Neural cadherin is expressed in human gametes and participates in sperm-oocyte interaction events

Neural cadherin (N-cadherin) is a transmembrane glycoprotein involved in calcium-dependent cell-cell adhesion and signalling events. The previous evidence shows N-cadherin expression in the human gonads and gametes; however, N-cadherin subcellular localization in human spermatozoa and oocytes, and its involvement in fertilization remain to be characterized. In this study, expression of N-cadherin in human spermatozoa and testis was confirmed by RT-PCR and protein forms were identified using Western immunoblotting. N-cadherin localization in testicular and ejaculated spermatozoa, in cells that had undergone capacitation and acrosomal exocytosis, as well as in oocytes was assessed using immunocytochemistry. Participation of the adhesion protein in fertilization was evaluated using the HemiZona Assay (HZA) and the zona pellucida (ZP)-free hamster oocyte sperm penetration assay (SPA). Both the N-cadherin transcript and the mature protein form (135 kDa) were found in spermatozoa and testis. The protein was mainly immunolocalized in the acrosomal region of testicular, non-capacitated and capacitated spermatozoa, and was found in the equatorial segment after acrosomal exocytosis. N-cadherin was also detected in oocytes, in conjunction with beta-catenin, a member of the adhesion complex. Sperm incubation with anti N-cadherin antibodies did not affect their ability to interact with homologous ZP in the HZA; by contrast, presence of the antibodies in the SPA led to a significant (p < 0.01) reduction in the percentage of penetrated oocytes. In conjunction, results indicate that N-cadherin is a sperm protein of testicular origin localized in cellular regions involved in gamete interaction. N-cadherin would not participate in sperm-ZP interaction, but it would have a role in sperm-oolemma adhesion/fusion events.