Meeting Abstract
The cnidarians – organisms unified in a single phylum based on their use of cnidocytes to capture prey and for defense from predators – occupy a key phylogenetic position as the sister group to the bilaterians. Given their experimental tractability and great potential as emerging models for the study of regeneration, stem cell biology, and allorecognition, we are sequencing and annotating the genomes of two cnidarian species: Hydractinia echinata and Hydractinia symbiolongicarpus. What makes Hydractinia particularly attractive for study is that they possess a specific type of interstitial cell (or i-cell) that is pluripotent, expressing genes whose bilaterian homologs are known to be involved in stem cell biology. Hydractinia is also colonial, with a complex allorecognition system that lends itself to the study of host-graft rejection. Using PacBio, Illumina, and Dovetail-based strategies, high-coverage sequencing data indicate an estimated genome size of 774 Mb for H. echinata (84x coverage) and 514 Mb for H. symbiolongicarpus (94x coverage); these genomes are AT-rich (65%) and highly repetitive (47-51%). The vast majority of a set of evolutionarily conserved single-copy orthologs can be easily identified in these assemblies, and analyses of these whole-genome sequencing data have already provided important insights into the evolution of chromatin compaction, the mechanisms underlying allorecognition, and metazoan neurogenesis, while also establishing a strong foundation for future genomic and functional studies aimed at identifying new targets for therapies in regenerative medicine.
