J Niclas
Cell cycle regulation of dynein association with membranes modulates microtubule-based organelle transport.
J Niclas, V J Allan, R D Vale
DOI: https://doi.org/10.1083/jcb.133.3.585
Cytoplasmic dynein is a minus end-directed microtubule motor that performs distinct functions in interphase and mitosis. In interphase, dynein transports organelles along microtubules, whereas in metaphase this motor has been implicated in mitotic spindle formation and orientation as well as chromosome segregation. The manner in which dynein activity is regulated during the cell cycle, however, has not been resolved. In this study, we have examined the mechanism by which organelle transport is controlled by the cell cycle in extracts of Xenopus laevis eggs. Here, we show that photocleavage of the dynein heavy chain dramatically inhibits minus end-directed organelle transport and that purified dynein restores this motility, indicating that dynein is the predominant minus end-directed membrane motor in Xenopus egg extracts. By measuring the amount of dynein associated with isolated membranes, we find that cytoplasmic dynein and its activator dynactin detach from the membrane surface in metaphase extracts. The sevenfold decrease in membrane-associated dynein correlated well with the eightfold reduction in minus end-directed membrane transport observed in metaphase versus interphase extracts. Although dynein heavy or intermediate chain phosphorylation did not change in a cell cycle-dependent manner, the dynein light intermediate chain incorporated approximately 12-fold more radiolabeled phosphate in metaphase than in interphase extracts. These studies suggest that cell cycle-dependent phosphorylation of cytoplasmic dynein may regulate organelle transport by modulating the association of this motor with membranes.
Cloning and expression of a human kinesin heavy chain gene: interaction of the COOH-terminal domain with cytoplasmic microtubules in transfected CV-1 cells
F Navone, J Niclas, N Hom-Booher, L Sparks, HD Bernstein, G McCaffrey, RD Vale
DOI: https://doi.org/10.1083/jcb.117.6.1263
To understand the interactions between the microtubule-based motor protein kinesin and intracellular components, we have expressed the kinesin heavy chain and its different domains in CV-1 monkey kidney epithelial cells and examined their distributions by immunofluorescence microscopy. For this study, we cloned and sequenced cDNAs encoding a kinesin heavy chain from a human placental library. The human kinesin heavy chain exhibits a high level of sequence identity to the previously cloned invertebrate kinesin heavy chains; homologies between the COOH-terminal domain of human and invertebrate kinesins and the nonmotor domain of the Aspergillus kinesin-like protein bimC were also found. The gene encoding the human kinesin heavy chain also contains a small upstream open reading frame in a G-C rich 5' untranslated region, features that are associated with translational regulation in certain mRNAs. After transient expression in CV-1 cells, the kinesin heavy chain showed both a diffuse distribution and a filamentous staining pattern that coaligned with microtubules but not vimentin intermediate filaments. Altering the number and distribution of microtubules with taxol or nocodazole produced corresponding changes in the localization of the expressed kinesin heavy chain. The expressed NH2-terminal motor and the COOH-terminal tail domains, but not the alpha-helical coiled coil rod domain, also colocalized with microtubules. The finding that both the kinesin motor and tail domains can interact with cytoplasmic microtubules raises the possibility that kinesin could crossbridge and induce sliding between microtubules under certain circumstances.
Suppression of kinesin expression in cultured hippocampal neurons using antisense oligonucleotides.
A Ferreira, J Niclas, R D Vale, G Banker, K S Kosik
Kinesin, a microtubule-based force-generating molecule, is thought to translocate organelles along microtubules. To examine the function of kinesin in neurons, we sought to suppress kinesin heavy chain (KHC) expression in cultured hippocampal neurons using antisense oligonucleotides and study the phenotype of these KHC "null" cells. Two different antisense oligonucleotides complementary to the KHC sequence reduced the protein levels of the heavy chain by greater than 95% within 24 h after application and produced identical phenotypes. After inhibition of KHC expression for 24 or 48 h, neurons extended an array of neurites often with one neurite longer than the others; however, the length of all these neurites was significantly reduced. Inhibition of KHC expression also altered the distribution of GAP-43 and synapsin I, two proteins thought to be transported in association with membranous organelles. These proteins, which are normally localized at the tips of growing neurites, were confined to the cell body in antisense-treated cells. Treatment of the cells with the corresponding sense oligonucleotides affected neither the distribution of GAP-43 and synapsin I, nor the length of neurites. A full recovery of neurite length occurred after removal of the antisense oligonucleotides from the medium. These data indicate that KHC plays a role in the anterograde translocation of vesicles containing GAP-43 and synapsin I. A deficiency in vesicle delivery may also explain the inhibition of neurite outgrowth. Despite the inhibition of KHC and the failure of GAP-43 and synapsin I to move out of the cell body, hippocampal neurons can extend processes and acquire as asymmetric morphology.