Developmental Control of the Cell Cycle in Male Meiosis

描述(由申请人提供)：发育计划必须对正常胚胎发育、细胞分化、组织更新和修复以及预防癌症的细胞周期进程施加细胞类型特定的控制。发育调节细胞周期控制的一个突出例子是减数分裂细胞周期对所有有性繁殖都是必不可少的。减数分裂具有一个延长的G2期，即减数分裂前期，在此期间许多配子分化所需的基因被转录。雄性与雌性对减数分裂前期持续时间的控制不同。我们正在研究调节雄性果蝇减数分裂I的G2/M转变时间的机制，作为一个模式系统。我们发现，发育程序性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转变的时间，并通过两条独立的途径协调减数分裂细胞周期与精子细胞分化的转录程序。翻译抑制延迟了周期蛋白B的表达，而翻译控制将BULE蛋白的表达与精子细胞分化的转录程序联系起来。反过来，BOLE(人类BOLE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如何作用于CDC25/TWINE的翻译抑制，以及依赖于翻译起始机制成分elF4G的新的同源物elF4G2在成熟精母细胞中如何解除Cyclin B的翻译抑制的分子机制。我们将研究在未成熟精母细胞中延迟细胞周期蛋白B翻译的机制，包括RNA结合蛋白TSR的作用方式。为了发现导致减数分裂细胞周期进展依赖于精细胞分化基因在初级精母细胞中成功表达的调控机制，我们将鉴定c/S基因在ttaf突变精母细胞中负责翻译抑制BULEE的作用序列，筛选可能的结合翻译调控因子，并检测它们在体内的作用。为了发现BOLE的翻译是如何对tTAF功能做出反应的，我们将鉴定在tTAF控制下表达的候选翻译激活子，并确定异源表达是否允许在tTAF突变的精母细胞中进行BOLE翻译。我们的发现将阐明保守的RNA结合蛋白Boule的作用模式和调节，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.