Circadian Rhythms

Waking Up on a Cloudy Morning

Science's STKE  17 Dec 2002:
Vol. 2002, Issue 163, pp. tw472-TW472
DOI: 10.1126/stke.2002.163.tw472

Several photoreceptors have been proposed to be critical for synchronizing the mammalian circadian clock, but the most promising is melanopsin, which is found in specialized retinal ganglion cells. To test melanopsin's functional relevance, Ruby et al. and Panda et al. examined mice in which the gene for melanopsin has been deleted and found that light was still able to entrain the clock but not as effectively. At low light levels, however, light could not entrain the clock in the mice without melanopsin. Thus, melanopsin is not the only photoreceptor but appears to be the one specialized for ensuring entrainment at low light levels.

N. F. Ruby, T. J. Brennan, X. Xie, V. Cao, P. Franken, H. C. Heller, B. F. O'Hara, Role of melanopsin in circadian responses to light. Science 298, 2211-2213 (2002). [Abstract] [Full Text]

S. Panda, T. K. Sato, A. M. Castrucci, M. D. Rollag, W. J. DeGrip, J. B. Hogenesch, I. Provencio, S. A. Kay, Melanopsin (Opn4) requirement for normal light-induced circadian phase shifting. Science 298, 2213-2216 (2002). [Abstract] [Full Text]