Ancestrally marine threespine stickleback fish (Gasterosteus aculeatus) have undergone an adaptive radiation into freshwater environments throughout the Northern Hemisphere, creating an excellent model system for studying molecular adaptation and speciation. Ecological and behavioral factors have been suggested to underlie stickleback reproductive isolation and incipient speciation, but reproductive proteins mediating gamete recognition during fertilization have so far remained unexplored. To begin to investigate the contribution of reproductive proteins to stickleback reproductive isolation, we have characterized the stickleback egg coat proteome. We find that stickleback egg coats are comprised of homologs to the zona pellucida (ZP) proteins ZP1 and ZP3, as in other teleost fish. Our molecular evolutionary analyses indicate that across teleosts, ZP3 but not ZP1 has experienced positive Darwinian selection. Mammalian ZP3 is also rapidly evolving, and surprisingly some residues under selection in stickleback and mammalian ZP3 directly align. Despite broad homology, however, we find differences between mammalian and stickleback ZP proteins with respect to glycosylation, disulfide bonding, and sites of synthesis. Taken together, the changes we observe in stickleback ZP protein architecture suggest that the egg coats of stickleback fish, and perhaps fish more generally, have evolved to fulfill a more protective functional role than their mammalian counterparts.

中文翻译：

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蛋白质组学支持三刺棘鱼卵壳作为保护性卵母细胞包膜

祖传海洋三棘鱼 ( Gasterosteus aculeatus) 在整个北半球的淡水环境中经历了适应性辐射，为研究分子适应和物种形成创造了一个极好的模型系统。生态和行为因素被认为是刺鱼生殖隔离和早期物种形成的基础，但迄今为止尚未探索受精过程中介导配子识别的生殖蛋白。为了开始研究生殖蛋白对刺鱼生殖隔离的贡献，我们对刺鱼卵壳蛋白质组进行了表征。我们发现刺鱼卵的外皮由透明带 (ZP) 蛋白 ZP1 和 ZP3 的同源物组成，与其他硬骨鱼一样。我们的分子进化分析表明，在硬骨鱼中，ZP3而不是ZP1经历了积极的达尔文选择。哺乳动物ZP3也在迅速进化，令人惊讶的是，刺鱼和哺乳动物 ZP3 中选择的一些残基直接对齐。然而，尽管有广泛的同源性，但我们发现哺乳动物和刺鱼 ZP 蛋白在糖基化、二硫键和合成位点方面存在差异。总之，我们在棘鱼 ZP 蛋白结构中观察到的变化表明，棘鱼的蛋壳，也许更普遍的鱼，已经进化到比它们的哺乳动物对应物更具保护性的功能作用。