Boar sperm membranes antigens. II. Reorganization of an integral membrane antigen during capacitation and acrosome reaction.

The dynamics of the cell surface during the process of capacitation is impressively shown by means of a monoclonal antibody directed against the P86/5 antigen. This glycoprotein was located in the sperm plasma membrane using the colloidal gold method in combination with specimen preparation in toto. The antigen is absent at the rostral tip of non-capacitated spermatozoa, but forms clusters over the principal segment and the equatorial segment after induction of capacitation. This formation of microdomains with different properties may be a prerequisite for the onset of the acrosome reaction (AR). During AR the diffusion barrier for the P86/5 antigen breakes down and the antigen occupies now the rostral crescent-like area of the sperm head. These observations are discussed with respect to zona binding and induction of the AR in boar spermatozoa.