睾丸优势表达蛋白MRNIP在精母细胞减数分裂过程中的功能研究

Meiosis is an important biological event during spermatogenesis. Abnormal meiosis can lead to spermatogenetic arrest and male infertility, while the precise mechanism is not well known. In our previous work, we successfully constructed proteome profiles for human and mouse testis, and among them, we focused on a testicular predominantly expressed protein, MRNIP. We found that MRNIP was predominantly expressed in mouse testis and located in spermatocyte. By gene knock-out model, we found that deficiency of MRNIP caused male infertility, but not in female. Moreover, by morphological observation, we found that MRNIP-deficient mouse was azoospermic due to meiosis arrest and unrepaired DSB. In this study, we will explore the influence of MRNIP deletion in the processes of spermatocyte meiosis and elucidate the function of MRNIP during meiosis in-depth. The study will be helpful to understand the mechanism of meiosis and provide a scientific basis for clinical diagnosis and treatment of male infertility.

减数分裂是精子发生过程中一项重要的生物学过程。减数分裂的异常会导致精子发生障碍，诱发男性不育，然而其中确切的调节机制尚不明确。申请人前期在本课题组构建的人和小鼠睾丸蛋白质谱系中关注到一个睾丸优势表达蛋白--MRNIP。前期研究表明，MRNIP在小鼠睾丸中呈现优势表达，并且定位于精母细胞。应用基因敲除模型，我们发现缺失MRNIP的小鼠表现为雄性不育，雌性可育。进一步，形态学观察发现缺失MRNIP的小鼠附睾内无成熟精子，精子发生阻滞在精母细胞阶段，DSB修复障碍。基此，本研究将在上述预实验基础上通过MRNIP敲除小鼠模型揭示MRNIP缺失影响精母细胞减数分裂的具体环节，深入阐明MRNIP在减数分裂过程中的功能。本研究将帮助理解减数分裂的调控机制，并为男性不育的诊疗提供了理论依据。

DNA 双链断裂（DSB）是减数分裂染色体同源重组的开始，由SPO11 介导形成受损的DNA。随即非姐妹染色单体开始进行等位基因互换，最后由DMC1和RAD51 开始介导断裂DNA 的修复。MRN 复合物（MRE11-RAD50-NBS1Complex）在DSB 形成和修复过程中也发挥了重要作用，该复合物在各物种间高度保守。MRN 复合物同时具有单链/双链核酸内切酶的活性和 3'→5' 核酸外切酶的活性，DSB 发生后，MRN 复合物作为核酸内切酶使SPO11 结合链上产生缺口，该缺口可为MRE11 提供3'→5'外切位点，从而释放SPO11，并生成3'单链DNA。然而，MRN 复合物是如何识别DNA 断裂位点，其参与的DSB 应答是受何种因子调节，这些问题仍有待研究。本研究中，我们报道了MRN 相互作用蛋白MRNIP，其在小鼠睾丸优势表达，我们构建了Mrnip 基因3’端突变模型小鼠，表型分析提示Mrnip 突变会导致减数分裂过程中异常的联会、HR 受损和雄性生育能力降低。综上所述，MRNIP是一种新的HR 因子，可能通过调节MRN 复合体促进减数分裂进展。