Dynamics of gradient sensing in single cells

描述(由申请人提供)：生命系统使用有关外部条件的信息和从它们的基因组中检索的信息来确定它们未来的行动。决定未来行为的信息的中心性决定了生物系统和其他复杂的物理系统之间的关键区别。在后生动物中，对细胞外环境中的调节分子做出反应的决策对于从受精卵发育成体和维持成体至关重要。因此，我们希望了解细胞如何将细胞外信号转换为定量测量，以及细胞如何传输和操作这些信息。我们对一个原型细胞信号系统--酿酒酵母信息素反应系统的持续研究，为这些问题提供了见解。这些发现来自于使用工程蛋白报告程序和图像细胞术对系统运行中的分子事件进行量化的单细胞实验。尽管这些研究成果丰硕，但这些研究所需的简化忽略了后生动物信号的一个关键方面：协调许多关键细胞决定的细胞外调节分子以梯度分布。调节配体分子的梯度在脊椎动物中普遍存在。脊椎动物细胞在整个发育和成年过程中，能够正确地确定梯度中的配体浓度(对于命运决定)，正确地确定配体梯度向量(对于极性决定)，以及在这些确定中限制细胞到细胞的变异(对于细胞群体的一致反应)是至关重要的。与脊椎动物信号系统一样，酵母原型系统使细胞能够读取配体梯度的浓度和极性向量。我们将使用酵母系统来了解细胞用来确定梯度中的浓度和极性向量的生物物理和分子机制，以及在这些测定中限制细胞间差异的机制。单细胞实验能力的极大提高和微流控设备的最新发展使这项工作成为可能，从而能够以良好控制的梯度进行大量细胞的实验观察。在接下来的五年里，对于梯度中的细胞，我们将阐明生物物理和分子机制，使浓度测定的速度和准确性成为可能，使快速和准确的梯度测定成为可能，并通过限制这些测定中的细胞间差异使细胞群体的反应更加连贯。对细胞如何做出这些决定并限制细胞间差异的基于机制的定量理解将促进基本知识，并可能提出操纵特定量化行为的途径，以达到治疗目的。

DESCRIPTION (provided by applicant): Living systems use information about external conditions and information retrieved from their genomes to determine their future actions. The centrality of information in determining future behavior defines a key difference between biological systems and other complex physical systems. In metazoans, decision making in response to regulatory molecules in the extracellular environment is critical for development of the adult organism from the zygote and for maintenance of the adult soma. We therefore wish to understand how cells convert extracellular signals into quantitative measurements and how cells transmit and operate on this information. Our continuing studies of a prototypic cell signaling system, the Saccharomyces cerevisiae pheromone response system, have provided insights into these questions. Findings have come from experiments on single cells using engineered protein reporters and image cytometry to quantify molecular events in system operation. Although fruitful, the simplification required for these studies neglects a key aspect of metazoan signaling: the extracellular regulatory molecules that orchestrate many key cell decisions are distributed in gradients. Gradients of regulatory ligand molecules are ubiquitous in vertebrates. The ability of vertebrate cells to correctly determine ligand concentration in gradients (for fate decisions), to correctly determine the ligand gradient vector (for polarity decisions), and to limit cell-to-cell variation in these determinations (for coherent responses by cell populations) is critical throughout development and adult life. Like vertebrate signaling systems, the prototype yeast system enables cells to read concentration and polarity vector of a ligand gradient. We will use the yeast system to understand the biophysical and molecular mechanisms cells use to determine concentration and polarity vector in gradients and that limit cell-to-cell-variation in these determinations. This work has been made possible by greatly increased single cell experimental abilities and recent development of microfludic devices allowing experimental observation of large numbers of cells in well-controlled gradients. During the next five years, for cells in gradients, we will elucidate biophysical and molecular mechanisms that bring about the speed and accuracy of concentration determination, that enable quick and accurate gradient determination, and that make the responses of cell populations more coherent by restricting cell-to-cell variation in these determinations. A mechanism-based quantitative understanding of how cells make these determinations and limit cell-to-cell variation in them would advance basic knowledge and would likely suggest paths to manipulate particular quantitative behaviors in order to achieve therapeutic ends.