The GPCR repertoire in the demosponge Amphimedon queenslandica: insights into the GPCR system at the early divergence of animals

Background: G protein-coupled receptors (GPCRs) play a central role in eukaryotic signal transduction. However, the GPCR component of this signalling system, at the early origins of metazoans is not fully understood. Here we aim to identify and classify GPCRs in Amphimedon queenslandica (sponge), a member of the Porifera (one of the earliest diverging metazoan lineages). Furthermore, phylogenetic comparisons of sponge GPCRs with eumetazoan and bilaterian GPCRs will be essential to our understanding of the GPCR system at the roots of metazoan evolution.
Results: We present a curated list of 220 GPCRs in the sponge genome after excluding incomplete sequences and false positives from our initial dataset of 282 predicted GPCR sequences obtained using Pfam search. Phylogenetic analysis reveals that the sponge contains members belonging to four of the five major GRAFS families including Glutamate (33), Rhodopsin (126), Adhesion (40), and Frizzled (3). Interestingly, the sponge Rhodopsin fami...