Presence of TGF-beta-like molecules in the embryonic development of the mollusc Viviparus ater

The expression of TGF-b1- and TGF-b type II receptor-like molecules was examined by immunocytochemistry in the course of the embryonic development of the gonochoristic gastropod Viviparus ater. This species has a direct development that occurs in the lower part of the oviduct; the progeny leaves the parent as juvenile snails. Embryo stages, based on major diameter size, were expressed as a percentage of total embryonic development (E0 = fertilized egg; E100 = hatching). TGF-b1- and TGF-b type II receptor-like molecules were detected early at E10 (10% of embryonic development), in the cytoplasm and plasma membrane of large mesenchymal storage cells that surrounded the forming tissue and organs. The immunoreactivity (IR) was observed during further development in cells of the organizing central nervous ganglia, sense organs, heart, foot, mantle and in hemocytes of hematic lacunae present in developing organs. In embryos from 50% development to hatching the IR increased in central nervous system, heart, sense organs and gills. The distrubution pattern of immunoreactive cells suggest a role of TGF-b1-like molecules in the embryonic microenvironment of the mollusc. These molecules appeared early, seem to act in a paracrine and autocrine manner and to be involved in organ pattern formation. In more advanced stages these molecules may act in tissue re-organization and growth of organs as the developmental consequence of gastropod torsion in order to shape the embryo and adult body plans.