Laboratory of Reproductive and Developmental Biology, Graduate School of Life Science, Hokkaido University, Sapporo 060-0810, Japan.
Laboratory of Reproductive and Developmental Biology, Department of Biological Sciences, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan.
Biochem Biophys Res Commun. 2014 May 23;448(1):22-7. doi: 10.1016/j.bbrc.2014.04.020. Epub 2014 Apr 13.
In immature zebrafish oocytes, dormant cyclin B1 mRNAs localize to the animal polar cytoplasm as aggregates. After hormonal stimulation, cyclin B1 mRNAs are dispersed and translationally activated, which are necessary and sufficient for the induction of zebrafish oocyte maturation. Besides cytoplasmic polyadenylation element-binding protein (CPEB) and cis-acting elements in the 3' untranslated region (UTR), Pumilio1 and a cis-acting element in the coding region of cyclin B1 mRNA are important for the subcellular localization and timing of translational activation of the mRNA. However, mechanisms underlying the spatio-temporal control of cyclin B1 mRNA translation during oocyte maturation are not fully understood. We report that insulin-like growth factor 2 mRNA-binding protein 3 (IMP3), which was initially described as a protein bound to Vg1 mRNA localized to the vegetal pole of Xenopus oocytes, binds to the 3' UTR of cyclin B1 mRNA that localizes to the animal pole of zebrafish oocytes. IMP3 and cyclin B1 mRNA co-localize to the animal polar cytoplasm of immature oocytes, but in mature oocytes, IMP3 dissociates from the mRNA despite the fact that its protein content and phosphorylation state are unchanged during oocyte maturation. IMP3 interacts with Pumilio1 and CPEB in an mRNA-dependent manner in immature oocytes but not in mature oocytes. Overexpression of IMP3 and injection of anti-IMP3 antibody delayed the progression of oocyte maturation. On the basis of these results, we propose that IMP3 represses the translation of cyclin B1 mRNA in immature zebrafish oocytes and that its release from the mRNA triggers the translational activation.
在未成熟的斑马鱼卵母细胞中，休眠的细胞周期蛋白 B1 mRNA 作为聚集体定位于动物极细胞质中。在激素刺激后，细胞周期蛋白 B1 mRNA 被分散并翻译激活，这对于诱导斑马鱼卵母细胞成熟是必要且充分的。除了细胞质多聚腺苷酸化元件结合蛋白（CPEB）和 3'非翻译区（UTR）中的顺式作用元件外，Pumilio1 和细胞周期蛋白 B1 mRNA 编码区中的顺式作用元件对于 mRNA 的亚细胞定位和翻译激活的时间至关重要。然而，卵母细胞成熟过程中细胞周期蛋白 B1 mRNA 翻译的时空调控机制尚不完全清楚。我们报告称，最初被描述为与 Vg1 mRNA 结合并定位于非洲爪蟾卵母细胞植物极的胰岛素样生长因子 2 mRNA 结合蛋白 3（IMP3），与定位于斑马鱼卵母细胞动物极的细胞周期蛋白 B1 mRNA 的 3'UTR 结合。IMP3 和细胞周期蛋白 B1 mRNA 共同定位于未成熟卵母细胞的动物极细胞质中，但在成熟卵母细胞中，尽管其蛋白含量和磷酸化状态在卵母细胞成熟过程中不变，但 IMP3 从 mRNA 上解离。IMP3 在未成熟卵母细胞中以依赖于 mRNA 的方式与 Pumilio1 和 CPEB 相互作用，但在成熟卵母细胞中则不然。IMP3 的过表达和抗 IMP3 抗体的注射延迟了卵母细胞成熟的进程。基于这些结果，我们提出 IMP3 抑制未成熟斑马鱼卵母细胞中细胞周期蛋白 B1 mRNA 的翻译，并且其从 mRNA 上的释放触发了翻译激活。
