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。配子发生中的错误会造成从不育到将染色体异常传递给下一代的各种后果。然而，对精子发生和卵子发生都至关重要的信号级联仍然知之甚少。蛋白激酶和磷酸酶介导的蛋白质动态磷酸化是真核细胞确保有丝分裂和减数分裂按正确顺序进行的主要机制之一，只有在细胞内和细胞外条件有利的情况下才能进行。这个项目的重点是VRK1蛋白激酶，它参与了从无脊椎动物到哺乳动物的各种生物的细胞增殖调控。果蝇和线虫中的VRK1同源基因是必需的蛋白质，其破坏会导致与减数分裂缺陷相关的不孕。最近，我们已经培育出基因靶向的小鼠，它们对VRK1的表达具有亚形性。在纯合子状态下，雄性和雌性VRK1缺陷小鼠都是不育的，表明VRK在生育中的作用在进化上是保守的。在雄性小鼠中，这种不育与精原细胞的严重和进行性丧失有关。在这项建议的目标1中，我们将进一步研究这种表型，并测试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。我们还将探索另一种假设，即VRK1缺陷的Sertoli细胞不能提供有能力支持正在进行的精子发生的利基。VRK1表达缺失的雌性小鼠也是不育的；因此，了解VRK1缺失如何影响雌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缺陷小鼠的卵巢卵泡成熟和排卵正常进行。因此，我们推测，在卵母细胞中，VRK1可能是恢复和完成减数分裂最关键的。我们的初步数据首次证明VRK1在哺乳动物配子发生中发挥关键作用。由于VRK1的缺失而导致的严重不孕症表明，对VRK1的更多了解可能会提供与人类生殖密切相关的新见解。深入了解调控配子发生的信号通路将为抗击不育提供新的途径，并为男性避孕药的开发提供新的靶点。 公共卫生相关性：我们对VRK1蛋白激酶及其对男性和女性生育能力的贡献的研究对人类健康具有重要影响。了解VRK1介导的信号通路如何影响精子发生和卵子发生，将加深我们对人类不育原因的理解，并阐明男性避孕的新靶点。

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.