Tetrad Graduate Program, University of California, San Francisco, San Francisco, CA.
Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, CA.
J Cell Biol. 2020 Aug 3;219(8). doi: 10.1083/jcb.201911090.
At cell division, the mammalian kinetochore binds many spindle microtubules that make up the kinetochore-fiber. To segregate chromosomes, the kinetochore-fiber must be dynamic and generate and respond to force. Yet, how it remodels under force remains poorly understood. Kinetochore-fibers cannot be reconstituted in vitro, and exerting controlled forces in vivo remains challenging. Here, we use microneedles to pull on mammalian kinetochore-fibers and probe how sustained force regulates their dynamics and structure. We show that force lengthens kinetochore-fibers by persistently favoring plus-end polymerization, not by increasing polymerization rate. We demonstrate that force suppresses depolymerization at both plus and minus ends, rather than sliding microtubules within the kinetochore-fiber. Finally, we observe that kinetochore-fibers break but do not detach from kinetochores or poles. Together, this work suggests an engineering principle for spindle structural homeostasis: different physical mechanisms of local force dissipation by the k-fiber limit force transmission to preserve robust spindle structure. These findings may inform how other dynamic, force-generating cellular machines achieve mechanical robustness.
在细胞分裂过程中，哺乳动物的动粒与许多纺锤体微管结合，构成动粒微管纤维。为了分离染色体，动粒微管纤维必须具有动态性，并产生和响应力。然而，其在力的作用下如何重塑仍然知之甚少。动粒微管纤维不能在体外重建，并且在体内施加可控力仍然具有挑战性。在这里，我们使用微针来拉动哺乳动物的动粒微管纤维，并探究持续力如何调节其动力学和结构。我们表明，力通过持续有利于正极聚合而不是增加聚合速率来延长动粒微管纤维。我们证明，力抑制了正极和负极的解聚，而不是滑动微管在动粒微管纤维内。最后，我们观察到动粒微管纤维断裂，但不会从动粒或极体上脱离。总之，这项工作提出了一个纺锤体结构稳态的工程原理：动粒纤维局部力耗散的不同物理机制限制了力的传递，以保持强壮的纺锤体结构。这些发现可能为其他动态、产生力的细胞机器如何实现机械鲁棒性提供信息。
