Contribution of de novo synthesis of Gαs-proteins to 1-methyladenine production in starfish ovarian follicle cells stimulated by relaxin-like gonad-stimulating substance.

ABSTRACT

In starfish, the peptide hormone gonad-stimulating substance (GSS) secreted from nervous tissue stimulates oocyte maturation to induce 1-methyladenine (1-MeAde) production by ovarian follicle cells. The hormonal action of GSS on follicle cells involves its receptor, G-proteins and adenylyl cyclase. However, GSS failed to induce 1-MeAde and cAMP production in follicle cells of ovaries during oogenesis. At the maturation stage, follicle cells acquired the potential to respond to GSS by producing 1-MeAde and cAMP. Adenylyl cyclase activity in follicle cells of fully grown stage ovaries was also stimulated by GSS in the presence of GTP. These activations depended on the size of oocytes in ovaries. The α subunit of Gs-proteins was not detected immunologically in follicle cells of oogenesis stage ovaries, although Gαi and Gαq were detectable. Using specific primers for Gαs and Gαi, expression levels of Gαs in follicle cells were found to increase significantly as the size of oocytes in ovaries increased, whereas the mRNA levels of Gαi were almost constant regardless of oocyte size. These findings strongly suggest the potential of follicle cells to respond to GSS by producing 1-MeAde and cAMP is brought by de novo synthesis of Gαs-proteins.