TY - JOUR T1 - The genome of the contractile demosponge <em>Tethya wilhelma</em> and the evolution of metazoan neural signalling pathways JF - bioRxiv DO - 10.1101/120998 SP - 120998 AU - Warren R. Francis AU - Michael Eitel AU - Sergio Vargas AU - Marcin Adamski AU - Steven H.D. Haddock AU - Stefan Krebs AU - Helmut Blum AU - Dirk Erpenbeck AU - Gert Wörheide Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/04/12/120998.abstract N2 - Porifera are a diverse animal phylum with species performing important ecological roles in aquatic ecosystems, and have become models for multicellularity and early-animal evolution. Demosponges form the largest class in sponges, but previous studies have relied on the only draft demosponge genome of Amphimedon queenslandica. Here we present the 125-megabase draft genome of a contractile laboratory demosponge Tethya wilhelma, sequenced to almost 150x coverage. We explore the genetic repertoire of transporters, receptors, and neurotransmitter metabolism across early-branching metazoans in the context of the evolution of these gene families. Presence of many genes is highly variable across animal groups, with many gene family expansions and losses. Three sponge classes show lineage-specific expansions of GABA-B receptors, far exceeding the gene number in vertebrates, while ctenophores appear to have secondarily lost most genes in the GABA pathway. Both GABA and glutamate receptors show lineage-specific domain rearrangements, making it difficult to trace the evolution of these gene families. Gene sets in the examined taxa suggest that nervous systems evolved independently at least twice and either changed function or were lost in sponges. Changes in gene content are consistent with the view that ctenophores and sponges are the earliest-branching metazoan lineages and provide additional support for the proposed clade of Placozoa/Cnidaria/Bilateria. ER -