Developmental expression of G protein α subunits in mouse spermatogenic cells: Evidence that G αi is associated with the developing acrosome

Abstract

Guanine nucleotide-binding proteins (G proteins) are important signal transducing molecules found in all cells. G proteins are associated with the plasma membrane/outer acrosomal membrane region of acrosome-intact sperm and at least one G protein is involved in the zona pellucida-induced acrosome reaction. With the goal of elucidating the functions of these proteins during spermatogenesis, we investigated the types of G proteins present in spermatogenic cells and when they first become associated with the developing acrosome. Using bacterial toxin-catalyzed [ 32P]ADP-ribosylation in conjunction with immunoprecipitation and immunofluorescence utilizing antibodies directed against specific regions of various G protein isotypes, the α subunits of G i1, G i2, G i3, and G o were detected in mouse spermatocytes and spermatids. An antiserum recognizing a conserved sequence of G αi subtypes localized to the proacrosomal granules of spermatocytes and the developing acrosome of spermatids. Levels of G αo diminished as spermatocytes developed into spermatids such that G αo was not detected in cauda epididymal sperm. Immunoreactivity using G αo-specific antisera did not display a distinct regionalization within any of the spermatogenic cell types. G αs was not detected in the developing spermatogenic cells or sperm. The association of G αi with the developing acrosome suggests a role for G proteins may have a role in acrosome biogenesis as well as being part of a complex required later for signal transduction leading to acrosomal exocytosis.