Organization of the smallest eukaryotic spindle.
Organization of the smallest eukaryotic spindle.
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DOI：
10.1016/j.cub.2011.08.021
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发表时间：
2011-09-27
期刊：
影响因子：
9.2
通讯作者：
Jensen, Grant J.
中科院分区：
文献类型：
--
作者：
Gan, Lu;Ladinsky, Mark S.;Jensen, Grant J.
对后生动物、植物和真菌中有丝分裂的研究已经集中在高度保守的有丝分裂模式上，在这种模式下，成对的姐妹染色单体附着在来自相反纺锤体极的动粒微管(KMT)上。一旦每条染色体连接到它自己的一个或多个kmt上，纺锤体检查点就被释放，后期促进复合体被激活，姐妹染色单体凝聚力丧失。然而，不同的物种在这些事件的超微结构和时间上都有所不同。例如，据报道，一些单细胞真核生物的kmt比染色体还少。如果是真的，这将是重要的，因为尚不清楚如何满足主轴检查点的要求。然而，在这些研究中的绝大多数，有丝分裂细胞被化学固定在室温下，然后染色。由于化学固定的速度很慢(从几秒钟到几个小时)，动态的和/或细小的结构，如纺锤体MTS和运动中枢并不总是被保存下来，这留下了很大的不确定性。事实上，在其中一些案例中，后来的高分辨率研究推翻了早先的说法。在这里，我们表明，在金黄色葡萄球菌(已知的最小真核生物)中，有丝分裂确实比染色体涉及更少的纺锤体微管。人工阻止有丝分裂，然后使用高压冷冻细胞的电子断层扫描，纺锤体在塑料中和在三维中的近自然(冷冻-水合)状态下被成像到“大分子”分辨率。有丝分裂细胞在其核内有一个独特的无异染色质的纺锤体通道，在纺锤体通道的两端各有4个短的、不完整的(未闭合的)微管。此外，多达两个长的微管延伸到主轴隧道的中心。然而，O.Tauri的纺锤体检查点机制似乎是典型的，因为微管聚合和蛋白酶体的抑制剂阻碍了有丝分裂，许多已知的纺锤体检查点基因的同源基因存在于基因组中。综上所述，这些数据表明，金牛座的20条染色体在物理上是捆绑在一起的，并被分离成一个或少数几个组。
Studies of mitosis in metazoans, plants, and fungi have converged on a highly conserved model of mitosis in which paired sister chromatids attach to kinetochore microtubules (kMTs) emanating from opposite spindle poles. Once each chromosome is attached to one or more of its own kMTs, the spindle checkpoint is released, the anaphase-promoting complex is activated and sister-chromatid cohesion is lost. Different species vary, however, in both the ultrastructure and timing of these events. Some unicellular eukaryotes, for instance, have been reported to have fewer kMTs than chromosomes. If true, this would be important because it is unclear how the spindle checkpoint could be satisfied. In the vast majority of these studies, however, mitotic cells were chemically fixed at room temperature and then stained. Because chemical fixation is slow (taking from seconds to hours), dynamic and/or small structures like spindle MTs and kinetochores are not always preserved, leaving substantial uncertainty. Indeed in some of these cases, later higher-resolution studies have reversed earlier claims. Here we show that in Ostreococcus tauri (the smallest eukaryote known), mitosis does indeed involve fewer spindle microtubules than chromosomes. O. tauri cultures were artificially arrested in mitosis and then using electron tomography of high-pressure-frozen cells, spindles were imaged both in plastic and in a near-native ("frozen-hydrated") state in 3-D to "macromolecular" resolution. Mitotic cells have a distinctive heterochromatin-free “spindle tunnel” in their nuclei with ~4 short, incomplete (unclosed) microtubules at each end of the spindle tunnel. In addition, up to two long microtubules extend into the center of the spindle tunnel. O. tauri's spindle checkpoint machinery seems typical, however, since inhibitors of microtubule polymerization and proteasomes stall mitosis, and homologs of many known spindle checkpoint genes are present in the genome. Taken together, these data suggest that O. tauri's 20 chromosomes are physically bundled and segregated as just one or a small number of groups.
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