Many translationally repressed mRNAs are deposited in the oocyte cytoplasm for progression of the meiotic cell cycle and early development. mos and cyclin B1 mRNAs encode proteins promoting oocyte meiosis, and translational control of these mRNAs is important for normal progression of meiotic cell division. We previously demonstrated that cyclin B1 mRNA forms RNA granules in the zebrafish and mouse oocyte cytoplasm and that the formation of RNA granules is crucial for regulating the timing of translational activation of the mRNA. However, whether the granule formation is specific to cyclin B1 mRNA remains unknown. In this study, we found that zebrafish mos mRNA forms granules distinct from those of cyclin B1 mRNA. Fluorescent in situ hybridization analysis showed that cyclin B1 RNA granules were assembled in dense clusters, while mos RNA granules were distributed diffusely in the animal polar cytoplasm. Sucrose density gradient ultracentrifugation analysis showed that the density of mos RNA granules was partly lower than that of cyclin B1 mRNA. Similar to cyclin B1 RNA granules, mos RNA granules were disassembled after initiation of oocyte maturation at the timing at which the poly(A) tail was elongated. However, while almost all of the granules of cyclin B1 were disassembled simultaneously, a fraction of mos RNA granules firstly disappeared and then a large part of them was disassembled. In addition, while cyclin B1 RNA granules were disassembled in a manner dependent on actin filament depolymerization, certain fractions of mos RNA granules were disassembled independently of actin filaments. These results suggest that cytoplasmic regulation of translationally repressed mRNAs by formation of different RNA granules is a key mechanism for translational control of distinct mRNAs in the oocyte.

中文翻译：

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斑马鱼卵母细胞中mos RNA颗粒的形成与cyclin B1 RNA颗粒的分布，密度和调控不同。

许多受翻译抑制的mRNA沉积在卵母细胞的细胞质中，以促进减数分裂细胞周期的发展和早期发育。mos和cyclin B1 mRNA编码促进卵母细胞减数分裂的蛋白，这些mRNA的翻译控制对于减数分裂细胞正常发育很重要。我们以前证明，cyclin B1 mRNA在斑马鱼和小鼠卵母细胞的细胞质中形成RNA颗粒，而RNA颗粒的形成对于调节mRNA的翻译激活时间至关重要。但是，颗粒形成是否特定于细胞周期蛋白B1 mRNA仍是未知的。在这项研究中，我们发现斑马鱼mos mRNA形成的颗粒不同于cyclin B1 mRNA的颗粒。荧光原位杂交分析表明，cyclin B1 RNA颗粒聚集在密集的簇中，而mos RNA颗粒则分散在动物的极性细胞质中。蔗糖密度梯度超速离心分析显示，mos RNA颗粒的密度部分低于细胞周期蛋白B1 mRNA的密度。类似于细胞周期蛋白B1 RNA颗粒，在延长poly（A）尾巴的时间开始卵母细胞成熟后，将mos RNA颗粒解体。但是，虽然几乎同时拆卸了细胞周期蛋白B1的所有颗粒，但一部分mos RNA颗粒首先消失，然后分解了很大一部分。另外，虽然以依赖于肌动蛋白丝解聚的方式拆卸细胞周期蛋白B1 RNA颗粒，但某些部分的mos RNA颗粒部分却独立于肌动蛋白丝而被拆卸。