Antigens Recognized by Monoclonal Antibody to Mouse Acrosomal Components Differ in Guinea Pig Spermatogenic Cells and Sperm1

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Abstract
Monoclonal antibody 1D4 reacts with a glycoconjugate antigen of the developing mouse spermatid acrosome until the terminal steps of spermiogenesis. Although 1D4 does not label the acrosome of mouse epididymal spermatozoa, it does bind to the acrosomal region of guinea pig epididymal sperm. Here we report that the antigens recognized in extracts of guinea pig spermatogenic cells and sperm are different from those detected in mouse spermatids. Three major bands of reactivity with apparent molecular weights (Mr) of 97,000-145,000, 180,000, and > 200,000 were detected in extracts of guinea pig sperm. Soluble antigens with the same molecular weights were released after the acrosome reaction was induced with ionophore A23187. On two-dimensional immunoblots, 1D4 recognized a microheterogeneous population of molecules in guinea pig sperm extracts. The molecules recognized by this antibody are not major Concanavalin A receptors and do not react strongly with periodic acid-Schiff''s stain or periodic acid-dansylbydrazine. However, comparisons of immunoblots of sperm extracts indicate that 1D4 reacted with antigens having similar molecular weights to glycoconjugates recognized by antibodies J1 and C6. Immunofluorescent labeling of guinea pig germ cells showed that 1D4 reacted only with the acrosomes of developing spermatids and sperm, and occasionally with the juxtanuclear region of spermatocytes. In general, staining was associated with the periphery of the acrosome and not with the acrosomal granule. Immunoblots of extracts of guinea pig spermatocytes, round spermatids, condensing spermatids, and sperm demonstrated that the antigens change during germ cell differentiation. Thus, 1D4 can be used as a marker of the developing acrosome for studies of the synthesis, structure, and assembly of the sperm organelle.