Sperm antigen MSH27 participates in sperm-egg membrane fusion

A monoclonal antibody (mAb), MSH27 has been selected from an mAb library which has been prepared with separated mouse sperm heads as antigens. Three aspects of evidence indicated that the MSH27 antigen was involved in the process of sperm-egg membrane fusion. After the acrosome reaction, the antigen was located at sperm equatorial segment and in postacrosomal area, where, it was widely accepted, the sperm-egg membrane fusion initially occurred. Inin vitro fertilization, the MSH27 antibody could decrease the index of sperm-egg membrane fusion, but made no effects on sperm approaching and binding to the plasma membrane of eggs. The inhibition showed an antibody concentration-dependent manner, with a rate decrease of 90% at 600 μg/mL immuno-globulin IgM. Furthermore, the antigen was able to affect the sperm-egg membrane fusion directly. The fusion index was obviously reduced after the zona-free eggs were exposed to the antigen purified by immuno-affinity chromatography. These, all together, demonstrated that the MSH27 antigen played an important role in spermegg membrane fusion.