Actin polymerization in the equatorial and postacrosomal regions of guinea pig spermatozoa during the acrosome reaction is regulated by G proteins.
The acrosome reaction (AR) is an exocytotic process of spermatozoa, and an absolute requirement for fertilization. During AR, actin polymerization is necessary in the equatorial and postacrosomal regions of guinea pig sperm for spermatozoa incorporation deep into the egg cytoplasm, but not for plasma membrane (PM) fusion nor the early steps of egg activation. To identify the mechanisms involved in this sperm actin polymerization, we searched for the protein members, known to be involved in a highly conserved model, that may apply to any cellular process in which de novo actin polymerization occurs from G protein activation. WASP, Arp 2/3, profilins I and II, and Cdc42, RhoA and RhoB GTPases were localized by indirect immunofluorescence (IIF) in guinea pig spermatozoa and their presence corroborated by Western blotting. WASP and profilin II were translocated to the postacrosomal region (Arp2/3 already were there) in long-term capacitated and acrosome-reacted spermatozoa, at the same time as actin polymerization occurred. These events were inhibited by GDP-beta-S and promoted by lysophosphatidic acid (LPA) and GTP-gamma-S, a small GTPase inhibitor and two activators, respectively. By immunoprecipitation, Cdc42-WASp association was identified in capacitated but not in noncapacitated gametes. Polymerized actin in the postacrosomal region is apparently anchored both to the postacrosomal perinuclear theca region and the overlying PM. Results suggest that GTPases are involved in sperm actin polymerization, in the postacrosomal region and the mechanism for polymerization might fit a previously proposed model (Mullins, 2000: Curr Opin Cell Biol 12:91-96).
Delgado-Buenrostro
Norma Laura
NL
Departamento de Biología Celular, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, 07000 México D.F., México.
Hernández-González
Enrique O
EO
Segura-Nieto
Magdalena
M
Mújica
Adela
A
D000177:Acrosome / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D020101:Acrosome Reaction / Q000502:physiology*; D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins / Q000378:metabolism*; D000818:Animals; D003285:Contractile Proteins / Q000032:analysis / Q000502:physiology; D003598:Cytoskeletal Proteins / Q000032:analysis / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006168:Guinea Pigs; D008246:Lysophospholipids / Q000494:pharmacology; D008297:Male; D008840:Microfilament Proteins / Q000032:analysis / Q000502:physiology; D051304:Profilins; D011506:Proteins / Q000032:analysis / Q000502:physiology; D013075:Sperm Capacitation / Q000187:drug effects / Q000502:physiology; D013094:Spermatozoa / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D051316:Wiskott-Aldrich Syndrome Protein; D020764:cdc42 GTP-Binding Protein / Q000032:analysis / Q000502:physiology; D020741:rho GTP-Binding Proteins / Q000032:analysis / Q000502:physiology*; D020742:rhoA GTP-Binding Protein / Q000032:analysis / Q000502:physiology; D020743:rhoB GTP-Binding Protein / Q000032:analysis / Q000502:physiology
D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins; D003285:Contractile Proteins; D003598:Cytoskeletal Proteins; D008246:Lysophospholipids; D008840:Microfilament Proteins; D051304:Profilins; D011506:Proteins; D051316:Wiskott-Aldrich Syndrome Protein; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D020764:cdc42 GTP-Binding Protein; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein; D020743:rhoB GTP-Binding Protein; C032881:lysophosphatidic acid