Meeting Abstract
The cnidarians – organisms unified in a single phylum based on their use of cnidocytes to capture prey and defense from predators – occupy a key phylogenetic position as the sister group to the bilaterians. Given their experimental tractability and great potential for studying regeneration and allorecognition, we have sequenced and annotated the genomes of two cnidarian species: Hydractinia echinata and Hydractinia symbiolongicarpus. The remarkable regenerative capacity of these species is conferred by migratory interstitial cells (or i-cells) that are pluripotent, expressing genes whose bilaterian homologs are known to be involved in stem cell biology. Using PacBio, Illumina, and Dovetail-based strategies, high-coverage sequencing data indicate a genome size of 774 Mb for H. echinata (84x coverage) and 514 Mb for H. symbiolongicarpus (94x); these genomes are AT-rich (65%) and highly repetitive (>46%). The vast majority of evolutionarily conserved single-copy orthologs have been identified in these assemblies, and analyses of these whole-genome sequencing data have already provided important insights into the evolution of chromatin compaction and sex determination. These data have also revealed a heretofore-underappreciated complexity of the mechanisms controlling allorecognition in these colonial organisms with the discovery of a new set of candidate allorecognition genes. Our genome-scale data have established a strong foundation for identifying evolutionary novelties contained within these genomes and for functional studies aimed at identifying new targets for therapies in regenerative medicine.
