Bamba Chisa, Bobinnec Yves, Fukuda Makoto, Nishida Eisuke
Department of Cell and Developmental Biology, Graduate School of Biostudies, Kyoto University, Japan.
Curr Biol. 2002 Mar 19;12(6):503-7. doi: 10.1016/s0960-9822(02)00741-8.
The GTPase Ran is known to regulate transport of proteins across the nuclear envelope. Recently, Ran has been shown to promote microtubule polymerization and spindle assembly around chromatin in Xenopus mitotic extracts and to stimulate nuclear envelope assembly in Xenopus or HeLa cell extracts. However, these in vitro findings have not been tested in living cells and do not necessarily describe the generalized model of Ran functions. Here we present several lines of evidence that Ran is indispensable for correct chromosome positioning and nuclear envelope assembly in C. elegans. Embryos deprived of Ran by RNAi showed metaphase chromosome misalignment and aberrant chromosome segregation, while astral microtubules seemed unaffected. Depletion of RCC1 or RanGAP by RNAi resulted in essentially the same defects. The immunofluorescent staining showed that Ran localizes to kinetochore regions of metaphase and anaphase chromosomes, suggesting the role of Ran in linking chromosomes to kinetochore microtubules. Ran was shown to localize to the nuclear envelope at telophase and during interphase in early embryos, and the depletion of Ran resulted in failure of nuclear envelope assembly. Thus, Ran is crucially involved in chromosome positioning and nuclear envelope assembly in C. elegans.
已知GTP酶Ran可调节蛋白质通过核膜的运输。最近，在非洲爪蟾有丝分裂提取物中，Ran已被证明可促进微管聚合以及染色质周围的纺锤体组装，并在非洲爪蟾或HeLa细胞提取物中刺激核膜组装。然而，这些体外研究结果尚未在活细胞中得到验证，也不一定能描述Ran功能的通用模型。在此，我们提供了几条证据表明Ran对于秀丽隐杆线虫中正确的染色体定位和核膜组装是不可或缺的。通过RNA干扰去除Ran的胚胎显示中期染色体排列不齐和异常的染色体分离，而星体微管似乎未受影响。通过RNA干扰使RCC1或RanGAP缺失也导致了基本相同的缺陷。免疫荧光染色显示Ran定位于中期和后期染色体的动粒区域，这表明Ran在将染色体与动粒微管连接中发挥作用。在末期以及早期胚胎的间期，Ran定位于核膜，去除Ran会导致核膜组装失败。因此，Ran在秀丽隐杆线虫的染色体定位和核膜组装中起着至关重要的作用。
