Temporal and Spatial Control of B subtilis cytokinesis

描述(申请人提供)：细胞如何决定何时何地分裂仍然是现代生物学的一大谜团。在空间上，分工受到严格监管，以确保隔膜的准确定位。在时间上，分裂与DNA复制和染色体分离相协调。从细菌到酵母再到人类，细胞分裂是通过在新生的分裂部位形成一个细胞骨架蛋白质环来启动的。该环确定分割隔膜的位置，并用作装配分割装置的框架。在细菌中，这个环由基本的微管蛋白样GTP酶FtsZ组成。这项建议的重点是控制土壤细菌枯草杆菌FtsZ环形成的调控网络。建立分裂位点并将FtsZ环的形成与细胞周期联系在一起的因素仍不清楚。因此，要想了解细菌分裂的空间和时间调节，就需要确定响应细胞周期信号在中间细胞刺激FtsZ环形成并在其他所有位置抑制FtsZ环形成的细胞和分子机制。Ezra是一种有助于将FtsZ环形成限制在中细胞的因子，它是通过经典的遗传筛选确定的。初步的生化数据表明，Ezra与FtsZ直接相互作用，通过使FtsZ聚合物失稳来抑制环的形成。这项提议有三个主要目标。第一，表征Ezra阻止异位FtsZ环形成的分子机制。第二，克隆和鉴定weet-2基因，它是一种突变，使细胞分裂和生长分离，导致形成小细胞，许多细胞的大小不到野生型枯草杆菌的25%。第三，扩展遗传筛选以确定额外的因素：(I)促进中细胞FtsZ环的形成，(Ii)将FtsZ环的形成与细胞周期偶联，(Iii)在不适当的位置抑制FtsZ环的形成。作为细菌细胞分裂机制的重要组成部分，FtsZ和影响其活性的因素有望成为开发新抗生素的潜在靶点。此外，这项工作不仅应该阐明细菌的细胞分裂，而且应该阐明细胞质分裂对所有生物体的基础方面。了解正常控制细胞分裂的分子机制将有助于确定它们在肿瘤发生过程中失败的原因，从而导致癌细胞的异常分裂和快速增殖特征。

DESCRIPTION (provided by applicant): How cells determine when and where to divide remains one of the great mysteries of modern biology. Spatially, division is tightly regulated to ensure the accurate positioning of septa. Temporally, division is coordinated with DNA replication and chromosome segregation. From bacteria to yeast to humans, cell division is initiated by the formation of a ring of a cytoskeletal protein at the nascent division site. This ring establishes the location of the division septum and serves as a framework for assembly of the division apparatus. In bacteria this ring is composed of the essential tubulin-like GTPase FtsZ. This proposal focuses on the regulatory networks that govern FtsZ ring formation in the soil bacterium B. subtilis. The factors that establish the division site and couple FtsZ ring formation to the cell cycle remain unknown. Comprehending the spatial and temporal regulation of bacterial division thus requires the identification of the cellular and molecular mechanisms that stimulate FtsZ ring formation at midcell in response to cell cycle cues and inhibit FtsZ ring formation at all other sites. EzrA, a factor that helps restrict FtsZ ring formation to midcell, was identified through classical genetic screens. Preliminary biochemical data suggest that EzrA interacts directly with FtsZ to inhibit ring formation by destabilization of FtsZ polymers. This proposal has three major goals. One, to characterize the molecular mechanism by which EzrA prevents ectopic FtsZ ring formation. Two, to clone and to characterize the gene identified by wee2, a mutation that uncouples cell division from growth, leading to the formation of small cells, many less than 25% the size of wild type B. subtilis. Three, to extend genetic screens to identify additional factors that (i) promote FtsZ ring formation at midcell, (ii) couple FtsZ ring formation to the cell cycle, and (iii) inhibit FtsZ ring formation at inappropriate sites. As essential components of the bacterial cell division machinery, FtsZ and the factors governing its activity hold promise as potential targets for the development of new antibiotics. Furthermore, this work should illuminate not only bacterial cell division, but also aspects of cytokinesis fundamental to all organisms. Understanding the molecular mechanisms that normally control cell division will help identify why they fail during oncogenesis, leading to the aberrant divisions and rapid proliferation characteristic of cancer cells.