Cysteine-RIch Secretory Proteins (CRISP) are expressed in the reproductive tract of mammalian males and are involved in fertilization and related processes. Due to their important role in sperm performance and sperm-egg interaction, these genes are likely to be exposed to strong selective pressures, including postcopulatory sexual selection and/or male-female coevolution. We here perform a comparative evolutionary analysis of Crisp genes in mammals. Currently, the nomenclature of CRISP genes is confusing, as a consequence of discrepancies between assignments of orthologs, particularly due to numbering of CRISP genes. This may generate problems when performing comparative evolutionary analyses of mammalian clades and species. To avoid such problems, we first carried out a study of possible orthologous relationships and putative origins of the known CRISP gene sequences. Furthermore, and with the aim to facilitate analyses, we here propose a different nomenclature for CRISP genes (EVAC1–4, “EVolutionarily-analyzed CRISP”) to be used in an evolutionary context. We found differing selective pressures among Crisp genes. CRISP1/4 (EVAC1) and CRISP2 (EVAC2) orthologs are found across eutherian mammals and seem to be conserved in general, but show signs of positive selection in primate CRISP1/4 (EVAC1). Rodent Crisp1 (Evac3a) seems to evolve under a comparatively more relaxed constraint with positive selection on codon sites. Finally, murine Crisp3 (Evac4), which appears to be specific to the genus Mus, shows signs of possible positive selection. We further provide evidence for sexual selection on the sequence of one of these genes (Crisp1/4) that, unlike others, is thought to be exclusively expressed in male reproductive tissues. We found differing selective pressures among CRISP genes and sexual selection as a contributing factor in CRISP1/4 gene sequence evolution. Our evolutionary analysis of this unique set of genes contributes to a better understanding of Crisp function in particular and the influence of sexual selection on reproductive mechanisms in general.

中文翻译：

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哺乳动物富含半胱氨酸分泌蛋白 (CRISP) 的基因编码进化分析。


富含半胱氨酸的分泌蛋白 (CRISP) 在雄性哺乳动物的生殖道中表达，并参与受精和相关过程。由于它们在精子性能和精卵相互作用中发挥重要作用，这些基因可能会受到强大的选择压力，包括交配后性选择和/或男女共同进化。我们在这里对哺乳动物的 Crisp 基因进行比较进化分析。目前，由于直向同源物分配之间的差异，特别是由于 CRISP 基因的编号，CRISP 基因的命名法令人困惑。在对哺乳动物进化枝和物种进行比较进化分析时，这可能会产生问题。为了避免此类问题，我们首先对已知 CRISP 基因序列可能的直系同源关系和推定起源进行了研究。此外，为了便于分析，我们在这里提出了在进化背景下使用 CRISP 基因的不同命名法（EVAC1-4，“进化分析的 CRISP”）。我们发现 Crisp 基因之间存在不同的选择压力。 CRISP1/4 (EVAC1) 和 CRISP2 (EVAC2) 直向同源物在真兽类哺乳动物中被发现，并且总体上似乎是保守的，但在灵长类动物 CRISP1/4 (EVAC1) 中显示出正选择的迹象。 Rodent Crisp1 (Evac3a) 似乎是在相对更宽松的约束下进化的，对密码子位点进行正向选择。最后，鼠类 Crisp3 (Evac4)，似乎是鼠属特有的，显示出可能的正选择的迹象。我们进一步为这些基因之一（Crisp1/4）的序列提供了性选择的证据，与其他基因不同，该基因被认为只在雄性生殖组织中表达。 我们发现 CRISP 基因之间不同的选择压力和性选择是 CRISP1/4 基因序列进化的一个促成因素。我们对这组独特基因的进化分析有助于更好地理解 Crisp 功能，以及性选择对生殖机制的一般影响。