Hox and Wnt pattern the primary body axis of an anthozoan cnidarian before gastrulation

Abstract

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. Here we report a previously unrecognized domain of Hox expression in the starlet sea anemone, Nematostella vectensis, beginning at early blastula stages. We explore the relationship of two opposing Hox genes (NvAx6/NvAx1) expressed on each side of the blastula during early development. Functional perturbation reveals that NvAx6 and NvAx1 not only regulate their respective expression domains, but also interact with Wnt genes to pattern the entire oral-aboral axis. These findings suggest an ancient link between Hox/Wnt patterning during axis formation and indicate that oral-aboral domains are likely established during blastula formation in anthozoan cnidarians.