P34H sperm protein is preferentially expressed by the human corpus epididymidis

During epididymal transit, mammalian spermatozoa acquire new surface proteins that are necessary for gamete interaction. We have previously described a 34-kDa human epididymal sperm protein, P34H, that has been shown to be involved in sperm-zona pellucida interaction. In the present study, we report the cloning and characterization of the full-length complementary DNA encoding human P34H. The predicted amino acid sequence revealed 65% identity with P26h, the hamster counterpart of the P34H. The deduced P34H amino acid sequence revealed a 71% similarity with a pig lung tetrameric carbonyl reductase, a member of the short chain dehydrogenase/ reductase family proteins. Northern blot analysis revealed that P34H messenger RNA (mRNA) was highly expressed in the human epididymis, principally in the corpus region. A single 912-bp P34H transcript was detected. In situ hybridization experiments showed that the P34H mRNA was predominantly expressed in the proximal and distal sections of the corpus epididymidis. The staining was restricted to the principal cells of the epididymal epithelium. The localization of P34H mRNA was in agreement with the appearance of P34H protein along the male reproductive tract. Western blot analysis revealed that recombinant P34H expressed by a yeast expression system, is antigenically related to the native P34H 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 marker of epididymal sperm maturation in humans.