Hagan I, Yanagida M
School of Biological Sciences, University of Manchester, UK.
J Cell Sci. 1997 Aug;110 ( Pt 16):1851-66. doi: 10.1242/jcs.110.16.1851.
Specific changes in spatial order occur during cell cycle progression in fission yeast. Growth of the rod-shaped cells is highly regulated and undergoes a cell cycle and size-regulated switch from monopolar to bipolar tip extension. During both phases of growth, the interphase nucleus is maintained in a central location. Following the separation of the genome to the cell tips in mitosis, the two nuclei migrate back towards the cell equator before stopping in two new positions that will become the middle of the two new cells. Here we use simultaneous labeling of microtubules, chromatin and spindle pole bodies in wild-type and cdc mutants, to show that nuclear positioning is achieved by regulation of spindle pole body-mediated nuclear migration. We show that the number and location of nuclear positioning signals is regulated in a cell cycle-specific manner and that spindle pole body-mediated forces are likely to be responsible for maintaining correct nuclear position once the nuclei have reached the appropriate position in the cell. Accentuating the movement of the nuclei back towards the cell equator after mitosis by artificially increasing cell length shows that the spindle pole body leads the nucleus during this migration. When multiple spindle pole bodies are associated with the same or different nuclei they all go to the same point indicating that the different spindle pole bodies are responding to the same positional cue. In a septation-defective mutant cell, which contains four nuclei, the spindle pole bodies on the four different nuclei initially group as two pairs in regions that would become the middle of the new cells, were the cell able to divide. In the subsequent interphase, the nuclei aggregate as a group of four in the centre of the cell. The presence of two or three clusters of spindle pole bodies in larger cells with eight nuclei suggests that the mechanisms specifying the normally central location for multiple nuclei may be unable to operate properly as the cells get larger. Perturbation of microtubules with the microtubule poison thiabendazole prevents the spindle pole body clustering in septation mutants, demonstrating that nuclear positioning requires a functional microtubule cytoskeleton.
在裂殖酵母的细胞周期进程中会发生空间顺序的特定变化。杆状细胞的生长受到高度调控，并经历一个由细胞周期和大小调节的从单极到双极顶端延伸的转变。在两个生长阶段，间期细胞核都保持在细胞中央位置。在有丝分裂过程中基因组分离到细胞顶端后，两个细胞核在停止于两个新位置（将成为两个新细胞的中间位置）之前，会朝着细胞赤道迁移回来。在这里，我们通过对野生型和cdc突变体中的微管、染色质和纺锤极体进行同时标记，来表明细胞核定位是通过纺锤极体介导的核迁移调控实现的。我们表明，核定位信号的数量和位置是以细胞周期特异性方式调控的，并且一旦细胞核到达细胞中的适当位置，纺锤极体介导的力可能负责维持正确的核位置。通过人为增加细胞长度来增强有丝分裂后细胞核向细胞赤道的回移运动，表明在这种迁移过程中纺锤极体引导着细胞核。当多个纺锤极体与相同或不同的细胞核相关联时，它们都会移向同一点，这表明不同的纺锤极体对相同的位置线索做出反应。在一个含有四个细胞核的分隔缺陷突变体细胞中，四个不同细胞核上的纺锤极体最初在细胞能够分裂时将成为新细胞中间的区域聚为两对。在随后的间期，细胞核在细胞中央聚为一组四个。在具有八个细胞核的较大细胞中存在两到三个纺锤极体簇，这表明随着细胞变大，指定多个细胞核正常中央位置的机制可能无法正常运作。用微管毒素噻苯咪唑干扰微管会阻止分隔突变体中的纺锤极体聚集，这表明细胞核定位需要功能性的微管细胞骨架。
