Regulation of polarized cell growth by GTPases

极性的建立和定向的细胞分裂是许多生物体发育的中心。单元格 发芽酵母S.erev/S/ae根据其细胞类型表现出两种截然不同的发芽模式， 反映了细胞极化的遗传编程。据认为，细胞对特定类型的细胞作出反应 皮质标记物，与质膜相关。所有单元格类型都使用共同的下游 极性建立的途径，涉及Ras和Rho家族GTP酶Rsr1/Bud1和CDc42。 尽管目前对许多参与发芽的蛋白质都有了解，但极性是如何形成的 在空间上定义的地点在很大程度上是未知的。这个提案的重点是一个大分子复合体是如何 指定特定的萌芽位置被组装，以及如何在空间和 世俗的态度。基于遗传和生化数据，假设GTP酶调控 极性建立的各个步骤。为了检验这一假设，多方向的方法将是 使用分子遗传学、生物化学和细胞生物学方法进行的。具体目标是 理解：1)指定芽位置的大分子复合体是如何组装的，以及如何瞬时地 空间信息在每个细胞分裂周期中被遗传；2)Rsr1的调节因子Bud2和Bud5如何， 与每种细胞类型中不同的空间地标相互作用，以及这种相互作用是否调节它们的活动； 3)Rsr1是如何调控Cdc24的，这是一个针对Cdc42的全环基金，以及CDc42复合体在芽位的组装。 尽管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还需要肌动蛋白细胞骨架的持续变化。 对伤口愈合过程中看到的内部和外部信号作出反应，或在感染期间发生趋化作用。 了解酵母极性形成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。考虑到结构和 在真核生物中GTP酶及其调控因子的功能保守，所获得的知识也将使 洞察这些正常发育的关键调节因子的新机制，预计将 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.