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其基因组中检索的信息来确定其未来的行为。信息在决定未来行为中的中心地位决定了生物系统和其他复杂物理系统之间的关键区别。在后生动物中，响应细胞外环境中调节分子的决策对于从受精卵发育成体细胞和维持成体细胞至关重要。因此，我们希望了解细胞如何将细胞外信号转化为定量测量，以及细胞如何传递和操作这些信息。我们对一种原型细胞信号系统——酿酒酵母信息素反应系统的持续研究，为这些问题提供了新的见解。研究结果来自单细胞实验，使用工程蛋白报告和图像细胞术来量化系统运行中的分子事件。虽然有成果，但这些研究所需的简化忽略了后生动物信号传导的一个关键方面：协调许多关键细胞决策的细胞外调节分子呈梯度分布。调节配体分子的梯度在脊椎动物中普遍存在。脊椎动物细胞正确确定梯度配体浓度（用于命运决定）、正确确定配体梯度载体（用于极性决定）以及在这些决定中限制细胞间变异（用于细胞群体的一致反应）的能力在整个发育和成年生活中至关重要。像脊椎动物的信号系统一样，酵母原型系统使细胞能够读取配体梯度的浓度和极性矢量。我们将使用酵母系统来了解细胞用于确定梯度浓度和极性矢量的生物物理和分子机制，以及在这些决定中限制细胞间变异的机制。由于单细胞实验能力的大大提高和微流体装置的最新发展，使得这项工作成为可能，微流体装置允许在良好控制的梯度下对大量细胞进行实验观察。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，这些机制将带来浓度测定的速度和准确性，从而实现快速准确的梯度测定，并通过限制这些测定中的细胞间变异使细胞群体的反应更加一致。基于机制的定量理解细胞如何做出这些决定并限制细胞间的变异，将推进基本知识，并可能提出操纵特定定量行为以实现治疗目的的途径。

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.