Hoxgenes pattern the primary body axis of an anthozoan cnidarian prior to gastrulation

Hox gene transcription factors are important regulators of positional identity along the anterior-posterior axis in bilaterian animals. Cnidarians (e.g. sea anemones, corals and hydroids) are the sister group to the Bilateria and possess genes related to both anterior and central/posterior class Hox genes. In the absence of a conserved set of Hox genes among other early branching animal clades, cnidarians provide the best opportunity to learn about the emergence of this gene family. We report a previously unrecognized domain of Hox expression in the starlet sea anemone, Nematostella vectensis , beginning at early blastula stages. Functional perturbation reveals that two Hox genes not only regulate their respective expression domains, but interact with one another to pattern the entire oral-aboral axis mediated by Wnt signaling. This suggests an ancient link between Hox / Wnt patterning of the oral-aboral axis and suggest that these domains are likely established during blastula formation in anthozoan cnidarians.