1. Field of the Invention
The present invention relates to a nucleotide sequence of a testis-specific gene in avian species and a method for identifying a testicular cell of avian species.
2. Description of the Related Art
Expressed sequence tags (ESTs) are short segments of deoxyribonucleic acid (DNA) that are generated from either one or both ends of expressed gene transcripts (Adams M. D., et al., (1991) Complementary DNA sequencing: expressed sequence tags and human genome project. Science 252, 1651-6). Most of the ESTs were produced for genome-wide analysis using microarray technology and deposited in the dbEST (Boguski M. S., et al., (1993) dbEST—database for “expressed sequence tags”. Nature Genetics 4, 332-3) of the National Center for Biotechnology Information (NCBI). Currently, the dbEST is the most abundant source of new coding sequences. Up to Jul. 23, 2004, 22,830,690 ESTs from 721 species were deposited in the dbEST. In the species having relatively higher number of ESTs compared with its protein sequences, the EST data are probably more important resources for extracting biological and evolutionary information of the species.
Especially, the number of EST sequences in the chicken (Gallus gallus), which is currently reported 495,089, is more than 60-folds than that of protein sequences. Based on plenty of the chicken EST data, the institute for genomic research (TIGR) have produced Gallus gallus gene index (GGGI). The TIGR gene indices consisted of clusters of EST sequences and the clustered elements were evaluated to produce a set of unique and virtual transcripts with high fidelity, called Tentative Consensus (TC) sequences (Quackenbush J., et al., (2000) The TIGR gene indices: reconstruction and representation of expressed gene sequences. Nucleic Acids Research 28, 141-5). To date, TIGR has assembled the chicken ESTs with chicken transcripts into 43,866 TC sequences.
The testis is the organ that produces sperm, and during spermatogenesis transcriptional regulation within germ cells is carefully orchestrated (P. Sassone-Corsi, Unique chromatin remodeling and transcriptional regulation in spermatogenesis. Science 296 (2002) 2176-2178). Sperms develop in association with highly specialized somatic testicular cells, such as Sertoli cells and Leydig cells. During the differentiation of germ cells into spermatozoa, a complex paracrine dialogue with Sertoli cells occurs (M. K. Skinner, et al., Cell-cell interactions and the regulation of testis function, Ann. N.Y. Acad. Sci. 637 (1991) 354-363). Endocrine activity such as testosterone secretion by Leydig cells promotes germ cell differentiation (M. D. Griswold, The central role of Sertoli cells in spermatogenesis, Semin. Cell Dev. Biol. 9 (1998) 411-416). Thus, it has been speculated that the testis has specialized transcription complexes that coordinate the differentiation program of spermatogenesis. In birds, the female is the heterogametic (ZW) sex, but genes on the W chromosome do not influence gonadal development in the way that the SRY gene on the mammalian Y chromosome does. No sex-chromosome-specific SOX gene homologous to the mammalian sex-determining gene SRY has been found in birds (R. Griffiths, The isolation of conserved DNA sequences related to the human sex-determining region Y gene from the lesser black-backed gull (Larus fuscus), Proc. R. Soc. Lond. B. Biol. Sci. 244 (1991) 123-8). However, SRY-like HMG-box gene 9 (SOX9) may influence gonadal development by the initiation of transcription of anti-Müllerian hormone (AMH) during the early stages of chick gonad differentiation (E. Oréal, et al., Early expression of AMH in chicken embryonic gonads precedes testicular SOX9 expression, Dev. Dyn. (1998) 522-32). The avian DMRT1 gene is located on the Z chromosome (I. Nanda, et al., 300 million years of conserved synteny between chicken Z and human chromosome 9, Nat. Genet. 21 (1999) 258-259) and is expressed more strongly in male than in female embryonic gonads, (C. S. Raymond, et al., Expression of Dmrt1 in the Genital Ridge of Mouse and Chicken Embryos Suggests a Role in Vertebrate Sexual Development, Dev. Biol. 215 (1999) 208-220; C. A. Smith, et al., Conservation of a sex-determining gene, Nature 402 (1999) 601-2; Z. Shan, et al., Sex-specific expression of an evolutionarily conserved male regulatory gene, DMRT1, in birds. Cytogenet. Cell. Genet. 89 (2000) 252-7).
It is therefore thought that numerous genes affect male germ cell development in birds and, that some of these may be expressed in a testis-specific pattern. The chicken is one of the most important model organisms for the study of germ-line development, as its embryonic development occurs in ovo.
Throughout this application, various publications are referenced and citations are provided in parentheses. The disclosure of these publications in their entities are hereby incorporated by references into this application in order to more fully describe this invention and the state of the art to which this invention pertains.