Keeping an eye on retinal clocks

Circadian pacemakers that drive rhythmicity in retinal function are found i n both invertebrates and vertebrates. They have been localized to photorece ptors in molluscs, amphibians, and mammals. Like other circadian pacemakers , they entrain to light, oscillate based on a negative feedback between tra nscription and translation of clock genes, and control a variety of physiol ogical and behavioral rhythms that often includes rhythmic melatonin produc tion. As a highly organized and accessible tissue, the retina is particular ly well suited for the study of the input-output pathways and the mechanism for rhythm generation. Impressive advances can now be expected as research ers apply new molecular techniques toward looking into the eye's clock.