Department of Biological Sciences, University of Wisconsin-Whitewater, Whitewater, WI 53190, USA.
Department of Cell Biology & Biochemistry, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA.
Int J Mol Sci. 2024 Mar 25;25(7):3652. doi: 10.3390/ijms25073652.
Immunodominant alloantigens in pig sperm membranes include 15 known gene products and a previously undiscovered r 20,000 sperm membrane-specific protein (SMA20). Here we characterize SMA20 and identify it as the unannotated pig ortholog of PMIS2. A composite SMA20 cDNA encoded a 126 amino acid polypeptide comprising two predicted transmembrane segments and an N-terminal alanine- and proline (AP)-rich region with no apparent signal peptide. The Northern blots showed that the composite SMA20 cDNA was derived from a 1.1 kb testis-specific transcript. A BLASTp search retrieved no SMA20 match from the pig genome, but it did retrieve a 99% match to the gene product in warthog. Sequence identity to predicted PMIS2 orthologs from other placental mammals ranged from no more than 80% overall in Cetartiodactyla to less than 60% in Primates, with the AP-rich region showing the highest divergence, including, in the extreme, its absence in most rodents, including the mouse. SMA20 immunoreactivity localized to the acrosome/apical head of methanol-fixed boar spermatozoa but not live, motile cells. Ultrastructurally, the SMA20 AP-rich domain immunolocalized to the inner leaflet of the plasma membrane, the outer acrosomal membrane, and the acrosomal contents of ejaculated spermatozoa. Gene name search failed to retrieve annotated from most mammalian genomes. Nevertheless, individual pairwise interrogation of loci spanning - identified in all placental mammals, but not in marsupials or monotremes. We conclude that the gene encoding sperm-specific SMA20/PMIS2 arose de novo in Eutheria after divergence from Metatheria, whereupon rapid molecular evolution likely drove the acquisition of a species-divergent function unique to fertilization in placental mammals.
猪精子膜中的免疫优势同种抗原包括 15 种已知的基因产物和一种以前未发现的 r 20,000 精子膜特异性蛋白（SMA20）。在这里，我们对 SMA20 进行了特征描述，并将其鉴定为未注释的猪 PMIS2 直系同源物。复合 SMA20 cDNA 编码一个 126 个氨基酸的多肽，包含两个预测的跨膜片段和一个 N 端丙氨酸和脯氨酸（AP）丰富区，没有明显的信号肽。Northern blot 显示，复合 SMA20 cDNA 来源于 1.1kb 的睾丸特异性转录物。BLASTp 搜索未从猪基因组中检索到 SMA20 匹配物，但检索到疣猪的 基因产物的 99%匹配物。与其他胎盘哺乳动物的预测 PMIS2 直系同源物的序列同一性在偶蹄目动物中总体不超过 80%，在灵长类动物中不超过 60%，AP 丰富区显示出最高的差异，包括在大多数啮齿动物中，包括老鼠，其缺失。SMA20 免疫反应性定位于甲醇固定公猪精子的顶体/头部，但不在活的、运动的细胞上。超微结构上，SMA20 的 AP 丰富域免疫定位于质膜的内叶、外顶体膜和射出精子的顶体内容物。基因名称搜索未能从大多数哺乳动物基因组中检索到注释的 。然而，对跨越 -的基因座的个体成对询问在所有胎盘哺乳动物中鉴定出 ，但在有袋动物或单孔目动物中没有。我们得出结论，编码精子特异性 SMA20/PMIS2 的基因在从有袋动物分化后，在真兽类中是新出现的，此后快速的分子进化可能导致了一种独特的物种分化功能的获得，这种功能在胎盘哺乳动物的受精中是独特的。
