Abstract

Evolution of body axes in Eumetazoa: what can we learn from Cnidaria?

It has been suggested that Wnt signaling established the primary anterior-posterior body axis, and BMP signaling defined the secondary dorso-ventral body axis in the last common ancestor of Bilateria. The phylum Cnidaria, a sister group of the Bilateria, includes mostly radially symmetric animals like jellyfish and hydroids. Additionally, it contains its own class of bilaterally symmetric animals, the Anthozoa (corals, sea anemones). Apart from the main oral-aboral axis common to all cnidarians, the anthozoans have a secondary “directive” axis orthogonal to the primary one. Strikingly, like in Bilateria, the primary oral-aboral axis is specified by Wnt signaling, and BMP signaling is involved in defining the secondary directive axis in a sea anemone /Nematostella vectensis/. This adds to the long-standing debate whether any of the cnidarian body axes are homologous to any of the bilaterian ones. I will address the question of how the body axes are established in /Nematostella vectensis/ and if any of the cnidarian body axes are homologous to any of the bilaterian ones.