ANNUAL CYCLE OF EXPRESSION OF CONNECTIVE-TISSUE POLYPEPTIDE MARKERS IN THE MANTLE OF THE MUSSEL MYTILUS-GALLOPROVINCIALIS

We suggest that gonad development in the mantle tissue of the bivalve mollusc Mytilus galloprovincialis Lmk. is an example of epithelial/mes enchymal interactions (i.e. soma/germline interactions) and morphogene sis in the adult state. According to this concept, the aim of the pres ent study was to use biochemical and immunochemical methods for identi fying and characterizing the mantle cell polypeptide markers whose exp ression is seasonally and morphogenetically regulated. We showed for t he first time that hi. galloprovincialis mantle, of both males and fem ales, contains polypeptides (with an apparent mel. wt of 45 to 53 kDa) specific for connective tissue (''mantle connective tissue polypeptid es''; MCTPs). Electrophoretic, immunoblotting and immunofluorescent ex periments demonstrated that MCTPs are primarily localized in the adipo granular (ADG) cells, and their expression in the mantle is seasonally regulated. There is a positive correlation between MCTP expression an d connective tissue volume in the mantle. MCTPs are overexpressed duri ng the rest period, when the mantle consists of connective tissue main ly, whereas mature gonads contain only trace amounts of MCTPs. Moreove r, there is a temporal correlation between the onset and decrease of M CTP expression and the appearance and disappearance of the ADG cells i n the mantle. MCTP localization in the mantle tissue should not be ass ociated with the ADG cells only, because positive immunofluorescence w as also detected in follicle membranes (but not in germ cells) and sup erficial mantle epithelium. Using immunoblotting and immunofluorescenc e, MCTPs were found in the connective tissue of the mantle, posterior adductor muscle and visceral mass, but not gills, foot or hepatopancre as. Possible mechanisms by which MCTPs could participate in the annual processes of mantle gonad/connective tissue development and involutio n are discussed.