Pertussis toxin-sensitive G protein participating in starfish oocyte maturation induced by 1-methyladenine

Motonori Hoshi, Kazuyoshi Chiba, Midori Matsumoto, Hirohiko Tadenuma, Katsunobu Takahashi, Toshiaki Katada

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

1-Methyladenine (1-MA) secreted from the follicle cells is the biological signal for meiosis reinitiation of starfish oocytes. The signal of 1-MA is transduced into cytoplasmic formation of maturation-promoting factor (MPF) that eventually induces a germinal vesicle breakdown (GVBD). Microinjection of pertussis toxin (PTX) inhibited 1-MA-induced GVBD in Asterina pectinifera and Asterina (Patiria) miniata. PTX-inhibition of GVBD was rescued by the injection of MPF into PTX-preinjected oocytes. Most of the PTX-and MPF-double injected eggs were fertilized and underwent cleavage, suggesting the presence of a GTP-binding protein (G protein) specific for 1-MA signal transduction. Indeed, plasma membrane preparations of A. pectinifera oocytes contained a G protein consisting of 39-kDa α, 37-kDa β, and 8-kDa γ subunits. The a subunit contained a site for ADP-ribosylation catalyzed by PTX. It was also recognized by antibodies specific for a common GTP-binding site of mammalian a subunits or a carboxy-terminal ADP-ribosylation site of mammalian inhibitory G protein (Gi) α subunits. Its gene was 74% and 83.7% identical to the rat Gi-2α gene in nucleotide and deduced amino acid sequences, respectively. The 39-kDa α subunit shared the common GTP-binding site of mammalian G protein a subunits and the PTX-catalyzed ADP-ribosylation site of mammalian Giα subunits as expected from the immunoreactivity. The oocyte membranes had apparently two forms of 1-MA receptors with high and low affinities. The high-affinity form was converted into the low-affinity one in the presence of a non-hydrolyzable analogue of GTP. The 39-kDa α subunit of starfish G protein was also ADP-ribosylated by cholera toxin only when 1-MA was added to the membranes. These results indicate that in starfish oocyte membranes, 1-MA receptors are functionally coupled with the 39-kDa PTX-substrate G protein that transduces the signal into the formation of a cytoplasmic factor (MPF) and eventually into the reinitiation of meiosis.

Original languageEnglish
Pages (from-to)1-10
Number of pages10
JournalInvertebrate Reproduction and Development
Volume22
Issue number1-3
DOIs
Publication statusPublished - 1992 Dec
Externally publishedYes

Keywords

  • 1-methyladenine
  • Asterina pectinifera
  • G protein
  • Oocyte maturation
  • Pertussis toxin
  • Signal transduction
  • Starfish

ASJC Scopus subject areas

  • Animal Science and Zoology
  • Developmental Biology

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