BBB seminar: Ulrich Technau
Reconstructing the Urmetazoa: The cnidarians and the evolution of developmental mechanisms
Sars International Centre for Marine Molecular Biology, Bergen
Cnidaria are basal Metazoa which arose early in animal evolution and are the best studied outgroup for the Bilateria, to which the majority of animals belongs. They are considered to be radially symmetric and diploblastic, i.e. they consist of endoderm and ectoderm only and lack true mesoderm. In an attempt to trace the evolution of the mesoderm, we isolated a number of "mesodermal" genes from the cnidarians Hydra and Nematostella. We investigated in more detail the role of Brachyury, a T-box transcription factor in these animals as well as in heterologous systems. The expression analysis of a number of further mesodermal marker genes in Nematostella indicates that the diploblastic common ancestor of Cnidaria and Bilateria possessed already the molecular machinery necessary to make mesoderm. More recently, we carried out an extensive EST screen in Nematostella. Our analysis revealed an unexpected complexity of the genetic repertoire of these simple animals, indicating that the common ancestor of Cnidaria and Bilateria was genetically highly complex. The data further emphasize the importance of gene loss during the evolution of most extant animal lineages, including the major model organisms such as Drosophila and C. elegans.