mCRY1 and mCRY2 Are Essential Components of the Negative Limb of the Circadian Clock Feedback Loop

• Published in: Cell 1999-07, Vol.98 (2), p.193-205
• Main Authors: Kume, Kazuhiko, Zylka, Mark J, Sriram, Sathyanarayanan, Shearman, Lauren P, Weaver, David R, Jin, Xiaowei, Maywood, Elizabeth S, Hastings, Michael H, Reppert, Steven M
• Format: Article
• Language: English
• Subjects: 3T3 Cells; Animals; ARNTL Transcription Factors; Basic Helix-Loop-Helix Transcription Factors; Biological Clocks - physiology; Blotting, Western; Cell Cycle Proteins; Cell Nucleus - metabolism; CLOCK Proteins; Cloning, Molecular; COS Cells; Cryptochromes; Drosophila Proteins; Eye Proteins; Feedback - physiology; Female; Flavoproteins - analysis; Flavoproteins - genetics; Flavoproteins - metabolism; Gene Expression - physiology; Humans; Male; Mice; Mice, Inbred BALB C; Mice, Knockout; Molecular Sequence Data; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; Period Circadian Proteins; Photoreceptor Cells, Invertebrate; Receptors, G-Protein-Coupled; RNA, Messenger - metabolism; Suprachiasmatic Nucleus - chemistry; Suprachiasmatic Nucleus - metabolism; Trans-Activators - genetics; Trans-Activators - metabolism; Transcription Factors - genetics; Transcription Factors - metabolism; Transcription, Genetic - physiology
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/S0092-8674(00)81014-4

We determined that two mouse cryptochrome genes, mCry1 and mCry2, act in the negative limb of the clock feedback loop. In cell lines, mPER proteins (alone or in combination) have modest effects on their cellular location and ability to inhibit CLOCK:BMAL1-mediated transcription. This suggested cryptochrome involvement in the negative limb of the feedback loop. Indeed, mCry1 and mCry2 RNA levels are reduced in the central and peripheral clocks of Clock/Clock mutant mice. mCRY1 and mCRY2 are nuclear proteins that interact with each of the mPER proteins, translocate each mPER protein from cytoplasm to nucleus, and are rhythmically expressed in the suprachiasmatic circadian clock. Luciferase reporter gene assays show that mCRY1 or mCRY2 alone abrogates CLOCK:BMAL1–E box–mediated transcription. The mPER and mCRY proteins appear to inhibit the transcriptional complex differentially.