Scientists report proof this week that melanopsin protein mediates the circadian clock. The findings, published in Nature and Science, confirm the theory that melanopsin triggers photosensitivity and describe surprising similarities between vertebrate and invertebrate cell phototransduction cascades.

"It's almost a paradigm, thinking about vertebrate and invertebrate opsins in this way," Satchin Panda, author of the Sciencestudy, told The Scientist. "We see that light sensing and time- keeping is conserved [through evolution]." In his study, published online in advance of print, Panda, of the Salk Institute in La Jolla, Calif., describes melanopsin's ability to active the G-protein signaling pathway in Xenopus oocytes.

The papers follow the publication earlier this month in PNAS of a study that found that Xenopus' dermal melanosomes use a phosphoinositide signaling pathway similar to that of invertebrates. That study was functional confirmation of earlier molecular analyses, which showed that Xenopus melanophores and...

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