Meeting Abstract

66.7  Friday, Jan. 6  The Genome of the Ctenophore Pleurobrachia bachei: Molecular Insights into Independent Origins of Nervous Systems MOROZ, LL*; KOHN, A; CITARELLA , M; GRIGORENKO, A; KOCOT , K.; HALANYCH, K; ROGAEV, E; Univ of Florida; Univ of Florida; Univ of Florida; Univ of Massachusetts Med Sch; Univ of Alabama; Univ of Alabama; Univ of Massachusetts Med Sch moroz@whitney.ufl.edu

Our understanding of the origins and early evolution of animals is controversial because of limited data from basal Metazoa. The phylum Ctenophora (comb jellies) is one of the earliest animal lineages with well-recognized nervous and “true” mesoderm-derived muscular systems. The sea gooseberry (Pleurobrachia), has one of the most compact genomes within this group. These holoplanktonic predators have sophisticated ciliated locomotion, unique glue-based capture mechanisms and distinct development. Using 454/Roche and Illumina sequencing we achieved ~1,000x coverage of the genome. We then performed RNA-seq profiling from major tissues (~2,000x coverage) to validate the initial genome assembly and annotation: 96% of predicted gene models are supported by transcriptome data. As a result, our phylogenomic analysis is consistent with the most basal phylogenetic position of Ctenophores within the animal tree. This hypothesis is further supported by comparative analysis of selected gene families (including the apparent absence of HOX genes in Pleurobrachia). Second, our experimental data indicate that the nervous system in ctenophores is one of the most distinct in its morphological and molecular organization. Many “classical bilaterian neuron-specific” genes either are not present or, if present, they are not expressed in neurons. Finally, we identified novel markers for ctenophores neurons. Combined, these data suggest that at least some of the ctenophore neural populations were evolved independently from those in other animals.