The Synapsis Checkpoint in C. elegans Meiosis

描述(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，这样在受精后恢复二倍体基因组。减数分裂过程中染色体的正确分离取决于减数分裂前期发生的事件，如同源染色体的联会和交叉重组。染色体分离的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做出反应，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，这条途径是由非突触配对中心(PC)特异性激活的，PC是线虫中促进突触的染色体位点。此外，检查点需要线虫与PCH2的同源物，PCH2是一种萌发的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，阐述染色质状态(S)如何有助于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中定位PCH-2，识别与PCH-2相互作用的蛋白质，并研究PCH-2是否特异性地修改一类重要的SC组件，来确定在正常减数分裂过程中如何监控联会复合体(SC)的组装。此外，我们将通过进行RNA干扰筛查来确定检查点的其他组件，该筛查将专注于满足特定表达和表型特征标准的候选基因。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的凋亡机制，以响应检查点的激活。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过程中是如何被监控的，以及未突触或不适当突触的同系物是如何产生检查点信号的，该信号最终被转化为凋亡反应，以避免产生非整倍体配子。 与公共卫生相关：减数分裂产生配子，如卵子和精子。检查点监测减数分裂事件，以确保配子具有正确的染色体数量。如果配子的染色体数目不正确，那么受精产生的胚胎通常是不能存活的。有时，胚胎会继承一条额外的染色体，这种染色体不会致命，但会导致出生缺陷。对减数分裂检查点的研究可以揭示确保基因组完整性的一般机制。

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. PUBLIC HEALTH RELEVANCE: Meiosis produces gametes, such as eggs and sperm. Checkpoints monitor meiotic events to ensure that gametes have the correct number of chromosomes. If a gamete has an incorrect number of chromosomes, the embryo that results from fertilization is often inviable. Occasionally, an embryo inherits an extra chromosome that is not lethal but can cause birth defects. An investigation of meiotic checkpoints can reveal general mechanisms that ensure genomic integrity.