Meeting Abstract

P1.67  Monday, Jan. 4  Origins Of Triploblasty: What Corals Can Tell Us. LOEFFLER, J.*; MARTINDALE, M.Q.; Kewalo Marine Laboratories, University of Hawaii at Manoa; Kewalo Marine Laboratories, University of Hawaii at Manoa jorik@hawaii.edu

In bilaterians, a single embryonic endomesodermal tissue segregates into mesoderm and endoderm during gastrulation. The evolutionary origin of this tissue and its derivatives is unknown. The sequencing of the genome of the sea anemone Nematostella vectensis (Cnidaria, Anthozoa) has revealed that a large set of genes involved in forming endomesodermal and subsequently mesodermal tissue in triploblasts are also present in this basal metazoan. Expression of these genes occurs at the blastopore early during gastrulation and for some, extends into the developing gastrodermis. This observation, and the fact that the gastrodermis has bifunctional capacities, absorptive and contractile, led to the idea that an ancestral endomesoderm existed in the last common cnidarian/bilaterian ancestor. Genes involved in formation of this tissue were recruited to perform novel roles in specifying endoderm and mesoderm in the evolving triploblasts. Anthozoans are thought to be the earliest branching cnidarians. To further investigate ancestral endomesodermal genes, it is important to examine different members of this class. We identified and characterized brachyury, snail, foxA, moxC and otx in the coral Fungia scutaria. Bilaterian homologs of these genes are associated with endomesoderm formation or mesoderm differentiation. In Fungia, they are expressed around the blastopore and, all but brachyury, in the developing gastrodermis, a pattern similar to what has been observed in Nematostella. This supports the idea that these genes had ancient functions in tissue specification before the origin of mesoderm. We are investigating spatial and temporal expression patterns of additional endomesodermal genes in Fungia to gain deeper insight into the ancestral endomesodermal network.