Control of Oocyte Maturation in C. elegans

卵母细胞成熟和排卵是有性繁殖所必需的基本生物学过程。在卵母细胞成熟过程中，由于CDC2/CyclinB蛋白激酶成熟促进因子(MPF)的激活，卵母细胞从前期进入减数分裂M期。在许多物种中，激素触发信号转导级联，促进卵母细胞成熟和排卵，但一个主要悬而未决的问题是涉及的详细分子机制。如果不能正确地调控这一关键的减数分裂细胞周期转变，可能会导致不孕、流产或唐氏综合症。促进哺乳动物卵母细胞成熟的信号尚不清楚，也没有在任何生物体中鉴定出成熟诱导物质的受体。为了补充脊椎动物的研究，我们使用线虫秀丽线虫作为模型，研究通过细胞间信号控制卵母细胞成熟和排卵。我们的研究表明，精子细胞骨架蛋白是主要的精子蛋白(MSP)，是促进线虫卵母细胞成熟和性腺鞘细胞收缩的两部分信号。我们已经证明MSP与卵母细胞结合并激活保守的MAPK级联反应。我们的结果表明，MSP与卵母细胞的结合需要VAB-1 Eph受体酪氨酸激酶的功能和高度保守的Hem家族蛋白SIM-2。MSP信号导致多种细胞反应，包括M期进入、皮质细胞骨架重排、减数分裂纺锤体组装和性腺鞘细胞收缩。这些反应是排卵、受精和完成减数分裂所必需的。为了阐明细胞外信号促进卵母细胞成熟和排卵的机制，我们采取了多管齐下的方法，研究了MSP信号、候选受体和潜在的下游信号机制。这一建议旨在：1)确定向卵母细胞和鞘细胞传递信号的保守的MSP结构域；2)确定MSP是否与卵母细胞上的VAB-1(Eph)受体和SIM-2 HEM-2相关蛋白结合以促进成熟；以及3)对MSP信号通路进行遗传分析。

Oocyte maturation and ovulation are essential biological processes required for sexual reproduction. During oocyte maturation, oocytes enter meiotic M phase from prophase due to activation of the Cdc2/CyclinB protein kinase, maturation- promoting factor (MPF). In many species, hormones trigger signal transduction cascades that promote oocyte maturation and ovulation, but a major outstanding question concerns the detailed molecular mechanisms involved. A failure to correctly regulate this critical meiotic cell cycle transition can result in infertility, miscarriage, or Down's syndrome. The signal that promotes oocyte maturation in mammals is not known, and a receptor for a maturation-inducing substance has not been identified in any organism. To complement studies in vertebrates, we are using the nematode Caenorhaditis elegans as a model for studying the control of oocyte maturation and ovulation by intercellular signaling. Our studies demonstrate that a sperm cytoskeletal protein, the major sperm protein (MSP), is a bipartite signal that promotes oocyte maturation and gonadal sheath cell contraction in C. elegans. We have shown that MSP binds to oocytes and activates the conserved MAP kinase cascade. Our results indicate that MSP binding to oocytes requires the function of the VAB-1 Eph receptor tyrosine kinase and a highly conserved Hem family protein, SIM-2. MSP signaling results in diverse cellular responses including M-phase entry, cortical cytoskeletal rearrangement, meiotic spindle assembly, and gonadal sheath cell contraction. These responses are required for ovulation, fertilization, and completion of the meiotic divisions. To elucidate the mechanisms by which extracellular signals promote oocyte maturation and ovulation, we are taking a multipronged approach by studying the MSP signal, candidate receptors, and potential downstream signaling mechanisms. This proposal aims to: 1) define the conserved MSP domains that signal to oocytes and sheath cells; 2) determine whether MSP binds to the VAB-1 (Eph) receptor and the SIM-2 HEM-2-related protein on oocytes to promote maturation; and 3) conduct a genetic analysis of the MSP signaling pathway.