Annual cycle of expression of connective tissue polypeptide markers in the mantle of the musselMytilus galloprovincialis

We suggest that gonad development in the mantle tissue of the bivalve molluscMytilus galloprovincialis Lmk. is an example of epithelial/mesenchymal interactions (i.e. soma/germline interactions) and morphogenesis in the adult state. According to this concept, the aim of the present study was to use biochemical and immunochemical methods for identifying and characterizing the mantle cell polypeptide markers whose expression is seasonally and morphogenetically regulated. We showed for the first time thatM. galloprovincialis mantle, of both males and females, contains polypeptides (with an apparent mol. wt of 45 to 53 kDa) specific for connective tissue (mantle connective tissue polypeptides; MCTPs). Electrophoretic, immunoblotting and immunofluorescent experiments demonstrated that MCTPs are primarily localized in the adipogranular (ADG) cells, and their expression in the mantle is seasonally regulated. There is a positive correlation between MCTP expression and connective tissue volume in the mantle. MCTPs are overexpressed during the rest period, when the mantle consists of connective tissue mainly, whereas mature gonads contain only trace amounts of MCTPs. Moreover, there is a temporal correlation between the onset and decrease of MCTP expression and the appearance and disappearance of the ADG cells in the mantle. MCTP localization in the mantle tissue should not be associated with the ADG cells only, because positive immunofluorescence was also detected in follicle membranes (but not in germ cells) and superficial mantle epithelium. Using immunoblotting and immunofluorescence, MCTPs were found in the connective tissue of the mantle, posterior adductor muscle and visceral mass, but not gills, foot or hepatopancreas. Possible mechanisms by which MCTPs could participate in the annual processes of mantle gonad/connective tissue development and involution are discussed.