A microtubule-based machine called the mitotic spindle segregates chromosomes when eukaryotic cells divide. In the fission yeast S. pombe, which undergoes closed mitosis, the spindle forms a single bundle of microtubules inside the nucleus. During elongation, the spindle extends via antiparallel microtubule sliding by molecular motors. These extensile forces from the spindle are thought to resist compressive forces from the nucleus. We probe the mechanism and maintenance of this force balance via laser ablation of spindles at various stages of mitosis. We find that spindle pole bodies collapse toward each other following ablation, but spindle geometry is often rescued, allowing spindles to resume elongation. While this basic behavior has been previously observed, many questions remain about this phenomenon’s dynamics, mechanics, and molecular requirements. In this work, we find that previously hypothesized viscoelastic relaxation of the nucleus cannot fully explain spindle shortening in response to laser ablation. Instead, spindle collapse requires microtubule dynamics and is powered at least partly by the minus-end directed motor protein dynein. These results suggest a role for dynein in redundantly supporting force balance and bipolarity in the S. pombe spindle.

中文翻译：

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粟酒裂殖酵母消融后纺锤体的塌陷是由微管和运动蛋白动力蛋白介导的

当真核细胞分裂时，一种基于微管的机器称为有丝分裂纺锤体，将染色体分离。在裂殖酵母中，粟酒裂殖酵母，它经历了封闭的有丝分裂，纺锤体在细胞核内形成了单束微管。在伸长过程中，主轴通过分子电动机的反平行微管滑动而延伸。这些来自主轴的拉伸力被认为可以抵抗来自细胞核的压缩力。我们通过在有丝分裂的各个阶段通过激光切除纺锤体来探讨这种力平衡的机理和维持情况。我们发现，主轴极体在消融后会彼此塌陷，但通常会挽救主轴的几何形状，从而使主轴恢复伸长状态。尽管以前已经观察到了这种基本行为，但有关此现象的动力学，力学和分子要求仍然存在许多问题。在这项工作中，我们发现以前假设的核粘弹性松弛不能完全解释响应激光烧蚀的纺锤缩短。取而代之的是，纺锤塌陷需要微管动力学，并且至少部分地由负端定向的运动蛋白动力蛋白提供动力。这些结果表明，动力蛋白在冗余支持力平衡和双极性中的作用。S. pombe主轴。