MELANOPSIN - AN OPSIN IN MELANOPHORES, BRAIN, AND EYE

We have identified an opsin, melanopsin, in photosensitive dermal mela nophores of Xenopus laevis. Its deduced amino acid sequence shares gre atest homology with cephalopod opsins, The predicted secondary structu re of melanopsin indicates the presence of a long cytoplasmic tail wit h multiple putative phosphorylation sites, suggesting that this opsin' s function may be finely regulated, Melanopsin mRNA is expressed in hy pothalamic sites thought to contain deep brain photoreceptors and in t he iris, a structure known to be directly photosensitive in amphibians . Melanopsin message is also localized in retinal cells residing in th e outermost lamina of the inner nuclear layer where horizontal cells a re typically found, Its expression in retinal and nonretinal tissues s uggests a role in vision and nonvisual photoreceptive tasks, such as p hotic control of skin pigmentation, pupillary aperture, and circadian and photoperiodic physiology.