Meeting Abstract

11.7  Friday, Jan. 4  Quest for Muscle Specific Genes in Pleurobrachia bachei : Had mesoderm independently evolved in Ctenophores? FODOR, A*; KOHN, A.B.; SWALLA, B.J.; MOROZ, L.L.; Univ of Florida; Univ of Florida; Univ of Washington; Univ of Florida zebinini@gmail.com

The nature and development of a mesoderm in basal metazoans has been questioned for over a hundred years, with arguments based on Porifera as the most basally branched lineage and Cnidarians possessing a diploblastic body plan with myoepithelial cell. However recent phylogenetic analysis suggests that Ctenophora may be the earliest lineage of animals, yet processing true neurons and muscles and remarkably complex behaviors. To address the molecular bases of the origins of muscular organization, we searched for the presence of mesoderm and muscle specific genes in the genome of Pleurobrachia bachei. Although some well-known bilaterian myogenic transcription factors were absent in the ctenophore genome, we found and cloned several muscle markers such as tropomyosin and calponin as well as β-catenin and 2 T-Box transcription factors. Interestingly, in situ hybridization of these genes showed expression not only in the muscular regions of P. bachei, but in the epidermal tissues as well, indicating there is an unknown function for these genes in non-muscular cells. At the same time some well-defined muscles were either not labeled or the expression of relative muscular markers was relatively low. The expression patterns for selected genes were also quite variable in P. bachei embryos. Our data suggest that ctenophores might represent a unique example of parallel evolution of mesoderm and muscular organization where many features in this lineage had evolved independently from cnidarians and bilaterian animals.