Pre-Bilaterian Origins of the Hox Cluster and the Hox Code: Evidence from the Sea Anemone, <em>Nematostella vectensis</em> Joseph F. Ryan Maureen E. Mazza Kevin Pang David Q. Matus Andreas D. Baxevanis Mark Q. Martindale John R. Finnerty 10.1371/journal.pone.0000153 https://plos.figshare.com/articles/dataset/Pre_Bilaterian_Origins_of_the_Hox_Cluster_and_the_Hox_Code_Evidence_from_the_Sea_Anemone_Nematostella_vectensis__/152428 <div><h3>Background</h3><p>Hox genes were critical to many morphological innovations of bilaterian animals. However, early Hox evolution remains obscure. Phylogenetic, developmental, and genomic analyses on the cnidarian sea anemone <em>Nematostella vectensis</em> challenge recent claims that the Hox code is a bilaterian invention and that no “true” Hox genes exist in the phylum Cnidaria.</p> <h3>Methodology/Principal Findings</h3><p>Phylogenetic analyses of 18 Hox-related genes from <em>Nematostella</em> identify putative Hox1, Hox2, and Hox9+ genes. Statistical comparisons among competing hypotheses bolster these findings, including an explicit consideration of the gene losses implied by alternate topologies. <em>In situ</em> hybridization studies of 20 Hox-related genes reveal that multiple Hox genes are expressed in distinct regions along the primary body axis, supporting the existence of a pre-bilaterian Hox code. Additionally, several Hox genes are expressed in nested domains along the secondary body axis, suggesting a role in “dorsoventral” patterning.</p> <h3>Conclusions/Significance</h3><p>A cluster of anterior and posterior Hox genes, as well as ParaHox cluster of genes evolved prior to the cnidarian-bilaterian split. There is evidence to suggest that these clusters were formed from a series of tandem gene duplication events and played a role in patterning both the primary and secondary body axes in a bilaterally symmetrical common ancestor. Cnidarians and bilaterians shared a common ancestor some 570 to 700 million years ago, and as such, are derived from a common body plan. Our work reveals several conserved genetic components that are found in both of these diverse lineages. This finding is consistent with the hypothesis that a set of developmental rules established in the common ancestor of cnidarians and bilaterians is still at work today.</p> </div> 2007-01-24 00:40:28 pre-bilaterian origins hox