Bull subfertility is associated with low levels of a sperm membrane antigen

Abstract

During epididymal transit, mammalian spermatozoa acquire new surface antigens that may participate in gamete interaction. We have previously described a 26 kDa (P26h) epididymal hamster sperm protein that is proposed to be involved in fertilization. We have also identified its human homolog, P34H. Variability in the amount of P34H on spermatozoa from fertile and idiopathic infertile men provides strong evidence that this protein is a potential marker of male fertility. Since these sperm antigens constitute a family of proteins with common antigenicity, we have investigated the presence of a related protein in bovine sperm. In the present study, a P26h antiserum recognized two bull sperm proteins of 21 kDa and 25 kDa (MW) on SDS-PAGE. We showed that P25b could be extracted with detergent as a surface protein, whereas the P21b was associated with non-soluble intracellular structures. Sonication of whole sperm cell suspensions and subsequent Percoll gradient centrifugation revealed that P21b may be a flagellar protein whereas the P25b may be located in the head region. Western blot analysis was used to determine the amount of P25b and P21b proteins present on spermatozoa obtained from fertile and subfertile bulls. P21b protein levels were similar in fertile and subfertile bulls, but P25b protein levels were variable. Thus, all bulls with high Non-Return Rates (fertile bulls) demonstrated high amounts of P25b, whereas P25b levels were decreased in semen from subfertile bulls. We conclude that the protein P25b is a potential fertility marker in the bull and consequently may provide an invaluation tool for the evaluation of bull fertility. Mol. Reprod. Dev. 52:57–65, 1999. © 1999 Wiley-Liss, Inc.