Molecular cloning and characterization of HE1, a major secretory protein of the human epididymis

The cDNA sequence of HE1, a novel human epididymal gene product isolated by differential screening, predicts an abundant, small secretory glycopeptide. HE1 is encoded by a single copy gene and seems to be well conserved among mammals. The predicted HE1 peptide is identical to that of EPI-1, the chimpanzee homologous gene product, and to ESP14.6, the macaque homologous product. Its tentative N-terminus also shows similarity to that of a major porcine epididymal sperm-associated glycopeptide. Northern blot analysis of various bovine and rat tissues indicated that their HE1-homologous gene products showed highly increased expression in the epididymis, suggesting that the tissue distribution observed in humans is also conserved. With use of antipeptide antibodies, HE1-related antigen was shown by immunohistochemical methods to be present within the epithelium and lumen of the human corpus epididymidis. High amounts were also present in the lumen of the cauda epididymidis and deferent duct. Moreover, HE1 seemed to be associated with epididymal spermatozoa, and association with ejaculated spermatozoa remained doubtful. With Western blotting, an antiserum raised against the synthetic HE1 epitope specifically cross-reacted with proteins of human seminal plasma in the range of 25-27 kDa. An antiserum raised against chimpanzee EPI-1 recognized human seminal plasma antigens of the same apparent molecular size.