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

项目概要/摘要 减数分裂过程中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物通过交叉（一种重组产物）来束缚 交换同源臂。减数分裂过程中诱导 DNA 双链断裂，从而引发 重组。只有一小部分断裂会成为交叉，其余的则修复为 非交叉，是一种类似于补丁的修复，有助于配对，但不能连接同源物。因此， 有利于非交叉的交叉失调可能导致异常的染色体分离。一个 染色体和生殖生物学的基本问题是细胞如何确保每个细胞之间的交叉 同系物。为了设计防止减数分裂中染色体错误分离的疗法，需要了解 需要减数分裂重组的分子基础。我们开发了可以 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，涉及的替代途径 溶解交叉前体的结构选择性核酸内切酶和复合物产生非交叉 代替交叉，导致交叉成熟效率低下。结果，交叉出现在较低的位置 密度导致染色体错误分离。我们发现年轻人的交叉密度同样较低 精母细胞揭示了年轻父亲更有可能生出患有唐氏病的孩子的根本原因 综合症。该提案将研究 1) 重组途径何时在减数分裂前期发挥作用 精母细胞和卵母细胞，2) 是否存在暂时调节的表达、定位或活性 执行重组途径的酶的变化，以及 3) 青少年以什么方式 精母细胞与人类卵母细胞相似。总而言之，拟议研究的成功实施将 全面了解为什么精母细胞减数分裂重组会随着年龄的增长而改变， 染色体如何因此而错误分离。

PROJECT SUMMARY/ABSTRACT 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.