Analysis of the role of the VRK1 protein kinase in mammalian fertility

描述（申请人提供）：配子发生是一个高度调控的过程，对动物物种的维持具有深远的重要性。配子发生错误的后果从不育到染色体异常遗传给下一代不等。然而，对精子发生和卵子发生至关重要的信号级联仍然知之甚少。由蛋白激酶和磷酸酶介导的动态蛋白磷酸化是真核细胞使用的主要机制之一，它确保有丝分裂和减数分裂细胞分裂的阶段以正确的顺序发生，并且只有在细胞内和细胞外条件有利时才会发生。这个项目的重点是VRK1蛋白激酶，它参与从无脊椎动物到哺乳动物的生物细胞增殖的调节。果蝇和秀丽隐杆线虫的VRK1同源物是必需的蛋白质，其破坏导致与减数分裂缺陷相关的不育。最近，我们已经产生了VRK1表达的半拟态基因靶向小鼠。在纯合子状态下，雄性和雌性vrk1缺陷小鼠都是不育的，这表明VRK在生育中的作用是进化保守的。在雄性小鼠中，这种不孕症与严重的进行性精原细胞丧失有关。在本提案的目的1中，我们将进一步研究这种表型，并验证VRK1缺失导致精原干细胞增殖和/或分化中的细胞自主缺陷的假设。我们还将探讨另一种假设，即VRK1缺乏的支持细胞不能提供一个能够支持正在进行的精子发生的生态位。VRK1表达半胚的雌性小鼠也具有不育性；因此，了解VRK1缺失如何影响女性生育能力将是本提案目标2的重点。有趣的是，与雄性的缺陷相反，初步的组织学分析显示，vrk缺陷小鼠的卵泡成熟和排卵正常进行。因此，我们假设，在卵母细胞内，VRK1可能对减数分裂的恢复和完成最为关键。我们的初步数据提供了VRK1在哺乳动物配子发生中起关键作用的第一个证据。由于其耗竭而导致的严重不孕症表明，对VRK1的更深入了解可能会为人类生殖提供重要相关的新见解。对调控配子体发生的信号通路的深入了解将为治疗不育症提供新的方法，并为开发男性避孕药提供新的目标。

DESCRIPTION (provided by applicant): Gametogenesis is a highly regulated process that has profound importance for the maintenance of animal species. Errors in gametogenesis have consequences that range from infertility to the transmission of chromosome abnormalities to the next generation. However, the signaling cascades critical to both spermatogenesis and oogenesis are still poorly understood. Dynamic protein phosphorylation, mediated by protein kinases and phosphatases, is one of the major mechanisms used by eukaryotic cells to ensure that the phases of mitotic and meiotic cell division occur in the correct sequence and only when intracellular and extracellular conditions are favorable. The focus of this project is the VRK1 protein kinase, which is involved in the regulation of cell proliferation in organisms ranging from invertebrates to mammals. The VRK1 orthologs in Drosophila and C. elegans are essential proteins whose disruption causes sterility associated with meiotic defects. Recently, we have generated gene-targeted mice that are hypomorphic for the expression of VRK1. In the homozygous state, both the male and female VRK1-deficient mice are infertile, indicating that the role of VRK in fertility is evolutionarily conserved. In male mice, this infertility is associated with a severe and progressive loss of spermatogonia. In Aim 1 of this proposal, we will investigate this phenotype further and test the hypothesis that VRK1 depletion leads to a cell-autonomous defect in the proliferation and/or differentiation of spermatogonial stem cells. We will also explore the alternative hypothesis that VRK1- deficient Sertoli cells cannot provide a niche that is competent to support ongoing spermatogenesis. Female mice that are hypomorphic for VRK1 expression are also infertile; understanding how VRK1 depletion impacts female fertility will therefore be the focus of Aim 2 of this proposal. Interestingly, in contrast to the defect in males, preliminary histological analyses reveal that maturation of ovarian follicles and ovulation proceed normally in VRK-deficient mice. We therefore hypothesize that, within oocytes, VRK1 may be most critical for the resumption and completion of meiosis. Our preliminary data provides the first evidence that VRK1 plays a key role in mammalian gametogenesis. The severe infertility that results from its depletion suggests that a greater understanding of VRK1 may provide novel insights of significant relevance to human reproduction. A deeper understanding of the signaling pathways that regulate gametogenesis will provide new approaches with which to combat infertility and new targets for the development of male contraceptives. PUBLIC HEALTH RELEVANCE: Our studies of the VRK1 protein kinase and its contribution to male and female fertility have important implications for human health. Understanding how the signaling pathways mediated by VRK1 affect spermatogenesis and oogenesis will deepen our understanding of the causes of human infertility and elucidate new targets for male contraception.