Lateral diffusion of a human sperm-head antigen during incubation in a capacitation medium and induction of the acrosome reaction in vitro

摘要

Summary. An integral component of human spermatozoa, a glycoprotein of Mr 143 000 (two subunits of Mr 76 000 and 67 000) was recognized by the a-HS 1A.1 monoclonal antibody. The antigen was localized on the plasma membrane over the sperm head, as demonstrated by transmission electron microscopy. The antigen– antibody binding on gametes during changes in their functional state was followed by an indirect immunofluorescence assay of live human spermatozoa. In freshly ejaculated spermatozoa the antibody binding pattern revealed a patchwork quilt-like topography of the plasma membrane over the acrosome; the percentage of positive cells varied from 20 to 78% with a mean of 50% (n = 82). Incubation in a capacitation medium could increase this percentage up to 98%, revealing new epitopes in an energy-dependent and temperature-independent manner; concomitantly, a part of the antigen migrated in energy-independent and temperature-dependent manner and accumulated in a ring over the postacrosome. When an acrosome reaction was induced in vitro in the presence of Ca2+ with either A23187, ionomycin or human follicular fluid, the HS 1A.1 antigen migrated until immobilization in a well defined pattern around the equatorial segment (single band) or around the equatorial and postacrosomal segments (2 or, seldom, 3 bands). The new antigen localization resulted from a lateral diffusion of pre-existing molecules, occurred in only a few minutes, did not require energy and was temperature-dependent. At the same time, the well outlined large patch burst into a multitude of small spots before vanishing. This veil-like labelling was often observed in spermatozoa kept in the seminal plasma or treated with a metabolic poison.