Developmental control of cell cycle exit

描述（由申请人提供）：一个未解决的发展之谜涉及如何控制生长和形态。细胞增殖的调控是这个问题的核心，而在细胞分化过程中控制细胞周期阻滞的机制尤为重要。细胞周期退出在癌变和伤口愈合和再生过程中也很关键，细胞周期退出被绕过，而在伤口愈合和再生过程中，细胞周期退出被逆转以允许新的增殖。虽然细胞周期退出已经在细胞培养和几种模式生物体内进行了研究，但分化信号与细胞周期控制装置耦合的机制仍然知之甚少。目前还没有通用的范式来解释细胞分化与G1阻滞之间普遍存在的耦合。本研究旨在研究果蝇在胚胎、翅膀和眼睛这三种具有良好特征的环境中细胞周期的分化。我们将验证分化信号通过E2F/ rb独立机制主要抑制细胞周期控制基因转录的假设。在Aim 1中，我们操纵已知细胞周期控制基因的活性，以确定触发细胞周期退出的机制，并分析退出过程中基因表达的变化。在Aim 2中，我们研究了关键细胞周期控制基因cyclin E的转录调控区域，以鉴定在分化时介导其沉默的顺式作用元件和最终的反式作用因子。在Aim 3中，我们在苍蝇中进行遗传筛选，以鉴定对细胞周期退出具有重要功能的新基因。综合结果应区分文献中提出的许多可能的细胞周期退出解释，确定介导细胞周期退出的新基因产物，并为未来研究分化信号如何与细胞周期控制装置相结合提供一个工作范例。由于协调组织模式、细胞分化和细胞周期控制的遗传网络在果蝇和人类之间是保守的，因此本文获得的结果应该为正在进行的人类发育和疾病研究提供信息。

DESCRIPTION (provided by applicant): An unsolved mystery of development concerns how growth and form are controlled. The regulation of cell proliferation is central to this problem, and the mechanisms controlling cell cycle arrest upon cell differentiation are particularly relevant. Cell cycle exit is also critical in carcinogenesis, where it is bypassed, and in wound healing and regeneration, where it is reversed to allow renewed proliferation. While cell cycle exit has been studied in cell culture and in vivo in several model organisms, the mechanisms that couple differentiation signals to the cell cycle control apparatus remain poorly understood. No general paradigm exists explaining the ubiquitous coupling of cell differentiation to G1 arrest. This proposal is to study cell cycle exit at differentiation in Drosophila in three well-characterized contexts: the embryo, the wing, and the eye. We will test the hypothesis that differentiation signals dominantly suppress the transcription of cell cycle control genes via an E2F/RB-independent mechanism. In Aim 1, we manipulate the activity of known cell cycle control genes to define the mechanism that triggers cell cycle exit, and we also analyze changes in gene expression during the exit process. In Aim 2, we study the transcriptional regulatory region of the critical cell cycle control gene, cyclin E, to identify cis-acting elements, and eventually trans-acting factors, that mediate its silencing at differentiation. In Aim 3 we perform genetic screens in the fly to identify novel genes that are functionally important for cell cycle exit. The combined results should distinguish between the many plausible explanations of cell cycle exit suggested in the literature, identify new gene products that mediate cell cycle exit, and provide a working paradigm for future studies of how differentiation signals interface with the cell cycle control apparatus. Because the genetic networks that orchestrate tissue patterning, cell differentiation, and cell cycle control are conserved between Drosophila and man, the results obtained herein should inform ongoing studies of human development and disease.