Meeting Abstract
P2.43 Jan. 5 Isolation and Expression of Homeobox Genes in the Ctenophora PANG, K.*; MARTINDALE, M.Q.; University of Hawaii; University of Hawaii kpang@hawaii.edu
Homeobox genes are a large family of transcription factors that play integral roles in such processes as the development of the major body axis and cell specification in all metazoans thus studied. Extensive duplications and diversifications of these genes are thought to have led to the different body forms in the Bilateria. This radiation was present in the ancestor of cnidarians and bilaterians, as shown by the presence of about 130 homeobox genes of distinct classes in the sea anemone Nematostella vectensis. Placozoans and poriferans have a much lower overall number and diversity of homeobox genes, however complete genome sequencing of these phyla is currently underway and will reveal their complete repertoire in the near future. In ctenophores, the final phylum of non-bilaterian metazoans, only a single authentic homeobox gene has been published, a Tlx-like ortholog belonging to the ANTP class from Pleurobrachia pileus. Molecular phylogenetics suggest that ctenophores are sister to the group containing cnidarians and bilaterians, and therefore occupy a pivitol position in studying the evolution of homeobox genes in the Metazoa. Ctenophores have a complex development, characterized by a phylum-specific cleavage program, biradial symmetry, extensive nervous system composed of a nerve net and apical organ, and definitive muscle cells derived from endomesodermal lineages. We performed an extensive PCR screen for homeobox genes in the ctenophore, Mnemiopsis leidyi. We were able to isolate four ANTP class genes, three PRD class genes, and three SINE class genes. We performed in situ hybridizations to determine their expressions from embryonic to cydippid stages. They are expressed in discreet patterns that are associated with specific cell types or regions of the body. A complete genome-sequencing project is needed to identify the entire complement of this important family of developmental regulatory genes.
