Identification of a Surface Glycoprotein on Porcine Spermatozoa and Its Alteration During Epididymal Maturation1

A boar sperm glycoprotein antigen S2 P3 was monitored with fluorescein isothiocyanate labeled antisera to S2 P3. The antigen was localized in the testes only on clumped elongate spermatids. Earlier spermatogenic stages did not fluoresce. Spermatozoa showed decreasing S2 P3 immunofluorescence with progression through the epididymis. The immunofluorescence was distributed along the entire sperm membrane but appeared denser at the postacrosomal region and on proximal cytoplasmic droplets. A marked decrease of S2 P3 immunofluorescence on spermatozoa occurred in Region Da, the beginning of the corpus epididymidis. Glycoprotein S2 P3 immunofluorescence was always confined to the epididymal luminal contents and was never seen in epididymal tissue. The quantitative alteration of this antigen on spermatozoa was studied by ferritin-labeled antibodies to S2 P3 and x-ray dispersive analysis. These results generally confirmed the immunofluorescent observations. However, nonspecific binding of ferritin label by the more mature (corpus and cauda) epididymal spermatozoa prevented accurate quantitation.