HINMAN, Veronica, F*; DAVIDSON, Eric, H; Caltech; Caltech: Evolution of Mesoderm Specification in Echinoderms: Gene Regulatory Network Architectural Reorganization Across Immense Periods of Evolutionary Time

This presentation will focus on the gene regulatory network (GRN) evolution of endomesodermal specification among echinoderms. GRNs detail the regulatory interconnections that prescribe developmental fate. Currently, there exists an extensive GRN that describes the specification of endoderm and mesoderm in echinoid echinoderms (sea urchins). This GRN serves as an excellent platform for evolutionary comparisons of GRNs in other taxa. Such comparisons will reveal the architectural reorganization of GRNs that must underlie evolutionary change in morphological features. We have previously shown that the early GRN that specifies the very beginnings of endomesodermal specification in sea urchins is highly conserved in the starfish Asterina miniata, although these two classes of echinoderms last shared a common ancestor around 500MYA. In later development, in both taxa, the endomesoderm is further specified as endoderm or mesoderm. In sea urchins, the mesoderm is specified by a Delta signal from a cell lineage (the micromeres) that is completely absent in starfish, and in fact in all other classes of echinoderms. This method of mesoderm specification must therefore be a derived feature of sea urchins. Embryological and phylogenetic evidence meanwhile suggests that starfish mesoderm specification is more likely pleisiomorphic. A comparison of GRNs involved in specification of the mesoderm in starfish and sea urchin will be presented.