Presence of N-cadherin transcripts in mature spermatozoa

The essential mechanism involved in sperm-oolemma fusion has yet to be elucidated. Recognition and binding is initiated by specific cell surface receptor engagement between gametes. Fusion between hamster oolemma and spermatozoa is prevented in the presence of trypsin in Ca(2+)-free media, as is oocyte activation, implicating a cadherin-like adhesion. Cadherins are a family of Ca(2+)-dependent adhesion molecules that bind homotypically with their target, are morphoregulatory and function eptopically to affect tissue form and function. Cadherins and cadherin-associated molecules have been identified in testes and germinal cells, as well as ejaculated spermatozoa. Moreover, cadherins are also present in oocytes and may suggest a cadherin-mediated adhesion in sperm-oocyte interaction. We have detected antigenic epitopes recognized by N-cadherin monoclonal antibodies diffusely distributed over the entire sperm head. In addition, Western blot analysis confirmed the presence of an antibody reactive peptide in spermatozoa, testis and ovary protein extracts at the expected molecular weight for authentic N-cadherin. Total RNA was isolated from mature motile spermatozoa, as well as ovary and testis tissue, and served as template for reverse transcription-polymerase chain reaction (RT-PCR) with N-cadherin specific primers. Alignment of sequences from PCR products of testis, ovary and spermatozoa with published N-cadherin sequence was identical except for occasional base changes. We intend to develop methods to analyse this transcript from small numbers of spermatozoa from a variety of donors to determine if defects in cadherin distribution or structure may predict reduced male fertility.