Meeting Abstract

108.1  Sunday, Jan. 6  Post-synaptic Density (PSD) and Axon Guidance Genes in the Transcriptomes of 8 Sponges FARRAR, N*; RIESGO, A; LEYS, S; University of Alberta; Centro de Estudios Avanzados de Blanes-CSIC, Harvard University; University of Alberta nfarrar@ualberta.ca

Sponges are morphologically simple metazoans that lack nerves or any form of synapse, yet the genome of the sponge Amphimedon possesses nearly all the genes required for synaptic communication. It is possible that Amphimedon is unusual among sponges in either lacking clearly identifiable synapses or in possessing PSD genes that are used for other functions. Here we report on findings from the transcriptomes of 8 sponges which represent all 4 sponge classes: Hexactinellida (Aphrocallistes vastus), Calcarea (Sycon cactus), Homoscleromorpha (Corticium candelabrum), and Demospongiae (Spongilla lacustris, Petrosia ficiformis, Pseudospongos suberitoides, Ircinia fasciculate). We used HMMer and BLAST search tools to find gene homologs in each of the transcriptomes and confirmed gene identity by phylogenetic analysis. As in Amphimedon, all 8 sponge transcriptomes possess many of the PSD genes. Among the sponges, Aphrocallistes shows the greatest number of PSD gene absences. Furthermore, while Amphimedon lacks ionotropic glutamate receptors (iGluRs), Corticium, Sycon and Ircinia have genes which Blast to iGluRs and contain motifs present in these channels. We also searched the transcriptomes for classical axon guidance molecules. Molecules identified in some sponge transcriptomes include netrin, deleted in colorectal cancer (DCC), unc5, neogenin, slit, robo, semaphorin, neuropilin and the cell adhesion molecule, DSCAM. The widespread presence of synaptic and neurodevelopmental molecules in sponges strongly implies these molecules functioned in other pathways or systems before being coopted into the neural tissues and systems of other metazoans, or that sponges lost neuronal tissues.