Lower eukaryotic cells such as Schizosaccharomyces pombe employ closed mitosis for their division where the nuclear envelope remains intact despite undergoing severe deformation. However, how forces generated by growing spindle microtubules overcome resistance from the deformed nuclear membrane as well as the viscous surrounding to drive the progression of closed mitosis remains unclear. In this study, by integrating microtubule dynamics with membrane elasticity and viscous cytoplasm response, we developed a mechanics model to bridge molecular activities and nuclear envelope shape evolution. It was predicted that, starting from a sphere, the nuclear envelope will undergo initial elongation, necking and final spindle poles separation to become a barbell at the end of closed mitosis, in good agreement with our experimental observations. Furthermore, these three deformation stages were found to be correlated with a gradually increased, a suddenly dropped and an almost constant poleward force generated by polymerizing microtubules. Finally, from energy analysis we showed that membrane tension plays a dominant role in resisting the deformation of the nuclear envelope while contribution from viscous dissipation is largely negligible.

低级真核细胞，如粟酒裂殖酵母进行封闭有丝分裂的分裂，尽管经历了严重的变形，其核膜仍保持完整。然而，由不断增长的纺锤体微管产生的力如何克服来自变形核膜的阻力以及驱动封闭有丝分裂进程的粘性周围环境尚不清楚。在这项研究中，通过将微管动力学与膜弹性和粘性细胞质反应相结合，我们开发了一种力学模型来桥接分子活性和核包膜形状演变。据预测，从球形开始，核包膜将经历初始伸长，颈缩和最后的纺锤极分离，并在封闭的有丝分裂结束时变成杠铃，这与我们的实验观察非常吻合。此外，这三个变形阶段与微管聚合产生的逐渐增加，突然下降和几乎恒定的向极力有关。最后，从能量分析中我们可以看出，膜张力在抵抗核包膜变形中起主要作用，而粘性耗散的贡献可忽略不计。