Cell growth control by cell and organelle size-dependent ribosome biogenesis

描述（由申请人提供） 摘要：从胚胎发育到致癌的生物过程都依赖于细胞生长和大小的调节或失调;尽管有这种重要的生物医学意义，但细胞“知道”生长到一定大小的机制仍然知之甚少。除了少数例外，几乎所有关于细胞大小控制的当前想法都基于 传统的范式集中在信号网络，如TOR代谢途径，或细胞周期途径。然而，我们甚至缺乏一个基本的机械理解的方式，其中细胞变量，如基因组含量（倍性）和核糖体生物合成活性发挥其众所周知的影响细胞大小，特别是在细胞大小的上下文中的多细胞生物体内稳态。我们对这一关键生物过程的理解存在根本性的差距，这突出表明迫切需要新的方法来定量地观察细胞大小控制。 我们最近提出了一个新的概念，即非膜结合的核糖核蛋白（RNP）体，包括核糖体产生的核仁，是快速RNA加工的动态液相微反应器。我们以前对其他无序液体样体的研究表明，核仁的大小应该与细胞的大小成比例。然而，基本的生物物理学考虑表明，不同大小的核仁将在不同的温度下产生核糖体亚基。 费率;大细胞中的大核仁可能无法满足稳定细胞生长所需的核糖体，这为细胞大小反馈和生长控制提供了生物物理机制。为了验证这一假设，我们将使用新的成像为基础的测定来测量不同大小的单个核仁的功能，利用一个生物化学可访问的非洲爪蟾卵母细胞系统。然后，我们将研究这种大小依赖的活动的后果，解剖核仁大小和活动之间的关系，和细胞大小，在多细胞蠕虫秀丽隐杆线虫。使用3D共聚焦成像和自定义图像分析算法，我们将在二倍体和四倍体蠕虫中测量改变的核仁大小和生物合成活性对细胞大小的影响。最后，我们将发展理论生物物理模型，以了解这些数据的基础上的核糖体RNA加工速率的大小依赖性的动态液体状核仁物质。 公共卫生相关性：从胚胎发育到癌症的生物过程都依赖于细胞生长和大小的调节或失调。核仁是一种核细胞器，在细胞生长控制中起着众所周知的作用。该提议旨在确定核仁可以提供细胞大小反馈以调节细胞生长的生物物理机制，这将对理解和控制生理和疾病驱动的细胞生长过程具有重要意义。

DESCRIPTION (Provided by the applicant) Abstract: Biological processes ranging from embryonic development to carcinogenesis rely on the regulation or dysregulation of cell growth and size; despite this central biomedical importance, the mechanisms by which cells ""know"" to grow to a certain size remain poorly understood. With few exceptions, virtually all current thinking about cell size control is based on traditional paradigms that focus on signaling networks such as the TOR metabolic pathway, or the cell cycle pathway. However, we lack even a basic mechanistic understanding of the way in which cellular variables such as genomic content (ploidy) and ribosome biosynthetic activity exert their well-known effects on cell size, particularly in the context of cell size homeostasis i multicellular organisms. The fundamental gap in our understanding of this critical biological process underscores the urgent need for new ways of quantitatively looking at cell size control. We recently introduced the novel concept that non-membrane bound ribonucleoprotein (RNP) bodies, including the ribosome-producing nucleolus, are dynamic liquid phase micro-reactors for rapid RNA processing. Our previous studies with other disordered liquid-like bodies suggest that the size of nucleoli should scale with the size of cells. However, basic biophysical considerations suggest that nucleoli of different size will produce ribosomal subunits at different rates; large nucleoli in large cells may not be able to keep up with the ribosome requirements for steady cell growth, providing a biophysical mechanism for cell size feedback and growth control. To test this hypothesis, we will use novel imaging-based assays to measure the function of individual nucleoli of different size, utilizing a biochemically accessible Xenopus oocyte system. We will then examine the consequences of this size- dependent activity, dissecting the relationship between nucleolus size and activity, and cell size, within the multicellular worm C.elegans. Using 3D confocal imaging and custom image analysis algorithms, we will measure the effects of altered nucleolus size and biosynthetic activity on cell size, in both diploid and tetraploid worms. Finally, we will develop theoretical biophysical models for understanding these data based on the size dependence of the rate of ribosomal RNA processing within the dynamic liquid- like nucleolar material. Public Health Relevance: Biological processes ranging from embryonic development to cancer all rely on the regulation or dysregulation of cell growth and size. The nucleolus is a nuclear organelle that plays a well known role in cell growth control. This proposal seeks to identify the biophysical mechanism by which the nucleolus may provide cell size feedback for regulating cell growth, which will have important implications for understanding and controlling physiological and disease driven cell growth processes.