Mechanisms that coordinate cell size with mitotic entry

描述（由申请人提供）：各种各样的细胞类型延迟细胞周期转变，直到它们达到临界尺寸阈值，但是测量尺寸并将此信息传递给核心细胞周期机制的机制在很大程度上是未知的。在分裂酵母中，Cdr2蛋白激酶将细胞大小测量与有丝分裂进入联系起来，是一个保守的蛋白激酶家族的一部分，该家族在酵母和人类细胞中下调有丝分裂抑制剂Wee1。为了理解Cdr2在细胞大小检查点中的功能，定义控制Cdr2活性和定位的上游信号是很重要的。我们正在使用遗传、生化和显微镜相结合的方法来鉴定Cdr2调节回路，并确定它们的输入输出行为如何依赖于细胞大小。我们最初的工作涉及到Cdr2的三个分子“输入”信号：极性激酶Pom1、甲基转移酶Skb1和Cdr2激活环中未知激酶的磷酸化。该项目的具体目标是：(1)确定Pom1磷酸化如何抑制细胞中的Cdr2，(2)确定控制Cdr2的Skb1信号通路，以及(3)确定Cdr2激活环磷酸化在有丝分裂大小控制系统中的作用。这些目标的成功完成将通过确定通过核心细胞周期蛋白的活动协调细胞生长和分裂的机制来推进科学知识。此外，我们发现的大小机制将为大小如何控制其他生物系统的活动提供见解。

DESCRIPTION (provided by applicant): A wide variety of cell types delay cell cycle transitions until they reach a critical size threshold, but the mechanisms that measure size and transmit this information to the core cell cycle machinery are largely unknown. The protein kinase Cdr2 connects cell size measurement with mitotic entry in fission yeast, and is part of a conserved family of protein kinases that down- regulate the mitotic inhibitor Wee1 in yeast and human cells. To understand the function of Cdr2 in cell size checkpoints, it is important to define the upstream signals that control Cdr2 activity and localization. We are using combined genetic, biochemical, and microscopy approaches to identify Cdr2 regulatory circuits and to determine how their input-output behaviors depend on cell size. Our initial work implicates three molecular "input" signals to Cdr2: the polarity kinase Pom1, the methyltransferase Skb1, and phosphorylation in the Cdr2 activation loop by an unknown kinase. The specific aims of the project are to: (1) define how phosphorylation by Pom1 inhibits Cdr2 in cells, (2) identify the Skb1 signaling pathway that controls Cdr2, and (3) determine the role of Cdr2 activation loop phosphorylation in the mitotic size control system. Successful completion of these goals will advance scientific knowledge by identifying the mechanisms that coordinate cell growth and division through the activity of core cell cycle proteins. Moreover, the sizing mechanisms that we uncover will provide insights for how size controls the activity of other biological systems. PUBLIC HEALTH RELEVANCE: Defects in the mitotic entry control system can lead to genomic instability, a hallmark of cancer. We will use the model organism fission yeast to define of the upstream signals that govern this cell cycle transition. These findings will be important to understand the cellular mechanisms that prevent untimely and inappropriate cell divisions, which contribute to human diseases such as cancer.