Melanopsin and other novel mammalian opsins

Within the past decade, several non-canonical opsins have been identified in mammals. These include RGR, peropsin, melanopsin, encephalopsin, and neuropsin. Although all are expressed in the eye, it is likely that they serve to mediate non-visual effects of light on physiology. Some of these opsins, however, may play an indirect role in vision by generating appropriate retinoid chromophores for the rod and cone visual pigments or by regulating the sensitivity of the visual system. Here, we survey the current state of knowledge regarding these opsins.