Tremblay Karine, Vigneault Christian, McGraw Serge, Sirard Marc-André
Centre de Recherche en Biologie de la Reproduction, Département des Sciences Animales, Université Laval,Sainte-Foy, Québec, Canada G1K 7P4.
Biol Reprod. 2005 Apr;72(4):1037-44. doi: 10.1095/biolreprod.104.034793. Epub 2004 Dec 15.
Oocytes can synthesize and store maternal mRNA in an inactive translational state until the start of in vitro maturation. Cytoplasmic polyadenylation, driven by 3'-untranslated region (UTR) cis-acting cytoplasmic polyadenylation element (CPE), is associated with translational activation of cyclin B1 mRNA during maturation. The main aim of the present study was to investigate if bovine oocyte cyclin B1 mRNA undergoes cytoplasmic polyadenylation/translation during in vitro maturation, as in other species. We have found that cyclin B1 mRNA is present in two isoforms, consisting of the same open reading frame but with different 3'-UTR lengths. Only the longest isoform (cyclin B1L) has a putative CPE sequence and other regulatory sequences, and its mRNA level decreases during early embryo development. The polyadenylation state of cyclin B1L during in vitro maturation was studied. Results demonstrated that cyclin B1L bears a relatively long poly(A) tail in germinal vesicle-stage oocytes, which is further lengthened at 10 h of maturation, before metaphase I. Interestingly, cyclin B1L bears a short poly(A) tail when the ovaries and the oocytes are transported and manipulated on ice to stop the polyadenylation process. Cytoplasmic polyadenylation most probably occurs during ovary transport in warm saline, when oocytes are still in their follicular environment. Our results also show a link between cytoplasmic polyadenylation of cyclin B1 and translation/appearance of cyclin B1 protein before in vitro maturation.
卵母细胞能够以非活性翻译状态合成并储存母体mRNA，直至体外成熟开始。由3'非翻译区（UTR）顺式作用细胞质聚腺苷酸化元件（CPE）驱动的细胞质聚腺苷酸化，与成熟过程中细胞周期蛋白B1 mRNA的翻译激活相关。本研究的主要目的是调查牛卵母细胞周期蛋白B1 mRNA在体外成熟过程中是否如其他物种一样经历细胞质聚腺苷酸化/翻译。我们发现细胞周期蛋白B1 mRNA存在两种异构体，它们具有相同的开放阅读框，但3'-UTR长度不同。只有最长的异构体（细胞周期蛋白B1L）具有推定的CPE序列和其他调控序列，并且其mRNA水平在早期胚胎发育过程中降低。研究了细胞周期蛋白B1L在体外成熟过程中的聚腺苷酸化状态。结果表明，细胞周期蛋白B1L在生发泡期卵母细胞中具有相对较长的聚（A）尾，在成熟10小时、中期I之前进一步延长。有趣的是，当卵巢和卵母细胞在冰上运输和操作以停止聚腺苷酸化过程时，细胞周期蛋白B1L具有短聚（A）尾。细胞质聚腺苷酸化很可能发生在温暖盐水中卵巢运输期间，此时卵母细胞仍处于卵泡环境中。我们的结果还显示了细胞周期蛋白B1的细胞质聚腺苷酸化与体外成熟前细胞周期蛋白B1蛋白的翻译/出现之间的联系。
