Meeting Abstract

32.1  Sunday, Jan. 5 08:00  Origin and Lineage-Specific Evolution of Ligand-gated Ion Channels in Basal Metazoans and Bilaterians KOHN, A.B.*; MOROZ, L.L.; UF, Whitney lab; UF, Whitney lab and Dept of Neuroscience abkohn@msn.com

Ligand-gated ion channels (LGICs) or ionotropic receptors are transmembrane ion channels that are opened or closed in response to the binding of a chemical messenger such as a transmitter or signaling peptide or even metabolite and protons. They are vital for virtual all aspects of neural signaling and nervous system evolution. There are three major classes of such ionotropic receptors: cys-loop receptors, ATP-gated channels, ionotropic glutamate receptors, etc. – with over 70 LGICs in humans. Here, we have reconstructed the evolution of major families of these channels with an evidence of parallel recruitment of different transmitter systems in both basal metazoans and different bilaterian lineages. Specifically, we used information from two newly sequenced genomes of the ctenophore Pleurobrachia bachei and the sea slug Aplysia californica as well as from more than three dozen deep transcriptomes from both basal metazoans and bilaterians (focusing on Lophotrochozoa). For example, the ctenophore genomes and their transcriptomes do not have cys-loop receptors; however there is a considerable diversity within other classes of receptors, significantly greater than previously described for any other basal metazoan. We also showed that the cys-loop receptors are underrepresented in many lophotrochozoans including Aplysia. In contrast, ionotropic glutamate receptors (iGluR) underwent an extraordinary expansion in both ctenophores and molluscs with numerous lineage-specific innovations and the origin of new iGluR classes that are missing in vertebrates.We also showed that the increase in a complexity of some iGluRs is based upon different molecular mechanisms suggesting an independent origin of selected postsynaptic complexes associated with glutamergic signaling.