Analysis of meiotic chromosome synapsis in yeast

描述（由申请人提供）：减数分裂是一种特殊的细胞分裂，用于有性生殖生物从二倍体细胞产生单倍体配子。染色体数目的减少是通过在单轮染色体复制之后进行两轮染色体分离来完成的。人类减数分裂染色体分离失败会导致不孕症和出生缺陷，如21三体，这是美国智力迟钝的主要原因。此外，减数分裂染色体分离需要程序性双链断裂（DSBs）的修复。有丝分裂细胞中的DSB修复对基因组完整性和预防癌症至关重要。出芽酵母是研究减数分裂的一个很好的模式系统。小鼠和酵母同源减数分裂基因突变的表型相似，表明酵母减数分裂的研究可能对人类减数分裂有启发作用。第一次减数分裂（MI）的独特之处在于姐妹染色单体分离到同一极点（称为还原分离）。适当的MI分离要求同源染色体通过非姐妹染色单体之间的交叉结合姐妹染色单体内聚而相互连接。最近的研究表明，在减数分裂期间，非姐妹染色单体之间的交叉部分是由姐妹染色单体之间DSB修复的主动抑制所促进的。这种抑制是由Mek1介导的，一种减数分裂特异性丝氨酸/苏氨酸激酶。了解Mek1抑制姐妹染色单体减数分裂修复的分子机制需要鉴定被该激酶磷酸化的底物。我们将使用新的生化和遗传策略来鉴定Mek1靶点，并表征这些蛋白的磷酸化缺陷版本，阐明这一过程。此外，我们将测试一个特定的模型如何内聚蛋白可能参与抑制减数分裂姐妹DSB修复。减数分裂dsb的修复利用两种重组酶进行链入侵：减数分裂特异性重组酶Dmc1和营养细胞中的主要重组酶Rad51。在减数分裂重组过程中，这两条链交换蛋白的作用如何协调尚不清楚。最近的生化实验表明，通过Mek1磷酸化辅助蛋白Rad54介导的调节Rad51活性的新机制。一个目标是确定这种机制是否在减数分裂细胞中起作用。

DESCRIPTION (provided by applicant): Meiosis is a specialized cell division used by sexually reproducing organisms to produce haploid gametes from diploid cells. This reduction in chromosome number is accomplished by having two rounds of chromosome segregation follow a single round of chromosome duplication. Failures in meiotic chromosome segregation in humans lead to infertility and birth defects such as Trisomy 21, the leading cause of mental retardation in the United States. In addition, meiotic chromosome segregation requires the repair of programmed double strand breaks (DSBs). DSB repair in mitotically dividing cells is critical for genome integrity and the prevention of cancer. Budding yeast is an excellent model system for studying meiosis. Mice and yeast mutated for orthologous meiotic genes are phenotypically similar, demonstrating that studies of meiosis in yeast are likely to be illuminating with regard to meiosis in humans. The first meiotic division (MI) is unique in that sister chromatids segregate to the same pole (called reductional segregation). Proper MI segregation requires that homologous chromosomes be connected to each other by crossovers between non-sister chromatids in combination with sister chromatid cohesion. Recent work has shown that crossing over between non-sister chromatids during meiosis is promoted in part by active suppression of DSB repair between sister chromatids. This suppression is mediated by Mek1, a meiosis-specific serine/threonine kinase. Understanding the molecular mechanism by which Mek1 inhibits meiotic sister chromatid repair requires identification of the substrates phosphorylated by this kinase. We will use novel biochemical and genetic strategies to identify Mek1 targets and characterize phosphorylation- defective versions of these proteins elucidate this process. In addition we will test a specific model for how cohesins may be involved in suppressing meiotic intersister DSB repair. Repair of meiotic DSBs utilizes two recombinases for strand invasion: Dmc1, which is meiosis-specific and Rad51, the major recombinase in vegetative cells. How the action of these two strand exchange proteins is coordinated during meiotic recombination not yet understood. Recent biochemical experiments have suggested a novel mechanism for regulating Rad51 activity mediated by Mek1 phosphorylation of an accessory protein, Rad54. One goal is to determine whether this mechanism functions in meiotic cells. PUBLIC HEALTH RELEVANCE: Failures in the evolutionarily conserved cell division of meiosis result in infertility and birth defects such as Down syndrome. Proper meiotic chromosome segregation requires double strand break repair-a process also required to maintain genome integrity and prevent cancer. This grant is focused on understanding the molecular basis for proper chromosome behavior during meiosis-knowledge that may ultimately lead to the diagnosis and/or prevention of certain types of infertility, birth defects and even cancer.