| The specific aim of this project has been to study whether the evolution of the highly derived radial body plan of the Echinodermata was associated with recruitment of body patterning genes into new developmental roles. The process by which body-patterning genes take on new developmental functions is called genetic recruitment. Molecular evolution of gene cis-regulatory regions results in the establishment of novel regulatory binding sites with the consequence that, in addition to existing regulatory interactions, the gene becomes integrated into new regulatory networks, resulting in novel expression domains and new downstream targets. The expression of three body patterning genes in representative species from four of the five echinoderm classes was investigated. Expression of these genes in derived echinoderm morphology, such as the water vascular system, suggests that these genes have been recruited into new roles during the evolution of the phylum. A more detailed comparative analysis of gene expression during larval development between closely related species revealed substantial differences in expression domains. This suggests that body-patterning genes may be involved in the evolution of larval morphology. The results of this study, along with other comparative developmental data, are revealing that body patterning genes, when viewed in a phylogenetic context, have quite rich evolutionary histories, play many developmental roles between phyla and routinely carry out multiple roles within one species. |
