Wadsworth Center, New York State Department of Health, Albany, NY.
Wadsworth Center, New York State Department of Health, Albany, NY
J Cell Biol. 2018 Aug 6;217(8):2647-2659. doi: 10.1083/jcb.201710094. Epub 2018 Jun 15.
For proper segregation during cell division, each chromosome must connect to the poles of the spindle via microtubule bundles termed kinetochore fibers (K-fibers). K-fibers form by two distinct mechanisms: (1) capture of astral microtubules nucleated at the centrosome by the chromosomes' kinetochores or (2) attachment of kinetochores to noncentrosomal microtubules with subsequent transport of the minus ends of these microtubules toward the spindle poles. The relative contributions of these alternative mechanisms to normal spindle assembly remain unknown. In this study, we report that most kinetochores in human cells develop K-fibers via the second mechanism. Correlative light electron microscopy demonstrates that from the onset of spindle assembly, short randomly oriented noncentrosomal microtubules appear in the immediate vicinity of the kinetochores. Initially, these microtubules interact with the kinetochores laterally, but end-on attachments form rapidly in the first 3 min of prometaphase. Conversion from lateral to end-on interactions is impeded upon inhibition of the plus end-directed kinetochore-associated kinesin CenpE.
为了在细胞分裂过程中进行正确的分离，每个染色体都必须通过称为动粒纤维（K 纤维）的微管束连接到纺锤体的两极。K 纤维通过两种不同的机制形成：（1）由染色体的动粒捕获由中心体起始的星体微管，或（2）动粒附着到非中心体微管上，随后这些微管的负端向纺锤体极运输。这些替代机制对正常纺锤体组装的相对贡献尚不清楚。在这项研究中，我们报告说，人类细胞中的大多数动粒通过第二种机制形成 K 纤维。相关的光电子显微镜显示，从纺锤体组装开始，短的随机定向的非中心体微管出现在动粒的附近。最初，这些微管与动粒侧向相互作用，但在前期的前 3 分钟内，端到端的附着迅速形成。当抑制指向微管正极的动粒相关驱动蛋白 CenpE 时，从侧向相互作用到端到端相互作用的转换会受到阻碍。
