How age-dependent alterations in meiotic recombination cause chromosome mis-segregation in sperm

项目总结 减数分裂过程中的染色体分离错误是导致不孕、流产和出生的主要原因。 缺陷。忠实的分离需要同源基因被交叉连接，这是重组产物 交换同种手臂的人。DNA双链断裂在减数分裂过程中被诱导 重组。只有一小部分中断成为交叉，其余的修复为 非交叉，这是促进配对的补丁状修复，但不能连接同源基因。因此， 有利于非交叉的交叉调节失调会导致异常的染色体分离。一个 染色体和生殖生物学中的基本问题是细胞如何确保它们之间的交叉 同源同源。为了设计治疗方法来防止减数分裂中的染色体错误分离，理解 减数分裂重组的分子基础是必需的。我们已经开发出一种可以 以高分辨率区分小鼠精母细胞中主要重组途径的贡献。 利用这项技术，我们发现在幼年小鼠精母细胞中，涉及到 结构选择性内切酶和溶解交叉前体的复合体产生非交叉 而不是交叉，导致交叉成熟效率低下。因此，在较低的位置发现了交叉 密度导致染色体错误分离。我们在年轻人中发现了同样较低的交叉密度 精母细胞是年轻父亲更有可能生下唐氏症孩子的根本原因 综合症。这项建议将调查1)重组途径在减数分裂前期的作用 精母细胞和卵母细胞，2)是否有时间调节的表达、定位或活性 执行重组途径的酶的变化，以及3)青少年人类是以什么方式 精母细胞与人类卵母细胞相似。综上所述，拟议研究的成功执行将 全面了解为什么精母细胞减数分裂重组随年龄而改变 因此染色体是如何错误分离的。

PROJECT SUMMARY Errors of chromosome segregation during meiosis are a leading cause of infertility, miscarriage, and birth defects. Faithful segregation requires homologs to become tethered by crossovers, a recombination product that exchanges homolog arms. DNA double-strand breaks are induced during meiosis to provoke recombination. Only a small subset of breaks become crossovers with the remaining repaired as noncrossovers, which are patch-like repairs that facilitate pairing, but cannot connect homologs. Thus, dysregulation of crossovers in favor of noncrossovers can lead to aberrant chromosome segregation. A fundamental question in chromosome and reproductive biology is how cells ensure crossovers between each homolog. In order to design therapies to prevent chromosome mis-segregation in meiosis, an understanding of the molecular underpinnings of meiotic recombination is required. We have developed assays that can distinguish contributions from the major recombination pathways at high resolution in mouse spermatocytes. Using this technology, we found that in juvenile mouse spermatocytes, alternative pathways involving structure-selective endonucleases and complexes that dissolve crossover precursors generate noncrossovers in lieu of crossovers, causing crossover maturation inefficiency. As a result, crossovers are found at lower density leading to chromosome mis-segregation. We found similarly lower crossover density in young human spermatocytes suggesting a root cause for why younger fathers are more likely to have children with Down syndrome. This proposal will investigate 1) when recombination pathways act during meiotic prophase in spermatocytes and oocytes, 2) whether there are temporally regulated expression, localization, or activity changes of enzymes that execute recombination pathways, and 3) in what way are juvenile human spermatocytes like human oocytes. Taken together, the successful execution of the proposed research will provide a comprehensive understanding of why meiotic recombination is altered with age in spermatocytes and how chromosomes mis-segregate as a consequence.