Local photic entrainment of the retinal circadian oscillator in the absence of rods, cones, and melanopsin

Significance The physiology of the mammalian retina is governed by a molecular circadian clock. The retina is also the sole photoreceptive tissue for the synchronization of the master circadian clock, the suprachiasmatic nucleus (SCN), to light/dark cycles. The SCN synchronizes the phases of peripheral clocks throughout the body. It is unknown whether the retina is entrained by the SCN, or is directly entrained by light/dark signals. We report that the retinal circadian clock synchronizes directly to light/dark cycles, independent of the SCN phase. Unexpectedly, the retina uses photoreceptors distinct from those used for circadian photoreception or vision for this entrainment.