Identification and localization of G protein subunits in human spermatozoa

Abstract

Antibodies to α and β subunits of guanine nucleotide regulatory proteins (G proteins) were used to identify which G proteins are present in mature human spermatozoa and to determine their subcellular localization. Immunoblots of membranes from spermatozoa demonstrate the presence of Gα(i2), Gα(i3), Gα(q/11) and Gβ35 and the absence of Gα(i1), Gα(0), Gα(s), Gα12, Gα13, Gα16, Gα(z) and Gβ36. Indirect immunofluorescence demonstrates the presence of Gα(q/11) in the acrosome, with the highest proportion in the equatorial segment. Gα(i2) is present in the acrosome, midpiece and tailpiece and Gα(i3) in the postnuclear cap, midpiece and tailpiece. The Gβ35 subunit is found mostly in the midpiece, with marginal labelling of the head, tailpiece and the equatorial segment of the acrosome. The distinct pattern of distribution of G proteins suggests that they may couple to receptors or effectors which also have discrete regions of localization in spermatozoa. These highly localized signal transduction pathways may regulate discrete functions, such as activation of the acrosome reaction, fusion with the oocyte and motility.