Genetic and Molecular Analysis of Oocyte Meiotic Prophase Arrest in C. elegans

9506220减数分裂I前期细胞周期的程序性停滞基本上是所有多细胞动物卵子发生的保守特征。从海星到人类，生物体中的卵母细胞一直保持这种停滞状态，直到排卵，其机制尚不清楚。这项建议介绍了一种分离和表征减数分裂前期细胞周期停滞的分子调控因子的遗传策略。最近在线虫秀丽线虫中进行的遗传筛查发现，在MI前期的终变期未能维持卵母细胞停滞的突变体。在OAR-1和OAR-2突变体(OAR=卵母细胞减数分裂前期停滞缺陷)中，卵母细胞离开停滞并在内丝分裂中复制它们的DNA。已经开发出了区分Oar突变体和其他产生内有丝分裂卵母细胞的突变体的策略。重要的是，已经获得了一个与OAR相反的表型突变；olk-1(olk=卵母细胞停滞锁定)卵母细胞在通常失去停滞的情况下保持停滞。在维持减数分裂停滞的过程中，很可能涉及到从胞体到卵母细胞的细胞通讯。对OAR-1的分析与需要细胞信号来维持减数分裂停滞的结论是一致的；克隆显示OAL-1编码一种在其他系统中已知的Sec61p伽马蛋白，以促进蛋白质转位到内质网，马赛克分析表明，OAR-1活性是在胚系中特定需要的，以防止卵母细胞停滞的丢失。因此，OAR-1可以将跨膜受体转移到卵母细胞表面，以接收停滞信号。这一建议将启动对线虫卵母细胞减数分裂前期停滞维持途径的更广泛的遗传学和分子研究。Schedl博士将：1)使用遗传筛查确定卵母细胞减数分裂前期停滞所必需的基因；2)从遗传和表型上描述OAR集合中的突变体；3)对停滞的“loc-1”突变体olk-1进行基因表征。***

9506220 Schedl Arrest of the cell cycle in prophase of meiosis I is a conserved feature of oogenesis in essentially all multicellular animals. Oocytes in organisms from starfish to humans maintain this arrested state until ovulation by a mechanisms that is not well understood. This proposal introduces a genetic strategy for isolating and characterizing molecular regulators of meiotic prophase cell cycle arrest. Recent genetic screens performed in the nematode Caenorhabditis elegans have identified mutants where oocyte arrest in diakinesis of MI prophase fails to be maintained. In oar-1 and oar-2 mutants (oar= oocyte meiotic prophase arrest defective), oocytes leave arrest and endomitotically replicate their DNA. Strategies have been developed to distinguish Oar mutants from other mutants producing endomitotic oocytes. Importantly, a mutant has been obtained with a phenotype opposite to Oar; olk-1 (olk= oocyte arrest lock) oocytes maintain arrest under conditions when arrest is usually lost. It is likely that the pathway for maintenance of meiotic arrest defined by the oar and olk genes involves cell cell communication from the soma to the oocyte. Analysis of oar-1 is consistent with the conclusion that a cell cell signal is needed to maintain meiotic arrest; cloning reveals that oal-1 encodes a Sec61p gamma protein known in other systems to facilitate protein translocation into the ER, and mosaic analysis shows oar-1 activity is needed specifically in the germline to prevent loss of oocyte arrest. Oar-1 may therefore act to translocate a transmembrane receptor to the oocyte surface for reception of the arrest signal. This proposal will initiate a more extensive genetic and molecular investigation of the pathway maintaining oocyte meiotic prophase arrest in C. elegans. Dr. Schedl will:1) Identify genes necessary for oocyte meiotic prophase arrest using a genetic screen, 2) Genetically and phenotypically characterize mutants in the oar collection, and 3) Genet ically characterize the arrest "loc-1" mutant, olk-1. ***