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

描述(由申请人提供) 摘要：从胚胎发育到癌变的生物学过程依赖于细胞生长和大小的调节或失调；尽管细胞在生物医学上具有重要意义，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，几乎所有当前关于单元格大小控制的想法都是基于 传统的模式侧重于信号网络，如TOR代谢途径，或细胞周期途径。然而，我们甚至缺乏对诸如基因组含量(倍性)和核糖体生物合成活性等细胞变量如何对细胞大小产生众所周知的影响的基本机制的了解，特别是在多细胞生物体的细胞大小动态平衡的背景下。我们对这一关键生物学过程的理解存在根本差距，这突显了迫切需要新的方法来定量地看待细胞大小控制。我们最近引入了一个新的概念，即非膜结合的核糖核蛋白(RNP)小体，包括产生核糖体的核仁，是用于快速处理RNA的动态液相微反应器。我们之前对其他无序的类液体物体的研究表明，核仁的大小应该随着细胞的大小而变化。然而，基本的生物物理考虑表明，不同大小的核仁会在不同的时间产生核糖体亚基。 速度：大细胞中的大核仁可能无法跟上细胞稳定生长所需的核糖体，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，我们将使用新的基于成像的分析方法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哇卵母细胞系统。然后，我们将研究这种大小依赖的活动的后果，解剖多细胞蠕虫中核仁大小和活动以及细胞大小之间的关系。使用3D共聚焦成像和定制的图像分析算法，我们将测量二倍体和四倍体蠕虫中改变的核仁大小和生物合成活性对细胞大小的影响。最后，我们将基于动态类液体核仁材料中核糖体RNA处理速度的大小依赖关系，开发用于理解这些数据的理论生物物理模型。 公共卫生相关性：从胚胎发育到癌症的各种生物学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，在细胞生长控制中扮演着众所周知的角色。这一建议试图确定核仁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.