Localized Surface Antigens of Guinea Pig Sperm Migrate to New Regions Prior to Fertilization DIANA GOLD MYLES and PAUL PRIMAKOFF

We have previously defined distinct Iocalizations of antigens on the surface of the guinea pig sperm using monoclonal antibodies. In the present study we have demonstrated that these antigen Iocalizations are dynamic and can be altered during changes in the functional state of the sperm. Before the sperm is capable of fertilizing the egg, it must undergo capacitation and an exocytic event, the acrosome reaction. Prior to capacitation, the antigen recognized by the monoclonal antibody, PT-1, was restricted to the posterior tail region (principle piece and end piece). After incubation in capacitating media at 37°C for 1 h, 100% of the sperm population showed migration of the PT-1 antigen onto the anterior tail. This redistribution of surface antigen resulted from a migration of the surface molecules originally present on the posterior tail. It did not occur in the presence of metabolic poisons or when tail-beating was prevented. It was temperature-dependent, and did not require exogenous Ca 2+. Since the PT-1 antigen is freely diffusing on the posterior tail before migration, the mechanism of redistribution could involve the alteration of a presumptive membrane barrier. In addition, we observed the redistribution of a second surface antigen after the acrosome reaction. The antigen recognized by the monoclonal antibody, PH-20, was localized exclusively in the posterior head region of acrosome-intact sperm. Within 7-10 min of induction of the acrosome reaction with Ca 2+ and A23187, 90-100% of the acrosome-reacted sperm population no longer demonstrated binding of the PH-20 antibody on the posterior head, but showed binding instead on the inner acrosomal membrane. This redistribution of the PH-20 antigen also resulted from the migration of pre-existing surface molecules, but did not appear to require energy. The migration of PH-20 antigen was a selective process; other antigens localized to the posterior head region did not leave the posterior head after the acrosome reaction. These rearrangements of cell surface molecules may act to regulate cell surface function during fertilization. The arrangement of molecules into discrete domains on the surface of cells is now known to be of widespread occurrence (1-11). Membrane topography may reflect the functional geometry of the cell; for example, in intestinal epithelial cells digestive enzymes are enriched on the apical surface (12). Alternatively, the topographical distribution of cell surface molecules may control their function by determining the environment of the molecule or interactions between surface molecules. The sperm cell is one ofthe mammalian cell types in which surface molecules are localized in domains. Using monoclonal antibodies to the guinea pig sperm surface, we have demonstrated that there are a minimum of 12 different antigens localized in five different patterns (10). 11 of these antigens have been identified as proteins. Evidence from other investigators indicates that these surface domains also differ in their lipid composition (5). In this paper, we describe two topographical rearrangements of localized cell surface molecules. The rearrangements occurred before fertilization during steps that altered the functional state of the sperm. When mammalian sperm are either ejaculated or removed from the cauda epididymis they are unable to fertilize eggs. In the female reproductive tract, sperm undergo a set of alterations, collectively called capacitation, that makes them competent for fertilization. This process of capacitation can be mimicked in vitro by incubation in defined media. Capacitation leads to the exocytotic acrosome reaction and a change in motility pattern of the sperm. Only THE JOURNAL OF CELL BIOLOGY • VOLUME 99 NOVEMBER 1984 1634-1641 1634 © The Rockefeller University Press • 0021-9525/84/11/1634/08 $1.00 on F ebuary 1, 2013 jcb.rress.org D ow nladed fom Published November 1, 1984