A receptor linked to a Gi-family G-protein functions in initiating oocyte maturation in starfish but not frogs.
The stimulation of oocyte maturation by 1-methyladenine in starfish, and by a steroid in frogs, has been proposed to involve G-protein-coupled receptors. To examine whether activation of receptors linked to G(i) or G(z) was sufficient to cause oocyte maturation, we expressed mammalian G(i)- and G(z)-linked receptors in starfish and frog oocytes. Application of the corresponding agonists caused meiosis to resume in the starfish but not the frog oocytes. We confirmed that the receptors were effectively expressed in the frog oocytes by using a chimeric G-protein, G(qi), that converts input from G(i)- and G(z)-linked receptors to a G(q) output and results in a contraction of the oocyte's pigment. These results argue against G(i) or G(z) functioning to cause maturation in frog oocytes. Consistently, maturation-inducing steroids did not cause pigment contraction in frog oocytes expressing G(qi), and G(z) protein was not detectable in frog oocytes. For starfish oocytes, however, our results support the conclusion that G(i) functions in 1-methyladenine signaling and suggest the possibility of using frog oocyte pigment contraction as an assay to identify the 1-methyladenine receptor. To test this concept, we coexpressed G(qi) and a starfish adenosine receptor in frog oocytes and showed that applying adenosine caused pigment contraction.
Kalinowski
Rebecca R
RR
Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06032, USA.
Jaffe
Laurinda A
LA
Foltz
Kathy R
KR
Giusti
Andrew F
AF
D000818:Animals; D001483:Base Sequence; D002455:Cell Division; D017931:DNA Primers; D018076:DNA, Complementary; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D008540:Meiosis; D009865:Oocytes / Q000166:cytology* / Q000187:drug effects; D011374:Progesterone / Q000494:pharmacology; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics; D018047:Receptors, Purinergic P1 / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013215:Starfish; D014982:Xenopus laevis
D017931:DNA Primers; D018076:DNA, Complementary; D012333:RNA, Messenger; D018047:Receptors, Purinergic P1; D011374:Progesterone; D019206:GTP-Binding Protein alpha Subunits, Gi-Go