Meeting Abstract

54.3  Tuesday, Jan. 5  Investigating the role of the Nodal signaling pathway in a indirect developing hemichordate, Ptychodera flava RöTTINGER, E*; DUBOC, T; MARTINDALE, MQ; Kewalo Marine Laboratory, University of Hawaii; Kewalo Marine Laboratory, University of Hawaii; Kewalo Marine Laboratory, University of Hawaii rottinge@hawaii.edu

Deuterostomes are a group of animals composed of chordates, echinoderms and hemichordates, and perhaps xenoturbellids. A historically unresolved and controversial question in evolutionary biology is the nature of the deuterostome ancestor and the origin of the chordate body plan. Hemichordates are a highly informative group because of their unique phylogenetic position among deuterostomes and the morphological similarities they share with chordates. In chordates, the genes encoding the TGFβ family member Nodal appear to play conserved roles in mesoderm and endoderm formation and patterning of the embryo along the dorso-ventral (D/V) and left-right (L/R) axes. Recently, the first non-chordate orthologs of Nodal have been described and analyzed in echinoderms and gastropods. Gene expression data and functional experiments in echinoderms have revealed that while the Nodal pathway in echinoderm is – like in chordates – involved in the patterning of the D/V and L/R axes, it does not appear to be involved in endomesoderm (EM) induction. Interestingly, in gastropodes, Nodal function seems to be required to trigger left or right handed coiling of the shell, suggesting an ancestral role of this pathway in establishing L/R asymmetries, co-opted in deuterostomes to pattern the D/V axis and in chordates to induce EM formation. In order to analyze the role of the Nodal signaling pathway in hemichordates, we cloned the main actors of this pathway from the indirect developing Hawaiian acorn worm, Ptychodera flava. Data using inhibitor and activation experiments, combined with gene expression analysis, suggest that the Nodal pathway is involved in mesoderm formation and D/V axis specification during early development, but no role in L/R asymmetry has yet been found.