The Synapsis Checkpoint in C. elegans Meiosis

描述（由申请人提供）：减数分裂从二倍体细胞产生单倍体配子，如精子和卵子，这样二倍体基因组在受精后恢复。减数分裂过程中染色体的正确分离取决于减数分裂前期的事件，如同源染色体的突触和交叉重组。染色体分离错误通常对受精卵是致命的，但也可能导致癌症易感性或发育障碍。我们已经确定了一个减数分裂检查点，它对同源突触中的缺陷作出反应，独立于DNA损伤/重组检查点，并激活细胞凋亡以避免非整倍体配子的产生。并不是所有的非突触序列都有能力触发这个检查点；相反，这条通路是由未突触配对中心（PCs）特异性激活的，PCs是线虫中促进突触的染色体位点。此外，检查点需要秀丽隐杆线虫的同源基因PCH2（一种出芽酵母减数分裂检查点基因），这表明检测突触失败的分子机制是保守的。结合遗传学、生物化学和细胞学方法，我们计划进一步研究突触检查点。我们将通过研究染色质修饰酶在这些顺式作用位点的作用来解决染色质状态如何促进pc激活突触检查点的能力。我们将通过在野生型和突变背景下定位PCH-2，鉴定与PCH-2相互作用的蛋白质，并研究PCH-2是否特异性修饰一类重要的SC成分，来确定在正常减数分裂过程中如何监测突触复合体（SC）的组装。此外，我们将通过进行RNA干扰筛选来识别检查点的其他成分，该筛选将侧重于满足特定表达和表型谱标准的候选基因。这个筛选已经确定了一个假定的转录因子作为检查点组件，我们将测试该因子是否直接调节核心凋亡机制以响应检查点激活。这些互补的方法将使我们能够从分子和机制上了解同源突触在减数分裂期间是如何被监测的，以及未突触或不适当突触的同源物是如何产生检查点信号的，该信号最终被翻译成凋亡反应，以避免产生非整倍体配子。

DESCRIPTION (provided by applicant): Meiosis generates haploid gametes, such as sperm and eggs, from a diploid cell such that a diploid genome is restored upon fertilization. The proper segregation of chromosomes during the meiotic divisions depends on events in meiotic prophase, such as synapsis of homologous chromosomes and crossover recombination. Errors in chromosome segregation are usually fatal to the fertilized zygote but can also result in cancer predisposition or developmental disorders. We have identified a meiotic checkpoint that responds to defects in homolog synapsis, independent of a DNA damage/recombination checkpoint, and activates apoptosis to avoid the generation of aneuploid gametes. Not all unsynapsed sequences have the capacity to trigger this checkpoint; rather, this pathway is specifically activated by unsynapsed Pairing Centers (PCs), chromosome sites that promote synapsis in C. elegans. Furthermore, the checkpoint requires the C. elegans homolog of PCH2, a budding yeast meiotic checkpoint gene, suggesting that the molecular mechanism that detects synaptic failure is conserved. Using a combination of genetic, biochemical and cytological approaches, we plan to further investigate the synapsis checkpoint. We will address how chromatin state(s) contributes to the ability of PCs to activate the synapsis checkpoint by studying the role of chromatin-modifying enzymes at these cis-acting sites. We will determine how the assembly of the synaptonemal complex (SC) is monitored during a normal meiosis by localizing PCH-2 in wildtype and mutant backgrounds, identifying proteins that interact with PCH-2 and investigating whether PCH-2 specifically modifies an important class of SC components. Furthermore, we will identify additional components of the checkpoint by undertaking an RNA interference screen that will focus on candidate genes that fulfill specific expression and phenotypic profile criteria. This screen has identified a putative transcription factor as a checkpoint component and we will test whether this factor directly regulates the core apoptotic machinery in response to checkpoint activation. These complementary approaches will enable us to gain a molecular and mechanistic understanding of how homolog synapsis is monitored during meiosis and how an unsynapsed or inappropriately synapsed homolog generates a checkpoint signal that is ultimately translated into an apoptotic response to avoid the production of aneuploid gametes.