PABPN1 promotes meiotic maturation of oocytes by interacting with PAPOLA

Poly(A) polymerase alpha (PAPalpha ), as the specific mRNA polyadenylation enzyme in the cytoplasm of mammalian oocytes, is essential for oocytes to exclude the first polar body. However, PAPalpha knockout did not affect germinal vesicles breakdown (GVBD) of oocytes, and the mechanism needs to be further explored. In this study, we identified that PAPalpha work together with poly(A)-bound RNA binding protein PABPN1 to promote the rupture of germinal vesicles in mammalian oocytes. The protein level of Pabpn1 gradually increases with the meiotic maturation of oocytes. The oocytes specifically knocked out Pabpn1 at the primary follicle stage could develop into the fully grown (FGO) stage, but hardly could enter into the meiotic process. The activated form of CDK1 was injected into Pabpn1-null oocytes, the oocytes could enter into meiotic process. The translational activity of Pabpn1-null oocytes was significantly lower than that of wild-type oocytes during meiosis. In particular, the expression level of protein (BTG4 and CDC25), which were essential for the meiotic maturation of oocytes, were significantly decreased. Therefore, during the oocyte meiosis process, PABPN1 and PAPalpha jointly promote the oocyte to enter the meiosis process. Examination of WT and Pabpn1-null transcriptome in oocytes聚腺苷酸聚合酶α（Poly(A) polymerase alpha, PAPα）作为哺乳动物卵母细胞细胞质中特异性的mRNA多聚腺苷酸化酶，对卵母细胞排出第一极体至关重要。然而，PAPα基因敲除并不会影响卵母细胞的生发泡破裂（germinal vesicles breakdown, GVBD），其具体机制仍有待进一步探究。本研究发现，PAPα可与聚腺苷酸结合RNA结合蛋白PABPN1（poly(A)-bound RNA binding protein PABPN1）协同作用，促进哺乳动物卵母细胞的生发泡破裂。Pabpn1的蛋白表达水平随卵母细胞减数分裂成熟进程逐渐升高。在初级卵泡阶段特异性敲除Pabpn1的卵母细胞可发育至完全生长卵母细胞（FGO）阶段，但几乎无法进入减数分裂过程。将活化形式的细胞周期蛋白依赖性激酶1（CDK1）注射至Pabpn1基因敲除的卵母细胞后，这些卵母细胞即可进入减数分裂过程。在减数分裂期间，Pabpn1基因敲除卵母细胞的翻译活性显著低于野生型卵母细胞。尤为关键的是，对卵母细胞减数分裂成熟至关重要的BTG4和CDC25蛋白的表达水平显著下调。因此，在卵母细胞减数分裂过程中，PABPN1与PAPα协同促进卵母细胞进入减数分裂阶段。对卵母细胞的野生型与Pabpn1基因敲除样本的转录组进行了检测。