Sexual differentiation of reproductive tissue in bivalve molluscs: identification of male associated polypeptide in the mantle of Mytilus galloprovincialis Lmk.

We have addressed the question of sexual reproductive tissue dimorphism in bivalve molluscs, Mytilus galloprovincialis Lmk, which is a stable gonochoric species although with no apparent differences in gonad morphology of both sexes. At all periods of the annual cycle the proteins specific of male/female gonads were identified. One of these proteins, "male-associated polypeptide" with apparent MW 39 kDa (MAP-39), has been biochemically and immunochemically characterized. MAP-39 concentration in male mature gonads achieved up to 10% of the total soluble protein while in female ones only traces of this protein could be detected. In male mantle, MAP-39 expression was associated with the process of gonad development and maturation as well as gamete spawning, although this polypeptide has been localized in fibroblast-like cells, membrane of follicles and connective tissue matrix of the mantle but not in germinal cells.