Molecular biology of species-specific sperm and zona pellucida interactions

透明带是哺乳动物卵母细胞周围的细胞外基质，由三种糖蛋白组成，分别为ZP1（ZPB）、ZP2（ZPA）和ZP3（ZPC）。在受精过程中，透明带糖蛋白起着识别精子、诱导顶体反应和防止多精等重要作用。本研究旨在探讨猪透明带糖蛋白2 （pZP2）在小鼠透明带中的表达与掺入的分子机制。通过在小鼠ZP2启动子下游放置一个编码猪ZP2的迷你基因，制备了一个转基因构建体。利用这种结构，我们获得了4个携带猪ZP2基因的小鼠品系。该转基因蛋白仅在生长中的卵母细胞中合成，并在卵巢内卵母细胞表面表达。然而，在排卵的卵子中没有检测到它。此外，pZP2转基因并没有挽救zp2敲除带缺陷小鼠的表型。这些结果表明，在转基因小鼠中，猪ZP2被合成，但没有融入小鼠透明带，可能是由于未能与小鼠ZP的其他成分（ZP1和ZP3）结合。由此得出结论，透明带是由组成蛋白以分子特异性的方式构成的。

The zona pellucida, an extracellular matrix surrounding mammalian oocytes, is composed of three glycoproteins designated as ZP1(ZPB), ZP2(ZPA) and ZP3(ZPC). During fertilization, zona pellucida glycoproteins play several critical roles such as recognition of sperm, induction of the acrosome reaction and prevention of polyspermy. The purpose of this study was to examine the molecular mechanism of expression and incorporation of pig zona pellucida glycoprotein 2 (pZP2) in mouse zona pellucida. A transgene construct was prepared by placing a minigene that encodes pig ZP2 downstream from the promoter of mouse ZP2. Using this construct, we obtained four mouse lines harboring the pig ZP2 gene. The transgenic protein was found to be synthesized only in growing oocytes and expressed on the surface of the oocytes within the ovary. However, it was not detected in ovulated eggs. Furthermore, the pZP2 transgene did not rescue the phenotype in ZP2-knockout zona-deficient mice. These results indicated that in transgenic mice pig ZP2 is synthesized but not incorporated into the mouse zona pellucida, possibly due to failure to combine with other mouse ZP components (ZP1 and ZP3). It is therefore concluded that the zona pellucida is constituted from the component proteins in a molecular species-specific manner.