title: G(alpha)s levels regulate Xenopus laevis oocyte maturation.
abstract: Progesterone, produced by follicular cells, induces Xenopus laevis oocyte maturation through a very early event that inhibits the activity of the adenylyl cyclase effector system. The participation of a G-protein has been implicated, based on the fact that the inhibitory effect of the steroid is GTP-dependent, and it has been proposed that progesterone acts interfering with G(alpha)s function at the plasma membrane. Here we investigate whether the change in oocyte G(alpha)s levels affects the maturation process induced by progesterone. Overexpression of X. laevis wild type (wt) G(alpha)s and the constitutive activated G(alpha)s(QL) mutant, both blocked progesterone-induced maturation, G(alpha)s(QL) being much more effective than the wt protein. On the other hand, depletion of G(alpha)s, by the use of antisense oligonucleotides, caused spontaneous maturation measured as MAPK activation, indicating clearly that the presence of G(alpha)s is necessary to keep oocytes arrested. Overexpression of three different G-protein coupled receptors (GPCR), the beta2-adrenergic receptor and the m4 and m5 muscarinic receptors, all caused inhibition of MAPK activation induced by progesterone. These receptors, upon their activation with the respective ligands, might be inducing the release of G(beta)gamma from their respective G(alpha), which together with endogenous G(alpha)s-GTP, activate adenylyl cyclase. Our results indicate that G(alpha)s plays an important role in the maturation process and support previous findings of G(beta)gamma participation, suggesting the presence of a mechanism where a constitutively activated G(alpha)s subunit, together with the G(beta)gamma heterodimer, both maintain high levels of intracellular cAMP levels, blocking the G2/M transition.
authors.affiliation: Departmento de Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile.
authors.forename: Ximena
authors.initials: X
authors.lastname: Romo
authors.forename: M Victoria
authors.initials: MV
authors.lastname: Hinrichs
authors.forename: Leonardo
authors.initials: L
authors.lastname: Guzmán
authors.forename: Juan
authors.initials: J
authors.lastname: Olate
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D004527:Egg Proteins / Q000502:physiology; D005260:Female; D016195:G2 Phase / Q000187:drug effects; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000235:genetics / Q000502:physiology*; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D006160:Guanosine Triphosphate / Q000502:physiology; D020962:Heterotrimeric GTP-Binding Proteins / Q000502:physiology; D020935:MAP Kinase Signaling System / Q000502:physiology; D008954:Models, Biological; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology; D009866:Oogenesis / Q000502:physiology*; D011374:Progesterone / Q000037:antagonists & inhibitors; D018343:Receptors, Adrenergic, beta-2 / Q000502:physiology; D011956:Receptors, Cell Surface / Q000502:physiology; D011976:Receptors, Muscarinic / Q000502:physiology; D015290:Second Messenger Systems / Q000502:physiology; D014982:Xenopus laevis / Q000502:physiology*
chemical_list: D004527:Egg Proteins; C118981:G-protein Beta gamma; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D020319:Oligodeoxyribonucleotides, Antisense; D018343:Receptors, Adrenergic, beta-2; D011956:Receptors, Cell Surface; D011976:Receptors, Muscarinic; D011374:Progesterone; D006160:Guanosine Triphosphate; D019205:GTP-Binding Protein alpha Subunits, Gs; D020962:Heterotrimeric GTP-Binding Proteins; D000262:Adenylyl Cyclases