Pertussis toxin-sensitive G protein participating in starfish oocyte maturation induced by 1-methyladenine
作者:
MOTONORI HOSHI,
KAZUYOSHI CHIBA,
MIDORI MATSUMOTO,
HIROHIKO TADENUMA,
KATSUNOBU TAKAHASHI,
TOSHIAKI KATADA,
期刊:
Invertebrate Reproduction & Development
(Taylor Available online 1992)
卷期:
Volume 22,
issue 1-3
页码: 1-9
ISSN:0792-4259
年代: 1992
DOI:10.1080/07924259.1992.9672250
出版商: Taylor & Francis Group
关键词: 1-methyladenine;oocyte maturation;signal transduction;G protein;pertussis toxin;starfish;Asterina pectinifera
数据来源: Taylor
摘要:
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 inAsterina pectiniferaandAsterina (Patina) 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 ofA. pectiniferaoocytes contained a G protein consisting of 39-kDa α, 37-kDa β, and 8-kDa γ subunits. The α 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 α 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 α 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.
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