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

项目概要/摘要 减数分裂期间染色体分离错误是导致不育、流产和出生的主要原因 缺陷忠实的分离需要同源物被杂交（一种重组产物）所束缚 交换同源武器。DNA双链断裂在减数分裂过程中被诱导， 重组只有一小部分断裂成为交叉，其余的修复为 noncrossovers，这是补丁样修复，促进配对，但不能连接同源。因此，在本发明中， 有利于非交换的交换的失调可导致异常的染色体分离。一 染色体和生殖生物学中的一个基本问题是细胞如何确保彼此之间的交叉 同源物为了设计治疗方法以防止减数分裂中的染色体错误分离，了解 需要减数分裂重组的分子基础。我们已经开发出一种检测方法， 在小鼠精母细胞中以高分辨率区分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， 结构选择性核酸内切酶和溶解交叉前体的复合物产生非交叉 代替交叉，导致交叉成熟效率低下。因此，交叉发现在较低的 密度导致染色体错误分离。我们发现年轻人的交叉密度也同样较低 精母细胞提示了为什么年轻父亲更有可能生下唐氏症孩子的根本原因 综合征该建议将研究1）重组途径何时在减数分裂前期起作用， 精母细胞和卵母细胞，2）是否存在时间调节的表达、定位或活性 执行重组途径的酶的变化，以及3）青少年人类以何种方式 像人类卵母细胞一样的精母细胞。总之，成功执行拟议的研究将 提供了一个全面的理解，为什么减数分裂重组是随着年龄的变化，精母细胞， 染色体是如何错误分离的

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.