Cryptochromes circadian clock

Sancar, A., Regulation of the mammalian circadian clock by cryptochrome, J. Biol. Chem., 279, 34079, 2004. 

Partch, C. L. et al., Postranslational regulation of mammalian circadian clock by cryptochrome and proteinphosphatase 5, Proc Aarf Acad. Sci. USA, 103, 10467, 2006. Briggs, W.R., Christie, J.M., and Salomon, M., Phototropins a new family of flavinbinding blue light receptors in plants, Antioxid. Redox Signal, 3, 775, 2001. Briggs,W.R. et al.. The phototropin family of photoreceptors. Plant Cell, 13, 993, 2001. 

Albus H, Bonnefont X, Chaves I et al 2002 Cryptochrome-deficient mice lack circadian electrical activity in the suprachiasmatic nuclei. Curr Biol 12 1130—1133 Balsalobre A, Brown SA, Marcacci L et al 2000 Resetting of circadian time in peripheral tissues by glucocorticoid signaling. Science 289 2344—2347 Berson DM, Dunn FA, Takao M 2002 Phototransduction by retinal ganghon cells that set the circadian clock. Science 295 1070—1073... 

Helfrich-Forster C, Winter C, Hofbauer A, Hall JC, Stanewsky R 2001 The circadian clock of fruit flies is blind after elimination of all known photoreceptors. Neuron 30 249-261 Lin FJ, Song W, Meyer-Bernstein E, Naidoo N, Sehgal A 2001 Photic signaling by cryptochrome in the Drosophilacitcidiaa system. Mol Cell Biol 21 7287-7294 Mas P, Devlin PF, Panda S, Kay SA 2000 Functional Interaction of phytochrome B and cryptochrome 2. Nature 408 207-211... 

Somers DE, Devlin PF, Kay SA 1998 Phytochromes and cryptochromes in the entrainment of th Arabidopsis circadian clock. Science 282 1488-1490 Stanewsky R, Kaneko M, Emery P et al 1998 The cryb mutation identifies cryptochrome as a circadian photoreceptor in Drosophila. Cell 95 681-692 Wang ZY, Tobin EM 1998 Constitutive expression of the CIRCADIAN CLOCK ASSOCIATED 1 CCAl gene disrupts circadian rhythms and suppresses its own expression. Cell 93 1207-1217... 

Cryptochrome genes have been found in many organisms. In the fly Drosophila cryptochrome appears to interact directly with the clock proteins that control the circadian cycle. Most important are products of two genes per (period) and tim (timeless). They are helix-loop-helix DNA binding proteins that form heterodimers, are translocated to the nucleus, and repress their own transcription. Morning light leads to a rapid disappearance of e TIM protein. The cryptochrome CRY appears to react directly with TIM to inactivate it. However, details remain to be learned. " The circadian clock mechanism appears to be universal and the cryptochrome-2 mcryl gene) appears to function in the mouse. A human cDNA clone was found to have a 48% identity with a relative of cryptochromes, the (6-4) photolyase of Drosophila. 

Cryptochrome/photolyase blue light photoreceptor family. The photoreceptors in this family are flavoproteins. They have a wide range of functions including circadian clock regulation, seed germination, and pigment accumulation. 

In contrast to the paucity of biochemical data on the photosensory functions of cryptochromes, there are extensive genetic and cell biology data on the roles of cryptochromes in blue light, photoreception in plants and animals, and circadian clock regulation in animals (Gashmore, 2003 Lin and Shalitin, 2003 Sancar, 2003). In Arabidopsis, blue light inhibits elongation of hypocotyls in a cryptochrome-dependent manner. In animals. 

Sancar, A., Thompson, C. L., Thresher, R. J., Araujo, F., Mo, J., Ozgur, S., Vagas, E., Dawut, L., and Selby, C. P. (2000). Photolyase/cryptochrome family blue-light photoreceptors use light energy to repair DNA or set the circadian clock. CM Spring Harbor Symp. Quant. Biol. 65, 157—171. 

Thompson, C. L., and Sancar, A. (2002). Photolyase/cryptochrome blue-light photoreceptors use photon energy to repair DNA and reset the circadian clock. Oncogene 21, 9043-9056. 

T6th, R., Kevei, E., Hall, A., Millar, A.J., Nagy.E, and Kozma-Bogndr, L., Circadian clock-regulated expression of phytochrome and cryptochrome genes in Arabidopsis, Plant Physiol, 127,1607,2001. 

Surprisingly, cryptochrome was not found solely in the retina. In addition to low levels found in all tissues, Cryl was also expressed in the SCN, and Cryl mRNA oscillated with circadian rhythmicity, which indicated an additional role for cryptochrome in circadian clock function. Based on the mRNA expression pattern, we postulated a role for Cry2 in circadian photoreception in the retina as well as a hght-independent role for Cryl in the circadian clock mechanism in the SCN. 

While cryptochrome s role in the circadian clock mechanism is clear, its light-dependent function remains to be elucidated. The evidence for cryptochrome as a blue-light circadian photoreceptor is the following ... 

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