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动。信息在决定未来行为中的中心地位，定义了生物系统与其他复杂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作出反应的决策对于从受精卵发育成成体生物体和维持成体索马至关重要。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，以及细胞如何传输和操作这些信息。我们的原型细胞信号系统，酿酒酵母信息素反应系统的持续研究，这些问题提供了见解。这些发现来自于使用工程蛋白报告基因和图像细胞术对单细胞进行的实验，以量化系统操作中的分子事件。虽然成果丰硕，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定的细胞外调节分子是以梯度分布的。 调节配体分子的衍生物在脊椎动物中普遍存在。脊椎动物细胞正确确定梯度中的配体浓度（用于命运决定）、正确确定配体梯度载体（用于极性决定）以及在这些确定中限制细胞间变异（用于细胞群的一致响应）的能力在整个发育和成年期至关重要。 像脊椎动物信号系统一样，原型酵母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中的浓度和极性载体的生物物理和分子机制，以及这些确定中限制细胞间差异的机制。这项工作已经成为可能，大大增加了单细胞实验能力和最近开发的微流控装置，允许实验观察大量的细胞在良好控制的梯度。 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，这些机制带来了浓度测定的速度和准确性，能够快速准确地确定梯度，并通过限制这些测定中的细胞间变异来使细胞群的反应更加一致。基于机制的定量理解细胞如何做出这些决定并限制其中的细胞间变异将推进基础知识，并可能提出操纵特定定量行为以实现治疗目的的途径。 公共卫生相关性：这项工作将帮助我们了解细胞如何读取梯度信号分子的数量和方向，以及细胞群如何通过以相同的方式阅读这些信号分子来做出一致的反应。在包括人类在内的多细胞动物中，这些过程对于从受精卵发育成人，维持成人身体（因为组织中的细胞死亡，新的细胞取代它们）以及癌症（特别是实体瘤）的发展至关重要。理解将指导未来的基础研究，并可能为治疗干预提供途径。

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. PUBLIC HEALTH RELEVANCE: This work will help us understand how cells read amounts and directions of signal molecules in gradients, and how groups of cells respond coherently by reading these the same way. In multicellular animals, including humans, these processes are critical for development of the adult from the fertilized egg, for maintenance of the adult body (as cells in tissues die and new ones replace them), and during development of cancers (particularly solid tumors). Understanding will guide future basic research and may suggest paths for therapeutic interventions.