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Masatoshi Mita – One of the best experts on this subject based on the ideXlab platform.

  • Effect of Relaxin-Like Gonad-Stimulating Substance on Gamete Shedding and 1Methyladenine Production in Starfish Ovaries
    Sexual Reproduction in Animals and Plants, 2014
    Co-Authors: Masatoshi Mita, Yuki Takeshige, Masaru Nakamura

    Abstract:

    As in lower vertebrates, starfish oocyte maturation and ovulation are induced by a hormonal substance. Gonad-stimulating substance (GSS) is the first mediator in inducing these maturation and ovulation. GSS secreted from the nervous system acts on the ovary to produce 1Methyladenine (1-MeAde) as a maturation-inducing hormone. 1-MeAde induces germinal vesicle breakdown (GVBD) and follicular envelope breakdown (FEBD), releasing the oocyte from the ovaries, that is, spawning. Recently, GSS was purified from the radial nerves of the starfish Asterina pectinifera and its chemical structure was determined to be a relaxin-like peptide. To further elucidate the physiological roles of GSS on oocyte maturation and ovulation, this study examined the effect of synthetic GSS on 1-MeAde production in intact ovaries, folliculated oocytes, isolated follicle cells, and spawned ovaries containing follicle cells of the starfish (sea star) A. pectinifera. Spawning was induced by synthetic GSS as a dose-dependent manner. However, a high concentration of GSS failed to induce spawning. 1-MeAde production in an ovarian fragment also declined at a high concentration of GSS. Similar dual effects of GSS were observed in folliculated oocytes. In contrast, 1-MeAde production in isolated follicle cells and spawned ovaries did not decrease at a high concentration of GSS. Interestingly, egg jelly inhibited GSS-induced 1-MeAde production in follicle cells. These results may suggest that egg jelly disturbs GSS action on 1-MeAde production and spawning in ovaries.

  • Incapacity of 1Methyladenine Production to Relaxin-Like Gonad-Stimulating Substance in Ca2+-Free Seawater-Treated Starfish Ovarian Follicle Cells
    Sexual Reproduction in Animals and Plants, 2014
    Co-Authors: Miho Watanabe, Kazutoshi Yamamoto, Masatoshi Mita

    Abstract:

    Previous studies have shown that brief treatment of follicle cells from ovaries of the starfish Asterina pectinifera with Ca2+-free seawater (CaFSW) deprived the follicle cells of their capacity to respond to gonad-stimulating substance (GSS). To elucidate the failure of GSS, this study examined the hormonal action of GSS on CaFSW-treated follicle cells of A. pectinifera, particularly the mode of signal transduction. GSS failed to stimulate the production of 1Methyladenine (1-MeAde) and cyclic AMP (cAMP) in CaFSW-treated follicle cells and the incapacity was irreversible. According to competitive experiments using radioiodinated and radioinert GSS, highly specific binding was observed in follicle cells, although their affinities and binding sites in CaFSW-treated follicle cells were absolutely inferior to those in intact cells. Furthermore, GSS did not stimulate adenylyl cyclase in membrane preparations of CaFSW-treated follicle cells. Both Gsα and Giα were detected immunologically in membranes of CaFSW-treated follicle cells as well as those of nontreated cells. These results suggest that signal transduction for GSS in CaFSW-treated follicle cells does not flow readily from GSS receptors to G proteins.

  • Contribution of de novo synthesis of Gαs-proteins to 1Methyladenine production in starfish ovarian follicle cells stimulated by relaxin-like gonad-stimulating substance
    Biochemical and Biophysical Research Communications, 2013
    Co-Authors: Masatoshi Mita, Shogo Haraguchi, Haruka Uzawa, Kazuyoshi Tsutsui

    Abstract:

    In starfish, the peptide hormone gonad-stimulating substance (GSS) secreted from nervous tissue stimulates oocyte maturation to induce 1Methyladenine (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.

Motonori Hoshi – One of the best experts on this subject based on the ideXlab platform.

  • G-Protein βγ Subunit-Dependent Phosphorylation of 62-kDa Protein in the Early Signaling Pathway of Starfish Oocyte Maturation Induced by 1Methyladenine
    Developmental Biology, 1999
    Co-Authors: Tsuyoshi Nakano, Motonori Hoshi, Toshiaki Katada, Kenji Kontani, Hiroshi Kurosu, Kazuyoshi Chiba

    Abstract:

    Abstract In starfish oocytes, maturation is induced by a hormone, 1Methyladenine (1-MA), that binds to the receptors exposed to the outer surface of the plasma membrane. The signal of 1-MA stimulates the heterotrimeric G protein, resulting in dissociation of the βγ subunit of G protein (Gβγ) from a pertussis toxin-sensitive G i -type α subunit. To investigate the targets for Gβγ, we analyzed 1-MA- or Gβγ-dependent phosphorylation using in vivo and in vitro systems. A 62-kDa protein was phosphorylated immediately after 1-MA treatment in intact oocytes. In the cell-free preparations, the 62-kDa protein was also phosphorylated on serine residue(s) immediately after addition of 1-MA or Gβγ. The Gβγ-dependent phosphorylation of the 62-kDa protein was inhibited by wortmannin or LY294002, which are mechanistically different inhibitors of phosphatidylinositol 3-kinase (PI3K). LY294002 also inhibited Gβγ- as well as 1-MA-induced maturation of oocytes. Taken together, these results indicate that the 62-kDa protein functions downstream of Gβγ and PI3K in the early signaling pathway of 1-MA-induced starfish oocyte maturation. The phosphorylation of the 62-kDa protein may be required for the activation of maturation-promoting factor.

  • G protein function in starfish oocyte maturation
    Invertebrate Reproduction & Development, 1996
    Co-Authors: Kazuyoshi Chiba, Motonori Hoshi

    Abstract:

    Summary Oocyte maturation of starfish is induced by 1Methyladenine. 1Methyladenine binds to the receptor exposed to the outer surface of the plasma membrane and me signal of 1Methyladenine is transduced to the heterotrimeric G protein, resulting in dissociation of Gβγ from Gα. The dissociated Gβγ is likely to interact with the cytoplasmic effector, which is responsible for formation of MPF and for induction of GVBD. The G protein βγ subunit distributes segmentally on the continuous cytokeratin filaments as well as on the plasma membrane.

  • G-protein-mediated signal transduction for meiosis reinitiation in starfish oocyte
    Progress in Cell Cycle Research, 1995
    Co-Authors: Kazuyoshi Chiba, Motonori Hoshi

    Abstract:

    Starfish oocyte maturation is induced by 1Methyladenine. There were apparently two forms of 1Methyladenine receptor affected by GTPγS. Pertussis toxin ADP-ribosylated the 39-kDa α subunit of a G protein and inhibited maturation. Also, the G protein was ADP- ribosylated by cholera toxin only when 1Methyladenine was added. The purified G protein had an heterotrimeric structure consisting of 39 kDa a, 37 kDa β, and 8 kDa γ subunits. The deduced amino acid sequence of the cDNA of starfish Gα was 89% identical to mammalian Gi-1 α. The purified starfish βγsubunits induced maturation when they were microinjected into oocytes.

Kazuyoshi Chiba – One of the best experts on this subject based on the ideXlab platform.

  • G-Protein βγ Subunit-Dependent Phosphorylation of 62-kDa Protein in the Early Signaling Pathway of Starfish Oocyte Maturation Induced by 1Methyladenine
    Developmental Biology, 1999
    Co-Authors: Tsuyoshi Nakano, Motonori Hoshi, Toshiaki Katada, Kenji Kontani, Hiroshi Kurosu, Kazuyoshi Chiba

    Abstract:

    Abstract In starfish oocytes, maturation is induced by a hormone, 1Methyladenine (1-MA), that binds to the receptors exposed to the outer surface of the plasma membrane. The signal of 1-MA stimulates the heterotrimeric G protein, resulting in dissociation of the βγ subunit of G protein (Gβγ) from a pertussis toxin-sensitive G i -type α subunit. To investigate the targets for Gβγ, we analyzed 1-MA- or Gβγ-dependent phosphorylation using in vivo and in vitro systems. A 62-kDa protein was phosphorylated immediately after 1-MA treatment in intact oocytes. In the cell-free preparations, the 62-kDa protein was also phosphorylated on serine residue(s) immediately after addition of 1-MA or Gβγ. The Gβγ-dependent phosphorylation of the 62-kDa protein was inhibited by wortmannin or LY294002, which are mechanistically different inhibitors of phosphatidylinositol 3-kinase (PI3K). LY294002 also inhibited Gβγ- as well as 1-MA-induced maturation of oocytes. Taken together, these results indicate that the 62-kDa protein functions downstream of Gβγ and PI3K in the early signaling pathway of 1-MA-induced starfish oocyte maturation. The phosphorylation of the 62-kDa protein may be required for the activation of maturation-promoting factor.

  • G protein function in starfish oocyte maturation
    Invertebrate Reproduction & Development, 1996
    Co-Authors: Kazuyoshi Chiba, Motonori Hoshi

    Abstract:

    Summary Oocyte maturation of starfish is induced by 1Methyladenine. 1Methyladenine binds to the receptor exposed to the outer surface of the plasma membrane and me signal of 1Methyladenine is transduced to the heterotrimeric G protein, resulting in dissociation of Gβγ from Gα. The dissociated Gβγ is likely to interact with the cytoplasmic effector, which is responsible for formation of MPF and for induction of GVBD. The G protein βγ subunit distributes segmentally on the continuous cytokeratin filaments as well as on the plasma membrane.

  • G-protein-mediated signal transduction for meiosis reinitiation in starfish oocyte
    Progress in Cell Cycle Research, 1995
    Co-Authors: Kazuyoshi Chiba, Motonori Hoshi

    Abstract:

    Starfish oocyte maturation is induced by 1Methyladenine. There were apparently two forms of 1Methyladenine receptor affected by GTPγS. Pertussis toxin ADP-ribosylated the 39-kDa α subunit of a G protein and inhibited maturation. Also, the G protein was ADP- ribosylated by cholera toxin only when 1Methyladenine was added. The purified G protein had an heterotrimeric structure consisting of 39 kDa a, 37 kDa β, and 8 kDa γ subunits. The deduced amino acid sequence of the cDNA of starfish Gα was 89% identical to mammalian Gi-1 α. The purified starfish βγsubunits induced maturation when they were microinjected into oocytes.