Dr. Joseph Ryan from the Sars International Centre for Marine Molecular Biology, Bergen, Norway will present recent work of his and coworkers in the NCB seminar series. All welcome!
The sequence of the Mnemiopsis leidyi genome provides evidence supporting the independent evolution of a nervous system and mesodermal cell types in ctenophores
Ctenophores or comb jellies are amongst the most visually striking and voracious animals in the animal kingdom. As one of the most distant relatives of bilateral animals (bilaterians), they are critical for reconstructing events that occurred early in animal evolution. Nevertheless, the exact phylogenetic position of the group has been in dispute for over a century. We used next-generation sequencing technologies to sequence, assemble, and annotate the ~150-megabase genome of the ctenophore Mnemiopsis leidyi. Our extensive phylogenomic analyses provide no support for a sister relationship between ctenophores and cnidarians; instead, they support Ctenophora as either the sister group to all other animals or as sister to all animals except sponges. This phylogeny is in line with our gene family and signaling pathway studies. The presence and absence of nervous system genes in Mnemiopsis is more similar to the aneural sponges than to cnidarians suggesting that ctenophores evolved an independent nervous system and/or that some degree of a nervous system was lost in sponges and placozoans. Furthermore, the vast majority of genes involved in the specification and differentiation of mesoderm in bilaterians are absent from the Mnemiopsis genome. This is surprising given that Mnemiopsis and other ctenophores possess definitive mesodermal musculature, and suggests that the mesodermal cell types of ctenophores evolved independently of other animals. This work enhances the genomic resolution at the base of the animal tree, gives compelling evidence for the independent evolution of major organ systems and paves the way for a new burst of ecological, evolutionary, developmental, and genomic interest in ctenophores.