Developmental Control of the Cell Cycle in Male Meiosis

描述（由申请人提供）：发育项目必须对正常胚胎发育、细胞分化、组织更新和修复以及癌症预防的细胞周期进程施加细胞类型特异性控制。发育调节细胞周期控制的一个显著例子是减数分裂细胞周期对所有有性生殖至关重要。减数分裂具有延长的G2期，减数分裂前期，在此期间许多配子分化所需的基因被转录。减数分裂前期的持续时间在雄性和雌性的控制不同。我们正在研究调节雄性果蝇减数分裂I的G2/M转换时间的机制，作为一个模型系统。我们发现发育程序化的翻译控制通过两条独立的途径调节雄性减数分裂I的G2/M过渡的时间，并通过精子分化的转录程序协调减数分裂细胞周期的进程。翻译抑制延迟了细胞周期蛋白B的表达，而翻译控制将圆孔蛋白的表达与精子分化的转录程序联系起来。反过来，boule（人类boule和D/\Z的同源物）调节细胞周期磷酸酶cdc25/twine的翻译。我们将研究Boule如何缓解cdc25/twine的翻译抑制的分子机制，以及成熟精子细胞中Cyclin B的翻译抑制如何依赖于elF4G2（翻译起始机制组件elF4G的新同源物）。我们将研究细胞周期蛋白B蛋白在未成熟精母细胞中延迟翻译的机制，包括RNA结合蛋白Tsr的作用模式。为了发现减数分裂细胞周期进程依赖于原代精母细胞中精子分化基因的成功表达的调控机制，我们将在tTAF突变的精母细胞中鉴定负责翻译抑制的c/s^作用序列，筛选可能结合的翻译调节因子，并测试它们在体内的作用。为了发现在tTAF的作用下，球泡的翻译是如何被抑制的，我们将鉴定在tTAF控制下表达的候选翻译激活因子，并确定在tTAF突变的精细胞中外源表达是否允许球泡翻译。我们的发现将阐明保守的RNA结合蛋白Boule的作用模式和调控，并提出在哺乳动物精子发生过程中测试类似功能的机制。

DESCRIPTION (provided by applicant): Developmental programs must impose cell type specific controls on cell cycle progression for normal embryonic development, cell differentiation, tissue renewal and repair, and prevention of cancer. A striking case of developmental^ regulated cell cycle control is the meiotic cell cycle essential for all sexual reproduction. Meiosis features an extended G2 phase, meiotic prophase, during which many genes required for gamete differentiation are transcribed. The duration of meiotic prophase is controlled differently in males than in females. We are investigating the mechanisms that regulate timing of the G2/M transition of meiosis I in males in Drosophila as a model system. We found that developmental^ programmed translational control regulates timing of the G2/M transition of male meiosis I and coordinates meiotic cell cycle progression with the transcription program for spermatid differentiation by two independent pathways. Translational repression delays expression of cyclin B protein, and translational controls link expression of boule protein to the transcriptional program for spermatid differentiation. In turn, boule (a homolog of human BOULE and D/\Z), regulates translation of the cell cycle phosphatase cdc25/twine. We will investigate the molecular mechanisms of how Boule acts to relieve translational repression of cdc25/twine and how translational repression of Cyclin B is relieved in mature spermatocytes, dependant on elF4G2, a novel homolog of the translational initiation machinery component elF4G. We will investigate the mechanisms that delay translation of cyclin B protein in immature spermatocytes, including the mode of action of the RNA binding protein Tsr. To discover the regulatory mechanisms that make meiotic cell cycle progression depend on successful expression of spermatid differentiation genes in primary spermatocytes, we will identify c/s^ acting sequences responsible for translational repression of boule in tTAF mutant spermatocytes, screen for possible translational regulators that bind, and test their role in vivo. To discover how translation of boule is derepressed in response to tTAF function, we will identify candidate translational activators expressed under tTAF control, and determine whether heterologous expression allows boule translation in tTAF mutant spermatocytes. Our findings will illuminate the mode of action and regulation of the conserved RNA binding protein Boule and suggest mechanisms to test for similar function during mammalian spermatogenesis.