NEDERBRAGT, A.J.*; DICTUS, W.J.A.G.; VANLOON, A.E.: Conserved Gene Networks in Development: The Engrailed and Dpp Homologues in Molluscan Shell Development

During Drosophila development the engrailed/hedgehog/decapentaplegic gene network functions in setting up boundaries between different compartments, e.g. between anterior and posterior compartments in imaginal discs. Here, engrailed is expressed in cells on one side of the border. These cells then secrete the hedgehog gene product that reaches the other side of the border where it induces the expression of decapentaplegic (dpp) . We are investigating the possible role of this network during the development of the gastropod mollusk Patella vulgata. We have cloned the Patella vulgata homologues of engrailed and dpp and analyzed their spatio-temporal expression patterns by in situ hybridization. The Patella engrailed and dpp genes are expressed at the border between the shell forming epithelium and adjacent ectodermal non-shell forming cells, with engrailed being expressed by the shell forming cells. Previous research in our lab has shown that the cells of the shell forming mantle edge can communicate via gap junctions with each other, but not with surrounding tissue. This shows that there is a communication compartment boundary between the Patella engrailed and dpp expressing cells. Interestingly, insect imaginal disc compartments are also communication compartments. Our results show that the gene network involving engrailed and dpp, has a conserved function between Drosophila, Patella and other animal systems, namely setting up boundaries between developmental compartments. To further confirm this hypothesis, we have recently isolated a Patella hedgehog homologue and are investigating its role in setting up this boundary.