Meeting Abstract
Illuminating the origins and evolution of vision in animals hinges on understanding the evolution of the underlying gene families. The most crucial of these genes is the photosensitive G-protein coupled receptor (GPCR), Opsin. GPCRs are a family of diverse sensory and signaling proteins, and until recently, Opsins were thought to be the only light sensitive GPCRs. This hypothesis was supported by an ultra-conserved lysine found in all functional Opsins. The lysine allows the Opsin to bind a chromophore that induces signaling when it absorbs a photon. However, recent studies hypothesized that there are alternate binding sites also capable of facilitating retinal binding. If these binding sites exist in non-Opsin GPCRs, we must change the way we think about the origins and evolution of vision in animals. However, support for alternate binding sites in GPCRs is scarce, with only a single publication showing evidence of functional light sensitivity outside of Opsins. Here, we construct a phylogeny of GPCRs and reconstruct ancestral states to show that light sensitivity in GPCRs likely first evolved at the ancestor of Opsins and not before. However, we also find at least thirteen other independent origins of a putative light-sensitive alternate site across non-opsin GPCRs. Additionally, we investigate the broader question of how the emergence of image forming vision effects Opsin family evolution. We find that Opsins involved in image formation maintain duplicate copies at a higher rate when associated with a yet unknown character. Our results suggest that light sensitivity may have evolved multiple times within GPCRs and that Opsins emerged early as a specialized and efficient photosensor.
