Signaling mechanisms in cell polarity in yeast

描述（由申请人提供）：我的长期目标是使用遗传上易处理的真核生物酿酒酵母来确定细胞极性建立和维持的分子机制。更具体地说，我有兴趣了解Cdc 42 p，一个进化上保守的小GTdR，如何通过独立的途径控制肌动蛋白细胞骨架和septins的组织。以前，我们已经表明，Msb 3 p和Msb 4p，在酵母中的一对高度同源的蛋白质，作为cdc 42突变的剂量依赖性抑制剂的功能，这两种蛋白质也调节分泌作为GTP酶激活蛋白（GAP）的Rab GTP酶Sec 4p的功能，因此，定义Cdc 42 p介导的信号通路和Sec 4p介导的分泌之间的分子联系。最近，我们发现Msb 3 p和Msb 4p直接与Cdc 42 p-GDP结合，也与Spa 2 p结合，Spa 2 p是一种“极化体”的支架蛋白，也包括Cdc 42 p和肌动蛋白结合蛋白Bud 6p;因此，定义了从Cdc 42 p到肌动蛋白组织的具体途径。目前，我们正试图确定详细的生物化学机制的极化体的功能，其组成部分是进化保守的。我们最近的工作的另一条线已经导致了一个两步模型的septin-ring形成在细胞周期的开始：septins的招聘到初始芽网站和组装的招聘septins到皮质环。cdc 42 p在这两个步骤中都起作用。有了这个框架，我们正试图定义Axl 2 p，I型膜，和Rgalp，Cdc 42 p GAP，在septin组织中的作用。最后，我们已经分离出PXL 1作为几个cdc 42-Ts等位基因的多拷贝抑制基因。Pxllp在氨基酸序列和结构组织上与桩蛋白（paxillin）具有广泛的相似性，桩蛋白是一种对发育和细胞运动至关重要的粘着斑蛋白。我们正在使用Pxllp作为模型来了解这个蛋白质家族如何通过其C-末端LIM结构域靶向离散的细胞位置，这是桩蛋白生物学中的一个关键空白。Cdc 42 p的同源物参与多种细胞过程，例如细胞极性、细胞迁移和细胞生长控制。此外，哺乳动物中Cdc 42 p活性的失调与严重疾病如癌症有关。因此，研究Cdc 42 p在酵母中的信号转导机制将在基础生物学和临床科学中具有深远的意义。

DESCRIPTION (provided by applicant): My long-term objective is to use the genetically tractable eukaryote Saccharomyces cerevisiae to determine the molecular mechanisms underlying the establishment and maintenance of cell polarity. More specifically y, I am interested in understanding how Cdc42p, an evolutionarily conserved small GTPase, controls the organization of the actin cytoskeleton and of the septins through independent pathways. Previously, we have shown that Msb3p and Msb4p, a pair of highly homologous proteins in yeast, function as dosage-dependent suppressors of cdc42 mutations and that both proteins also regulate secretion by functioning as GTPase-activating proteins (GAPs) for the Rab GTPase Sec4p; thus, defining a molecular linkage between Cdc42p-mediated signaling pathway and Sec4p-mediated secretion. Recently, we found that Msb3p and Msb4p bind directly to Cdc42p-GDP and also to Spa2p, a scaffold protein of the "polarisome" that also includes the formin Bnilp and the actin-binding protein Bud6p; thus, defining a concrete pathway from Cdc42p to actin organization. Currently, we are trying to determine the detailed biochemical mechanisms underlying the function of the polarisome, the components of which are evolutionarily conserved. Another line of our recent work has led to a two-step model on the septin-ring formation at the beginning of the cell cycle: the recruitment of septins to the incipient bud site and the assembly of the recruited septins into a cortical ring. Cdc42p plays a role in both steps. With this framework, we are trying to define the role of Axl2p, a type I membrane, and Rgalp, a Cdc42p GAP, in septin organization. Finally, we have isolated PXL1 as a multicopy suppressor of several cdc42-Ts alleles. Pxllp shows extensive similarity in amino-acid sequence and structural organization with paxillin, a focal adhesion protein that is essential for development and cell motility. We are using Pxllp as a model to understand how this family of proteins is targeted to discrete cellular locations through their C-terminal LIM domains, a crucial gap in paxillin biology. Homologs of Cdc42p are involved in diverse cellular processes, such as cell polarity, cell migration, and cell growth control. In addition, deregulation of Cdc42p activity in mammals is associated with serious diseases, such as cancer. Thus, studying the signaling mechanisms of Cdc42p in yeast will have profound implications in basic biology and clinical sciences.