摘要
Reproductive proteins are among the most rapidly evolving classes of proteins. For a subset of these, rapid evolution is driven by positive Darwinian selection despite vital, well-conserved, reproductive functions. Izumo1 is the only essential sperm–egg fusion protein currently known on mammalian sperm, and its egg receptor (Juno; formerly Folr4) was recently discovered. Male knockout mice for Izumo1 and female knockout mice for Juno are both healthy but sterile. Here, both sperm–egg binding proteins are shown to be evolving under positive selection. Within mammals, coevolution of Izumo1 and Juno is also uncovered, suggesting that similar forces have shaped the evolutionary histories of these binding partners within Mammalia. Additionally, genomic analyses reveal an ancient origin for the Izumo gene family, initially reported as conserved exclusively in mammals. Newly identified Izumo1 orthologues could serve reproductive functions in birds, fish and reptiles. Surprisingly, these same analyses support Juno's presence in mammals alone, suggesting a recent mammalian-specific duplication and neofunctionalization of the ancestral folate receptor. Despite the indispensability of their reproductive interaction, and their apparent coevolution within Mammalia, this binding pair arose through strikingly different evolutionary forces.
摘要译文
生殖蛋白是最快速发展的蛋白质类别之一。对于其中的一部分，快速进化是由积极的达尔文选择驱动的，尽管重要的，保守的，生殖功能。 Izumo1是目前哺乳动物精子中唯一已知的精子 - 卵子融合蛋白，最近发现了它的卵子受体（Juno;以前称为Folr4）。Izumo1的雄性敲除小鼠和Juno的雌性敲除小鼠都是健康但无菌的。在这里，两种精子 - 卵子结合蛋白都显示出在正选择下进化。在哺乳动物中，Izumo1和Juno的共同进化也被发现，这表明类似的力量已经塑造了这些结合伙伴在哺乳动物中的进化历史。另外，基因组分析揭示了Izumo基因家族的古老起源，最初报道仅在哺乳动物中保守。新发现的Izumo1直系同源物可以为鸟类，鱼类和爬行动物提供生殖功能。令人惊讶的是，这些相同的分析仅支持Juno在哺乳动物中的存在，提示最近的哺乳动物特异性复制和祖先叶酸受体的新功能化。尽管他们的生殖互动不可或缺，并且它们在哺乳动物中明显的共同进化，这种结合对通过惊人不同的进化力产生。
Phil Grayson[1]. Izumo1 and Juno: the evolutionary origins and coevolution of essential sperm–egg binding partners[J]. Royal Society Open Science, 2015,2(12)