Melanopsin signaling and nonvisual ocular photoreception

Organisms, ranging from cyanobacteria to mammals, use an intrinsic circadian clock and photosensors to regulate behavior and physiology in resonance with geophysical time. In mammals, an endogenous master clock functions in the suprachiasmatic nuclei (SCN) of the hypothalamus, and is entrained to the day-night cycle by direct light input from the retina. Appropriate photoentrainment is essential for general health, as shift work and similar chronic circadian desynchronization have been shown to be major risk factors in several sleep disorders, metabolic syndromes, and in cancer (reviewed in (1)). Understanding the molecular processes underlying photoentrainment will therefore help identify new strategies and targets for therapeutic intervention in these disorders.