Reversible vitamin A-dependent arrest of spermatogonia

描述（由申请人提供）：本项目的广泛，长期目标是基于维生素a缺乏症（VAD）睾丸中精原细胞（Spg）可逆停止的合理设计避孕策略。我们的目的是揭示在这个模型中可逆地抑制Spg的具体机制。在VAD睾丸上皮的两种相关细胞类型（阻滞Spg细胞和支持细胞）中，只有支持细胞表达大量的视黄酸受体α (rar α)。因此，我们的总体假设是：来自支持细胞的旁分泌信号介导了维生素A对Spg的影响。我们的工作假设是，支持细胞衍生的激活素抑制VAD睾丸中的Spg，维生素A通过下调激活素和上调其结合蛋白卵泡抑素样蛋白来拯救增殖。这个初始资助期的目标是通过确定特定信号分子和途径在维生素a依赖性调节Spg增殖过程中发挥的作用来确定未来的避孕靶点。我们打算通过完成以下具体目标来实现这一目标：(1)验证我们的预测，即维生素A调节特定的信号因子（激活素、抑制素）、结合蛋白（卵泡抑素、卵泡抑素相关蛋白）和受体（激活素受体i和ii）。(2)确定睾丸中的维生素A状态是否调节激活素受体下游的smad依赖信号通路和周期蛋白依赖激酶抑制剂的合成，从而影响精原细胞周期的变化。(3)测试候选因子对Spg增殖的调节作用，并验证激活素依赖信号调节周期蛋白依赖激酶抑制剂影响这些变化的假设。(4)确定参与精原细胞可逆性VAD停搏的其他旁分泌因子和受体。完成这些目标将定义特定的机制，逆转遗传程序中指导精原细胞增殖的内在检查点，这是我们设计成功的男性避孕药目标的重大进展。

DESCRIPTION (provided by applicant): The broad, long-range objective of this project is the rational design of contraceptive strategies based on the reversible arrest of spermatogonia (Spg) in the vitamin A-deficient (VAD) testis. Our intent is to uncover specific mechanisms that reversibly arrest Spg in this model. Of the two pertinent cell types (arrested Spg and Sertoli cells) in the epithelium of the VAD testis, only the Sertoli cell expresses significant amounts of retinoic acid receptor-alpha (RARalpha). Thus, our overall hypothesis: paracrine signal(s) from Sertoli cells mediate the effects of vitamin A on Spg. Our working hypothesis is that Sertoli cell-derived activin arrests Spg in the VAD testis and that vitamin A rescues proliferation by down-regulating activin and up-regulating its binding protein follistatin-like protein. The objectives of this initial funding period are to identify future contraceptive targets by determining the role specific signaling molecules and pathways play during the vitamin A-dependent regulation of Spg proliferation. We intend to accomplish this by completing the following specific aims: (1) Test our prediction that vitamin A regulates specific signaling factors (activin, inhibin), binding proteins (follistatin, follistatin-related protein) and receptors (activin receptors i & ii). (2) Determine whether the vitamin a status of the testis regulates smad-dependent signaling pathways downstream of the activin receptor and synthesis of cyclin-dependent kinase inhibitor(s) to effect changes in the spermatogonial cell cycle. (3) Test the efficacy of candidate factors to regulate the proliferation of Spg and test our hypothesis that activin-dependent signaling regulates cyclin-dependent kinase inhibitors to effect these changes. (4) Identify additional paracrine factors and receptors that participate in the reversible VAD arrest of spermatogonia. Completing these aims will define specific mechanisms that reverse an intrinsic checkpoint in the genetic program directing spermatogonial proliferation, a significant advance towards our goal of designing a successful male contraceptive.