胞质分裂是细胞周期的最后一步，它把一个细胞一分为二。胞质分裂期间，中央纺锤体发出信号使收缩环在细胞中部形成，确保遗传物质被平均分配。调控收缩环位置的信号由三个关键蛋白质组成： centralspindlin, Ect2 和 RhoA。Centralspindlin 是一个蛋白质复合物，包含一个微管驱动蛋白亚基，对中央纺锤体的形成起关键作用。Centralspindlin 把Ect2招募到细胞中央，Ect2激活下游的信号分子RhoA。RhoA作用于一系列效应蛋白，使收缩环在细胞皮层下组装和收缩。然而，centralspindlin如何使微管聚集成束,形成中央纺锤体的机理并不清楚。Centralspindlin 招募 Ect2，Ect2激活RhoA的机理也不知道。在这个项目中，我们将用多种生物物理和细胞生物学手段研究胞质分裂的这一关键信号通路，以期揭示有丝分裂时选定分裂面位置的分子机理。

Cytokinesis is the last step of cell cycle, which physically separates a cell into two. Central spindle microtubules rearrange during cytokinesis, which derive the signals to place the actomyosin contractile ring at the midzone to ensure the genetic materials are evenly participated into daughter cells. The key signaling pathway that regulates the placement of the contractile ring consists of the centralspindlin complex, Ect2 and RhoA. The centralspindlin complex has a kinesin subunit, walks to and accumulates at the interdigited central spindle microtubules, which in turn promotes formation of the central spindle. The centralspindlin complex recruits a guanine-nucleotide exchange factor (GEF) Ect2, which activate small GTPase RhoA, a master signaling molecule that is critical for the assembly, anchorage and contraction of the contractile ring at the cleavage furrow. How the centralspindlin complex walks along and bundles central spindle microtubule remain elusive. How the centralspindlin complex recruits and activates Ect2, and how Ect2 selectively activates RhoA are unknown. In this proposal, we are planning to use various tools in biophysics and cell biology to study this key signaling pathway (microtubule-centralspindlin-Ect2-RhoA) of cytokinesis, and to provide physical insights into the molecular mechanism in regulation of the placement of the division plane in mitosis of somatic cells.