Spatiotemporal modeling of signal transduction in yeast

描述(申请人提供)：检测和响应信号分子的空间梯度的能力是真核细胞中许多生物学过程的基础，如分化、迁移和形态发生。虽然对信号转导和梯度传感所需的蛋白质了解很多，但它们相互作用以传递有关环境的信息并创造蛋白质活性内部梯度的确切机制仍不清楚。这项建议旨在确定受体内吞作用在调节酿酒酵母交配反应中的信号活性和梯度感觉中的作用。酵母根据信息素的浓度进行发育决定。在高信息素水平下，它们的生长停止并产生交配突起(“shmoo”形态)。在中等浓度时，它们沿着信息素梯度增加的方向伸长(化学营养生长)。这一决定要求交配反应途径传递有关外部信息素浓度的定量信息。通过数学建模和实验分析相结合的方法，我们积累了强有力的证据来支持信息素浓度信息的传递，而不是信号活动的幅度，而是信号的持续时间。这项提议的一个目标是检验受体内吞作用在这种“剂量-持续”转换中起重要作用的假设。一些实验和理论研究表明，受体内吞作用对于确定细胞极性很重要。最近的理论研究也表明，受体内吞作用提高了细胞检测外部信号分子梯度的能力。第二个目标是验证受体内吞增强酵母检测信息素梯度和跟踪随时间变化的梯度的能力的假设。具体目标是：目的1.确定受体内吞作用在调节信号活性中的作用。这一目标验证了受体内吞作用为剂量-持续时间编码提供了一种机制的假设。数学建模与实验方法相结合，以比较野生型和已定义的突变酵母菌株中的信号活性和反应。目的2.研究受体内吞作用在梯度感觉中的作用。这一目标使用数学和实验方法来检验受体内吞作用提高酵母检测信息素梯度的能力这一假说。目的3.表征酵母对不断变化的外部条件的反应能力。这一目的验证了受体内吞作用允许酵母跟踪依赖于时间的信息素梯度的假设。我们最近开发了一种微流体设备，允许及时调节梯度的方向，这是我们用于研究酵母跟踪不断变化的环境条件的能力的实验设计的关键特征。

DESCRIPTION (provided by applicant): The ability to detect and respond to spatial gradients of signaling molecules is fundamental for many biological processes in eukaryotic cells, such as differentiation, migration and morphogenesis. While much is known about the proteins that are required for signal transduction and gradient sensing, the precise mechanism by which they interact to transmit information about the environment and create internal gradients of protein activity remain unclear. This proposal seeks to establish the role of receptor endocytosis in modulating signaling activity and gradient sensing in the mating response of Saccharomyces cerevisiae (yeast). Yeast undergo a developmental decision based on the concentration of pheromone. At high pheromone levels, they growth arrest and generate a mating projection ("shmoo" morphology). At intermediate concentrations they elongate in the direction of an increasing pheromone gradient (chemotrophic growth). This decision requires that the mating response pathway transmit quantitative information about the external pheromone concentration. Through a combination of mathematical modeling and experimental analysis we accumulated strong evidence to support the idea that information about pheromone concentration is transmitted not as the amplitude of signal activity but as signal duration. One goal of this proposal is to test the hypothesis that receptor endocytosis plays an important role in this "dose-to-duration" conversion. Several experimental and theoretical investigations have suggested that receptor endocytosis is important for establishing cell polarity. Recent theoretical investigations also have suggested that receptor endocytosis increase cell's ability to detect external gradients of signaling molecules. A second goal is to test the hypothesis that receptor endocytosis increases yeast's ability to detect pheromone gradients and track gradients that change in time. The specific aims are: Aim 1. Characterize the role of receptor endocytosis in modulating signal activity. This aim tests the hypothesis that receptor endocytosis provides a mechanism for dose-to-duration encoding. Mathematical modeling is combined with experimental approaches to compare signal activity and responses in wild-type and defined mutant strains of yeast. Aim 2. Characterize the role of receptor endocytosis in gradient sensing. This aim uses mathematical and experimental approaches to test the hypothesis that receptor endocytosis increases yeast's ability to detect a pheromone gradient. Aim 3. Characterize yeast's ability to respond to changing external conditions. This aim tests the hypothesis that receptor endocytosis allows yeast to track time-dependent pheromone gradients. Our recent development of a microfluidics device that allows the direction of a gradient to be modulated in time is a critical feature of our experimental design for investigating yeast's ability to track changing environmental conditions.