Melanopsin ( <i>Opn4</i> ) Requirement for Normal Light-Induced Circadian Phase Shifting

TLDR

The suprachiasmatic nucleus entrains to the day/night cycle via retinal photoreceptors, with melanopsin (Opn4) a key opsin-based photopigment candidate for this entrainment. The study aimed to determine melanopsin’s role in light‑induced circadian phase resetting by generating melanopsin‑null mice. Melanopsin‑null mice (Opn4‑/‑) were created to assess light resetting of the circadian oscillator. While Opn4‑/‑ mice entrain normally to a light/dark cycle, they exhibit severely reduced phase resetting to brief monochromatic light pulses, underscoring melanopsin’s essential role in circadian photoentrainment.

Abstract

The master circadian oscillator in the hypothalamic suprachiasmatic nucleus is entrained to the day/night cycle by retinal photoreceptors. Melanopsin (Opn4), an opsin-based photopigment, is a primary candidate for photoreceptor-mediated entrainment. To investigate the functional role of melanopsin in light resetting of the oscillator, we generated melanopsin-null mice (Opn4-/-). These mice entrain to a light/dark cycle and do not exhibit any overt defect in circadian activity rhythms under constant darkness. However, they display severely attenuated phase resetting in response to brief pulses of monochromatic light, highlighting the critical role of melanopsin in circadian photoentrainment in mammals.