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On the cover: The anole lizard, like other reptiles including birds, relies on seven distinct photoreceptor types for vision: rods, four “ancestral” single cones (sensitive to red, green, blue, and ultraviolet), and two members of the so-called tetrapod double cone. Through comparative single-cell transcriptomics, Tommasini et al. trace the evolutionary origins of these cell types. Alongside the results from a parallel study by Liu et al., their findings support the orthology of single cones across vertebrates and shed new light on the mysterious evolutionary origins of double cones. Photo credit: ByChelo (pexels.com).

See also the dispatch by Almut Kelber

Tommasini D^§, Yoshimatsu T^§, Puthussery T^§, Baden T^§, Shekhar K^§. Comparative transcriptomic insights into the evolution of vertebrate photoreceptor types. Current Biology 35:1-12. direct link. pdf.

Baden T^§, Angueyra JM, Bosten JM, Collin SP, Conway B, Cortesi F, Dedek K, Euler T, Novales Flamarique I, Franklin A, Haverkamp S, Kelber A, Neuhauss SCF, Li W, Lucas R, Osorio DC, Shekhar K, Tommasini D, Yoshimatsu T, Corbo JC. A standardized nomenclature for the rods and cones of the vertebrate retina. PLoS Biology 23(5): e3003157. direct link. pdf.

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 type’s putative evolutionary history. 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.

Tommasini D^§, Yoshimatsu T^§, Puthussery T^§, Baden T^§, Shekhar K^§. Comparative transcriptomic insights into the evolution of vertebrate photoreceptor types. Current Biology 35:1-12. direct link. pdf.