BCAS2 regulates oocyte meiosis by participating in alternative mRNA splicing

Oocyte meiosis is an important factor affecting female reproduction. Breast cancer amplified sequence 2 (BCAS2) is a component of the spliceosome. Previous reports have shown that BCAS2 is critical in male germ cell meiosis, oocyte development, and early embryo genome integrity. However, the role of BCAS2 in oocyte meiosis has not been reported. We used Stra8-GFP-Cre mice to knock out BCAS2 during the pachytene phase of oocytes. The results of fertility tests showed that the cko mice were infertile. Morphological analysis showed that the number of primary follicles of 2M ovary was significantly reduced and follicle development was blocked. Further analysis showed that the number of primordial follicles decreased and follicle development slowed from 7dpp ovaries. Sequencing revealed that DNA damage in oocytes could not be repaired from 5dpp. There was an abnormality in meiosis, some oocytes could not reach the diplotene stage of meiosis, and more oocytes could not develop to the dictyate stage. AS analysis reveals that abnormal variable splicing of Dazl and Diaph2 Oogens-related genes in cKO mice, with involvement of the PRP19/CDC5l complex. BCAS2 was knocked out in ovarian oocytes, and 1dpp ovaries were taken to analyze and compare the gene expression profiles of RNA-Seq data between WT and knockout groups.卵母细胞减数分裂（Oocyte meiosis）是影响雌性生殖的关键因素。乳腺癌扩增序列2（Breast cancer amplified sequence 2，BCAS2）是剪接体的组成成分。既往研究表明，BCAS2在雄性生殖细胞减数分裂、卵母细胞发育及早期胚胎基因组完整性维持中发挥至关重要的作用。然而，BCAS2在卵母细胞减数分裂中的功能尚未见报道。本研究利用Stra8-GFP-Cre小鼠，在卵母细胞粗线期条件性敲除BCAS2。生育力检测结果显示，条件性敲除（cko）小鼠不育。形态学分析表明，2月龄（2M）卵巢的初级卵泡数量显著减少，卵泡发育受阻。进一步分析显示，自出生后7天（7dpp）的卵巢开始，原始卵泡数量下降且卵泡发育速率减缓。测序结果显示，自出生后5天（5dpp）起，卵母细胞的DNA损伤无法被有效修复。减数分裂过程出现异常：部分卵母细胞无法抵达减数分裂双线期，且更多卵母细胞无法发育至网状期（dictyate stage）。可变剪接（Alternative Splicing，AS）分析显示，条件性敲除小鼠中，卵母细胞相关基因Dazl与Diaph2存在异常可变剪接，且该过程涉及PRP19/CDC5l复合物。本研究在卵巢卵母细胞中敲除BCAS2，并取出生后1天（1dpp）的卵巢，分析对比野生型（Wild Type，WT）与敲除组的RNA测序（RNA-Seq）基因表达谱数据。