title: xRic-8 is a GEF for Gsalpha and participates in maintaining meiotic arrest in Xenopus laevis oocytes.
abstract: Immature stage VI Xenopus oocytes are arrested at the G(2)/M border of meiosis I until exposed to progesterone, which induces meiotic resumption through a non-genomic mechanism. One of the earliest events produced by this hormone is inhibition of the plasma membrane enzyme adenylyl cyclase (AC), with the concomitant drop in intracellular cAMP levels and reinitiation of the cell cycle. Recently Gsalpha and Gbetagamma have been shown to play an important role as positive regulators of Xenopus oocyte AC, maintaining the oocyte in the arrested state. However, a question that still remains unanswered, is how the activated state of Gsalpha and Gbetagamma is achieved in the immature oocyte, since no receptor or ligand have been found to be required. Here we provide evidence that xRic-8 can act in vitro and in vivo as a GEF for Gsalpha. Overexpression of xRic-8, through mRNA injection, greatly inhibits progesterone induced oocyte maturation and endogenous xRic-8 mRNA depletion, through siRNA microinjection, induces spontaneous oocyte maturation. These results suggest that xRic-8 is participating in the immature oocyte by keeping Gsalpha-Gbetagamma-AC signaling complex in an activated state and therefore maintaining G2 arrest.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile.
authors.forename: Ximena
authors.initials: X
authors.lastname: Romo
authors.forename: Pamela
authors.initials: P
authors.lastname: Pastén
authors.forename: Silvana
authors.initials: S
authors.lastname: Martínez
authors.forename: Ximena
authors.initials: X
authors.lastname: Soto
authors.forename: Pablo
authors.initials: P
authors.lastname: Lara
authors.forename: Antonieta Ramírez
authors.initials: AR
authors.lastname: de Arellano
authors.forename: Marcela
authors.initials: M
authors.lastname: Torrejón
authors.forename: Martín
authors.initials: M
authors.lastname: Montecino
authors.forename: María Victoria
authors.initials: MV
authors.lastname: Hinrichs
authors.forename: Juan
authors.initials: J
authors.lastname: Olate
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D005786:Gene Expression Regulation; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008540:Meiosis; D008969:Molecular Sequence Data; D009865:Oocytes / Q000166:cytology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D029867:Xenopus Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis / Q000378:metabolism*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C525833:Ric-8 protein, Xenopus; D029867:Xenopus Proteins; D019205:GTP-Binding Protein alpha Subunits, Gs