Extractions reveal specific argentophilic proteins in rat and bull sperm heads

Background: Silver-stainability (argentophilia) of cytoplastmic structures occurring in spermatids have been localized into the organizing perinuclear theca, but the biochemical nature and structural associations of these proteins with the cytoskeletal and membranous elements are unresolved and, therefore, were the aim of the present study. Methods: Light and electron microscopic analysis of the silver-stainability in the rat spermatids and spermatozoa was carried out in the intact testis tissue and epididymal spermatozoa and after their chemical and mechanical extraction. Correlation of argentophilia with specific proteins of rat and bovine spermatids and spermatozoa was investigated using a recently developed technique for silver nitrate staining of proteins on nitro-cellulose. Results: Sequential formation of the silver-stainable domains seemed to proceed from the argentophilic acrosomal ring. Various extractions indicated that argentophilia in the spermatids and spermatozoa was mainly associated with the perinuclear theca and to some extent to the plasma membrane. Hyamine-soluble extract from spermatozoa of rat and bull revealed only a single argentophilic protein of 130 kDa. Hyamine and SDS-soluble extracts of rat testis tissue contained an additional group of argentophilic polypeptides of lower molecular weight (115, 94, 36, 23, and 21 kDa). Conclusions: Reduction in the number of argentophilic proteins appears to be involved in a series of changes in the cyto-architecture of developing spermatids. Tentative cytoskeletal nature of argentophilic proteins remains to be identified. Nevertheless, they may have important physical relations with the higher-order organization of the sperm head cytoskeleton and overlying membranes. © 1994 Wiley-Liss, Inc.