ACTIN, ALPHA-ACTININ, AND SPECTRIN WITH SPECIFIC ASSOCIATIONS WITH THE POSTACROSOMAL AND ACROSOMAL DOMAINS OF BOVINE SPERMATOZOA

Background: Characteristic membrane changes in spermatozoa culminating in acrosome reaction and sperm-egg fusion, and suspected involvement of actin-containing cytoskeleton in membrane changes in general, promp ted us to investigate subcellular distribution of actin and actin-bind ing proteins in bovine spermatozoa subjected to various extractions wh ich sequentially denude the sperm investments. Methods: Spermatozoa we re treated with either 1% SDS, 0.1% Triton X-100, 0.1% Hyamine, or 1 M MgCl2 or were sonicated, Immunostaining of actin, alpha-actinin, spec trin, and acrosin as well as electron microscopic analysis of extracte d spermatozoa were carried out. Results: Extractions caused evaginatio n of the acrosomal lamina which retained focal contacts with the inner acrosomal membrane. Extractions further revealed lateral prongs at th e anterior border of the postacrosomal sheath, Labeling for alpha-acti nin and spectrin was localized in the acrosin-positive acrosomal lamin a, neck, and principal piece, the latter containing also relatively ex traction-resistant oligomeric or polymerized actin. In the postacrosom al area, actin was accumulated in the extraction-resistant posterior r ing structure and anteriorly at the sites apparently related to the la teral prongs, Notably, spectrin reactivity was enhanced by MgCl2 in he ad, neck, and principal piece, and sonication abolished cytoskeletal i mmunoreactivity in the head. Conclusions: Destabilization of membranes with selected extractions induces changes in the acrosomal lamina mim icking acrosomal vesicle formation. The lateral prongs and posterior r ing structure, respectively, may serve as anterior and posterior ancho rs for the extraction-resistant postacrosomal sheath. The lateral pron gs may also be a merger zone for actin, cw-actinin, and spectrin with important implication on sperm function. The latter two proteins may b e involved in acrosomal vesicle formation. It is apparent that extract ions have a significant effect on the detectability of sperm cytoskele tal elements. (C) 1995 Wiley-Liss, Inc.