在卵母细胞生物学中,长久以来已知透明带在分泌途径的下游操作三种细胞外功能,即,将卵母细胞包裹在卵泡中,介导精子-卵母细胞相互作用,防止胚胎过早接触输卵管上皮。本研究揭示了与其他三个功能根本不同的第四个功能,对小鼠胚胎细胞存活至关重要。有趣的是,受精后4天,小鼠透明带的三种蛋白质(ZP1,ZP2,ZP3)也大量存在于胚胎内部,如质谱所示,免疫印迹,和免疫荧光。与目前对ZP蛋白作用的理解相反,在中期II卵母细胞和受精卵的皮质下区域,ZP3与细胞骨架的关系比与分泌囊泡的关系更大,并且被排除在卵裂期胚胎的细胞-细胞接触区域之外。在受精的卵母细胞中修剪介导的ZP3敲低阻碍了第一次合子分裂,而ZP3过表达支持胚泡形成。ZP3敲低胚胎的转录组分析指出了在胚胎基因组激活的背景下细胞质翻译的缺陷。ZP3敲低过程中蛋白质合成的减少以及当Trim-away从一个细胞阶段推迟到两个细胞阶段晚期时缺乏裂解停滞支持了这一结论。这些数据限制了透明带蛋白仅在细胞外空间起作用的概念,还揭示了卵母细胞到胚胎过渡过程中的作用。最终,这些数据将ZP3纳入有助于小鼠卵母细胞发育能力的母体因素家族.
In oocyte biology, the zona pellucida has long been known to operate three extracellular functions downstream of the secretory pathway, namely, encasing the oocytes in ovarian follicles, mediating sperm-oocyte interaction, and preventing premature embryo contact with oviductal epithelium. The present study uncovers a fourth function that is fundamentally distinct from the other three, being critical for embryonic cell survival in mice. Intriguingly, the three proteins of the mouse zona pellucida (ZP1, ZP2, ZP3) were found abundantly present also inside the embryo 4 days after fertilization, as shown by mass spectrometry, immunoblotting, and immunofluorescence. Contrary to current understanding of the roles of ZP proteins, ZP3 was associated more with the cytoskeleton than with secretory vesicles in the subcortical region of metaphase II oocytes and zygotes, and was excluded from regions of cell-cell contact in cleavage-stage embryos. Trim-away-mediated knockdown of ZP3 in fertilized oocytes hampered the first zygotic cleavage, while ZP3 overexpression supported blastocyst formation. Transcriptome analysis of ZP3-knockdown embryos pointed at defects of cytoplasmic translation in the context of embryonic genome activation. This conclusion was supported by reduced protein synthesis in the ZP3-knockdown and by the lack of cleavage arrest when Trim-away was postponed from the one-cell to the late two-cell stage. These data place constraints on the notion that zona proteins only operate in the extracellular space, revealing also a role during the oocyte-to-embryo transition. Ultimately, these data recruit ZP3 into the family of maternal factors that contribute to developmental competence of mouse oocytes.