Regulation of Spermatogenesis by X-linked miRNAs

描述(申请人提供)：减数分裂性染色体失活(MSCI)在精子发生过程中的特征是在中晚期粗线期精母细胞中X和Y染色体上的基因转录沉默。MSCI被认为是未配对DNA减数分裂沉默的结果，因为在第一次减数分裂前期，X和Y染色体基本上保持未配对状态。因此，与女性胚胎或体细胞中X染色体失活不同，已有25%-30%的X连锁结构基因被报道逃脱了失活，而此前还没有关于初级精母细胞中逃脱MSCI沉默效应的基因的报道。然而，我们最近发现，许多X连锁的microRNAs(MiRNAs)是在粗线期精母细胞中转录和加工的。这种史无前例的MSCI逃逸表明，这些miRNAs在精子发生的这个阶段参与了一个或多个关键功能。我们的初步发现证实了这一点，即携带高比例X连锁miRNA基因敲除的细胞的嵌合小鼠在精子发生的减数分裂阶段表现为生育缺陷。这一点意义重大，因为尽管最近的报道描述了精子发生过程中大量的miRNAs和其他小的非编码RNA的表达，但基本上对这些RNA的功能知之甚少。在这个应用中，我们首先建议研究这些X连锁的miRNA基因逃脱MSCI的分子机制(目标1)。然后，我们建议测试关于这些miRNAs功能的两个假说(并不是相互排斥的)，包括它们作为常染色体mRNAs的转录后调节因子的作用，这些常染色体mRNAs是在减数分裂过程中合成的，但直到减数分裂后才被翻译(目标2)，以及它们在调节MSCI本身的过程中的作用(目标3)。这项研究具有很高的新颖性，因为它旨在揭示一种前所未有的逃避MSCI的机制，并确定那些在精子发生过程中经历这种逃避的X连锁miRNAs的实际功能。 公共卫生相关性：了解产生精子的分子和遗传机制对于诊断和治疗男性不育以及开发非激素男性专用避孕药至关重要。来自本研究的数据将有助于深入了解X-连锁miRNAs在控制精子产生和男性生育方面的功能。

DESCRIPTION (provided by applicant): Meiotic sex chromosome inactivation (MSCI) during spermatogenesis is characterized by transcriptional silencing of genes on both the X and Y chromosomes in mid to late pachytene spermatocytes. MSCI is believed to result from meiotic silencing of unpaired DNA because the X and Y chromosomes remain largely unpaired throughout first meiotic prophase. Thus, unlike X-chromosome inactivation in female embryonic or somatic cells, where 25-30% of X-linked structural genes have been reported to escape inactivation, there have been no previous reports of genes that escape the silencing effects of MSCI in primary spermatocytes. However, we recently discovered that many X-linked microRNAs (miRNAs) are transcribed and processed in pachytene spermatocytes. This unprecedented escape from MSCI suggests that these miRNAs participate in one or more critical functions at this stage of spermatogenesis. This is corroborated by our preliminary finding that chimeric mice carrying a high percentage of cells bearing a knockout of a major cluster of X-linked miRNA genes display a fertility defect manifest as a block during the meiotic phase of spermatogenesis. This is significant because despite recent reports describing expression of an abundance of miRNAs and other small, non-coding RNAs during spermatogenesis, essentially nothing is known about the function of any of these. In this application, we first propose to investigate the molecular mechanism by which these X-linked miRNA genes escape MSCI (Aim 1). We then propose to test two hypotheses (which are not mutually exclusive) regarding function of these miRNAs, including their role as post- transcriptional regulators of autosomal mRNAs that are synthesized during meiosis but not translated until the postmeiotic period (Aim 2), and their role in regulating the process of MSCI itself (Aim 3). This study is highly novel in that it is designed to reveal an unprecedented mechanism of escape from MSCI, and to identify actual functions of those X-linked miRNAs that undergo this escape during spermatogenesis. PUBLIC HEALTH RELEVANCE: Understanding the molecular and genetic mechanisms by which sperm are produced is critically important for diagnosis and treatment of male infertility, as well as for the development of non-hormonal male-specific contraceptives. Data from the present study will contribute insight into the function of X-linked miRNAs in the control of sperm production and male fertility.