P34H sperm protein is preferentially expressed by the human corpus epididymidis

During epididymal transit, mammalian spermatozoa acquire new surface protei ns that are necessary for gamete interaction. We have previously described a 34-kDa human epididymal sperm protein, P34H, that has been shown to be in volved in sperm-zona pellucida interaction. In the present study, we report the cloning and characterization of the full-length complementary DNA enco ding human P34H. The predicted amino acid sequence revealed 65% identity wi th P26h, the hamster counterpart of the P34H. The deduced P34H amino acid s equence revealed a 71% similarity with a pig lung tetrameric carbonyl reduc tase, a member of the short chain dehydrogenase/reductase family proteins. Northern blot analysis revealed that P34H messenger RNA (mRNA) was highly e xpressed in the human epididymis, principally in the corpus region. A singl e 912-bp P34H transcript was detected. In situ hybridization experiments sh owed that the P34H mRNA was predominantly expressed in the proximal and dis tal sections of the corpus epididymidis. The staining was restricted to the principal cells of the epididymal epithelium. The localization of P34H mRN A was in agreement with the appearance of P34H protein along the male repro ductive tract. Western blot analysis revealed that recombinant P34H express ed by a yeast expression system, is antigenically related to the native P34 H sperm protein. Based on its pattern of expression and its function in one of the key steps leading to fertilization, P34H can be considered as a mar ker of epididymal sperm maturation in humans.