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

细胞周期在减数分裂I前期停止是几乎所有多细胞动物的卵子发生的保守特征。从海星到人类，生物体中的卵母细胞在排卵前保持这种停滞状态，其机制尚不清楚。本文介绍了一种分离和表征减数分裂前期细胞周期阻滞分子调控因子的遗传策略。最近在秀丽隐杆线虫中进行的遗传筛选已经确定了突变体，其中卵母细胞在MI前期的代谢过程中无法维持。在oar-1和oar-2突变体（oar=卵母细胞减数分裂前期阻滞缺陷）中，卵母细胞离开阻滞并进行线粒体复制。已经开发出了将Oar突变体与其他产生内膜卵母细胞的突变体区分开来的策略。重要的是，已经获得了与Oar表型相反的突变体；olk-1 （olk=卵母细胞阻滞锁）卵母细胞在通常失去阻滞的条件下保持阻滞。由oar和olk基因决定的维持减数分裂停滞的途径很可能涉及从体细胞到卵母细胞的细胞通信。对oar-1的分析与细胞信号维持减数分裂停滞的结论是一致的；克隆表明，oar-1编码一种在其他系统中已知的Sec61p γ蛋白，促进蛋白转运到内质网，镶嵌分析表明，oar-1活性在种系中特别需要，以防止卵母细胞停滞的丧失。因此，Oar-1可能将跨膜受体转移到卵母细胞表面以接收阻滞信号。本研究将对秀丽隐杆线虫卵母细胞减数分裂前期阻滞的维持途径进行更广泛的遗传和分子研究。schel博士将：1)使用基因筛选鉴定卵母细胞减数分裂前期阻滞所需的基因，2)对收集的突变体进行遗传和表型表征，以及3)对阻滞“loc-1”突变体olk-1进行遗传表征。＊＊＊

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. ***