Identification and localization of G protein subunits in human spermatozoa

Antibodies to alpha and beta subunits of guanine nucleotide regulatory prot eins (G proteins) were used to identify which G proteins are present in mat ure human spermatozoa and to determine their subcellular localization. Immu noblots of membranes from spermatozoa demonstrate the presence of G alpha(i 2), G alpha(i3), G alpha(q/11) and G beta(35) and the absence of G alpha(i1 ), G alpha(o), G alpha(s), G alpha(12), G alpha(13), G alpha(16), G alpha(z ) and G beta(36). Indirect immunofluorescence demonstrates the presence of G alpha(q/11) in the acrosome, with the highest proportion in the equatoria l segment. G alpha(i2) is present in the acrosome, midpiece and tailpiece a nd G alpha(i3) in the postnuclear cap, midpiece and tailpiece. The G beta(3 5) subunit is found mostly in the midpiece, with marginal labelling of the head, tailpiece and the equatorial segment of the acrosome. The distinct pa ttern of distribution of G proteins suggests that they may couple to recept ors or effecters which also have discrete regions of localization in sperma tozoa. These highly localized signal transduction pathways may regulate dis crete functions, such as activation of the acrosome reaction, fusion with t he oocyte and motility.