Activation of a pertussis toxin-sensitive, inhibitory G-protein is necessary for steroid-mediated oocyte maturation in spotted seatrout.
Oocyte maturation (OM) is initiated in lower vertebrates and echinoderms when maturation-inducing substances (MIS) bind oocyte membrane receptors. This study tested the hypothesis that activation of a G(i) protein is necessary for MIS-mediated OM in spotted seatrout. Addition of MIS significantly decreased adenylyl cyclase activity in a steroid specific, pertussis toxin (PTX)-sensitive manner in oocyte membranes and microinjection of PTX into oocytes inhibited MIS-induced OM, suggesting the steroid activates a G(i) protein. MIS significantly increased [(35)S]GTPgammaS binding to ovarian membranes, confirming that MIS receptor binding activates a G-protein, and immunoprecipitation studies showed the increased [(35)S]GTPgammaS binding was associated with Galpha(i1-3) proteins. Radioligand binding studies in ovarian membranes using GTPgammaS and PTX demonstrated that the MIS binds a receptor coupled to a PTX-sensitive G-protein. This study provides the first direct evidence in a vertebrate model that MIS-induced activation of a G(i) protein is necessary for OM. These results support a mechanism of MIS action involving binding to a novel, G-protein coupled receptor and activation of an inhibitory G-protein, the most comprehensive and plausible model of MIS initiation of OM proposed to date.
Pace
Margaret C
MC
The University of Texas at Austin Marine Science Institute, 750 Channel View Drive, Port Aransas, TX 78373, USA. mpace@utmsi.utexas.edu
Thomas
Peter
P
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D003350:Cortodoxone / Q000031:analogs & derivatives / Q000494:pharmacology; D004789:Enzyme Activation; D005260:Female; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D009865:Oocytes / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development; D009866:Oogenesis / Q000187:drug effects / Q000502:physiology; D010473:Perciformes / Q000254:growth & development / Q000378:metabolism*; D037342:Pertussis Toxin / Q000494:pharmacology
C051954:17,20,21-trihydroxy-4-pregnen-3-one; D037342:Pertussis Toxin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D000262:Adenylyl Cyclases; D003350:Cortodoxone