Mechanisms of noise regulation in cell fate transitions

 描述（由申请人提供）：细胞行为受环境信号控制，包括营养素、渗透压、激素和神经递质。直到最近，研究人员才开始研究细胞对这些刺激的反应是如何变化的。该项目的重点是细胞信号转导中的噪声调节机制及其在决定细胞命运中的作用。我们的研究利用了酵母中的原型G蛋白信号通路。在该系统中，肽交配信息素激活细胞表面受体、G蛋白和MAP激酶信号级联。我们最近的工作表明，几个途径的组成部分以动态的方式来调节该途径的时间依赖性噪声特性。这一观察激发了我们的主要假设，即负责细胞间变异性的噪声源受到调节，以促进细胞在不断变化的环境条件下的存活。在某些情况下，波动可以作为“赌注对冲”机制，以使同基因细胞群体的反应多样化，而在其他情况下，当细胞面临多种竞争刺激时，可能需要噪声抑制来适当地协调反应途径。我们的研究计划使用微流体设备和荧光成像来跟踪在良好控制的环境中的单细胞，定量图像分析来表征信号传导和基因表达的波动，以及随机建模来建议和测试噪声调节机制。以下目标将用于确定噪声在塑造细胞行为中的作用，并确定调节其特性的生物回路：目标1分析噪声对细胞分化或增殖决定的影响。目的2分析噪声抑制所需的两个MAP激酶通路之间的协调机制，一个是促进分化，一个是适应渗透胁迫所需的。目的3分析噪声在向年龄依赖性不育转变中的作用。我们的发现将揭示调节噪声的信号通路的组织和逻辑，以及噪声在多大程度上影响细胞命运决定和存活。这种系统水平的原则可能是共享的许多信号通路的生物体，从酵母到人类。 酵母是这些分析的理想平台;群体中的所有细胞在遗传上都是相同的，并且可以在均匀且易于调节的生长条件下维持。基因的可操作性是无与伦比的，任何变化的后果都很容易量化。因此，通过遗传或环境变化来调节噪声，测量功能后果，开发计算模型并进行实验测试是可行的。这种综合方法对于假设生成和假设检验都是理想的。最后，酵母中的信号传导途径采用与人类中发现的那些同源的细胞表面受体、G蛋白、MAP激酶和细胞周期蛋白依赖性激酶（CDK）。因此，在酵母中发现的信号传导机制将为人类生理学和药理学提供信息。

 DESCRIPTION (provided by applicant): Cellular behavior is controlled by environmental signals including nutrients, osmotic stress, hormones and neurotransmitters. Only recently have investigators begun to address how the response to any of these stimuli varies from cell to cell. This project focuses on mechanisms of noise regulation in cellular signal transduction and their role in determining cell fate. Our investigation exploits a prototype G protein signaling pathway in yeast. In this system, a peptide mating pheromone activates a cell surface receptor, a G protein, and a MAP kinase signaling cascade. Our recent work revealed that several pathway components act in a dynamic manner to regulate the time-dependent noise characteristics of the pathway. This observation motivated our primary hypothesis that the sources of noise responsible for cell-to-cell variability are regulated to promote cellular survival under changing environmental conditions. In certain contexts, fluctuations may serve as "bet-hedging" mechanisms to diversify the response of a population of isogenic cells, whereas in other contexts noise suppression may be required to properly coordinate response pathways when cells are faced with multiple competition stimuli. Our research plan uses microfluidic devices and fluorescent imaging to follow single cells in well controlled environments, quantitative image analysis to characterize fluctuations in signaling and gene expression, and stochastic modeling to suggest and test noise regulation mechanisms. The following aims will be used to determine the role of noise in shaping cellular behavior and identify the biological circuits that regulate is properties: Aim 1 analyzes effects of noise on the cellular decision to differentiate or proliferat. Aim 2 analyzes mechanisms of noise suppression required for coordination between two MAP kinase pathways, one that promotes differentiation and one that is required for adaptation to osmotic stress. Aim 3 analyzes effects of noise in the transition to age-dependent sterility. Our findings will reveal the organization and logic of signaling circuits that regulate noise and to wht extent noise influences cell fate decisions and survival. Such systems level principles are likely to be shared by many signal pathways in organisms ranging from yeast to humans. Yeast is an ideal platform for these analyses; all of the cells in the population are genetically identical, an can be maintained under uniform and easily modulated growth conditions. Genetic manipulability is unparalleled and the consequences of any changes are easily quantified. Thus it is practical to modulate noise by genetic or environmental changes, measure the functional consequences, develop computational models and test them experimentally. This integrated approach is ideal for both hypothesis-generating and hypothesis- testing. Finally, the signaling pathway in yeast employs cell-surface receptors, G proteins, MAP kinases, and cyclin dependent kinases (CDKs) homologous to those found in humans. Thus signaling mechanisms identified in yeast will inform human physiology and pharmacology.