Sister Chromatid and Homolog Interactions in Meiosis

减数分裂中姐妹染色单体和同源物的相互作用

• 批准号: 0078138
• 负责人: Dean Dawson
• 金额: $ 37.5万
• 依托单位: Tufts University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-02-15 至 2004-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0078138&HistoricalAwards=false
• 关键词: Sister; Chromatid; Homolog; Interactions; Meiosis

Meiosis is the process used to generate haploid cells from diploid precursors. It is characterized by a single round of DNA replication followed by two rounds of chromosome segregation. In the first meiotic division, chromosomes pair with, then migrate away from, their homologues. A critical aspect of meiosis I is crossing-over, or exchange, between homologous chromosomes. This form of recombination may be part of a recognition process that allows chromosomes to align with their proper partner. This alignment culminates in formation of a proteinaceous structure, called the synaptonemal complex (SC), along the homologues. Crossovers also clearly play a role in providing a physical link between paired homologues, which allows the homologues to attach properly to spindle fibers that will mediate their segregation. Crossovers alone do not provide a stable linkage between homologues. Following DNA replication, each homologue is composed of two identical sister chromatids. The cohesion of these chromatids locks crossovers in place allowing the crossovers to act as a stable link between the homologues until anaphase I, at which time release of the sister arm cohesion allows the homologues to disjoin. Accordingly, mutants unable to completemeiotic recombination usually exhibit low fertility or sterility. However some organisms,including yeast, have mechanisms that insure the segregation of single pairs of chromosomesthat have failed to experience a crossover in an otherwise normal meiosis. This project addresses two questions. First, what types of interactions between chromosomes that have failed to experience an exchange enable them to segregate away from one another? Second, how do sister chromatids remain associated in meiosis I, thus helping crossovers to link homologues and ensuring that both sisters will stay joined until meiosis II? Experiments will test the model that interactions between the centromeres of test chromosomes mediate their disjunction at meiosis I. Cytological techniques will be used to test centromeric interactions occur between a pair of homeologues, specifically tagged with GFP. The second objective, to explore the behavior of sister chromatids in meiosis, will be addressed experimentally in three ways. First, experiments will be performed to determine whether the loss of meiotic sister cohesion observed in spo11 mutants (that do not initiate meiotic recombination) is due to a requirement for the Spo11 protein or alternatively a requirement for recombination initiation in meiotic sister chromatid cohesion. Second, the meiotic behavior of GFP-tagged sister chromatids will be observed cytologically in previously characterized meiotic mutants to explore the relationships of sister chromatid association, recombination and SC formation. Finally, the GFP tagged chromosomes will be monitored in a genetic screen to identify new genes involved in mediating proper sister chromatid behavior in meiosis. The experiments conducted in this work will help to elucidate the mechanism of chromosome segregation.

减数分裂是从二倍体前体产生单倍体细胞的过程。其特点是单轮 DNA 复制，然后是两轮染色体分离。在第一次减数分裂中，染色体与同源染色体配对，然后迁移离开。减数分裂 I 的一个关键方面是同源染色体之间的交叉或交换。这种形式的重组可能是识别过程的一部分，该过程允许染色体与其正确的伴侣对齐。这种排列最终沿着同源物形成一种蛋白质结构，称为联会复合体（SC）。交叉在成对同源物之间提供物理连接方面也显然发挥着作用，这使得同源物能够正确地附着到纺锤体纤维上，从而介导它们的分离。单独的交叉不能提供同源物之间的稳定连接。 DNA 复制后，每个同源物由两个相同的姐妹染色单体组成。这些染色单体的内聚力将交叉锁定在适当的位置，允许交叉充当同源物之间的稳定连接，直到后期 I，此时姐妹臂内聚力的释放使得同源物分离。因此，无法完成减数分裂重组的突变体通常表现出低育性或不育性。然而，包括酵母在内的一些生物体具有确保单对染色体分离的机制，这些染色体在正常的减数分裂中未能经历交叉。 该项目解决了两个问题。首先，未能经历交换的染色体之间哪些类型的相互作用使它们能够彼此分离？其次，姐妹染色单体如何在减数分裂 I 中保持关联，从而帮助交叉连接同源物并确保姐妹染色单体在减数分裂 II 之前保持连接？实验将测试模型，即测试染色体着丝粒之间的相互作用介导减数分裂 I 时的分离。细胞学技术将用于测试一对同源物之间发生的着丝粒相互作用，特别用 GFP 标记。第二个目标是探索减数分裂中姐妹染色单体的行为，将通过三种方式通过实验来解决。首先，将进行实验以确定在 spo11 突变体（不启动减数分裂重组）中观察到的减数分裂姐妹凝聚力的丧失是否是由于对 Spo11 蛋白的需要，或者是由于减数分裂姐妹染色单体凝聚力中重组起始的需要。其次，将在先前表征的减数分裂突变体中通过细胞学观察 GFP 标记的姐妹染色单体的减数分裂行为，以探索姐妹染色单体关联、重组和 SC 形成的关系。最后，将在遗传筛选中监测 GFP 标记的染色体，以识别参与介导减数分裂中正确姐妹染色单体行为的新基因。这项工作中进行的实验将有助于阐明染色体分离的机制。