Thimerosal triggers meiosis reinitiation in oocytes of the Japanese clam Ruditapes philippinarum by eliciting an intracellular Ca2+ surge.
Ovarian oocytes of the bivalve mollusc Ruditapes philippinarum are arrested during first meiotic prophase. Release from this blockade is triggered by the neurohormone serotonin (5HT or 5-hydroxytryptamine), which promotes germinal vesicle breakdown and drives these oocytes to a second arrest in metaphase I. 5HT action involves binding to a specific G protein-coupled receptor which results in a transient rise in IP3 and in the intracellular free Ca2+ concentration. Here we analyze the cytological effects and mode of action of the sulphydryl reagent thimerosal which could also trigger meiosis reinitiation in Ruditapes. No metaphase I spindle formed under these conditions since thimerosal was found to be able to preclude or reverse tubulin polymerization when applied to prophase- or to metaphase-arrested oocytes, respectively. Our results strongly suggest that the common final target for 5HT and thimerosal actions consists in a transient rise in internal free Ca2+ level that we could follow using Fluo3/AM as a probe. The effect of thimerosal in promoting oocyte maturation and increasing intracellular free Ca2+ concentration was improved by excess KCI. In addition, thimerosal, but not KCI, was found to facilitate 5HT-induced maturation at subthreshold hormone concentrations which, by themselves, did not produce an intracellular Ca2+ surge. These data suggest that thimerosal may inhibit Ca2+ pumps of the endoplasmic reticulum and unmask the plasma membrane voltage-sensitive Ca2+ channels which also appear after 5HT-induced GVBD.
Lippai
M
M
Laboratoire de Biologie moléculaire et cellulaire, UMR 49, Ecole Normale Supérieure de Lyon, France.
Gobet
I
I
Tomkowiak
M
M
Durocher
Y
Y
Leclerc
C
C
Moreau
M
M
Guerrier
P
P
D000814:Aniline Compounds; D000818:Animals; D049872:Bivalvia; D002118:Calcium / Q000378:metabolism*; D002875:Chromosomes / Q000648:ultrastructure; D005260:Female; D005456:Fluorescent Dyes; D008540:Meiosis / Q000187:drug effects*; D008870:Microtubules / Q000187:drug effects; D009865:Oocytes / Q000166:cytology* / Q000378:metabolism / Q000648:ultrastructure; D011189:Potassium Chloride / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D013849:Thimerosal / Q000494:pharmacology*; D014966:Xanthenes
D000814:Aniline Compounds; D005456:Fluorescent Dyes; D014966:Xanthenes; D013849:Thimerosal; C059715:Fluo-3; D012701:Serotonin; D011189:Potassium Chloride; D002118:Calcium