A Standardized Nomenclature for the Rods and Cones of the Vertebrate Retina

We propose a standardized naming system for vertebrate visual photoreceptors (i.e., rods and cones) that reflects our current understanding of their evolutionary history. Vertebrate photoreceptors have been studied for well over a century, but a fixed nomenclature for referring to orthologous cell types across diverse species has been lacking. Instead, photoreceptors have been variably - and often confusingly - named according to morphology, presence/absence of ‘rhodopsin,’ spectral sensitivity, chromophore usage, and/or the gene family of the opsin(s) they express. Here, we propose a unified nomenclature for vertebrate rods and cones that aligns with the naming systems of other retinal cell classes and that is based on the photoreceptor’s putative ancestral derivation. This classification is informed by the functional, anatomical, developmental and molecular identities of the neuron as a whole, including the expression of deeply conserved transcription factors required for development. The proposed names will be applicable across all vertebrates and indicative of the widest-possible range of properties, including their postsynaptic wiring, and hence will allude to their common and species-specific roles in vision. Furthermore, the naming system is open-ended to accommodate the future discovery of as-yet unknown photoreceptor types.