The Xenopus Clock gene is constitutively expressed in retinal photoreceptors

Many aspects of normal retinal physiology are controlled by a retinal circa dian clock. In Xenopus laevis, the photoreceptor cells within the retina co ntain a circadian clock that controls melatonin release. In this report we present the cloning and characterization of the Xenopus homolog of the Cloc k gene, known to be critical for normal circadian behavioral rhythms in the mouse. The Xenopus Clock gene is expressed primarily in photoreceptors wit hin the eye and is expressed at constant levels throughout the day. Analysi s of other tissues revealed that, as in other species, the Xenopus Clock ge ne is widely expressed. This characterization of the Clock gene provides a useful tool for further exploration of the role of the circadian clock in n ormal retinal function. (C) 2000 Elsevier Science B.V. All rights reserved.