Regulation of polarized cell growth by GTPases

极性建立和定向细胞分裂是许多生物体发育的核心。细胞 芽殖酵母S. Cerev/s/ae根据其细胞类型表现出两种不同的出芽模式， 反映了细胞极化的遗传程序。据信，细胞响应于细胞类型特异性的免疫应答。 皮质标记物，其与质膜相关。所有细胞类型使用一个共同的下游 极性建立途径，涉及Ras和Rho家族GTP酶Rsr 1/Bud 1和Cdc 42。 尽管目前的知识，许多蛋白质参与出芽，极性是如何建立向一个 空间上确定的地点在很大程度上是未知的。这项提案的重点是如何一个大分子复合物， 指定了一个特定的芽位点组装，以及极性建立如何在空间和 时间的方式。基于遗传和生物化学数据，假设GTP酶调节 极性建立的各种步骤。为了检验这一假设，将采用多方向的方法， 利用分子遗传学、生物化学和细胞生物学方法进行。具体的目标是 理解：1）指定芽位点的大分子复合物如何组装，以及瞬时的 空间信息在每个细胞分裂周期中被遗传; 2）Bud 2和Bud 5，Rsr 1的调节器， 与每种细胞类型中不同的空间地标相互作用，以及相互作用是否调节它们的活性; 3）Rsr 1如何调节Cdc 24、Cdc 42的GEF以及Cdc 42复合物在芽位点的组装。 虽然极性的建立是一个复杂的问题，但酵母的简单遗传学提供了独特的 有机会研究导致肌动蛋白细胞骨架极化组织的信号通路， 分子水平。哺乳动物细胞的发育也需要肌动蛋白细胞骨架的不断变化 响应于如在伤口愈合期间或感染期间的趋化性所见的内部和外部信号。 了解酵母中极性建立的分子机制有望提供 哺乳动物细胞中肌动蛋白细胞骨架组织的分子基础。由于结构和 在真核生物中GTP酶及其调节因子的功能保守性，所获得的知识也将允许 深入了解这些正常发育的关键调节因子的新机制，预计 与包括人类在内的大多数真核生物有关。

Polarity establishment and oriented cell divisions are central to the development of many organisms. Cells of the budding yeast S. cerev/s/ae exhibit two distinct patterns of budding depending on their cell type, reflecting genetic programming of cell polarization. It is believed that a cell responds to a cell-type-specific cortical marker, which is associated with the plasma membrane. All cell types use a common downstream pathway for polarity establishment, which involves the Ras and Rho family GTPases Rsr1/Bud1 and Cdc42. Despite current knowledge of many proteins involved in budding, how polarity is established toward a spatially defined site is largely unknown. This proposal focuses on how a macromolecular complex that specifies a specific bud site is assembled, and how polarity establishment is controlled in a spatial and temporal manner. Based on genetic and biochemical data, it is hypothesized that GTPases regulate various steps of polarity establishment. To test the hypothesis, multi-directional approaches will be undertaken using molecular genetic, biochemical, and cell biological methods. Specific aims are to understand: 1) How a macromolecular complex that specifies a bud site is assembled and how the transient spatial information is inherited in every cell division cycle; 2) how Bud2 and Bud5, regulators for Rsr1, interact with a distinct spatial landmark in each cell type, and whether the interactions regulate their activity; and 3) how Rsr1 regulates Cdc24, a GEF for Cdc42, and assembly of the Cdc42 complex at the bud site. Although polarity establishment is a complex problem, the facile genetics of yeast provides the unique opportunity to study a signaling pathway leading to polarized organization of the actin cytoskeleton at the molecular level. Development of mammalian cells also requires continual changes in the actin cytoskeleton in response to internal and external signals as seen during wound healing or chemotaxis during infection. Understanding the molecular mechanism underlying polarity establishment in yeast is expected to provide the molecular basis of actin cytoskeleton organization in mammalian cells. Given the structural and functional conservation of GTPases and their regulators in eukaryotes, knowledge gained will also allow an insight into novel mechanisms for these critical regulators of normal development, which is expected to relevant to most eukaryotes including humans.