Genetic and Molecular Analysis of Differentiation Mechanismsin Saccharomyces cerevisae

Myers 9604247该项目旨在表征对环境刺激做出反应的细胞形式和功能的特异性调节机制。 子囊菌Saccharomyces cerevisiae可以在酵母形式（YF）和假菌丝形式（PH）之间转换，以响应确定的培养条件。 在这种分化中受影响的细胞特征包括细胞形状、细胞大小、细胞极性和细胞分裂周期机制。 该项目已经确定了两种蛋白激酶，Elm 1 p和CDC 28，其中突变导致细胞在所有生长条件下采用假菌丝形式特征。 Elm 1 p功能的消除导致细胞组成性地采用假菌丝形式，表明这种蛋白质在不适当的环境中抑制假菌丝特征的发育。 一种或多种形式的细胞周期蛋白依赖性激酶复合物（CDK）（其中CDC 28是催化亚基）也调节酵母-假菌丝分化。 CDC 28中的特定氨基酸取代导致假菌丝形式的大多数方面的组成性执行。 这些数据与以下假设一致：各种信号传导过程影响CDC 28，作为响应，CDC 28以特定方式进行功能性修饰。 修饰的CDK活性然后引起假菌丝生长形式的各个方面发生。 以这种方式，CDK可以用于整合来自环境的各种输入信号，并控制是否执行某个微分过程的决策。 本项目的具体目标如下：1）确定CDK的改变是否是细胞获得假菌丝形态所必需的，以响应已知在野生型细胞中诱导这种分化过程的两种信号传导机制中的任一种; 2）表征酵母形态和假菌丝形态细胞中CDK之间的功能差异; 3）Elm 1 p与由SEL 2、SWE 1和CDC 28编码的进化上保守的蛋白激酶级联之间的相互作用的表征; 4）在该分化电路中起作用的其他蛋白的表征。 这项研究的完成将促进我们对遗传相同的细胞在不同功能形式之间转换的基本机制以及控制细胞分裂的机制的了解。 具有相同遗传信息的细胞可以采取各种各样的形状并执行许多不同的功能。 由于多细胞动物和植物是从单细胞发育而来的，因此必须存在特定的机制，使祖细胞的各种后代采用成熟生物体中可再生的特定形式和功能。 从根本上理解多细胞生物是如何产生的，需要了解这些机制，然而，目前对细胞被指示采取特定形状的方式知之甚少。 该项目使用一个易于处理的实验系统，其中细胞形状响应于外部信号而可重复地变化。 通过识别控制这种程序化形状变化的分子机制，可能获得关于多细胞生物体发育过程的基本信息。

Myers 9604247 This project seeks to characterize mechanisms that specifically regulate cellular form and function in response to environmental stimuli. The ascomycete Saccharomyces cerevisiae can switch between the yeast form (YF) and the pseudohyphal form (PH) in response to defined culture conditions. Cellular characteristics that are affected in this differentiation include cell shape, cell size, cell polarity, and cell division cycle mechanisms. This project has identified two protein kinases, Elm1p and CDC28, in which mutations cause cells to adopt pseudohyphal form characteristics in all growth conditions. Elimination of Elm1p function causes cells to adopt the pseudohyphal form constitutively, indicating that this protein inhibits development of pseudohyphal characteristics in inappropriate environments. One or more forms of the cyclin-dependent kinase complex (CDK) in which CDC28 is the catalytic subunit also regulates yeast- pseudohyphal differentiation. A specific amino acid substitution in CDC28 causes constitutive execution of most aspects of the pseudohyphal form. These data are consistent with the hypothesis that various signaling processes impinge on CDC28, which in response, is functionally modified in a specific way. Modified CDK activity then causes various aspects of the pseudohyphal growth form to occur. In this way CDK may function to integrate various input signals from the environment and control the decision of whether or not to execute a certain differentiation process. This project will address the following specific objectives: 1) Determination of whether CDK alteration is required for cells to attain the pseudohyphal form in response to either of two signaling regimes known to induce this differentiation process in wild type cells; 2) Characterization of the functional differences between CDK in yeast form- and pseudohyphal form cells; 3) Characterization of the interaction between Elm1p and the evolutionarily conserved protein kinase cascade coded for by SEL2, SWE1, and CDC28; 4) Characterization of additional proteins that function in this differentiation circuitry. Completion of this research will advance our knowledge of the basic mechanisms by which genetically identical cells convert between different functional forms, and the mechanisms by which cell division is controlled. Cells with identical genetic information can take a wide variety of shapes and execute many different functions. Because multicellular animals and plants develop from a single cell, specific mechanisms must exist that cause the various descendants of the progenitor cell to adopt the specific forms and functions that arise reproducibly in mature organisms. Fundamental understanding of how multicellular organisms arise requires an understanding of these mechanisms, however, little is understood currently about the ways in which cells are instructed to adopt a specific shape. This project uses a tractable experimental system in which cell shape changes reproducibly in response to an external signal. By discerning the molecular mechanism that control this programmed shape change, fundamental information regarding the processes by which multicellular organisms develop is likely to be obtained.