Cytokinetic events that promote actomyosin ring constriction and septum formation

适当的细胞分裂对生物体的生长、发育和生存至关重要。细胞分裂缺陷与发育异常和各种疾病有关。细胞分裂的最后阶段是胞质分裂，两个子细胞在物理上是分开的。成功的胞质分裂需要在时间和空间上都受到精确控制的多个步骤。人们对这种精确调控的性质和分子细节知之甚少。该项目旨在了解如何精确控制这一复杂的多步骤过程，以确保成功的细胞分离。细胞质分裂从酵母到哺乳动物在进化上是保守的，因此在酵母中学到的东西直接适用于哺乳动物(如人类)。分裂酵母是研究细胞分裂和胞质分裂的最好的模型系统之一。使用分裂酵母模型系统的初步工作已经非常清楚地揭示了细胞质分裂早期阶段的机制细节。解开分裂酵母胞质分裂中的分子细节将为研究复杂生物体中类似的过程提供一个范例，并将有助于更好地理解与胞质分裂相关的各种异常的病因学。胞质分裂是细胞分裂的最后一步，是所有细胞生存和发育的核心。胞质分裂是一个时间上有组织的多步骤过程，包括将一个细胞物理分离成两个细胞。首先，肌动球蛋白环形成，然后在膜沟形成的同时经历收缩和隔膜内陷。目前尚不清楚这些活动是如何在时间上组织的。在分裂酵母中，隔膜内移是膜沟形成的关键。向内的隔膜提供克服细胞内部膨胀压力所需的力量。肌动球蛋白环收缩和间隔内陷是如何同时发生的尚不清楚。在没有肌动球蛋白环的情况下，可以发生膜皱纹，那么肌动球蛋白环在胞质分裂中扮演什么角色？在环装配后的短等待时间后，会发生环收缩和间隔内陷。是什么触发了环收缩和间隔的形成？初步数据表明，环后组装，保守的GTP酶CDC42以一种独特的时空方式被激活。CDC42在胞质分裂过程中的激活模式取决于其激活剂Gef1和SCD1的定位。Gef1促进环上间隔合成蛋白的募集，以便及时启动环收缩和间隔内陷，而SCD1是正常间隔形成所必需的。Gef1还促进均匀的环状收缩和间隔内陷。基于这一数据，提出的中心假设是，CDC42的时空激活使组装的肌球蛋白环能够作为适当的环收缩和间隔形成的标志和指南。为了验证这一点，我们将致力于以下目标：1.确定在环组装后的分裂部位，CDC42如何在时空上被激活；2.确定环收缩和间隔形成是如何被CDC42时空激活所促进的；以及3.描述肌球蛋白环如何作为对称环收缩和间隔形成的标志和指南。该项目将结合活细胞成像、蛋白质动力学分析、遗传学和数学建模。这个项目将提供对独特的CDC42激活模式如何建立的更深入的理解，从而导致胞质分裂中的不同功能，并将提供对信号模式如何在细胞中组织复杂的多步骤过程的洞察。这个项目将对大多数真核生物中细胞质分裂的机械性低估有广泛的影响。

Proper cell division is critical for growth, development, and survival of an organism. Defects in cell division have been linked to developmental anomalies and various afflictions. The final stage of cell division is cytokinesis, where the two daughter cells are physically partitioned. Successful cytokinesis requires multiple steps that are precisely controlled both in time and space. The nature and molecular details of this precise regulation is poorly understood. This project aims at understanding how this complex multi-step process is precisely controlled to ensure successful cell separation. Cytokinesis is evolutionarily conserved from yeast to mammals and hence what is learned in yeast is directly applicable to mammals (such as humans). One of the best model systems to study cell division and cytokinesis is the fission yeast. Preliminary work using the fission yeast model system has, with great clarity, revealed the mechanistic details of the early stages of cytokinesis. Unraveling the molecular details in cytokinesis in the fission yeast will provide a paradigm to study similar processes in complex organisms and will lead to a better understanding of the etiology of various anomolies related to cytokinesis. Cytokinesis, the final step in cell division, is central to survival and development of all cells. Cytokinesis is a temporally organized multistep process that involves the physical separation of a cell into two. First, an actomyosin ring forms, which then undergoes constriction concurrent with septum ingression for membrane furrow formation. It is not clear how these events are temporally organized. In fission yeast, septum ingression is critical for membrane furrow formation. The ingressing septum provides the force required to overcome internal turgor pressure in the cell. It is not clear how actomyosin ring constriction and septum ingression occur concurrently. Membrane furrowing can occur without an actomyosin ring so what role does the actomyosin ring play in cytokinesis? Ring constriction and septum ingression occurs after a short waiting period, post ring assembly. What triggers the onset of ring constriction and septum formation? Preliminary data shows that post-ring assembly, the conserved GTPase Cdc42 is activated in a unique spatiotemporal manner. Cdc42 activation pattern during cytokinesis depends on the localization of its activators, Gef1 and Scd1. Gef1 promotes the recruitment of a septum synthesizing protein at the ring to allow timely onset of ring constriction and septum ingression, while Scd1 is required for normal septum formation. Gef1 also promotes uniform ring constriction and septum ingression. Based on this data the proposed central hypothesis is that spatiotemporal activation of Cdc42 enables the assembled actomyosin ring to act as a landmark and guide for proper ring constriction and septum formation. To test this, the following aims will be pursued; 1. To define how Cdc42 is spatiotemporally activated at the division site post ring assembly; 2. To determine how ring constriction and septum formation is promoted by spatiotemporal activation of Cdc42; and 3. To describe how the actomyosin ring acts as a landmark and guide for symmetric ring constriction and septum formation. This project will integrate live cell imaging, analysis of protein dynamics, genetics, and mathematical modeling. This project will provide a deeper understanding of how unique Cdc42 activation patterns are established, leading to distinct functions in cytokinesis and will provide insights into how signaling patterns organize complex multistep processes in the cell. This project will have widespread implications in the mechanistic understating of cytokinesis in most eukaryotes.