Developmental expression of G protein alpha subunits in mouse spermatogenic cells: evidence that G alpha i is associated with the developing acrosome.
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 alpha subunits of Gi1, Gi2, Gi3, and G(o) were detected in mouse spermatocytes and spermatids. An antiserum recognizing a conserved sequence of G alpha i subtypes localized to the proacrosomal granules of spermatocytes and the developing acrosome of spermatids. Levels of G alpha o diminished as spermatocytes developed into spermatids such that G alpha o was not detected in cauda epididymal sperm. Immunoreactivity using G alpha o-specific antisera did not display a distinct regionalization within any of the spermatogenic cell types. G alpha s was not detected in the developing spermatogenic cells or sperm. The association of G alpha i 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.
Karnik
N S
NS
Department of Obstetrics and Gynecology, University of Pennsylvania School of Medicine, Philadelphia 19104-6080.
Newman
S
S
Kopf
G S
GS
Gerton
G L
GL
D000177:Acrosome / Q000737:chemistry*; D000818:Animals; D000906:Antibodies; D002451:Cell Compartmentation; D019204:GTP-Binding Proteins / Q000032:analysis / Q000096:biosynthesis*; D046911:Macromolecular Substances; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D037342:Pertussis Toxin; D013087:Spermatids / Q000737:chemistry; D013090:Spermatocytes / Q000737:chemistry* / Q000254:growth & development; D010566:Virulence Factors, Bordetella
D000906:Antibodies; D046911:Macromolecular Substances; D010566:Virulence Factors, Bordetella; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins