TY - JOUR
T1 - Components of the signaling pathway linking the 1-methyladenine receptor to MPF activation and maturation in starfish oocytes
AU - Sadler, Kirsten C.
AU - Ruderman, Joan V.
PY - 1998/5/1
Y1 - 1998/5/1
N2 - Starfish oocytes are arrested at the G2/M-phase border of meiosis I. Exposure to their natural mitogen, 1-methyladenine (1-MA), leads to the activation of MPF and MAP kinase, resumption of the meiotic cell cycle, and fertilization competency. The 1-MA receptor has not yet been identified, but it is known to be linked functionally to a pertussis toxin-sensitive G- protein. Gβγ appears to be the major effector of the 1-MA receptor, since injection of Gβγ, but not activated Gα(i), leads to the activation of MPF, entry into meiosis, and oocyte maturation. The components that connect Gβγ to MPF and MAP kinase activation in oocytes are unknown. In mammalian cells, a novel phosphatidylinositol 3-kinase, PI-3 kinase-γ, links Gβγ to the MAP kinase activation pathway. Here we show that PI-3 kinase is required for starfish oocyte maturation. LY294002 and wortmannin, inhibitors of PI-3 kinase, block MPF and MAP kinase activation and entry into meiosis. Inhibition by LY294002 is reversible and limited to the hormone-dependent period. Neither inhibitor, however, blocks the earliest hormone-induced event, formation of actin spikes at the cell membrane. By contrast, pertussis toxin blocks both actin spiking and later events, arguing that PI-3 kinase functions downstream of Gβγ. Finally, we show that unlike the well-studied case in Xenopus oocytes, where MAP kinase is an essential component of the MPF activation pathway, MAP kinase is not required for either MPF activation or subsequent oocyte maturation in starfish. Instead, its major role appears to be suppression of DNA synthesis in unfertilized, haploid eggs.
AB - Starfish oocytes are arrested at the G2/M-phase border of meiosis I. Exposure to their natural mitogen, 1-methyladenine (1-MA), leads to the activation of MPF and MAP kinase, resumption of the meiotic cell cycle, and fertilization competency. The 1-MA receptor has not yet been identified, but it is known to be linked functionally to a pertussis toxin-sensitive G- protein. Gβγ appears to be the major effector of the 1-MA receptor, since injection of Gβγ, but not activated Gα(i), leads to the activation of MPF, entry into meiosis, and oocyte maturation. The components that connect Gβγ to MPF and MAP kinase activation in oocytes are unknown. In mammalian cells, a novel phosphatidylinositol 3-kinase, PI-3 kinase-γ, links Gβγ to the MAP kinase activation pathway. Here we show that PI-3 kinase is required for starfish oocyte maturation. LY294002 and wortmannin, inhibitors of PI-3 kinase, block MPF and MAP kinase activation and entry into meiosis. Inhibition by LY294002 is reversible and limited to the hormone-dependent period. Neither inhibitor, however, blocks the earliest hormone-induced event, formation of actin spikes at the cell membrane. By contrast, pertussis toxin blocks both actin spiking and later events, arguing that PI-3 kinase functions downstream of Gβγ. Finally, we show that unlike the well-studied case in Xenopus oocytes, where MAP kinase is an essential component of the MPF activation pathway, MAP kinase is not required for either MPF activation or subsequent oocyte maturation in starfish. Instead, its major role appears to be suppression of DNA synthesis in unfertilized, haploid eggs.
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U2 - 10.1006/dbio.1998.8869
DO - 10.1006/dbio.1998.8869
M3 - Article
C2 - 9578616
AN - SCOPUS:0032080365
VL - 197
SP - 25
EP - 38
JO - Developmental Biology
JF - Developmental Biology
SN - 0012-1606
IS - 1
ER -