Vicens Alberto, Roldan Eduardo R S
Reproductive Ecology and Biology Group, Museo Nacional de Ciencias Naturales (CSIC), Madrid, Spain.
Reproductive Ecology and Biology Group, Museo Nacional de Ciencias Naturales (CSIC), Madrid, Spain
Biol Reprod. 2014 May;90(5):113. doi: 10.1095/biolreprod.113.116871. Epub 2014 Mar 26.
Proteins involved in sexual reproduction are known to evolve rapidly, often as the result of positive Darwinian selection, although the selective forces driving such adaptive changes are poorly understood. A process of coevolution between proteins in male and female gametes may promote rapid divergence of fertilization proteins. In the mouse, only two proteins have been shown so far to be essential for sperm-egg fusion, IZUMO1 in the sperm cell and CD9 in the egg. The role of these proteins has not been fully elucidated, and it has been suggested that they may act as fusogens, interacting in trans with proteins on the other cell, or regulators of fusogens through cis interactions. Here we analyze the evolution of IZUMO1 and CD9 in a group of rodent species. To assess possible protein interactions between IZUMO1 and CD9, we examined potential coevolution based on analyses of correlated evolutionary rates. We found evidence that both proteins evolve adaptively, with a more intense signal of positive selection in IZUMO1. In addition, our findings suggest that these proteins may have some form of interaction, although they have not been regarded as fusogens interacting directly with each other. The adaptive divergence of IZUMO1 and CD9 could influence reproductive compatibility, and, thus, these proteins may participate in the establishment of specific sperm-egg recognition systems. Further studies are required to uncover the role of IZUMO1 and CD9 during gamete fusion in order to understand the molecular basis of their coevolution, as other selective forces could also lead to general signatures of coevolution.
已知参与有性生殖的蛋白质进化迅速，这通常是达尔文正选择的结果，尽管驱动这种适应性变化的选择力还知之甚少。雄配子和雌配子中蛋白质之间的协同进化过程可能会促进受精蛋白的快速分化。在小鼠中，到目前为止，只有两种蛋白质被证明对精卵融合至关重要，即精子细胞中的IZUMO1和卵细胞中的CD9。这些蛋白质的作用尚未完全阐明，有人认为它们可能作为融合蛋白，与另一细胞上的蛋白质进行反式相互作用，或者通过顺式相互作用作为融合蛋白的调节因子。在这里，我们分析了一组啮齿动物物种中IZUMO1和CD9的进化。为了评估IZUMO1和CD9之间可能的蛋白质相互作用，我们基于相关进化速率分析研究了潜在的协同进化。我们发现证据表明这两种蛋白质都适应性进化，IZUMO1中存在更强烈的正选择信号。此外，我们的研究结果表明这些蛋白质可能存在某种形式的相互作用，尽管它们未被视为直接相互作用的融合蛋白。IZUMO1和CD9的适应性分化可能会影响生殖兼容性，因此，这些蛋白质可能参与特定精卵识别系统的建立。需要进一步研究以揭示IZUMO1和CD9在配子融合过程中的作用，以便理解它们协同进化的分子基础，因为其他选择力也可能导致协同进化的一般特征。
