Cnidarian Zic Genes.

To understand the ancestral and evolved roles of zic homologs, it is important to reconstruct the putative roles of ancient zic homologs in the animal phylogeny. Most studies of zic genes have been conducted in model systems that are members of the bilaterian phylum. However, two additional phyla have zic homologs encoded in their genomes. The three animal phyla that contain zic homologs all share a common ancestor and collectively are termed the parahoxozoans (cnidarians (corals, sea anemones, and jellyfish), placozoans (Trichoplax adhaerens), and bilaterians (chordates, insects, nematodes, annelids, echinoderms, etc.). In this chapter we briefly discuss our understanding of zic genes in the parahoxozoans with a particular focus on how expression of cnidarian zic homologs in the medusozoan Hydra vulgaris and the anthozoan Nematostella vectensis informs our understanding of the putative ancestral roles zic homologs played in the cnidarian-bilaterian common ancestor.