Sexual differentiation of the somatic gonad tissue in marine bivalve mollusks: esterase- and fibronectin-like recognition signals

Textbooks usually indicate that in many species sex determination starts wi th gonad differentiation, triggered during early embryonic development. Onc e a primary somatic gonad is formed, the gonad-derived inductive signals ar e used to maintain the sex differentiation of germ cells. In marine bivalve s, sex is not determined until the germ cells are differentiated, whether t hat is in the larva or in the juvenile. As sex is often decided late in pos t-larval development, gonad differentiation starts in the adult state. It i s generally accepted that bivalves have no great difficulty in transforming from hermaphroditism to gonochorism and vice versa (Mackie, 1984). Our res ults focus attention on the patterns of gene expression in the "common" gon ad (i.e., ovotestis) of the simultaneous hermaphroditic scallop species, Pe cten maximus, during maturation and reproduction periods. In this species, as in almost all marine bivalves, the connective-tissue cell types present in the testis and ovary of the "common" gonad are essentially identical. Us ing biochemical, immunochemical and molecular approaches, we demonstrate fo r the first time that the scallop ovotestis is characterized by germ-cell-a ssociated somatic protein expression.