RECEPTION AND TRANSDUCTION OF THE SEROTONIN SIGNAL RESPONSIBLE FOR OOCYTE MEIOSIS REINITIATION IN BIVALVES

Prophase-arrested oocytes of Spisula solidissima complete maturation e ither upon fertilization, KCI treatment or serotonin (=5 HT, for 5-hyd roxytryptamine). In Ruditapes philippinarum, 5 HT stimulation is a nec essary prerequisite to get further development since prophase-arrested oocytes are not fertilizable. The neurohormone drives them to a secon d arrest in metaphase 1, at which time they can be activated by sperm or excess KCl. These contrasted situations rely on a difference in the kinetics of appearance of L-type voltage-dependent calcium channels w hich are required for ensuring sperm or KCl-dependent activations. Ser otonin-specific receptors have been characterized in both species and seem to mediate maturation by mobilizing internal and external Ca2+ io ns. In Ruditapes, transduction of the serotonin signal involves a coup ling of the receptor to G-proteins, which would activate phospholipase C, producing a transient peak of inositol trisphosphate (IP3) and an increase in the intracellular Ca2+ concentration Experimental argument s suggest that diacylglycerol exerts a negative retrocontrol on the ca lcium response by stimulating kinase C. Protein kinases activation and conditions responsible for the metaphase arrest are also discussed.