Characterization of Dopamine Receptors in Sepia officinalis (Cephalopoda): An Insight Into the Evolution of Dopamine Receptors in Bilateria.

Dopamine is present in all metazoans but signaling pathways and receptors characteristics have been studied mainly in vertebrates. We addressed this issue by studying dopamine receptors in cephalopods (Sepia officinalis), a clade well-known for its visual and cognitive behavior and its production of various neurotransmitters. For the first time, we have phylogenetically identified three distinct families of dopamine receptors in Sepia embryos, belonging to the D1-like, D2-like and "invertebrate-type dopamine receptors" (INDR). We confirm that the family of INDR is not specific to Ecdysozoans and might have already been present in the ancestor of bilaterians and secondarily lost in Olfactores. Through cellular signaling assays we were able to functionally confirm the identification of Sepia dopamine receptors and show that they use three different signaling pathways. Finally we showed that all these three receptors were differentially expressed in the eyes and central nervous system of Sepia officinalis at the time of their setting-up. It is therefore likely that different dopamine receptors and different signaling pathways contribute to different physiological processes. This study opens the way to physiological and molecular studies on the organization and role of these dopaminergic system in cephalopods.