A WNT of things to come: Evolution of Wnt signaling and polarity in cnidarians

The conserved family of Wnt signaling molecules mediates various developmental processes including governing cell fate, proliferation, and polarity. The diverse developmental functions of the Wnt genes in bilaterians have obscured the evolutionary origin of this important signaling pathway. Recent work in the Cnidaria has shown the diversity of Wnt genes, and regulatory components of Wnt signaling, evolved early in metazoan evolution, prior to the divergence of cnidarians and bilaterians. Evidence from Hydra and the sea anemone, Nematostella, demonstrates a role for Wnt signaling in axis formation and patterning, as well as gastrulation and germ-layer specification. In this review, we examine what is currently known about Wnt signaling in cnidarians, and discuss what this group of “simple” animals may reveal about the evolution of Wnt signaling and polarity.