Rods Are Rods and Cones Cones, and (Never) the Twain Shall Meet

AbstractMore than 100 photopigment G protein-coupled receptors (opsins) have been sequenced and organized into six classes. Rod photoreceptors in various species have been found to express an opsin from one of the two rhodopsin classes, while cones express an opsin from one of the four remaining classes. It has now been discovered (see Ma et al., in this issue of Neuron) that salamander short-wavelength sensitive cones and green rods express the same opsin, while manifesting other features that classically distinguish rods from cones