Meeting Abstract
The Wnt signaling pathway is a key regulator of body plan organization and axis formation in all metazoans. We have analyzed the developmental role of Wnt signaling in the hemichordate Saccoglossus kowalevskii to gain insights into deuterostome and bilaterian body plan evolution. Our data shows that S. kowalevskii is the only known bilaterian with the full Wnt ligand complement predicted for the bilaterian ancestor. We have analyzed the roles of Wnt signaling in endomesoderm formation (Darras et al. 2011), anteroposterior axis formation, and posterior axis elongation. We demonstrate that in S. kowalevskii these three patterning roles of canonical Wnt signaling can be identified as three independent and discreet phases during development. We further demonstrate that during the establishment of the A/P axis, Wnt signaling in S. kowalevskii establishes the two most anterior body regions (anterior, center), but surprisingly is not involved in the establishment of the most posterior domain around the blastopore. Following gastrulation, canonical Wnt signaling mediates posterior elongation of the axis in a feedback loop with brachyury, as has been described in chordates. We discuss the comparative implications of this work for understanding the evolution of the bilaterian A/P axis.
