Askjaer Peter, Galy Vincent, Hannak Eva, Mattaj Iain W
European Molecular Biology Laboratory, 69117 Heidelberg, Germany.
Mol Biol Cell. 2002 Dec;13(12):4355-70. doi: 10.1091/mbc.e02-06-0346.
The small GTPase Ran has been found to play pivotal roles in several aspects of cell function. We have investigated the role of the Ran GTPase cycle in spindle formation and nuclear envelope assembly in dividing Caenorhabditis elegans embryos in real time. We found that Ran and its cofactors RanBP2, RanGAP, and RCC1 are all essential for reformation of the nuclear envelope after cell division. Reducing the expression of any of these components of the Ran GTPase cycle by RNAi leads to strong extranuclear clustering of integral nuclear envelope proteins and nucleoporins. Ran, RanBP2, and RanGAP are also required for building a mitotic spindle, whereas astral microtubules are normal in the absence of these proteins. RCC1(RNAi) embryos have similar abnormalities in the initial phase of spindle formation but eventually recover to form a bipolar spindle. Irregular chromatin structures and chromatin bridges due to spindle failure were frequently observed in embryos where the Ran cycle was perturbed. In addition, connection between the centrosomes and the male pronucleus, and thus centrosome positioning, depends upon the Ran cycle components. Finally, we have demonstrated that both IMA-2 and IMB-1, the homologues of vertebrate importin alpha and beta, are essential for both spindle assembly and nuclear formation in early embryos.
小GTP酶Ran已被发现参与细胞功能的多个关键环节。我们实时研究了Ran GTP酶循环在秀丽隐杆线虫胚胎分裂过程中纺锤体形成和核膜组装中的作用。我们发现，Ran及其辅因子RanBP2、RanGAP和RCC1对于细胞分裂后核膜的重新形成均至关重要。通过RNA干扰降低Ran GTP酶循环中任何一种成分的表达，都会导致整合核膜蛋白和核孔蛋白在核外大量聚集。Ran、RanBP2和RanGAP对于有丝分裂纺锤体的构建也是必需的，而在没有这些蛋白质的情况下，星体微管是正常的。RCC1（RNA干扰）胚胎在纺锤体形成的初始阶段有类似的异常，但最终能恢复形成双极纺锤体。在Ran循环受到干扰的胚胎中，经常观察到由于纺锤体故障导致的不规则染色质结构和染色质桥。此外，中心体与雄性原核之间的连接以及中心体的定位取决于Ran循环成分。最后，我们证明，脊椎动物输入蛋白α和β的同源物IMA-2和IMB-1对于早期胚胎的纺锤体组装和细胞核形成均至关重要。
