Division of Biology, IISER Pune, Dr. Homi Bhabha Road, Pune, Maharashtra, 411008, India.
Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, UK.
Yeast. 2021 Jun;38(6):352-366. doi: 10.1002/yea.3552. Epub 2021 Feb 27.
Positioning the nucleus at the bud neck during Saccharomyces cerevisiae mitosis involves pulling forces of cytoplasmic dynein localized in the daughter cell. Although genetic analysis has revealed a complex network positioning the nucleus, quantification of the forces acting on the nucleus and the number of dyneins driving the process has remained difficult. To better understand the collective forces involved in nuclear positioning, we compare a model of dyneins-driven microtubule (MT) pulling, MT pushing, and cytoplasmic drag to experiments. During S. cerevisiae mitosis, MTs interacting with the cortex nucleated by the daughter spindle pole body (SPB) (SPB-D) are longer than the mother SPB (SPB-M), increasing further during spindle elongation in anaphase. Interphasic SPB mobility is effectively diffusive, while the mitotic mobility is directed. By optimizing a computational model of the mobility of the nucleus due to diffusion and MTs pushing at the cell membrane to experiment, we estimate the viscosity governing the drag force on nuclei during positioning. A force balance model of mitotic SPB mobility compared to experimental mobility suggests that even one or two dynein dimers are sufficient to move the nucleus in the bud neck. Using stochastic computer simulations of a budding cell, we find that punctate dynein localization can generate sufficient force to reel in the nucleus to the bud neck. Compared to uniform motor localization, puncta involve fewer motors suggesting a functional role for motor clustering. Stochastic simulations also suggest that a higher number of force generators than predicted by force balance may be required to ensure the robustness of spindle positioning.
在酿酒酵母有丝分裂过程中，将核定位在芽颈处需要细胞质动力蛋白在子细胞中的拉动力量。尽管遗传分析揭示了一个复杂的核定位网络，但对作用于核的力的定量和驱动该过程的动力蛋白数量的研究仍然具有挑战性。为了更好地理解核定位所涉及的集体力，我们将动力蛋白驱动的微管（MT）拉动、MT 推动和细胞质阻力的模型与实验进行了比较。在酿酒酵母有丝分裂过程中，与由子纺锤体极体（SPB）核化的皮层相互作用的 MT （SPB-D）比母 SPB （SPB-M）更长，在后期纺锤体伸长过程中进一步增加。间期中的 SPB 迁移是有效的扩散，而有丝分裂中的迁移是定向的。通过优化由于扩散和 MT 在细胞膜上推动核迁移的计算模型，我们估计了在定位过程中控制核上阻力的粘性。与实验迁移相比，有丝分裂 SPB 迁移的力平衡模型表明，即使有一个或两个动力蛋白二聚体也足以将核移动到芽颈。通过对出芽细胞的随机计算机模拟，我们发现点状动力蛋白定位可以产生足够的力将核拉回到芽颈。与均匀的马达定位相比，斑点涉及较少的马达，这表明马达聚类具有功能作用。随机模拟还表明，为了确保纺锤体定位的稳健性，可能需要比力平衡预测的更多数量的力发生器。
