Wadsworth Center, New York State Department of Health, Albany, NY 12201-509, USA.
Cell. 2011 Aug 19;146(4):555-67. doi: 10.1016/j.cell.2011.07.012.
Error-free chromosome segregation requires stable attachment of sister kinetochores to the opposite spindle poles (amphitelic attachment). Exactly how amphitelic attachments are achieved during spindle assembly remains elusive. We employed photoactivatable GFP and high-resolution live-cell confocal microscopy to visualize complete 3D movements of individual kinetochores throughout mitosis in nontransformed human cells. Combined with electron microscopy, molecular perturbations, and immunofluorescence analyses, this approach reveals unexpected details of chromosome behavior. Our data demonstrate that unstable lateral interactions between kinetochores and microtubules dominate during early prometaphase. These transient interactions lead to the reproducible arrangement of chromosomes in an equatorial ring on the surface of the nascent spindle. A computational model predicts that this toroidal distribution of chromosomes exposes kinetochores to a high density of microtubules which facilitates subsequent formation of amphitelic attachments. Thus, spindle formation involves a previously overlooked stage of chromosome prepositioning which promotes formation of amphitelic attachments.
染色体的正确分离需要姐妹动粒稳定地附着在纺锤体的两极（合体型附着）。在纺锤体组装过程中，合体型附着是如何实现的，目前仍不清楚。我们利用光活化 GFP 和高分辨率活细胞共聚焦显微镜，可视化非转化人细胞有丝分裂过程中单个动粒的完整 3D 运动。结合电子显微镜、分子扰动和免疫荧光分析，这种方法揭示了染色体行为的意想不到的细节。我们的数据表明，在早中期，动粒和微管之间不稳定的侧向相互作用占主导地位。这些短暂的相互作用导致染色体在新形成的纺锤体表面赤道环上重复排列。一个计算模型预测，这种染色体的环形分布使动粒暴露在高密度的微管中，这有利于随后形成合体型附着。因此，纺锤体的形成涉及到一个以前被忽视的染色体预定位阶段，它促进了合体型附着的形成。
