study assessing HER2 gene amplification using a quantitative polymerase chain reaction assay in a prospective series of 580 LNN patients demonstrated a statistically significant (p = 0.002) increased risk of disease recurrence in patients whose tumors showed approximately a twofold amplification of the HER2 gene (54).
1.2. HER2 Overexpression and Breast Cancer Treatment HER2 overexpression has been demonstrated to have utility as a predictive factor in breast cancer. A predictive factor provides information on tumor response to a particular drug or therapy. HER2 alterations provide predictive information both in the adjuvant and metastatic setting. Several reports from randomized controlled trials suggest that patients with HER2 positive tumors show a better response to anthracycline-based chemotherapy than patients with HER2 negative tumors. These studies have primarily assessed HER2 protein overexpression (55–57). HER2 gene amplification was assessed by FISH using the Vysis PathVysion HER2 DNA probe kit in a retrospective analysis of 524 tumor samples from patients who were enrolled in the CALGB 8869 clinical trial and and Vysis PathVysion PMA, 1998 (58). FISH analysis of the study specimens showed that there was a significant dose–response effect with anthracycline chemotherapy in patients with HER2 gene amplification, but not in patients lacking HER2 gene amplification. These results supported the United States Food and Drug Administration approval of the Vysis PathVysion HER2 DNA probe kit for use with
stage II, node-positive breast cancer patients. Examples of unambiguous HER2 gene amplification detected by FISH are shown in Fig. 1A, B. There is controversial evidence as to whether the HER2 status of tumors can predict patient response to hormonal therapy. Bianco et al. reported the results from 433 women with Stage I, II, or III (T3a) breast cancer enrolled in the Group of the University of Naples (GUN) trial (59). At a median followup of 14 yr, tamoxifen was effective in improving both disease-free survival (DFS) (p < 0.00001) and overall survival (OS) (p = 0.03). When the HER2–tamoxifen interaction was examined, it was found that tamoxifen was associated with improved DFS and OS only in HER2 negative patients, while showing a paradoxical detrimental effect in HER2 positive patients (59). A followup analysis in 2000 confirmed these findings (60). In contrast, other studies have not demonstrated such an association between HER2 positivity and a decreased response to endocrine therapy (61–63). Herceptin® (trastuzumab, Genentech, San Francisco, CA) is a modified monoclonal antibody to the HER2 protein that is believed to induce growth arrest of tumor cells by interfering with signaling initiated by HER2 protein on the cell surface and by triggering antibody-dependent cell-mediated cytotoxicity. In vitro studies have demonstrated that anti-HER2 antibodies dramatically reduce the growth of tumor cells bearing high levels of HER2 protein (64,65). Phase I and II clinical trials have demonstrated the efficacy and safety of Herceptin® when used alone or in combination with cisplatin (66,67). The pivotal phase III clinical trial (68) showed that the addition of Herceptin® to chemotherapy in patients with HER2 overexpressing tumors was associated with a longer time to disease progression (median 7.4 vs 4.6 mo, p < 0.001) and a lower death rate at one year (22 vs 33%, p = 0.008) when used as a first line therapy in the metastatic setting. In this trial, the HER2 status of patients' tumors was evaluated with an immunohistochemical assay referred to as the Clinical Trial Assay (CTA). Tumors were scored as 0, 1+, 2+ or 3+ and only patients with either 2+ or 3+ staining were considered eligible for the study (approx 1/3 patients). Results indicated that the beneficial effects of treatment were confined to the group of patients whose tumors demonstrated the strongest (3+) HER2 immunostaining (69,70). The United States Food and Drug Administration (FDA) approved the use of the Dako HercepTest™ for the immunohistochemical detection of HER2 overexpression in tumors of patients who are being considered for Herceptin® therapy in 1998. This test has not been directly studied in the setting of a clinical trial; however, it has been compared with the CTA in over 500 breast tumor samples obtained from the National Cancer Institute Breast Cancer Tissue Bank (69) Results indicate that, though there was a 79% concordance between the HercepTest™ and the CTA, 42% of tumors scored as 2+ by the HercepTest™ were negative (0 or 1+) by the CTA and therefore would not have met the entry criteria for inclusion in the randomized trial discussed above (70) . Since its FDA approval the HercepTest™ has been widely used clinically. However, several studies have reported a high false positivity with this immunoassay (71–79). Clearly there is a need to determine which method of HER2 status assessment best defines response in patients treated with Herceptin®.
Fig. 1. HER2 FISH in breast tumor interphase nuclei. The probe for HER2 is labeled red and probe for chromosome 17 centromere is labeled green. (Path Vysion HER-2DNA Probe kit, Vysis, Downers Grove, IL). Images captured using CytoVision software from Applied Imaging, Santa Clara, CA. (A) HER2 is highly amplified and chromosome 17 is present in the normal two copies. (B) HER2 is highly amplified and chromosome 17 is present in multiple copies. (C) HER2 is present in more than two copies and chromosome 17 is present in the normal two copies. (D) Cells with ≥5 copies of HER2 per cell and polysomy of chromosome 17. (E) Intratumor heterogeneity where there is HER2 amplification in cells of the DCIS (at right), but no amplification in invasive tumor cells (at left).
1.3. FISH Analysis of HER2 Amplification Because immunohistochemical (IHC) results for HER2 status have been so variable (52), there is great interest in assessing DNA copy number using FISH as a clinical diagnostic test. However, since IHC is considerably less expensive and less labor intensive to use, it remains the test most frequently employed to assess HER2 status in the diagnostic setting (80). Many labs propose using IHC as a screening tool with FISH as a confirmatory test for cases giving indeterminate IHC results. Reports comparing IHC results with FISH have found a high concordance in cases scored as highly positive with IHC or negative with IHC, but intermediate results (typically 2+ scores with HercepTest™) show little correlation to gene amplification (71–74,78). It has been suggested that some discordant results between IHC- and DNA-based assays can be explained by overexpression from a single copy of the HER2 gene. A recent report (79) analyzing levels of HER2 mRNA expression in discordant cases, however, has refuted this argument. A dilemma remains for cases with indeterminate IHC results where FISH analysis shows inconclusive results. These samples may have cells with polyploidy of chromosome 17 or borderline amplification levels of HER 2 in the context of chromosome 17 diploidy (Fig. 1C, D). HER2 gene copy number determined using FISH analysis correlates well with results obtained by Southern blot and dot-blot analysis (28,53), quantitative PCR (81,82) and comparative genomic hybridization (CGH) results (81,83–87). Concordance is improved when cells are microdissected to give a population enriched for tumor cells (88). FISH analysis allows assessment of gene amplification status on a cell by cell basis, so that intratumoral heterogeneity can be readily assessed, whereas Southern blotting, quantitative PCR, and CGH analysis detect gene alterations only when the majority of cells show the same change. Since FISH analysis can be performed in small populations or individual cells, it is ideal for the analysis of breast tumor core biopsy material. Biopsy material and material from the excision of solid tumors is typically fixed in formalin, embedded in paraffin, and subsequently sectioned and mounted on microscope slides for histological examination. Formalin-fixed, paraffin-embedded tissue samples can be stored for decades (see Note 1). FISH can be readily performed on sections from this archived material owing to the stability of DNA. Preservation of the tissue architecture is a major advantage of this procedure. This allows assessment of the amplification status in the invasive tumor, rather than in ductal carcinoma in situ or in adjacent premalignant lesions as shown in Fig. 1E. Analysis of HER 2 amplification by FISH can be reliably performed on fine needle aspirates of breast tumors (89–92), as well as on touch preparations of fresh tissue (93). FISH analysis of disaggregated nuclei or cytological smears may prove more amenable to automated image analysis than FISH performed in tissue sections.
2. Materials 2.1. Laboratory Equipment 1. Series of three 200-mL baths of xylene (or Hemo-D) and three 200-mL baths of absolute ethanol set up in a fume hood (for removing paraffin from tissue sections) and appropriate slide carrying racks.
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Slide dryer or hotplate set at 60°C. Two waterbaths: one set at 81°C and one set at 37°C. A set of 12 plastic Coplin jars. Sets of micropipetor and tips for measuring 2–10 µL and for measuring 200–1000 µL. Electronic timer for seconds. Forceps. Organosilane coated microscopy slides (Fisher Superfrost Plus). 22 × 22-mm square microscope slide coverslips. Elmer's rubber cement. Clear, colorless nail polish. Standard lab equipment used to make solutions: thermometer, balance, pH meter, magnetic stirrer and stir bars, 1–2 L beakers, series of graduated cylinders, clean, and sealable 500-mL bottles for storage of solutions. 13. Pyrex dish or plastic container with a snap-on lid and containing a thermometer to act as a humidified chamber. 14. A reliable incubator set at 37°C.
2.2. Solutions, Reagents 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
0.2 M HCl solution. 1 M NaSCN solution. 2X SSC stored as stock of 20X SSC (3 M sodium chloride, 0.3 M trisodium citrate, pH 7.2). 2X SSC with 0.3% NP-40 detergent. Deionized distilled water. Pepsin (Sigma P6887, porcine pepsin) used at 72,000 units of activity per 50 mL of 0.2 M HCl solution). Neutral buffered formalin. Ultrapure formamide: 50 mL prepared as 70% formamide and 30% 2X SSC. High grade absolute ethanol: 50 mL each prepared as 70%, 85%, and absolute alcohol. Probe: Vysis PathVysion HER2 DNA Probe Kit (30–161060). 4',6-Diaminidino-2-phenylindole (DAPI II with antifade) counterstain (Vysis, 30-804840).
2.3. Microscopy 1. Microscope capable of brightfield and fluorescence microscopy (illuminated with epifluorescence from a 100 W mercury lamp). 2. ×5 objective, ×40 objective, ×100 oil immersion objective. 3. Dichroic filters (Chroma, Germany). 1. Orange: peak excitation 559 ± 38 nm, peak emission 588 ± 48 nm. 2. Green: peak excitation 509 ± 31 nm, peak emission 538 ± 44 nm. 3. Blue: peak excitation 367 ± 61 nm, peak emission 452 ± 92 nm. 4. Appropriate immersion oil for fluorescence microscopy.
3. Methods 3.1. Cut and Mount Tissue Sections 1. Cut four micron thick sections from a formalin-fixed, paraffin-embedded tissue sample block and float in a 37°C waterbath. 2. Mount on positively charged microscopy slides. 3. Cut a corresponding tissue section adjacent in series and stain with hematoxylin and eosin (H&E) (see Note 2).
3.2. Remove Paraffin and Permeabilize Tissue Section 1. 2. 3. 4.
5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
Identify appropriate areas of tumor cells on H&E slide (see Note 3). Evaluate the slide for tissue composition, quality of fixation (see Note 4). Bake slides in a convection oven or in a slide dryer at 60°C for 2 h (see Note 5). Load slides into rack and remove paraffin from the tissue section by immersing the slides in a series of three xylene baths for 5 min each and then through three changes of absolute ethanol (see Note 6). Dry slides in slide dryer or on a hotplate for 3 min at 45°C. Immerse slides in 50 mL of 0.2N HCl in a Coplin jar at room temperature for 20 min. Wash slides by immersing them in 50 mL of distilled water in a Coplin jar for 1 min then through two washes of 3 min each of 2X SSC. Immerse slides in 1 M NaSCN at 81°C for 30 min (see Note 7). Wash slides in distilled water for 1 min and through two changes of 2X SSC for 3 min each (see Note 8). Immerse slides in the pepsin solution at 37°C for between 3–10 min (see Note 4 regarding appropriate time). Immerse the slides in 50 mL of fresh distilled water for 1 min and wash through two changes of 50 mL of 2X SSC. Dry slides at 45°C for 3 min. Secondary fixation: Immerse slides in 10% neutral buffered formalin for 10 min at room temperature (see Note 9). Wash slides for 3 min through two changes of 2X SSC. Dry at 45°C for 3 min (see Note 10). Denature DNA of cells in the tissue section by immersing the slides in 70% formamide/ 30% 2X SSC solution at 81°C in the waterbath for 5 min. Immediately immerse slides into successive baths of 70, 85%, and absolute ethanol for 1 min each (see Note 11). Allow slides to dry in 45°C heater for no more than 2 min.
3.3. Hybridization 1. Dim the lights in the room. 2. Using the micropipetor draw 10 µL of probe solution in a line across a coverslip (see Note 12). 3. Cover the tissue sample with the coverslip and seal the edges of the coverslip temporarily with a line of rubber cement. 4. Place the slide in a closed, humidified (but not dripping) chamber at 37°C for 18 h (overnight).
3.4. Post-Hybridization Wash 1. Set a 71°C waterbath to heat 50 mL of 2X SSC containing 0.3% nonidet (NP-40) detergent in a Coplin jar. 2. Dim the lights. 3. Take out the slides from the incubator, peel off the rubber cement with forceps, and soak the slides for several min in a Coplin jar filled with 2X SSC/0.3% NP at room temperature (see Note 13). 4. Place the slides (no more than four at a time) in the heated (72°C) Coplin jar of 2X SSC/ 0.3% NP for 2 min. 5. Remove the slides from the heated wash, dip quickly into a Coplin jar of room temperature 2X SSC, allow to air-dry. 6. Place 10 µL of DAPI on a coverslip, touch the slide to it, and invert (see Note 14).
7. Seal the edges of the coverslip with nail polish. 8. Store slides in a closed slide folder at –20°C. 9. Allow to warm to room temperature and wipe off condensation before viewing at the microscope.
3.5. Analysis 1. Using brightfield microscopy and a low power objective (×10 or ×4), scan the H&E microscopy slide and identify the areas of tumor cells that you wish to evaluate (see Note 15). 2. Count 60 tumor cells from several separated fields of view (see Note 16). 3. Record in a chart the red signals and green signal per cell for 60 tumor cells (see Notes 17–20).
4. Notes 1. We have had successful FISH preparations from blocks 20 yr old. 2. Tissue sections should be cut at a microtome by a skilled operator who consistently orients the sections in a uniform manner on the slides. 3. This should be done in consultation with a pathologist. The tissue sample should be checked to ascertain that it contains appropriate invasive tumor cells. Only invasive breast tumor cells should be scored. Invasive tumor cells must be distinguished from tumor cells of ductal carcinoma in situ, as well as lymphocytes, histiocytes, stromal fibroblasts, or adipocytes which typically appear on the same section. If your count includes proportions of cells with 2/2 counts and amplified cells, double check that you have not included normal tissue cells (especially infiltrating lymphocytes) in with the tumor cell count. The tissue section should be scanned on low power and suitable areas of tumor cells noted along with landmarks that will be useful subsequently to orient the FISH slide. Landmarks include blood vessels, areas of adipose tissue, areas of normal ducts, and areas of DCIS. Intratumoral heterogeneity should be noted for special attention when the FISH slide is analyzed. Note any irregularities in fixation or tissue distortion (particularly if the section was originally a frozen section), which can cause confusion in interpretation. We find it very useful to circle the tumor area on the coverslip of the H& E slide with a Sharpie™ marker for future reference. 4. The optimal length of protease treatment time will depend on the age of the block, the tissue composition, and quality of tissue fixation and needs to be determined before undertaking the FISH preparation procedures. Protease treatment should be decreased for core biopsies and any sections that contain few tumor cells or have large areas of necrosis. These samples need to be handled particularly carefully to avoid over-digestion. 5. Meanwhile, pour 50 mL of 1 M NaSCN into a Coplin jar and set in the waterbath. Adjust the waterbath so that the temperature of the solution reaches 81°C. 6. This should be done in a fume hood. These baths may be used for many slides over several months and renewed when they appear very dirty. 7. Meanwhile pour 50 mL of 0.2 N HCl in a Coplin jar and set in a second waterbath to heat solution to 37°C, thaw a frozen aliquot of pepsin, mix well into 0.2 N HCl. Make up and set aside: 35 mL of formamide mixed with 15 mL of 2X SSC, and 50 mL each of 70%, 85%, and absolute ethanol in separate Coplin jars. 8. Upon removing slides, turn waterbath temperature down and heat Coplin jar of 70% formamide, 30% 2X SSC until 71°C in the solution. 9. Slides from blocks that are old (>2–3 yr since surgery) show brighter signals if the secondary formalin fixation is omitted. 10. Take out probe to thaw. Ensure that the H&E slide is at hand for reference.
11. Steps 16 and 17 are omitted if a HyBrite chamber (Vysis 30-144010) is used. 12. Lay the coverslip on a clean brown paper towel on the bench top (for easier visibility). Hold the slide above the coverslip and with the target area of the tissue section facing the probe, lower the slide gently to touch the probe liquid. In one quick motion, pick up and invert the slide with the coverslip clinging to it. The probe should spread out quickly and evenly without air pockets across the slide under the coverslip. Mark a very small line on the slide with a permanent-marking pen at the top and bottom corners of the coverslipped area. 13. The coverslips should float off or will need to be pried off the slides very gently with forceps. Be careful not to scrape the tissue section, which is very vulnerable to damage at this point. 14. For very small areas of tumor cells we use 5 µL of probe and coverslip with an 18-mm coverslip, VWR Scientific, catalog number 48380046. 15. Locate any landmarks that are useful and switch over to the ×25 objective. Still using the H&E slide, turn on the fluorescence microscope and examine the area of interest noting where the landmarks are and how they appear under fluorescent light. With the previous views in mind, look at your FISH preparation slide under ×25 and try to locate the identical areas of cells. Identify areas of tumor cells and features of the surrounding tissue architecture. Switch to the ×100 objective and oil immersion and examine the field of view. The tumor cells should be free of connective tissue, but still closely associated in clusters as they appear in the H&E preparation. 16. Using a triple filter (orange/green/DAPI blue) you should be able to see complete blue staining of the nuclei with the HER2 probe appearing as sharp orange spots and the CEP 17 probe as green spots. Confirm that hybridization has occurred correctly by analyzing some of the stromal cells or adjacent lymphocyte nuclei for 2/2 counts. Look for tumor cells that are not overlapping and where signals are bright and discrete. Look for cells where there are two green signals and count the corresponding red signals. 17. Overdigestion with protease results in ragged looking clumps or isolated tumor cells with no surrounding tissue and can be remedied by repeating the preparation with less time in protease. Poor fixation produces "hollow" cells with black spaces showing through the DAPI staining although the tissue structure appears intact. Likely this cannot be improved by repeating the preparation and will require that you scan the slide very thoroughly in search of the best preserved areas for usable results or perform FISH on another block. Rate the technical quality of the slide preparation and use this to evaluate whether there is true monosomy or polysomy in your sample or whether the preparation should be repeated. 18. Very weak signals can be seen by viewing the slide with single band pass filters one at a time, i.e., view with the triple filter, keeping in view a particular nucleus in question, switch to the orange filter and then switch to green to confirm signals that were faint with the triple filter. 19. If there is suggested heterogeneity in the H&E preparation or IHC stained slide, sample 20 cells from each of the areas in question. We and others (Ridofi et al.) have documented samples where there is discordance between DCIS and invasive tumor components (Fig. 1E). 20. We suggest you take advantage of the possiblity with the Vysis probe kit to collect information about the number of green and red signals per cell. By keeping a record of individual cell counts you can evaluate the degree of heterogeneity and distribution of counts in your sample. This information is lost when all numbers are reported as averages. These considerations become very important when assessing borderline or low amplification cases.
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CGH in Cancer Investigations
25 Comparative Genomic Hybridization in Cancer Investigations Marjan M. Weiss, Mario A. J. A. Hermsen, Gerrit A. Meijer, and Paul J. van Diest 1. Introduction Comparative genomic hybridization (CGH) provides genome-scale overviews of chromosomal copy number changes in tumors (1). Unlike conventional cytogenetic analysis, it needs no cell culturing, making it applicable to practically any kind of clinical specimen from which DNA can be obtained, including archival paraffin embedded material (2). It maps the origins of amplified and deleted DNA sequences on normal chromosomes, thereby highlighting locations of important genes. However, this technique cannot detect subchromosomal changes, owing to its limited resolution, nor structural chromosomal changes such as translocations or inversions. By its nature, CGH is especially suitable for screening tumors in various stages of development, such as premalignant lesions, invasive carcinomas and metastases, pointing out the location of possible oncogenes or tumor suppressor genes that may play a role in the early onset of malignancy, tumor progression, or the process of metastasis. In addition, CGH can be used to compare different histological components within one tumor, enabling in a better understanding of the relation between phenotype and genotype, or to compare derivative cell lines with the original cell line. The principle of the technique is shown in Fig. 1. Labeled tumor DNA competes with differentially labeled normal DNA for hybridizing to normal human metaphase chromosomes. Using fluorescence microscopy and digital image processing, the ratio of the two is measured along the chromosomal axes. Digital image processing includes the following steps: (a) background subtraction, (b) segmentation of chromosomes and removal of nonchromosome objects, (c) normalization of the FITC/TRITC ratio for the whole metaphase, (d) interactive karyotyping, (e) scaling of chromosomes to a standard length. Deviations from the normal ratio of 1.0 at certain chromosome regions represent amplification or deletion of genetic material in the tumor, and may sometimes already be seen in a green and red overlay image of the hybridized metaphase From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
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Fig. 1. Schematic overview of the CGH technique. Tumor and reference DNA are labeled with a green and red fluorochrome, respectively, and hybridized to normal metaphase spreads. Images of the fluorescent signals are captured and the green-to-red signal ratios are digitally quantified for each chromosomal locus along the chromosomal axis. (Reprinted with permission from Human Pathology (2))
(Fig. 2A). However, digital image processing is necessary for adequate evaluation. The final result is a so-called relative copy number karyotype (see Fig. 2B) that shows an overview of chromosomal copy number changes in the tumor. The sensitivity of CGH depends on the purity of the tumor sample (see Note 1); admixture with normal cells will reduce the sensitivity of CGH and its inherent resolution. For deletions the limit of detection is 10 Mb, which is about the size of an average chromosome band, but smaller amplifications (down to 250 kb) may be detected when the number of copies is high (3) (see Fig. 3). The following steps are required to perform CGH: Normal metaphase preparation, DNA labeling, hybridization and washings, fluorescence microscopy, and capturing and analyzing images with dedicated computer software, including karyotyping. Applications of CGH in cancer research include screening of tumors for genetic aberrations (4–16), searching for genes involved in the carcinogenesis of particular subsets of cancers (17), analyzing tumors in experimental models in order to get more insight in tumor progression (18), diagnostic classification, (17) and prognosis assessment (19). Besides these oncological applications, CGH analysis has also been used to study chromosomal aberrations in fetal and neonatal genomes (20–22). A recent development is microarray CGH, which will increase the possibilities to use CGH-like techniques in routine diagnostic procedures (see Note 2).
Fig. 2. Relative copy number karyotype showing the quantitative analysis of a tumor. The mean green-to-red fluorescence ratios of the chromosomes of multiple metaphase spreads are plotted in a graph corresponding to the chromosome ideograms, together with the 95% confidence interval: gains at 1p, 1q, 2q, 3q, 7q, 8q, 9q, 10p, 14q, 15q, 16p/q, 17p/q, 19q, 20q, 21q, and 22q; losses at 1p, 3p, 4p, 4q, 5q, 6q, 8p, 9p, 10q, and Xp/q.
2. Materials 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Ham F10 culture medium (Gibco-BRL, Life Technologies, Paisley, UK). Fetal calf serum (Gibco-BRL, Life Technologies). L-glutamine (Gibco-BRL, Life Technologies). Penicillin/streptomycin (Gibco-BRL, Life Technologies). Phytohemagglutinin (Gibco-BRL, Life Technologies). Colchicine (Gibco-BRL, Life Technologies). KCl (0.075 M). Methanol/acetic acid 3:1. DNA polymerase I/DNase I (Gibco-BRL, Life Technologies). DNAse I (Gibco-BRL, Life Technologies). dNTP reaction mixture: 0.2 mM dATP, dCTP, dGTP (Roche Diagnostics Nederland BV, Almere, The Netherlands); 500 mM Tris-HCl, pH 7.8; 50 mM MgCl2; 100 µM dithiotreitol; 100 µg/mL bovine serum albumin (BSA). dTTP: 0.2 mM (Roche Diagnostics). Biotin-16-dUTP (1 nmol/µL) (Roche Diagnostics). Digoxigenin-11-dUTP (1 nmol/µL) (Roche Diagnostics). Human COT-1 DNA (Roche Diagnostics). Ethanol absolute.
Fig. 3. An example of a small high-level amplification in chromosome band 8p11 (top); An example of a small deletion (app. 10 Mb) in chromosome band 8q21 (bottom).
17. Ethanol 99.8%. 18. 3 M Sodium acetate tri-hydrate. 19. Hybridization mixture: 50% deionized formamide (v/v), 10% dextran sulfate, 2X SSC, pH 7.0. 20. 20X SSC: 0.3 M sodium citrate, 3 M sodium chloride, pH 7.0. 21. 10X TN: 1 M Tris-HCl, 1.5M NaCl, pH 7.5. 22. TNT: 50 mL 10X TN, 450 mL H2O, 1.25 mL 20% Tween-20. 23. TNB: 0.5% (w/v) blocking reagent (Roche Diagnostics) in 1 X TN. 24. Avidin-FITC 12.5 µg/mL (Sigma-Aldrich, Poole, Dorset, UK). 25. Sheep-anti-digoxgenin-TRITC 4.0 µg/mL (Roche Diagnostics). 26. Antifade solution: Vectashield (Vector, Peterborough, Cambridgeshire, UK). 27. DAPI: 350 ng/mL 4',6-di-amino-2-phenylindole in antifade solution.
3. Methods 3.1 Metaphase Preparation 1. Incubate 1 mL of heparinized blood with 9-mL Ham F10 culture medium containing 10% FCS, 1% L-glutamine, 1% penicilin and streptomycin, 1.5% phytohemagglutinin at 37°C in an atmosphere of 5% CO2 for 72 h. 2. Arrest cells in mitosis by 0.1 µg/mL colchicine for 30 min. 3. Spin down cells at 150g for 10 min. Discard the supernatant.
4. Resuspend pellet in 10 mL hypotonic KCl and incubate 20 min at room temperature. 5. Spin down cells at 150g for 10 min. Discard the supernatant. 6. Fix cells in 10 mL of 3:1 methanol/acetic acid by carefully adding small volumes under continuous mixing. 7. Spin down cells at 150g for 10 min. Discard supernatant. Repeat step 6. 8. Spin down cells at 150g for 10 min. Discard supernatant. 9. Resuspend cells in approx 1 mL of 3:1 methanol/acetic acid. 10. Mount one or two drops of the cell suspension by Pasteur pipet onto ethanol-cleaned slides. 11. Post-fix the slide immediately by some drops of 3/1 methanol/acetic acid. 12. Check the quality of the metaphases by phase-contrast microscope (see Note 3). 13. Slides are air dried overnight at room temperature and can be stored in dry conditions at –20°C.
3.2. DNA Labeling 1. Combine 1 µg DNA, 3 µL dNTP, 0.5 µL dTTP, 1 µL digoxigenin- or biotin-conjugated dUTP, 3 µL DNA polymerase I/DNase I, 0–1 µL diluted DNAse I (adjust this concentration to obtain the optimal fragment lengths). Add ddH2O to a vol of 30 µL. 2. Incubate 1.5–2 h at 15°C. 3. Inactivate enzymes at 70°C for 15 min. 4. Visualize 5 µL labeled DNA by gel electrophoresis through an ethidium bromide stained 1% (w/v) agarose gel. 5. Inspect the DNA fragment lengths with an ultraviolet transilluminator; the optimum smear is between 500 and 2000 kb in length (see Note 4).
3.3. Hybridization and Washing 1. Mix 10 µL labeled (usually with biotin) tumor with 10 µL labeled (usually with DIG) normal DNA and 40 µg unlabeled Cot-1 DNA. 2. Ethanol precipitate the sample by adding 0.1 vol of 3 M sodium acetate and 2 vol of ethanol and centrifuging at 12,000g for 30 min. 3. Decant the supernatant and air dry the pellet. 4. Dissolve the pellet in 6 µL hybridization mixture. 5. Denature a metaphase chromosome slide at 72°C in jar containing 70% (v/v) formamide and 2X SSC in a waterbath for 6 min (see Note 5). 6. Dehydrate the slide in an ethanol series (70, 96, and 100%). 7. Denature the DNA probe mixture at 80°C for 10 min. 8. Mount the probe mixture immediately on the metaphase slide. 9. Cover with a coverslip (18 × 18 mm) and seal with rubber cement. 10. Hybridize for 2–3 d in a humid incubator at 40°C. 11. Remove the coverslip carefully. 12. Wash for 5 min in 2X SSC at room temperature. 13. Wash 3 times for 5 min in 0.1X SSC at 45°C. 14. Wash for 5 min in TNT at room temperature. 15. Pre-incubate for 10 min in 100 µL of TNB under a cover slip (24 × 50 mm). 16. Incubate for 60 min in 100 µL of TNB with avidine-FITC (1/200) and sheep-anti-DIGTRITC (1/50) under a cover slip (24 × 50 mm) in humid chamber at 40°C (from now on keep the slide in the dark). 17. Wash 3× for 5 min in TNT at room temperature. 18. Wash for 5 min in 2X SSC at room temperature.
19. Dehydrate the slide in an ethanol series (70, 96, and 100%). 20. Mount 25 µL of antifade containing DAPI, cover with a cover slip (24 by 50 mm), and seal with rubber cement.
3.4. Fluorescence Microscopy and Image Analysis A fluorescence microscope equipped with three single band pass filters is suitable for CGH. DAPI (blue) is used for chromosome identification, FITC (green) for the hybridized tumor DNA, and TRITC (red) for the hybridized normal DNA detection. 1. Screen the slide for well-spread metaphases with a homogeneous green and red fluorescent signal and a low background (see Note 6). Capture three images (DAPI, FITC, TRITC) of each metaphase spread. 2. The averaged ratios of approx 8–12 metaphases are plotted along the corresponding chromosomes in a so-called relative copy number karyotype (Fig. 2). The significance of deviations from the 1.0 ratio can be evaluated with the help of the 95% confidence interval (CI), which can be plotted along with the averaged ratios (see Note 7).
4. Notes 1. When using tissue sections to isolate DNA from tumor cells, the admixture of normal cells (stroma or infiltrating lymphocytes) may present a problem. When a sample contains more than 25% normal cells microdissection could become necessary, depending on the ploidy of the tumor (23). This can be done manually or by advanced laser microdissection equipment (24,25). However, the latter yields only limited number of cells (hence DNA), necessitating universal DNA amplification techniques (26,27). These techniques are time consuming, expensive, and the user must perform good control experiments to ensure the reliability of CGH results. Another approach could be cell sorting (e.g., antibodies attached to magnetic beads or flow cytometric sorting), which may enable selection (and extraction) of tumor cells, or elimination of inflammatory cells from a tissue sample. 2. New developments: A new technique currently being developed in different laboratories is the microarray technique. Using metaphase chromosomes for hybridization limits the detection of events involving small regions (less than 10–20 Mb) of the genome. The array technique allows detecting DNA copy number changes (genomic DNA) in more detail, as well as analyzing gene expression using cDNA (complementary DNA). Most publications, so far, are on cDNA arrays (31–33). Recently, Pinkel et al. and Albertson et al. published articles on genomic DNA microarrays, describing a method to measure copy number fluorescence ratios on a set of clones that are located on chromosome 20. The technique provides a high resolution for measurement of gains and losses of DNA sequences in genomes of mammalian complexity (34,35). Microarray CGH will allow analysis of genetic aberrations in cancer with a high resolution, and refining the allocation of critical genes. Moreover, in clinical applications it could enable the identification of the status of certain disease-related genes. A detailed discussion can be found elsewhere (36,37). 3. High-quality metaphase preparations for CGH should preferentially contain an abundance of metaphases, have little residual cytoplasm (too much cytoplasm causes background and may prevent optimal denaturation), and minimal overlapping of the chromosomes. In addition, the chromosomes should have adequate length (400–550 bands) and not contain separated chromatids. Finally, for good banding strength, chromosomes should appear
dark, not shiny, when looking through a phase contrast microscope (28). It is important to test several batches of metaphase slides from different donors when setting up CGH, because their behavior in hybridization can be very different. Alternatively, fully prepared metaphase slides are commercially available. However, these slides also still need to be tested before use, and the quality is not necessarily better than that of in-houseproduced slides (prepared as described above). When biotinylated and DIG-conjugated deoxynucleotides (dUTPs) are incorporated into the DNA (indirect labeling), a detection step with fluorochrome-conjugated antibodies (avidin–FITC and sheep-anti-DIG–TRITC, respectively) is required after hybridization. Directly fluorochrome-conjugated deoxynucleotides render a smoother but weaker hybridization signal along the chromosomes. It is important that the labeled DNA fragments of both tumor and reference DNA are in the same range of lengths and are within the limits of 500–2000 bp. The time of denaturation is a variable that should be adjusted to each new batch of metaphase preparations. When the metaphase slides are denatured too long, the fluorescent signal probably will be strong, but the DAPI banding will be very bad, making karyotyping impossible. Conversely, when the slides are not denatured sufficiently, there will be a nice, easy-to-recognize banding DAPI pattern, but the signal will be too low and granular. The art of CGH is to find a balance between these two scenarios. The selection of good-quality metaphase spreads for digital image processing is crucial in the CGH. The fluorescent signal should be strong and homogeneous over the whole metaphase spread. The user should avoid metaphase spreads with many overlapping chromosomes or metaphase spreads with very small or very large chromosomes. The background should be low. Local high backgrounds are probably caused by residual cytoplasm. An even field illumination by the microscope is essential. Uneven illumination can cause gross artifacts. Furthermore, good-quality metaphases in CGH show dark centromeric regions as a sign of good blocking by Cot-1 DNA. Centromeres contain repetitive DNA sequences that are highly variable in length between individuals (and thus between tumor and reference DNA) and can therefore interfere with the CGH analysis. These repetitive sequences also occur to a lesser but nonetheless significant extent throughout the whole genome. Suboptimal blocking by Cot-1 DNA leads to reduced sensitivity. There are two ways to interpret the relative copy number karyotypes. Some researchers use fixed ratio limits, for example 0.85/1.15 or 0.75/1.25, depending on the quality of the hybridization (29). Others prefer to use the 95% CI, which takes into account the quality of the signal. According to the latter definition, deviations from normal are interpreted as loss or gain when the average ratio, together with the 95% CI, is clearly below or above ratio 1.0. In addition, the green-to-red fluorescent ratios at 1p32-pter, 16p, 19p/q, and 22q may occasionally be unreliable, leading to false positive interpretation (30). In general, these chromosomal regions are excluded from the CGH profile interpretation if it concerns low-level gains or losses.
References 1. Kallioniemi, A., Kallioniemi, O. P., Sudar, D., Rutovitz, D., Gray, J. W., Waldman, F., et al. (1992) Comparative genomic hybridization for molecular cytogenetic analysis of solid tumors. Science 258, 818–821. 2. Hermsen, M. A., Meijer, G. A., Baak, J. P., Joenje, H., and Walboomers, J. J. (1996) Comparative genomic hybridization: a new tool in cancer pathology. Hum. Pathol. 27, 342–349.
3. Kallioniemi, A., Kallioniemi, O. P., Piper, J., Tanner, M., Stokke, T., Chen, L., et al. (1994) Detection and mapping of amplified DNA sequences in breast cancer by comparative genomic hybridization. Proc. Natl. Acad. Sci. USA 91, 2156–2160. 4. Bentz, M., Dohner, H., and Huck, K. (1995) Comparative genomic hybridization in the investigation of myeloid leukemias. Genes Chromosom. Cancer 12, 193–200. 5. Hermsen, M. A., Baak, J. P., Meijer, G. A., et al. (1998) Genetic analysis of 53 lymph node-negative breast carcinomas by CGH and relation to clinical, pathological, morphometric, and DNA cytometric prognostic factors. J. Pathol. 186, 356–362. 6. Meijer, G. A., Hermsen, M. A. J. A., Baak, J. P. A. , et al. (1998) Progression from colorectal adenoma to carcinoma is associated with non-random chromosomal gains as detected by comparative genomic hybridisation. J. Clin. Pathol. 51, 901–909. 7. Monni, O., Oinonen, R., Elonen, E., et al. (1998) Gain of 3q and deletion of 11q22 are frequent aberrations in mantle cell lymphoma. Genes Chromosom. Canc. 21, 298–307. 8. Nupponen, N. N., Hyytinen, E. R., Kallioniemi, A. H., and Visakorpi, T. (1998) Genetic alterations in prostate cancer cell lines detected by comparative genomic hybridization. Cancer Genet. Cytogenet. 101, 53–57. 9. Ried, T., Knutzen, R., Steinbeck, R., Blegen, H., Schrock, E., Heselmeyer, K., et al. (1996) Comparative genomic hybridization reveals a specific pattern of chromosomal gains and losses during the genesis of colorectal tumors. Genes Chromosom. Cancer 15, 234–245. 10. Riopel, M. A., Spellerberg, A., Griffin, C. A., and Perlman, E. J. (1998) Genetic analysis of ovarian germ cell tumors by comparative genomic hybridization. Cancer Res. 58, 3105–3110. 11. Tarkkanen, M., Bohling, T., Gamberi, G., Ragazzini, P., Benassi, M. S., Kivioja, A., et al. (1998) Comparative genomic hybridization of low-grade central osteosarcoma. Modern Pathol. 11, 421–426. 12. Tirkkonen, M., Tanner, M., Karhu, R., Kallioniemi, A., Isola, J., and Kallioniemi, O. P. (1998) Molecular cytogenetics of primary breast cancer by CGH. Genes Chromosom. Cancer 21, 177–184. 13. Weber, R. G., Scheer, M., and Born, I. A. (1998) Recurrent chromosomal imbalances detected in biopsy material from oral premalignant and malignant lesions by combined tissue microdissection, universal DNA amplification, and comparative genomic hybridization. Am. J. Pathol. 153, 295–303. 14. Bastian, B. C., LeBoit, P. E., Hamm, H., Brocker, E. B., and Pinkel, D. (1998) Chromosomal gains and losses in primary cutaneous melanomas detected by comparative genomic hybridization. Cancer Res. 58, 2170–2175. 15. Taguchi, T., Cheng, G. Z., Bell, D. W., Balsara, B., Liu, Z., Siegfried, J. M., et al. (1997) Combined chromosome microdissection and comparative genomic hybridization detect multiple sites of amplification DNA in a human lung carcinoma cell line. Genes Chromosom. Cancer 20, 208–212. 16. Weber, R. G., Sommer, C., Albert, F. K., Kiessling, M., and Cremer, T. (1996) Clinically distinct subgroups of glioblastoma multiforme studied by comparative genomic hybridization. Lab. Invest. 74, 108–119. 17. Simon, R., Burger, H., Brinkschmidt, C., Bocker, W., Hertle, L., and Terpe, H. J. (1998) Chromosomal aberrations associated with invasion in papillary superficial bladder cancer. J. Pathol. 185, 345–351. 18. Tienari, J., Reima, I., Larramendy, M. L., Knuutila, S., von Boguslawsky, K., Kaartinen, M., et al. (1998) A cloned human germ cell tumor-derived cell line differentiating in culture. Int. J. Cancer 77, 710–719.
19. Isola, J. J., Kallioniemi, O. P., Chu, L. W., Fuqua, S. A., Hilsenbeck, S. G., Osborne, C. K., et al. (1995) Genetic aberrations detected by comparative genomic hybridization predict outcome in node-negative breast cancer. Am. J. Pathol. 147, 905–911. 20. Daniely, M., Aviram-Goldring, A., Barkai, G., and Goldman, B. (1998) Detection of chromosomal aberration in fetuses arising from recurrent spontaneous abortion by comparative genomic hybridization. Hum. Reprod. 13, 805–809. 21. Wang, B. B., Yu, L. C., Peng, W., Falk, R. E., Williams, J., III (1995) Prenatal identification of i(Yp) by molecular cytogenetic analysis. Prenat. Diagn. 15, 1115–1119. 22. Yu, L. C., Moore, D. H., Magrane, G., Cronin, J., Pinkel, D., Lebo, R. V., et al. (1997) Objective aneuploidy detection for fetal and neonatal screening using comparative genomic hybridization (CGH). Cytometry 28, 191–197. 23. Weiss, M. M., Hermsen, M. A., Meijer, G. A., van Grieken, N. C., Baak, J. P., Kuipers, E. J., et al. (1999) Comparative genomic hybridisation. Mol Pathol. 52, 243–251. 24. Zitzelsberger, H., Kulka, U., Lehmann, L., Walch, A., Smida, J., Aubele, M., et al. (1998) Genetic heterogeneity in a prostatic carcinoma and associated prostatic intraepithelial neoplasia as demonstrated by combined use of laser-microdissection, degenerate oligonucleotide primed PCR and comparative genomic hybridization. Virchows Archiv. 433, 297–304. 25. Fend, F. and Raffeld, M. (2000) Laser capture microdissection in pathology. J. Clin. Pathol. 53, 666–672. 26. Kuukasjarvi, T., Tanner, M., Pennanen, S., Karhu, R., Visakorpi, T., and Isola, J. (1997) Optimizing DOP-PCR for universal amplification of small DNA samples in comparative genomic hybridization. Genes Chromosom. Cancer 18, 94–101. 27. Lucito, R., Nakimura, M., West, J. A., Han, Y., Chin, K., Jensen, K., et al. (1998) Genetic analysis using genomic representations. Proc. Natl. Acad. Sci. USA 95, 4487–4492. 28. Karhu, R., Kahkonen, M., Kuukasjarvi, T., Pennanen, S., Tirkkonen, M., and Kallioniemi, O. (1997) Quality control of CGH: impact of metaphase chromosomes and the dynamic range of hybridization. Cytometry 28, 198–205. 29. Barth, T. F., Benner, A., Bentz, M., Dohner, H., Moller, P., and Lichter, P. (2000) Risk of false positive results in comparative genomic hybridization. Genes Chromosomes Cancer 28, 353–357. 30. Kallioniemi, O. P., Kallioniemi, A., Piper, J., Isola, J., Waldman, F. M., Gray, J. W., et al. (1994) Optimizing comparative genomic hybridization for analysis of DNA sequence copy number changes in solid tumors. Genes Chromosom. Cancer 10, 231–243. 31. Lu, J., Liu, Z., Xiong, M., Wang, Q., Wang, X., Yang, G., et al. (2001) Gene expression profile changes in initiation and progression of squamous cell carcinoma of esophagus. Int. J. Cancer 91, 288–294. 32. Schena, M., Shalon, D., and Davis, R. W. (1995) Quantitative monitoring of gene expression patterns with a complementary DNA microarray. Science 270, 467–470. 33. Welsh, J. B., Zarrinkar, P. P., Sapinoso, L. M., Kern, S. G., Behling, C. A., Monk, B. J., et al. (2001) Analysis of gene expression profiles in normal and neoplastic ovarian tissue samples identifies candidate molecular markers of epithelial ovarian cancer. Proc. Natl. Acad. Sci. USA 98, 1176–1181. 34. Pinkel, D., Segraves, R., Sudar, D., Clark, S., Poole, I., Kowbel, D., et al. (1998) High resolution analysis of DNA copy number variation using comparative genomic hybridization to microarrays. Nat. Genet. 20, 207–211.
35. Albertson, D. G., Ylstra, B., Segraves, R., Collins, C., Dairkee, S. H., Kowbel, D., et al. (2000) Quantitative mapping of amplicon structure by array CGH identifies CYP24 as a candidate oncogene. Nat. Genet. 25, 144–146. 36. Snijders, A. M., Meijer, G. A., Brakenhoff, R. H., van den Brule, A. J., and van Diest, P. J. (2000) Microarray techniques in pathology: tool or toy? Mol. Pathol. 53, 289–294. 37. Collins, F. S., Lander, E. S., and Southern, E. (1999) The chipping forecast. Nat. Genet. 21, 1–60.
Simultaneous Immunophenotyping and FISH
26 Simultaneous Fluorescence Immunophenotyping and FISH on Tumor Cells Yanming Zhang and Brigitte Schlegelberger 1. Introduction Chromosome aberrations are regularly detected in most hematologic neoplasms and in various solid tumors and are often associated with distinct morphologic and immunophenotypic features of certain clinico-pathologic entities of tumors (1–4). Detection of these chromosome abnormalitites provides the basis for a detailed diagnosis and for the genetic classification of tumors. Especially in leukemias and lymphomas, many primary chromosome aberrations are associated with the clinical course of the disease. Moreover, during tumor progression, additional chromosome aberrations occur. Therefore, cytogenetic findings are very helpful for predicting the prognosis and for choosing risk-adapted treatment strategies (5,6). Cytogenetic analysis by karyotyping remains the standard for the detection of numerical and structural chromosome aberrations, such as trisomies, monosomies, translocations, deletions, or inversions. This technique gives, at one glance, an overview of all microscopically visible chromosome aberrations. The molecular cytogenetic technique of fluorescent in situ hybridization (FISH) has been shown to be a very powerful tool for the detection of certain chromosome aberrations (7,8). By use of chromosome- or single-locus-specific DNA probes, FISH may detect these chromosome aberrations not only in metaphase, but also in interphase cells. Immunophenotyping is a routine technique in any pathology laboratory in support of a differential diagnosis. Leukemia and lymphoma cells express a defined pattern of antigens that allows one to identify the cellular origin of the tumor cells and trace them back to defined stages of the normal differentiation process.
1.1. Application of Simultaneous Fluorescence Immunophenotyping and FISH Simultaneous fluorescence immunophenotyping and FISH provides the advantages of both techniques and allows a simultaneous or sequential analysis of the phenotype From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
Zhang and Schlegelberger
and genotype of tumor cells at the single-cell level (9,10). By use of cell lineage and differentiation-associated monoclonal antibodies for immunophenotyping as well as DNA probes specific for known chromosome aberrations of a tumor for FISH, this combined technique makes it possible to compare and correlate particular genetic aberrations directly with the differentiation capacity of tumor cells. Thus, the cell lineage and differentiation stage of tumor cells can be defined (11,12). This approach also allows one to correlate the gene copy number and its protein expression level in the same cells (13). The power and the applicability of this technique in clinical studies and basic research have been extensively demonstrated in many studies on leukemias and lymphomas (9,14).
1.1.1. Defining Lineage Involvement of Tumor Cells Cytogenetic analysis, Southern blot, or PCR techniques are often used for detecting chromosome aberrations or gene rearrangements. However, with these methods, it is not possible to assign genetic changes to certain cell populations, since they either destruct the cell morphology or damage the cell surface antigens during the procedures. Simultaneous immunophenotyping and FISH allows one to define the immunophenotype of tumor cells with certain chromosome or gene aberrations. Several studies with this or a similar approach have revealed that in myeloproliferative diseases (MPDs) and myelodysplastic syndromes (MDSs), tumor cells may involve the lymphoid as well as all myeloid lineages (15–18). In most acute myeloid leukemias (AMLs) and acute lymphoid leukemias (ALLs), the chromosome abnormalities are restricted to the leukemic blasts (19–21). Using CD56 as a specific immunophenotypic marker for natural killer cells and 6q deletion or trisomy 7 as genetic markers, we performed simultaneous immunophenotyping and FISH on three patients with natural killer cell lymphomas and leukemias. In all three patients, we were able to demonstrate that these chromosome aberrations were restricted to the CD56-positive natural killer cell population, whereas CD3-positive T lymphocytes were not involved (Fig. 1A). Thus, natural killer cell lymphoma and leukemia is derived from mature natural killer cells, but not from T lymphocytes (22).
1.1.2. Determining the Differentiation Stage of Tumor Cells It is believed that any tumor results from accumulated genetic changes and chromosome aberrations. One critical problem is defining which stage of cell differentiation that these genetic changes occur. Simultaneous immunophenotyping and FISH could help to determine the differentiation stage of tumor cells in many leukemias and lymphomas. By use of this combination or modified techniques, MPD, MDS, and AML in some patients were shown to be stem cell diseases with commitment to all myeloid lineages and, in some patients, to the lymphoid lineage (15,16,19,23). In CML, tumor cells are derived from a stem cell with a capacity to differentiate into all myeloid and lymphoid lineages (24–26). The MLL gene on 11q23 is frequently involved in different chromosome translocations in de novo and therapy-related leukemia. These translocations result in chimeric genes that play an important role in leukemogenesis (1). In three patients with therapy-related leukemia, we performed simultaneous immunophenotyping with CD34 as a stem cell marker and a FISH study with a YAC
Fig. 1. Simultaneous fluorescence immunophenotyping and FISH on a natural killer cell leukemia. (A) Immunophenotyping with monoclonal mouse anti-human CD56 was performed to identify natural killer cells. Mouse anti-human CD56 was visualized with Cy3 (red). A biotinylated D7Z1 DNA probe specific for the centromere of chromosome 7 was detected with FITC (green) in FISH. The CD56-positive natural killer cell shows three hybridization signals for D7Z1, indicating trisomy 7, whereas the adjacent CD56-negative cells contain two regular hybridization signals for D7Z1. Thus, the tumor clone in the natural killer cell leukemia and lymphoma is restricted to CD56-positive natural killer cell population. (B) Monoclonal mouse anti-human Ki-67 antibody was visualized with Cy3 (red) in immunophenotyping study. A biotinylated D7Z1 probe specific for the centromere of chromosome 7 was detected with FITC (green)-conjugated avidin in the FISH study. The cells were counterstained with DAPI (blue). Two cells show three hybridization signals for D7Z1, indicating trisomy 7. These tumor cells also display a very strong fluorescence staining (red) with mouse anti-human Ki-67, indicating a high proliferation level. The adjacent cells contain two regular hybridization signals of D7Z1 and show a very weak or negative fluorescence staining with mouse anti-human Ki-67 antibody. Thus, in natural killer cell leukemia and lymphoma, chromosome aberrations are restricted to the CD56-positive tumor cell population and tumor cells have a much higher proliferation level than normal cells.
DNA probe containing the MLL gene. We were able to confirm that chromosome translocations involving MLL occurred in CD34-positive hematopoietic cells. Thus, therapy-related leukemia is derived from hematopoietic progenitor cells or even from stem cells (12).
1.1.3. Increasing the Detection Sensitivity of FISH Some tumors consist of a mixture of tumor and normal bystander cells. In this case, it may be difficult to reach the threshold for the detection of chromosome aberrations by FISH (7,8). Given that the tumor cells contain an antigen that is expressed only in a minority of normal cells, simultaneous immunophenotyping and FISH can overcome these difficulties. Because the tumor cell population can be recognized by the application of defined monoclonal antibodies, only cells with positive staining will be evaluated for certain chromosome aberrations by FISH. Thus, the evaluation will be restricted to this cell population, and many normal cells around or mixed with the tumor cells will be excluded from the analysis. Therefore, the sensitivity of detection of chromosome aberrations by FISH will be greatly improved. An example was demonstrated in our previous study on 30 patients with Hodgkin's disease (27). It is known that the typical CD30-positive HRS cells in Hodgkin's disease usually comprise only ~1–2% of the total cells. When FISH only is used, this percentage is just at or even beyond the cut-off limit for the detection of defined chromosome aberrations. Using simultaneous immunophenotyping and FISH, we were able to find that only CD30-positive HRS cells contained numerical chromosome aberrations in all 30 patients with Hodgkin's disease, whereas CD30-negative lymph node cells regularly had normal numbers of hybridization signals. This provided evidence that only CD30positive HRS cells belong to tumor clones (27). In addition, this technique may be useful in evaluating patient response to therapy by detecting minimal residual tumor cells, given that the tumor cells have an immunophenotype different from that of the normal cells.
1.1.4. Correlating the Gene Copy Number and its Protein Expression Level Simultaneous immunophenotyping and FISH enable us to compare the gene copy number with its protein expression level directly at the single-cell level. We applied this technique to six breast carcinoma cell lines and compared the copy number of the estrogen receptor (ESR) gene and the estrogen receptor (ER) expression pattern at the single cell level (13). We found that the tumor cells with a deletion of ESR had a ER expression level similar to those without a deletion; the ER expression level of tumor cells with 3–4 copies of ESR is at the same level as that of cells with two regular copies of ESR. Thus, the copy number of the ESR gene is not directly correlated with the expression of the ER, and a gene dosage effect attributable to loss of the ESR gene seems not to be the major cause of negative ER expression in breast carcinoma. Other mechanisms may be involved in determining the ER expression level.
1.1.5. Detecting the Proliferation Level of Tumor Cells In general, tumor cells have a proliferation advantage over normal cells and thus, are very active in cell division. The increased proliferation level of tumor cells may be
a part of the causes leading to an aggressive clinical course in some patients (28). Simultaneous immunophenotyping and FISH detect the proliferation level of tumor cells that have certain gene or chromosome aberrations. Using the Ki-67 antibody as a cell proliferation marker, we applied this combined technique to a natural killer cell leukemia. We found that the tumor cells with trisomy 7 as a tumor clone marker had a very high intensity of fluorescence staining with Ki-67 in immunophenotyping, whereas normal cells with two regular copies of chromosome 7 showed very weak or negative staining with Ki-67 (Fig. 1B). Thus, tumor cells in natural killer cell leukemia have a much higher proliferation ability than do normal cells.
2. Materials 2.1. Reagents 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.
Monoclonal mouse anti-human antibodies, such as CD4, CD8, and CD56. Human COT-1 DNA. Human placental DNA. Dextran sulfate. Sephadex G-50 minicolumn. Sonicated salmon sperm DNA. 70, 85, and 100% ethanol. Rubber cement. Deionized formamide. DAPI (4,6-diamidino-2-phenylindole). DABCO (1,4-diazabicyclo[2,2,2]octane). Normal mouse serum. Mouse monoclonal anti-digoxigenin antibody. Mouse anti-FITC antibody. AMCA-conjugated avidin. FITC-conjugated avidin. Biotinylated goat-anti-avidin antibody. Cy3-conjugated avidin. Cy3-conjugated goat anti-mouse antibody. Cy3-conjugated rabbit anti-goat antibody. Cy3-conjugated donkey anti-rabbit antibody. Cy3-conjugated rabbit anti-mouse antibody. Digoxigenin-conjugated sheep anti-mouse antibody. FITC-conjugated donkey anti-mouse antibody. FITC-conjugated sheep anti-digoxigenin antibody.
2.2. Buffers and Solutions 1. PN buffer: 0.1 M NaH2PO4, 0.1 M Na2HPO4, 0.03% NaN3 (poisonous), pH 8.0. 2. PNM buffer: Add 5 g dry milk powder to 100 mL PN buffer; heat to 50–60°C and stir overnight until completely dissolved. It can be stored at 4°C for several months or at –20°C for years. 3. 20X SSC: 3 M NaCl, 0.3 M sodium citrate, pH 7.0. 4. Antifade solution: Add 0.23 g DABCO and 10 mL PN-buffer to 90 mL glycerol; mix well. 5. DAPI solution: Dilute DAPI at 0.2 mg/mL in 2X SSC, pH 7.0, protect it from light at 4°C. 6. Carnoy's fixative: Freshly prepare 3:1 methanol:glacial acetic acid, and keep at 4°C.
7. 1% Paraformaldehyde: Add 1 g paraformaldehyde (CAUTION!!) to 100 mL distilled water, adjust to pH 7.0. This buffer may be stored at 4°C for 2 wk. 8. Hybridization master mix I: 60% formamide, 10% dextrane sulfate, 1X SSC. 9. Hybridization master mix II: 50% formamide, 10% dextrane sulfate, 2X SSC.
3. Methods 3.1. Slide Preparation For simultaneous immunophenotyping and FISH, cytospin preparations, smears, imprints, or cryostat sections may be used. Appropriate handling and preservation of the cells are critical for successful performance of the procedure. In general, freshly prepared slides should be air dried overnight at room temperature prior to being stored at –20°C or –80°C. Slides may be kept in this way for several weeks or even up to several years. After being taken out from freezers, slides should be thawed at room temperature and air dried for several minutes prior to use. Also, the morphology and location of cells should be checked under a phase contrast microscope before use. The following is a protocol for cytospin preparation. 1. Cut biospies such as lymph node or solid tumor tissue in PBS buffer into small pieces with needles and knives. 2. Collect the obtained cell suspension from the sample. 3. Spin at 200g for 10 min. 4. Discard the supernant and resuspend the cells in PBS buffer. 5. Determine the cell number. 6. Dilute or concentrate cells to 1 × 104/mL. 7. Add 200 µL of cells in a cytospin centrifuge and spin at 200g (800 rpm) for 5 min. 8. Air dry slides over night or for at least 2 h at room temperature. 9. Keep slides at –20°C.
3.2. Immunophenotyping Depending on the questions to be answered, single or double immunophenotyping may be performed. The following are two protocols for single and double immunophenotyping.
3.2.1. Immunophenotyping with a Single Antigen (such as CD4) 1. Take preserved slides out from –20°C freezer and air-dry for 10 min at room temperature. 2. Put slides in fresh acetone for 10 min at room temperature, followed by air-drying for a few minutes. 3. Rinse slides in PN buffer. 4. Incubate with primary monoclonal mouse antibody such as CD4: Add 100 µL mouse anti-human CD4 antibody diluted in PNM buffer to slides and incubate for 25 min at room temperature. Dilution of mouse anti-human antibody varies from 1:50 to 1:100, depending on quality of antibodies and antigen expression level of cells (see Note 1). 5. Wash with PN buffer three times, 5 min each, at room temperature. 6. Incubate with 100 µL Cy3-conjugated goat anti-mouse antibody diluted 1:200 in PNM buffer at room temperature for 25 min. 7. Wash with PN buffer three times, 5 min each, at room temperature. 8. Incubate with 100 µL Cy3-conjugated rabbit anti-goat antibody diluted 1:200 in PNM buffer at room temperature for 25 min.
9. Wash with PN buffer three times, 5 min each, at room temperature. 10. Incubate with 100 µL Cy3-conjugated donkey anti-rabbit antibody diluted 1:200 in PNM buffer at room temperature for 25 min. 11. Wash with PN buffer three times, 5 min each, at room temperature. 12. Fix the cells in 1% ice-cold paraformaldehyde solution for 1 min (see Note 2). 13. Wash in A. bidest once at room temperature. 14. Put slides in fresh Carnoy's fixative at 4°C for 10 min (see Note 2). 15. Wash slides in A. bidest for 2 min at room temperature. At this point, immunophenotyping may be checked under a fluorescence microscope. Mount the slides with PN buffer and cover with a coverslip and check whether certain cells show definitive fluorescence. If not, stop here and perform another control test with various concentrations of primary and secondary antibodies. Please note that the general fluorescence intensity of cells is relatively low when the slides are covered with PN buffer. Do not take long time for checking under microscope. 16. Dehydrate cells in a series of 70, 85, and 100% ethanol at room temperature for 3 min each, followed by air-drying at room temperature for at least 10 min. The cells are ready for FISH study (see Subheading 3.3.).
3.2.2. Double Immunophenotyping (such as CD4 and CD8) 3.2.2.1. IMMUNOPHENOTYPING FOR FIRST ANTIGEN (E.G., CD4) 1. Perform steps 1–3 in Subheading 3.2.1. 2. Incubate with 100 µL monoclonal mouse antibody against human CD4 1:50 to 1:100 diluted in PNM buffer at room temperature for 25 min (see Note 3). 3. Wash with PN buffer three times for 5 min each at room temperature. 4. Incubate with Cy3-conjugated rabbit anti-mouse antibody diluted 1:200 in PNM buffer at room temperature for 25 min. 5. Wash with PN buffer three times for 5 min each at room temperature. 6. Incubate with Cy3-conjugated donkey anti-rabbit antibody diluted 1:200 in PNM buffer at room temperature for 25 min. 7. Wash with PN buffer three times for 5 min each at room temperature. 8. Incubate with 20% normal mouse serum diluted in PNM buffer at room temperature for 15 min (do not wash the slides after incubation and go directly to Subheading 3.2.2.2.) (see Note 4).
3.2.2.2. IMMUNOPHENOTYPING FOR SECOND ANTIGEN (E.G., CD8) 1. Incubate with biotinylated monoclonal mouse antibody against human CD8 1:100 diluted in PNM buffer containing 20% mouse serum at (room temperature) RT for 25 min. 2. Wash with PN buffer three times, 5 min each, at room temperature. 3. Incubate with AMCA-conjugated avidin diluted 1:50 in PNM buffer at room temperature for 25 min. 4. Wash with PN buffer three times, 5 min each, at room temperature. 5. Incubate with biotinylated goat anti-avidin diluted 1:100 in PNM buffer at room temperature for 20 min. 6. Wash with PN buffer three times, 5 min each, at room temperature. 7. Incubate with AMCA-conjugated avidin diluted 1:50 in PNM buffer at room temperature for 25 min. To enhance the signal intensity, steps 5–7 may be repeated. 8. Put slides in 1% ice-cold paraformaldehyde solution to fix the cells.
9. 10. 11. 12.
Wash in A. bidest once at room temperature. Put slides in fresh Carnoy's fixative at 4°C for 10 min. Wash slides in A. bidest for 2 min at room temperature. Mount the slides with PN butter and check immunophenotyping under a fluorescence microscope as described in Subheading 3.2.1. 13. Dehydrate slides in a series of 70, 85, and 100% ethanol at room temperature for 3 min each, followed by air drying at room temperature for at least 10 min.
3.3. FISH 3.3.1. DNA Probe Preparation 3.3.1.1. REPETITIVE PROBES Many probes of this kind are commercially available from several biological companies, such as Vysis. In general, hybridization master mix I is used. However, if commercial probes are used, it is recommended to follow the manufacturer's instructions for probe preparation. 3.3.1.2. SINGLE COPY
LOCUS SPECIFIC DNA PROBES
Such probes are cloned in different vectors from phage to PAC, BAC, or YAC. After DNA labeling with biotin, digoxigenin, or fluorescence dyes such as Spectrum green or orange, DNA probes have to be precipitated to reduce the volume. Hybridization master mix II can be used for dissolving the probes. For some commercial probes, such as painting probes, this protocol is also applicable. It is necessary to follow the manufacturer's suggestions for probe preparation. For example, for preparation of DNA probes purchased from the Vysis, 1 µL of directly labeled probes should be premixed with 2 µL deionized water and 7 µL supplied CEP hybridization buffer. 3.2.1.3. DNA LABELING We recommend the use of commercial DNA nick-labeling kits from Life Technologies/Gibco for DNA labeling with biotin or digoxigenin. For each reaction, 1 µg of DNA probe is labeled at 15°C for 1 h. After labeling, the reaction is spun through a Sephadex G-50 minicolumn (Amersham Biotechnologies). Load 5 µL of the Nicktranslated probe on a 1% Agarose gel to check the size of the labeled DNA probe fragments. The fragments should be between 200–800 bp in length, with the majority between 300–600 bp. 3.3.1.4. PRECIPITATION OF LABELED DNA PROBE 1. Add the following in a 1.5-mL Eppendorf tube and keep at –70°C for 30 min: 5–10 µL labeled DNA, 5 µg human COT-1 DNA, 1 µg human placental DNA, 3 µg salmon sperm DNA, 1/10 vol 3 M NaOAc (pH 5.2), 2.5 vol 100% ethanol. 2. Centrifuge at 13000g for 30 min at 4°C. 3. Discard the supernatant, add 2 vol 70% ethanol to dissolve the remaining salt and spin again at the same speed for 10 min. 4. Air-dry at room temperature or by a Speed-vac. 5. Add 10 µL hybridization master mixture I or II and vortex to dissolve probes.
3.3.2. Hybridization If a single immunophenotyping is done, dual-color FISH with biotinylated and digoxigenin-labeled probes may be performed. In dual-color FISH, equal amounts of biotin- and digoxigenin-labeled probes are precipitated together and hybridized to cells. When double immunophenotyping is done, only a digoxigenin-labeled probe can be used in the FISH study (see Note 5). 1. Pipet 2–3 µL of hybridization mixture containing DNA probes to the cell-rich areas of the slides. 2. Cover with a 12-mm round coverslip. 3. Seal with rubber cement and let it dry. 4. Place the slides at the bottom of a metal box with a wet paper towel. After covering, put the metal box in a waterbath at 76°C for 5 min (see Note 6). 5. Transfer the box to a 37°C incubator. Hybridization takes from a few hours to overnight or even two days, depending on the DNA probe types. For repetitive DNA probes, hybridization may be just for 2 h, whereas for cDNA probes or chromosome painting probes, hybridization for 2 d are recommended.
3.3.3. Post-Hybridization Washes 1. Remove rubber cement. 2. Put the slides in pre-warmed 0.1X SSC buffer, pH 7.0, at 60°C in a waterbath and let coverslips fall down (see Note 7). 3. Wash slides in 0.1X SSC three times, 5 min each, with shaking. 4. Rinse slides in PN buffer for 3 min at room temperature.
3.3.4. Detecting Hybridization Signals The following protocol is used for detecting both biotin- and digoxigenin-labeled probes. In simultaneous double immunophenotyping and FISH, only digoxigeninlabeled probe should be used. The antibodies for detecting the biotinylated probe, i.e., AMCA-avidin and biotinylated goat anti-avidin, should be omitted in the following steps (see Note 5). 1. Incubate with a mixture of AMCA-conjugated avidin and monoclonal mouse antidigoxigenin antibody, both diluted 1:100 in PNM buffer, at room temperature for 25 min. 2. Wash with PN buffer three times, 5 min each, at room temperature. 3. Incubate with a mixture of biotinylated goat anti-avidin antibody and digoxigeninconjugated sheep anti-mouse antibody, both diluted 1:100 in PNM buffer, at room temperature for 25 min. 4. Wash with PN buffer three times, 5 min each, at room temperature. 5. Incubate with a mixture of AMCA-conjugated avidin and FITC-conjugated sheep antidigoxigenin antibody, both diluted 1:100 in PNM buffer, at room temperature for 25 min. 6. Wash with PN buffer three times, 5 min each, at room temperature. 7. Mount the slides with antifade medium. If only red and green fluorescence dyes are used in the study, cells may be stained with DAPI prior to mounting by putting slides in DAPI solution for 2 min followed by rinsing in 2X SSC. This counterstaining may help in defining the location of hybridization signals in certain cell nuclei.
3.4. Image Recording and Evaluation of Immunophenotyping and FISH Results The results of immunophenotyping and FISH may be evaluated simultaneously or sequentially under a fluorescence microscope, depending on the use of single-, dualor triple-dye fluorescence filter sets. The results may be photographed with a highspeed film (ASA 400) or recorded with a digital imaging system, such as ISIS from Metasystems. For evaluation of the results of immunophenotyping, it is important to distinguish true- from false-positive reactions that may result from background staining or cross-reaction of the antibodies used. Generally, the former shows a bright and fresh fluorescence, whereas the latter has a dim and weak or extremely bright fluorescence. For FISH analysis of immunophenotyped cells, only intact nonoverlapping cells should be evaluated. We generally analyze at least 50 positive cells and more than 100 negative cells per slide. More important, a blinded evaluation of these results should be performed by another independent observer.
4. Notes 1. For immunophenotyping, monoclonal mouse anti-human CD antibodies as well as polyclonal Cy3- or AMCA-conjugated antibodies are diluted from 1:50 to 1:200 in PNM buffer. The appropriate concentration depends on the quality of the antibodies and on the expression level of the antigen. For example, the strongly expressed CD3 on T lymphocytes may easily be detected by incubation of only the first or the first and the second antibodies. Thus, a control study should be done for each newly purchased antibody for determining its optimal concentration. In general, Cy3 and FITC are very strong and durable fluorescence dyes, whereas AMCA is weak and unstable. Immunophenotypes detected with Cy3 can be reviewed even after several weeks or months, whereas those detected with AMCA will disappear very soon. It is not possible to review slides detected with FITC later than after a few days, because of the background due to the auto-fluorescence of the cells. 2. For refixation after immunophenotyping, either 1 or 4% paraformaldehyde may be used. It can be stored for up to 2 wk at 4°C, whereas Carnoy's fixative must be freshly prepared each time. The times of refixation of these buffers are very critical for successful combination of immunophenotyping and FISH. The shorter the time that cells are fixed, the more fluorescence intensity is lost. However, too long fixation will result in a dramatically low hybridization efficency in FISH study. 3. For immunophenotyping, a negative control must be set up each time for exclusion of any false-positive results. Any fluorescence from this procedure represents nonspecific staining (noise). Replacing the monoclonal or primary antibody with water, PBS, or irrelevant isotype-matched antibodies could be used as negative control. In order to examine crossreactions or interruption of polyclonal antibody's chain derived from different animals, a control slide should be used in the double immunophenotyping study (23). 4. In double immunophenotyping experiments, incubation with 20% normal mouse serum containing high concentrations of mouse immunoglobulins is very important for successful second immunophenotyping. The free binding sites of the rabbit anti-mouse antibody are blocked and will not be able to bind with a second primary mouse anti-human antibodies (here, CD8 is used as an example). Do not wash slides after this incubation. Also, in FISH on double-immunophenotyped cells, do not use biotinylated probes, because they will bind nonspecifically to the antibody cascade of the second monoclonal mouse anti-human antibody, i.e., CD8.
5. Because of color fluorescence limitations, it is difficult in practice to combine three fluorescence colors, i.e., green (FITC), red (Cy3), and blue (AMCA), in one experiment. In fact, the blue fluorescence of AMCA is very weak and unstable, and it can be used only in detecting repetitive probes in FISH. On the other hand, FITC will decrease intensity faster than Cy3 after detection steps, and the contrast to background becomes less. Therefore, we suggest the use of the Cy3-conjugated antibodies for detecting weakly expressed antigens or small locus-specific DNA probes. 6. We do not find any difference between separate and combined denaturing of cellular DNA and probes. In many laboratories, targeted cellular DNA and probe DNA are denatured separately, followed by preannealing of the DNA probe with human Cot-1 DNA. We find that combined denaturing is faster, easier, and results in similar FISH results as separate denaturing procedures. 7. In the FISH study, we found that post-hybridization washing in 0.1X SSC three times at 60°C results in a washing efficiency equal to that of washing in 50% formamide/2X SSC at 42°C, whereas the former solution is much cheaper and not toxic.
Acknowledgment This work was supported by European Community grant QLG1-2000-00687 and by German Cancer Aid grant 10-1556-Schl4 .
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13. Zhang, Y., Siebert, R., Matthiesen, P., et al. (2000) Feasibility of simultaneous fluorescence immunophenotyping and fluorescence in situ hybridization study for the detection of estrogen receptor expression and deletions of the estrogen receptor gene in breast carcinoma cell lines. Virchows Arch. 436, 271–276. 14. Knuutila, S. (1997) Lineage specificity in hematological neoplasms. Br. J. Hematol. 96, 2–11. 15. Fagioli, F., Cuneo, A., Bardi, A., et al. (1995) Heterogeneity of lineage involvement by trisomy 8 in myelodysplastic syndrome. Cancer Genet. Cytogenet. 82, 116–122. 16. Gerritsen, W. R., Donohue, J., Bauman, J., et al. (1992) Clonal analysis of myelodysplastic syndrome: monosomy 7 is expressed in the myeloid lineage, but not in the lymphoid lineage as detected by fluorescent in situ hybridization. Blood 80, 217–224. 17. Kanfer, E. J., Price, C. M., Colman, S. M., and Barrett, A. J. (1992) Erythropoietinindependent colony growth in polycythaemia vera is not restricted to progenitor cells with trisomy of chromosome 8. Br. J. Haematol. 82, 773–774. 18. Kibbelaar, R. E., van Kamp, H., Dreef, E. J., et al. (1992) Combined immunophenotyping and DNA in situ hybridization to syndromes. Blood 79, 1823–1828. 19. Anastasi, J., Vardiman, J. W., Rudinsky, R., et al. (1991) Direct correlation of cytogenetic findings with cell morphology using in situ hybridization: an analysis of suspicious cells in bone marrow specimens of two patients completing therapy for acute lymphoblastic leukemia. Blood 77, 2456–2462. 20. El-Rifai, W., Larramendy, M. L., Ruutu, T. , and Knuutila, S. (1995) Lymphoid involvement in a patient with acute myeloid leukemia: a direct phenotypic and genotypic study of single cells. Gene Chromosom. Cancer 15, 34–37. 21. Haase, D., Feuring-Buske, M., Konemann, S., et al. (1995) Evidence for malignant transformation in acute myeloid leukemia at the level of early hematopoietic stem cells by cytogenetic analysis of CD34 positive subpopulations. Blood 86, 2906–2912. 22. Zhang, Y., Wong, K. F., Siebert, R., et al. (1999) Chromosome aberrations are restricted to the CD56+, CD3– tumor cell population in natural killer cell lymphomas: A combined immunophenotyping and FISH study. Br. J. Haematol. 105, 737–742. 23. Price, C. M., Kanfer, E. J., Colman, S. M., Westwood, N., Barrett, A. J., and Greaves, M. F. (1992) Simultaneous genotypic and immunophenotypic analysis of interphase cells using dual-color fluorescence: a demonstration of lineage involvement in polycythemia vera. Blood 80, 1033–1038. 24. Jonas, D., Lubbert, M., Kawasaki, E. S., et al. (1992) Clonal analysis of bcr-abl rearrangement in T lymphocytes from patients with chronic myelogenous leukemia. Blood 79, 1017–1023. 25. Clein, G. P. and Flemans, R. J. (1996) Involvement of the erythroid series in blastic crisis of chronic myeloid leukaemia: further evidence for the presence of Philadelphia chromosome in erythroblasts. Br. J. Haematol. 12, 754–758. 26. Fauser, A. A., Kanz, L., Bross, K. J., and Lohr, G. W. (1995) T cells and probably B cells arise from the malignant clone in chronic myelogenous leukemia. J. Clin. Invest. 75, 1080–1082. 27. Weber-Matthiesen, K., Deerberg, J., Poetsch, M., Grote, W., and Schlegelberger, B. (1995) Numerical chromosome aberrations are present within the CD30–positive Hodgkin and ReedSternberg cells in 100% of analysed cases of Hodgkin´s disease. Blood 86, 1464–1468. 28. Wong, K. F., Zhang, Y., and Chan, J. K. F. (1999) Cytogenetic abnormalities in natural killer cell lymphoma/leukemia—Is there a consistent pattern? Leukemia Lymphoma 34, 241–250.
BAC Resource
27 BAC Resource for Molecular Cytogenetics Xiao-Ning Chen and Julie R. Korenberg 1. Introduction Bacterial artificial chromosomes (BACs) are ideal materials to use for the purpose of integrating DNA sequence with cytogenetic markers. They have been the major vectors used in genome sequencing. BACs are also well suited for fluorescent in situ hybridization (FISH) in that they represent a stable and easily manipulated form of cloned DNA that produces bright, well-defined signals on metaphase and interphase chromosome preparations (1). To link chromosomal position with DNA sequence throughout the human genome, we have developed an integrated BAC resource (1) by using FISH, PCR, and sequencing. The Resource contains a total of 6000 randomly mapped BAC clones, out of which, 1021 are BAC-sequence-tagged sites (STS) pairs representing 957 BACs (Fig. 1). This tool can be now used to rapidly identify genes affected by chromosomal rearrangements seen in genetic disorders and cancers. After this initial development, an international effort has assembled a collection of BAC clones that are both sequence-tagged and mapped relative to cytogenetic bands using FISH, resulting in a collection of 7600 clones (2; see Note 1). Over the past decade, FISH has evolved into a method that is used in clinical and research laboratories around the world. FISH is capable of simultaneously detecting regions of homology among chromosomes and providing a window into the evolutionary history of exchanges, duplications, and rearrangements in the genome (1,2). In particular, the ability to hybridize complex DNA probes to specific metaphase chromosomes and interphase nuclei has made FISH an indispensable tool for both clinical diagnostics and basic research (3–6). However, the applications of FISH techniques were limited owing to lack of high-quality DNA probes that cover the whole genome. This situation has now been remedied by the generation of the BAC resource (1,2). We have described here a detailed protocol and examples of the applications using the Integrated BAC Resource for solving chromosomal puzzles that are beyond the resolution of standard cytogenetics. These include application to cancer genetics and analysis of germline chromosome aneuploidy (see Notes 2–4). From: Methods in Molecular Biology, Vol. 204: Molecular Cytogenetics: Protocols and Applications Edited by: Y. S. Fan © Humana Press Inc., Totowa, NJ
Chen and Korenberg
Fig. 1. An Integrated BAC Resource was developed using FISH and PCR to link chromosomal position with DNA sequence in the human genome (1). This map contains a total of 1021 BAC-STS pairs representing 957 BACs, each mapping to the position indicated by the vertical lines at the right of each chromosome ideogram. The length of the line indicates the resolution of the assignment, i.e, the outer boundaries of the band(s) within which the BAC signal is located as described in the methods. Although higher resolution may be obtained from our archived images, within a single band region, BACs are also ordered by the genetic and RH maps (1,16).
2. Materials 2.1. Equipment and Supplies 1. Fluorescence microscope (Zeiss Axiovert 135) with seven fluorescence filter sets (Chroma Technology). 2. Cooled-CCD camera (Photometrics CH250). 3. Phase microscope (Zeiss Axiophot 20).
394 4. 5. 6. 7. 8. 9.
Chen and Korenberg Slide warmer (Precision). Spectrophotometer (Beckman) or Fluorometry (Turner Designs). Shaking waterbath (Precision). Incubator oven (Fisher Science) set to 37°C. S/P Brand superfrost slides (25 × 75 mm) (Allegiance) S/P Brand coverglass (22 × 50 mm; 22 × 40 mm; 22 × 22 mm) (Allegiance).
2.2. Chemicals 2.2.1. BAC DNA Extraction 1. Terrific Broth (Life Technologies): Add 48.2 g/L of purified water. Mix well to dissolve, add 8 mL glycerol and then autoclave at 121°C for 15 min. Cool to 50°C, and add chloramphenicol (Sigma) to 12.5 µg/mL. 2. RNase solution: 50 mM Tris-HCl, pH 8, 10 mM EDTA and RNase A (100 µg/mL) (Life Technologies). 3. DNA extraction kit: NucleoBond Nucleic Acid Kit (ClonTech); QIAGEN Plasmid Midi/ Maxi kit (Qiagen). 4. Phenol: Chloroform (Life Technologies). 5. Agarose (Life Technologies). 6. 1 kb DNA marker (Gibco-BRL).
2.2.2. Chromosome Preparation 1. Cell culture medium: RPMI 1640 (Life Technologies) supplemented with L-glutamine (2 mM) (Sigma), 15% fetal calf serum (Sigma), penicillin (100 Iu/mL)( Life Technologies), streptomycin (0.05 mg/mL) (Life Technologies) and 0.02% phytohemagglutinin (Life Technologies). 2. Hank's BSS (Life Technologies). 3. 5-Bromode oxyuridine (Sigma). 4. Thymidine (Life Technologies). 5. Colcemid (Life Technologies), 10 mg/mL. Stored at 4°C. 6. Hypotonic solution (0.075 M KCl): 5.6g KCl/L of purified water. 7. Fixative: acetic acid/methanol: 1/3 (vol/vol). Make fresh right before use and keep on ice.
2.2.3. Probe DNA Labeling 1. 2. 3. 4. 5. 6.
Nick-translation kit and Bionicktranslation kit (Life Technologies) Store at –20°C. Digoxigenin-11-dUTP (Boehringer Mannheim), 1 mM. Store at –20°C. Fluorolink Cy3-dCTP (Amersham Pharmacia Biotech). Store at –20°C. Fluorolink Cy5-dCTP (Amersham Pharmacia Biotech). Store at –20°C. DNAse I (Gibco-BRL). G 50 Sephadex Quick spin column (Life Technologies).
2.2.4. FISH and Post-Hybridization Detection 1. 2. 3. 4. 5. 6. 7.
Human COT1™ DNA (Life Technologies), 1 mg/mL. Store at –20°C. Salmon sperm DNA (3'-5') Store at –20°C. 3 M Sodium acetate (Sigma). Bovine serum albumin (Sigma). Store at 4°C. FITC (avidin-conjugated fluorescein isothiocyanate) (Vecter Labs). Sheep-anti-digoxigenin-Rhodamine (Boehringer Mannheim). Chromomycin A3 (Sigma) 0.5 mg/mL (in 50% McIlvane's buffer).
8. Distamycin A (Sigma) 0.1 mg/mL (in 50% McIlvane's buffer). 9. Denaturing solution (70% formamide [EM Science]/2X SSC): add 35 mL formamide, 10 mL distilled water, 5 mL 20X SSC, pH 7.0. Store at 4°C. Prepare fresh every 2–4 wk. 10. Ethanol series: prepare 70, 80, and 100% ethanol in distilled water and keep on ice. 11. Hybridization Master Mix: 10% v/v dextran sulfate (Sigma), 50% formamide (EM Science), 2X SSC, pH 7.0. Store at –20°C. 12. Formamide (Fisher) and 2X SSC wash solution: add 15 mL 20X SSC, 60 mL distilled water, 75 mL formamide, pH 7.0. Store at 4°C. 13. 20X SSC: 3 M NaCl, 0.3 M Na3 citrate, pH 7.0. 14. 4X SSC/0.1% Tween-20 (Sigma): add 100 mL 20X SSC, 400 mL distilled water and 500 µL Tween-20. Mix well. 15. TE (Tris/EDTA) buffer: 1X TE is 10 mM Tris-HCl, 1 mM EDTA, pH 7.4, 7.5, or 8.0. 16. 1 M Tris-HCl, pH 7.5 or 8.0. 17. 0.5 M EDTA, pH 8.0. 18. McIlavane's buffer (pH 9.0): citric acid 0.63 g, sodium phosphate dibasic 6.19 g, 500 mL of purified water. 19. Antifade solution (7): Dissolve 100 mg p-phenylenediamine dihydrochloride (Sigma) in 10 mL PBS. Adjust to pH 8 with 0.5 M bicarbonate buffer (0.42 g NaHCO3 in 10 mL water, adjust pH 9.0 with NaOH). Add to 90 mL glycerol. Store in aliquotes at –20°C. The solution darkens with time, but remains effective even after a few years.
3. Methods (8) 3.1. Metaphase Preparation and Slide Selection (see Note 5) 1. Human peripheral lymphocytes are grown in cell culture medium for 72 h at 37°C. 2. The cells are blocked in S-phase by adding 5-bromode/oxyuridine (0.8 mg/mL) for 16 h. 3. The cells are then washed once with HBSS (Hanks' Balanced Salt Solution) to remove the synchronizing agent and are released by additional incubation for 6 h in cell culture medium with 2.5 µg/mL of thymidine. 4. Cultures are harvested by addition of 0.1 µg/mL of colcemid for 10 min followed by treatment with 10 mL 0.075 M KCl for 15 min at 37°C and fixation for 4× in a freshly made solution of methanol and glacial acid (3:1/v). 5. To obtain high quality chromosome preparations, metaphase spreads are prepared by letting one drop of cell suspension fall from 15 in on alcohol-cleaned slides, then placing above a container filled with heated (close to boiling) water for 20–40 s. This time varies with the ambient humidity and with the individual cell preparations. It must be determined for each cell preparation and checked using a phase contrast microscope. If there is cytoplasmic residue visible around the metaphase spread, wash the remaining cells with fixative several times before dropping. Ideally, the chromosomes in metaphase spreads should appear dark black (see Note 6). If chromosomes appear glassy or refractile, this suggests that the cells have dried too slowly. The slides are then kept in the dark for at least 2–3 wk at room temperature, and stored at –70°C until use. 6. Slides are reviewed before using for FISH. Look at the slide under phase contrast (×10), select a region of interest containing at least five metaphase spreads per field and mark the area at the edges of the cell spreads with a diamond tip pen. 7. The RNase treatment step is usually omitted if the slides are aged more than 2 wk. In general, it does not affect the ratio of signal to noise. If RNase treatment is used, 100 µg/mL RNase is used for 30 min at 37°C and is then followed by dehydration through an ethanol series (70, 90, and 100%).
3.2. BAC DNA Extraction (see Note 7) The following protocol is from Qiagen, good for preparing 20–50 µg of DNA (QIAGEN plasmid Midi/Maxi kit). Alternative protocols employ the NucleoBond BAC Miniprep kit or the NucleoBond BAC Maxi kit (ClonTech) according to the directions provided by the manufacturers. 1. Streak the bacterial culture on an LB agar plate containing chloramphenicol (12.5 µg/ mL) for overnight at 37°C. 2. Pick up single colonies and grow in 100 mL of LB containing chloramphenicol (12.5 µg/mL) for overnight at 37°C. Try to achieve an OD600 nm of 1.4–1.6. 3. Spin culture in 250 mL buckets using a GSA rotor/Sorval at 3000g for 15 min. 4. Resuspend bacterial pellet in 10 mL of RNAse solution. Pipet up and down using a 10 mL pipet and resuspend completely. Transfer cells to Oak Ridge tubes (Allegiance). 5. Add 10 mL of 0.2 M NaOH and 1% SDS. Mix tubes gently by inverting tubes repeatedly but slowly 10×. Incubate at room temperature for 5–10 min and make sure the solution turns from turbid to translucent. 6. Add 8 mL of chilled 3 M KAc, pH 5.5. Mix tubes gently by inverting slowly 10×. Excessive violent mixing will increase contamination with E. coli genomic DNA. Allow to stand on ice for 15 min. 7. Centrifuge at 4°C in a Sorvall RC 28S centrifuge using an SS34 rotor for eight tubes or an SA-600 (12 tubes). Spin at ~33,000g or more (16,000 rpm for the SA-600) for 30 min and remove the supernatant promptly. 8. Remove supernatant carefully using 25 mL pipet while avoiding debris. Place supernatant in a clean autoclaved Oak Ridge tube. 9. Centrifuge again as in step 6. Even though your supernatant may appear clear, you must centrifuge again since skipping this step will cause the column to clog. Transfer supernatant to a fresh 50 mL tubes and keep on ice. 10. Equilibrate "Qiagen-tip 100" columns with 4 mL of QBT buffer. 11. Apply the supernatant from step 8 to a Qiagen-tip 100 column. 12. Wash the Qiagen-tip 100 with 10 mL of QC buffer twice. 13. Elute the DNA from the column with 5 mL of 60°C-QF buffer. Collect the eluant in a 14-mL culture tube containing 5 mL of isopropanol. Use culture tubes from the VWR cat no. 60818-725 since these can withstand high G-forces. Thinner walled tubes can break. Oak Ridge tubes can be substituted, but the pellet is more difficult to observe. 14. Centrifuge tubes at 11,700g for 30 min at 4°C. For the Sorval SA-600 rotor, use 9000 rpm ~ 11,700g. 15. Wash pellet with 5 mL of 70% EtOH at room temperature. Spin again for 10 min. Carefully pour off supernatant. Air dry 10 min. This step removes excess salt from the BAC DNA preparation. 16. Resuspend pellets in 400 µL of TE buffer using pipet tips with the ends cut off. Because BAC DNAs are large, it may take some time to totally resuspend the DNA. You may want to let the tubes sit overnight at room temperature until the pellets are dissolved into TE buffer. Transfer DNA to a clean 1.5 mL Eppendorf tube. 17. Add 400 µL of phenol/chloroform (1:1) and vortex. Spin for 5 min at a maximum speed of any microcentrofuger (see Note 7). 18. Remove and transfer aqueous phase (top) to clean 1.5-mL tubes. 19. To precipitate the DNAs, add 40 µL of the 3 M NaOAc and 1100 µL of cold EtOH and keep at –20°C for 2 h .
20. Centrifuge at maximum speed for 30 min and wash pellet with 750 µL of cold 70% EtOH twice. 21. Dissolve pellet in 50 µL TE buffer and leave the tube at 4°C for overnight or at 37°C for overnight if the pellets are large. 22. Expect a total of 20–50 µg yield of a concentrations of about 0.5–1 µg/µL when resuspending in 50 µL. 23. Determine BAC DNA yield by UV spectrophotometry or fluorometry. Confirm BAC integrity by Agarose gel electrophoresis.
3.3. Probe DNA Labeling (see Note 8) The procedures below follow the protocol provided in the Nick-translation kits (Gibco-BRL Life Technologies). 1. Select the nucleotide to be used from one of the five mixes, which contain all dNTPs except those to be used for tagging with biotin or digoxigenin, and thaw it on ice. Keep the DNAse I/Polymerase I mix on ice or at –20°C before use. 2. Add the following reagents to a 1.5-mL microcentrifuge tube placed on ice and then mix briefly: 5 µL dNTP Mix, x µL solution containing 1 µg test DNA, 1 µL of digoxigenin11-dUTP (for digoxigenin labeling) and y µL distilled water to make a total of 42 µL volume. The volumes of x and y may vary depending on the concentration of DNA. 3. Add 5 µL of DNAse I/Pol mix and 3 µL of a 1/1000 dilution of DNAse I (3 mg/mL). Mix gently but thoroughly. Centrifuge for 5 s in a microcentrifuge to bring down the solution from the cap. 4. Incubate at 15°C for 60 min. 5. Take 5 µL of the labeling solution and run on a 1.2% nondenaturing agarose gel to check the fragment size by comparing with 1 kb DNA marker. 6. If the fragment size is within the size range of 100–500 bp, add 5 µL of Stop buffer. If the size is bigger than 500 bp, add 1/100 diluted DNAse I (3 mg/mL) to the tube and incubate for 15–40 min (The time length will depend on the measured size of the DNA fragments). 7. Unincorporated nucleotides are separated by chromatography (Sephadex G-50) or by using ethanol precipitation.
3.4. Fluorescence In Situ Hybridization (FISH) 3.4.1. Hybridization 1. Denature chromosome slides in denature solution at 67–70°C for 10 s–2 min (see Note 6). 2. Precipitate 100–200 ng probe DNA, 3 µg of Cot-1 DNA and 7 µg of sonicated salmon sperm DNA by using 3 M sodium acetate (10:1/v) and cold 100% Ethanol (2.5 X/v). Resuspend the pellet in 10 µL hybridization mixture. 3. Denature hybridization solution at 75°C in a waterbath for 5 min, move to 37°C waterbath for 30 min for preanealing. 4. Apply 10 µL of denatured and preannealed solution from step 3 to denatured chromosome slides. Place a coverslip on top of the solution, squeeze bubbles out and seal it with rubber cement. 5. Incubate the slides in a humidified chamber at 37°C overnight.
3.4.2. Post-Hybridization Washes and Detection (see Note 9) 1. Wash slides 4× in Coplin jars placed in a buffer containing 2X SSC and 50% formamide for 5 minutes each at 44°C. For directly labeled probes, go to the Subheading 3.5. after step 1.
2. Wash slides 3× at 50°C shaking waterbath for 5 min each in 0.1X with a gentle shaking. 3. Block sites of specific hybridization on slide with 100 µL of 4X SSC, 3% BSA and 0.1% Tween-20 covered with a 22 × 50 cm coverslip and incubate at 37°C for 20 min. 4. Remove the coverslip and drain the blocking solution very briefly. Then replace the blocking solution with a detection solution. For biotinylated probes, avidin-conjugated fluorescein isothiocyanate (FITC) is used (5 µg/mL in 0.4 µg/mL in 4X SSC, 1% BSA and 0.1% Tween-20), and for digoxigenin-labeled probes, sheep-anti-digoxigenin antibody is used (0.4 µg/mL in 4X SSC, 1% BSA and 0.1% Tween-20). 5. Cover chromosomal area with coverslips and incubate slides in a chamber (or a large Petridish) at 37°C for 30 min. 6. Remove coverslips and wash slides 3× in 2X SSC, 0.1% Tween-20 at 42°C for 5 min each.
3.5. Chromosome Counterstain (R Banding) (see Note 10) To view chromosome bands and fluorescence signals simultaneously, Chromomycin A3 and Distamycin A are used as a counterstain (8). This reverse banding pattern generates a more reproducible and higher resolution banding pattern than that the Q type pattern revealed by DAPI (9). Although the emission spectrum of chromomycin overlaps that of FITC, it can be separate by using the appropriate filter combination (8). 1. Rinse slides briefly in 1/2 McILavane's buffer, pH 9.0 prior to staining, shake off the excess fluid. 2. Place 100 µL of Chromomycin A3 (0.5 mg/mL in 50% McILavane's buffer, pH 9.0) onto slides for 40–60 min at room temperature. 3. Rinse slides in 50% McIlavane's buffer for 1 min at room temperature and shake off the excess fluid. 4. Place 50 µL of 0.1 mg/mL distamycin A on the slide for 1–2 min at room temperature. 5. Rinse slides in 1/2 McIlavane's buffer very briefly (10–20 s). 6. Place a very thin layer of antifade solution on slides and cover with a coverslip (20 × 50 cm).
3.6. Microscopy and Image Analysis (see Note 11) 1. Analysis of in situ hybridization preparations may be performed by visual inspection, photography, or electronic image capture combined with digital image processing, using two different types of Zeiss fluorescence microscopes. The Zeiss Axiophot 100 microscope was used for generating black and white photographs from experiments using single color FISH. Kodak Technical pan ASA100 black and white films were used. For capturing color images from single, dual or multicolor FISH experiments, the Zeiss Axiovert 135 microscope was equipped with a 200-W mercury lamp and combined with a Photometrics Cooled-CCD camera employing BDS (Biological Detection System) image software was used. 2. To view multiple-labeled probes that have been simultaneously hybridized to chromosome slides, images are viewed sequentially with single-bandpass filter sets or with multiple bandpass filter sets. In our hands, the images were acquired using a ×63, 1.2 N.A. objective and filter sets for excitation and observation of Texas Red or Rhodamine and FITC or Cy3 and CY5 fluorescence, respectively (Chroma Technology, Brattleboro, VT). Chromomycin A3 and Distamycin A reverse banded chromosomes are captured by using Quinacrine filter sets (ex. 440 nm; em. 495 nm) (8).
3. To detect chromosomal aneuploidy or rearrangement, a total of 20 metaphase cells are chosen in the best area to be evaluated. That area is represented by a higher signal to noise ratio and best metaphase spreads. The representation of the images are acquired and are stored in an image database. Only the raw images are saved. No enhancement, correction or modification should be performed at this stage.
4. Notes 1. When combined with a well-characterized reagent resource such as BACs, FISH is one of the most rapid and accurate methods for mapping human genes and novel chromosomal breakpoints. Moreover, the production of a reproducible high-resolution banding pattern has been highly useful for the FISH assignment of DNA fragments to human metaphase chromosomal bands essential for the sis and identification of chromosome rearrangements. Through sequence-linked BACs, a researcher can link the cytogenetic findings to a sequence rapidly, and further apply the information to a broad spectrum of molecular cytogenetic analyses. 2. We illustrate two applications that employ this integrated BAC resource for molecular cytogenetics: cancer and germline aneuploidy detection. Other applications discussed elsewhere include chromosome 21 analysis (10), cancer (11), Gene isolation (12) and genome organization and construction in Williams syndrome (13), and chromosomal anueploidy analysis (14). 3. In the first example (Fig. 2A), the BACs from the Resource are used in FISH analysis on chromosomes made from a thyroid follicular carcinoma. This assay was used to determine specific regions amplified on chromosome 2p21 previously defined by using Comparative Genomic Hybridization (CGH). This step was essential to link the low resolution of the amplification observed by CGH to the DNA sequence. This work led to the definition of a candidate gene, PKCε, that was then implicated for a role in thyroid tumorigenesis (11,15). The BACs used in this study demonstrated that chromosome band-specific BACs can facilitate identifying novel candidate gene(s) for tumorigenesis and determining the molecular structure of an amplified region. 4. In the second example of a chromosomal aneuploidy analysis (Fig. 2B), FISH was used to narrow a chromosomal breakpoint associated with a birth defect by using BACs linking to chromosome 21q22.1–22.3 and to chromosome band 8p23.3. In contrast to results with standard cytogenetics, we showed that translocation of the telomeric markers D21S348 through S100B was accompanied by the deletion of markers D21S65–D21S55. Clinically these results revealed deletion for the Down syndrome markers D21S55 and D21S65, but diploidy for the markers from this region to the telomere. For 8p, of six BACs mapping in the distal band, only the most telomeric was deleted, suggesting little contribution of the usual 8p deletion to the phenotypic defects of the child. This STS definition of the breakpoint region also provides links to in silico analyses of candidate genes for features defined in the child. 5. In order to produce consistent FISH mapping results, the following points should be taken into consideration. These involve each step, from chromosome preparation to image capture. One of the most important elements is to begin with high quality chromosome preparations. The DNA denaturation, hybridization, and probe detection parameters appear to be less important. We will describe these issues in sequential order as we go through the protocol. 6. The quality and the pretreatment of metaphase preparations are both critical to the success of signal production. A high quality chromosome preparation should meet the fol-
Fig. 2. (A) The FISH hybridization of BAC 1D9 on chromosomes derived from WRO, a cell line derived from a thyroid follicular carcinoma. In addition to the FITC signals (yellow dots) detected on band 2p21 of the three apparently normal copies of chromosome 2, distinct clusters of signals are seen, representing amplifications of band 2p21 shown both on double minute chromosomes and in the adjacent interphase nuclei. (B) Dual color FISH analysis of a translocation between chromosome 21 and 8 using STS linked BACs from the Integrated BAC Resource (1). BACs for D21S348 (labeled with biotin-14-dATP) and D21S231 (labeled with digoxigenin-11-dUTP) were cohybridized on metaphase chromosomes and detected with FITC (green signals) and Rhodamine (red signals) respectively. Both markers revealed a clear translocation from chromosome 21q22.3 to chromosome 8p23.3.
lowing criteria: (1) Metaphase spreads are evenly distributed on the slides with as little as possible residual cytoplasm; (2) few overlapping chromosomes; (3) metaphase spreads appearing dark black. To achieve this quality, the following parameters must be adjusted: hypotonic treatment time and fixation of cell pellets; dropping cell suspension and steaming slide during preparation; chromosome slide baking and finally; the length of chromo-
some denaturation. Fresh chromosome preparations need a shorter time of denaturation. The appropriate adjustments should result in chromosomes that are dark and not refractile. These should provide enhanced DNA target accessibility to the probe without undesirable loss of DNA from the target. 7. The best preparation of BAC DNAs is performed with kits that can be obtained from a number of companies. Steps 17–21 (Subheading 3.2.) are necessary for higher quality DNA extraction. The DNA should be free of contaminants that might inhibit DNA polymerases such as metals, detergents etc. In many cases, an alkaline lysis DNA isolation protocol followed by phenol-chloroform extraction and isopropanol precipitation is sufficient. 8. There are a number of different labeling methods that can be used to map BACs using FISH. These include Nick-translation or random priming, each employing either director indirect-labeling reagents. The probes labeled with Nick-translation give much higher hybridization signal to background noise ratio than that labeled with random priming, however, they use 10× more DNA. The commercially available reagents used for direct labeling, i.e., fluorochrome-labeled nucleotides, are more expensive than the reagents used for indirect labeling, i.e., biotin or digoxigenin. However, both labeling methods give equally bright signals when using BACs as probes. In our hands, Nick-translation was often used in the presence of either biotin-14-dATP or digoxigenin-11-dUTP (Boehringer Mannheim Biochemicals) for indirect-labeling and fluorolink Cy5-dCTP and
fluorolink Cy3-dCTP (Amersham Pharmacia Biotech) was used for direct labeling employing a Nick-translation Kit (Gibco-BRL). The procedures are performed according to the instructions provided with the kits, except for the DNAse concentration and the length of the incubation of Nick-translation (as described in this chapter). The fragment size after labeling is important and should be in the range of 300–500 bp. A fragment size of 1000 bp or above, results in high background and less intense signals, contributing to failure of experiments. 9. The blocking and detection steps are important, but straightforward as long as the correct solutions and procedures are used. However, a word of caution is in order for the step involving immunocytochemical signal detection. The slide should never be allowed to dry, not even a part of it. Although it is important to drain the liquid from the slides to prevent overdilution of the antibodies, the next solution, such as the blocking solution or antibodies, should be applied immediately. If the slides are allowed to dry, the signal to noise ratio can decrease significantly owing to highly increased background. The antibodies should be kept at –20°C in small aliquots. If stored for more than a year, the antibody concentration should be increased twofold. If it yields a high background, a Sephadex G-50 column can be used to purify the antibody. Usually, this will restore the signal to noise ratio. If it does not give sufficient signal, a fresh antibody should be obtained. 10. As we described previously (8), the best banding is obtained by using the most aged chromosomes, i.e. from months to as many years as 10. However, aged chromosomes do not produce the strongest signals. Therefore, to obtain optimal signals with clear banding, freshly prepared chromosomes need to be baked at 50–55°C for about 4 h (can be left for 15 h with no change in signal). Aging chromosomes at room temperature (20–25°C) for 2–4 wk will yield the best banding results, plus reasonably bright hybridization signals. After one month, the slides can be stored at –70°C until use. For fresh slides, the duration of staining with chromomycin A3 should be extended to 1.5 h, and for aged slides, the staining time may be as little as 30 min. The antifade solution is crucial to prevent fading, but only a thin layer should be used. 11. The metaphase selected for image capture and storage should meet the following criteria: (1) Strong but homogeneous hybridization signals; 2) low background; (3) little or no overlap of chromosomes; (4) relatively even condensation along the length of the chromosomes. Most fluorochromes fade quickly, including the reverse banding obtained with chromomycin. Thus, expose the slides to any excitation light only for the minimum amount of time. To map each BAC DNA, count at least 10–20 cells and save a minimum of two images for analysis and data basing. If needed, signals should be enhanced to identify additional sites that may have been missed due to low signal intensity. If BAC DNAs are used for cytogenetic analysis, a standard quality control protocol should be developed. This is crucial to the success of experiments.
References 1. Korenberg, J. R., Chen. X.-N., Sun, Z., et al. (1999) Human genome anatomy: BACs integrating the genetic and cytogenetic maps for bridging genome and biomedicine. Genome Res. 9, 994–1001. 2. Cheung, V. G., Nowak, N., Jang, W., et al. (2001) Integration of cytogenetic landmarks into the draft sequence of the human genome. Nature 409, 953–958. 3. Bolzer, A., Craig, J. M., Cremer, T., and Speicher, M. R. (1999) A complete set of repeatdepleted, PCR-amplifiable, human chromosome-specific painting probes. Cytogenet. Cell Genet. 84, 233–240.
4. Lichter, P. (1997) Multicolor FISHing: what's the catch? Trends Genet. 13, 475–479. 5. Langer, P. R., Waldrop, A. A., and Ward, D. C. (1981) Enzymatic synthesis of biotinlabeled polynucleotides: novel nucleic acid affinity probes. Proc. Natl. Acad. Sci. USA 11, 6633–6637. 6. Pinkel, D., Straume, T., and Gray, J. W. (1986) Cytogenetic analysis using quantitative, high-sensitivity, fluorescence hybridization. Proc. Natl. Acad. Sci. USA 83, 2934–2938. 7. Johnson, G. D. and Nogueira Araujo, G. M. (1981) A simple method of reducing the fading of immunofluorescence during microscopy. J. Immunol. Meth. 43, 349–350. 8. Korenberg, J. R. and Chen, X.-N. (1995) Human cDNA mapping using a high-resolution R-banding technique and fluorescence in situ hybridization. Cytogenet. Cell Genet. 69, 196–200. 9. Mitelman, E. (1995) ISCN 1995 An International System for Human Cytogenetic Nomenclature. 10. Hubert, R. S., Mitchell, S., Chen, X.-N., et al. (1997) BAC and PAC contigs covering 3.5 Mb of the Down syndrome congenital heart disease region between D21S55 and MX1 on chromosome 21. Genomics 41, 218–226. 11. Chen, X.-N., Knauf, J. A., Gonsky, R., et al. (1998) From amplification to gene in thyroid cancer: a high-resolution mapped bacterial-artificial-chromosome resource for cancer chromosome aberrations guides gene discovery after comparative genome hybridization. Am. J. Hum. Genet. 63, 625–637. 12. Yamakawa, K., Huo, Y. K., Haendelt, M. A., et al. (1998) DSCAM: a novel member of the immunoglobulin superfamily maps in a Down syndrome region and is involved in the development of the nervous system. Hum. Mol. Genet. 7, 227–237. 13. Korenberg, J. R., Chen, X.-N., Hirota, H., et al. (2000) VI. Genome structure and cognitive map of Williams syndrome. J. Cogn. Neurosci. 12(Suppl), 89–107. 14. Chen, X.-N., Mitchell, S., Sun, Z.-G, et al. (1996) The Integrated BAC Resource: A Powerful New Molecular Tool For Prenatal Genetics. Am. J. Hum. Genet. 59(suppl)(4), A12, Abstract #53 15. Knauf, J. A., Elisei, R., Mochly-Rosen, D., et al. (1999) Involvement of protein kinase Cepsilon (PKCepsilon) in thyroid cell death. A truncated chimeric PKCepsilon cloned from a thyroid cancer cell line protects thyroid cells from apoptosis. J. Biol. Chem. 274, 23414–23425. 16. Hudson, T. J., Stein, L. D., Gerety, S. S., et al. (1995) An STS-based map of the human genome. Science 270, 1945–1954.
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