Meeting Abstract

S9-2.2  Saturday, Jan. 7  The Genome of the Ctenophore, Mnemiopsis leidyi: Insights into the Origins of Morphological Complexity RYAN, J.F.; PANG, K.; SCHNITZLER, C.E.; NGUYEN, A.-D.; MORELAND, R.T.; HAVLAK, P.; PUTNAM, N.H.; NISC, ; WOLFSBERG, T.G.; MULLIKIN, J.C.; MARTINDALE, M.Q.; BAXEVANIS, A.D.*; NHGRI/NIH; Univ. of Hawaii; NHGRI/NIH; NHGRI/NIH; NHGRI/NIH; Rice Univ.; Rice Univ.; NHGRI/NIH; NHGRI/NIH; NHGRI/NIH; Univ. of Hawaii; NHGRI/NIH

Whole-genome sequencing of non-bilaterian animal species and their closest non-metazoan relatives has provided invaluable insight into the molecular innovations that have fueled the outbreak of diversity and complexity in the early evolution of animals. Until recently, the phylum Ctenophora was the only non-bilaterian metazoan lineage without a sequenced genome. To fill this void, we have sequenced, assembled, and annotated the 155 Mb Mnemiopsis genome at 12x coverage. In addition, RNAseq data from mixed-stage Mnemiopsis embryos were aligned to the genome and used as the basis for transcriptome annotation. Manual inspection of gene predictions was also performed against experimentally verified RACE transcripts. Based on this work, the Mnemiopsis genome is predicted to contain 16,545 genes and 91,482 exons. The availability of these high-quality, genome-scale sequence data has enabled us to answer some important questions regarding phylogenetic diversity and the evolution of proteins that play a fundamental role in metazoan development. Our initial analysis of the genome shows that many of the transcription factors and signaling pathway components present in other animal genomes are also present in the Mnemiopsis genome. However, several important developmental genes present in bilaterians, cnidarians, and placozoans are conspicuously absent in Mnemiopsis. These findings are consistent with recent molecular-based phylogenies and support the notion that ctenophores and sponges are the two earliest-branching animal lineages. Analysis of the gene content of these earliest metazoan groups is helping to redefine which components were required for the origin of morphological complexity and shed new light on the actual phylogenetic position of the ctenophores.