Immunogold electron microscopic localization of antigenic sites in the outer dense fiber region of rat sperm tail obtained by using antisera to two Sertoli cell secretory proteins

Abstract

Polyclonal antisera raised against polypeptide components of two rat Sertoli cell secretory proteins, designated protein S70 and S45-S35 heterodimeric protein on the basis of cell origin and estimated molecular weight, were used to identify antigenic sites in 1) rat testis, 2) cultured Sertoli cells, 3) developing spermatids (collected from spermatogenic stage-specific seminiferous tubular segments), and 4) epididymal sperm. Indirect immunofluorescence, immunoperoxidase, and immunogold electron microscopy (single and double labeling) were used. Immunocytochemical techniques have detected antigenic sites in 1) the cytoplasm of Sertoli cells in the intact seminiferous tubule and in culture in the form of a punctuate, granular-like pattern, and 2) the acrosome (but not the Golgi region) and tail of developing spermatids and sperm. In developing spermatids, the principal piece of the tail displays a characteristic apical-to-distal immunoreactive banding pattern that correlates both temporally and spatially with the reported multistep assembly of outer dense fibers along the axoneme. The immunoreactivity of the acrosome, connecting piece, and outer dense fibers of the sperm tail was confirmed by immunogold electron microscopy. A precise identification of the component(s) of the outer dense fiber region responsible for the antigenic homology with Sertoli cell secretory proteins is under investigation.