BRCA1在男性精母细胞减数分裂中的作用

Male infertility is a global problem. Although assisted reproduction can help males with defective spermatogenesis at late stages, efficient therapy is still lacking for early spermatogenesis abnormalities due to meiotic arrest. Therefore, it is urgent to understand male meiosis thoroughly in order to identify breakthroughs for therapy. DNA double-strand break repair is the basis for exchange of genetic material between homologous chromosomes during meiotic prophase, which is essential for meiosis. The sex chromosomes in male have little homology. As a result, the DNA repair is delayed on male sex chromosomes when compared to autosomes. Male sex chromosomes gather at the corner of the nucleus and form a XY body, a unique structure that recruits many DNA damage response proteins. Transcription on sex chromosomes is silenced, which is commonly known as meiotic sex chromosome inactivation (MSCI). It is essential that MSCI is established in XY body and DNA breaks are repaired. Otherwise, meiosis arrests and spermatogenesis fails. BRCA1 is a key DNA damage response protein in XY body, but it remain elusive how it is recruited there and what its function is. Our previous study suggests that BRCA1 is recruited to XY body in a unique way different from that in somatic cells, and might participates in repair of DNA breaks and establishment of MSCI. In this proposal, we plan to systematically investigate the roles of BRCA1 in male meiosis. We will examine the mechanism how BRCA1 localizes in XY body, and analyze the impact of its loss on DNA repair and MSCI using knockout mouse models. Collectively, our study will strengthen our understanding of male meiosis, which will be instructive for diagnosing the causes for male infertility.

目前对于精母细胞减数分裂停滞造成的男性不育缺乏有效治疗办法。因此有必要深入研究以找到治疗的突破口。DNA双链断裂修复是减数分裂前期同源染色体重组交叉的分子基础。由于缺乏同源染色体，男性的性染色体上DNA双链断裂修复滞后。性染色体形成XY小体，里面聚集DNA损伤应答蛋白，并启动性染色体的钝化(MSCI)抑制断裂DNA的转录。DNA双链断裂修复障碍或MSCI启动失败将使减数分裂停滞并导致男性不育。BRCA1是XY小体内一个重要的DNA损伤应答蛋白，但它的调控机理和功能还不清楚。我们前期研究发现它可能以独特的方式定位于XY小体，并可能介导DNA双链断裂修复和MSCI的启动。本项目将系统研究BRCA1在男性精母细胞减数分裂过程中的作用，包括它定位于XY小体的分子机理以及它的缺失对DNA双链断裂修复和MSCI启动的影响。研究结果将深化对男性精母细胞减数分裂的认识，并对男性不育的病因诊断有着指导意义。

精母细胞减数分裂前期程序性的DNA双链断裂与同源重组修复是同源染色体交叉形成与正确分离的前提，也是确保后代遗传物质重组交换及生物多样性的基础。BRCA1是一个重要的DNA双链断裂修复蛋白，其通过促进同源重组维持体细胞的基因组稳定性。虽然精母细胞减数分裂中的DNA双链断裂修复有着许多与体细胞内的不同之处，但BRCA1很可能在其中也起重要作用。由于BRCA1敲除小鼠胚胎致死导致BRCA1敲除的精母细胞无法获得，BRCA1在精母细胞减数分裂中的作用尚不清楚。本项目利用53BP1敲除小鼠雄性可育且可以拯救BRCA1敲除小鼠胚胎致死这一特点，获得了BRCA1-53BP1双敲除小鼠，并用其研究了BRCA1在精母细胞减数分裂中的作用。BRCA1-53BP1双敲除雄性小鼠不育，精母细胞减数分裂停滞在早粗线期，XY小体不能完全形成。机制研究发现BRCA1缺失对精母细胞减数分裂前期常染色体上的双链断裂修复无影响，但关键信号传导蛋白ATR不能从性染色体轴扩散到整个性染色体上，造成粗线期性染色体的沉默出现障碍从而导致精母细胞凋亡。本项目揭示了BRCA1在精母细胞减数分裂中的重要作用，深化了我们对精母细胞减数分裂中DNA双链断裂修复与染色体沉默机制的认识。