Seeing is essential for us, and so we wonder how easily it evolves? Its fundamental unit is the photoreceptor cell. Such a cell uses a molecular transduction system that detects photons and translates them into a cellular signal, which then the animal uses for behavior. Even though all animals share the molecular and cellular origin, they evolved a diversity of eyes independently. However, comparative vision research has only focused on a few taxa such as vertebrates, arthropods, and cephalopods. Therefore, our knowledge of eye evolution is limited. Fanworms evolved relatively recently eyes on their radioles, which are tentacles that form their fans. These radioles are used for respiration and collecting food particles. Fanforms are sessile and live in tubes. When their eyes see a predator, the worm quickly retreats into its tube to protect the fan. The eyes in different fanworm species evolved independently and thus probably also their phototransduction cascades. Therefore, fanworms are an ideal new model system to study eye evolution and the possible phototransduction cascades.
The overall objectives of the project were to determine all the phototransduction components in the eyes of two fan worm species: Spirobranchus corniculatus and Acromegalomma vesiculosum. The first step was to find putative opsin and G-alpha protein sequences in existing transcriptomes and identify those by phylogenetic reconstruction. The second step was to check whether mRNA of those sequences were expressed in the eyes of the focal species by in situ hybridization, and more importantly to check whether the opsin and the G-alpha protein mRNA were expressed in the same cell as this is required for the encoded proteins to interact with each other so that they can be part of the phototransduction cascade. The third step was to establish the interaction via electrophysiology with knock-down and pharmacology. Knowing the identity of the opsin and the G-protein narrows down significantly the possibilities of molecules that could be further downstream in the phototransduction cascade. These potential downstream molecules would be checked with the same methods whether they are indeed in the phototransduction cascade.
