Cryptochrome Drosophila

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. 

Shalitin D, Yang H, Mockler TC et al 2002 Regulation of A rahidopsis cryptochrome 2 by blue-light-dependent phosphorylation. Nature 417 763—767 Stanewsky R, Kaneko M, Emery P et al 1998 The cryb mutation identifies cryptochrome as a circadian photoreceptor in Drosophila. Cell 95 681-692 Takahashi JS, DeCoursey PJ, Bauman L, Menaker M 1984 Spectral sensitivity of a novel photoreceptive system mediating entrainment of mammalian circadian rhythms. Nature 308 186-188... 

The mammalian molecular oscillator, similar to that in Drosophila and Neurospora, is composed of two interconnected feedback loops, one within the negative limb and one within the positive limb. The members of the positive limb (CLOCK and BMALl) activate transcription of the genes encoding the negative limb components (cryptochromes and period proteins). PER and CRY proteins then form heterotypic protein complexes that are translocated into the nucleus, and once these complexes reach a critical threshold level, they suppress the activity of CLOCK and BMALL As a consequence, the concentration of CRY and PER proteins falls below the threshold required for autorepression, and a new cycle of CryjPer transcription can initiate (for review, see Reppert Weaver 2002). 

The same interlocked feedback loop mechanism is thought to operate in circadian oscillator cells throughout the Drosophila circadian system. However, studies of the blue Hght photoreceptor CRYPTOCHROME (CRY) suggest that central and peripheral oscillator mechanisms in Drosophila are not the same. Drosophila CRY was initially identified as a photoreceptor that mediates light... 

Emery P, So WV, Kaneko M, Hall JC, Rosbash M 1998 CRY, a Drosophila clock and light-regulated cryptochrome, is a major contributor to circadian rhythm resetting and photosensitivity. Cell 95 669-679... 

Ivanchenko M, Stanewsky R, Giebultowicz JM 2001 Circadian photoreception in Drosophila-, functions of cryptochrome in peripheral and central clocks. J Biol Rhythms 16 205-215... 

Krishnan B, Levine JD, Lynch MK et al 2001 A new role for cryptochrome in a Drosophila circadian oscillator. Nature 411 313-317... 

Lin FJ, Song W, Meyer-Bernstein E, Naidoo N, and Sehgal A (2001) Photic signaling by cryptochrome in the Drosophila circadian system. Molecular and Cell Biology 21, 7287-94. 

Fig. 3. Phylogentic relationship among select members of the photolyase/ cryptochrome family. Sequences were aligned with Clustal W, and the tree was produced by the Neighbor-Joining method using MEGA 2.1. Bootstrap confidence values are shown (values for interior branches >95% are statistically significant). At, Arabidopsis thaliana Dm, Drosophila melangaster Ec, Escherichia coli Hs, Homo sapiens Vc, Vibrio cholerae.

Gegear, R. J., Conelman, A., Waddell, S. (2008). Cryptochrome mediates light-dependent magnetosensitivity in Drosophila. Nature, 454,1014. 

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