MEIOSIS REINITIATION IN MOLLUSCAN OOCYTES - A MODEL TO STUDY THE TRANSDUCTION OF EXTRACELLULAR SIGNALS

G2-arrested marine invertebrate oocytes are triggered to re-enter the cell cycle by different extracellular signals (sperm, hormones and mim etics). They respond to competent signals either by germinal vesicle b reakdown (for those arrested in prophase I) or by polar body emission (for those arrested in metaphase I or II). These cellular responses ar e easy to observe and quantify thus making of meiosis reinitiation an attractive model to study the transduction of signals endogenous to oo cytes. Given the universal character of transmembrane coupling molecul es and intracellular effecters, the specificity of cell and, in partic ular, oocyte response to an extracellular signal are mediated by the p resence of specific receptors and by a specific set of intracellular e ffecters that are activated by them. In this paper we discuss the curr ent limitations in molecular and pharmacological identification and ch aracterization of invertebrate oocyte receptors. We next analyze signa lling pathways triggered by activation of relevant receptors and the c ross-talk existing between them. The above aspects are discussed on th e examples of serotonin-induced meiosis reinitiation in prophase I-arr ested oocytes of Spisula solidissima and on KCl-induced meiosis reinit iation of metaphase I-arrested Mytilus galloprovincialis oocytes taken as paradigms.