Expression of mCLOCK and other circadian clock-relevant proteins in the mouse suprachiasmatic nuclei.
Circadian timing in mammals is based upon the cell-autonomous clockwork located in the suprachiasmatic nuclei (SCN) of the hypothalamus. It is thought to involve interlocked feedback loops in which periodic transcriptional drive to core clock genes is mediated by CLOCK/BMAL1 heterodimers. Negative-feedback actions of the encoded proteins PER and CRY terminate this phase of the cycle. In lower species, rhythmic abundance of the mCLOCK homologue initiates the subsequent cycle. By contrast, it is proposed that the new circadian cycle in mammals is triggered by indirect, positive transcriptional actions leading to a subsequent surge in BMAL1. The aim of this study was to test predictions made by this model concerning the behaviour of the native clock factor mCLOCK in the mouse SCN. Using in situ hybridization, immunocytochemistry, Western blotting and immunoprecipitation, we demonstrate constitutive expression of mCLOCK as a nuclear antigen in the SCN. mCLOCK forms alternating, periodic associations with either mBMAL1 or the negative regulators mPER and mCRY. The results confirm predictions made by the "two-loop" model of the mouse clock, and further highlight the role of interlocked cycles of positive and negative transcriptional regulatory complexes at the heart of the circadian clockwork.
Maywood
E S
ES
Department of Anatomy, University of Cambridge, Hills Road, Cambridge CB2 2QH, UK.
O'Brien
J A
JA
Hastings
M H
MH
D056930:ARNTL Transcription Factors; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D001683:Biological Clocks / Q000235:genetics / Q000502:physiology; D015153:Blotting, Western; D056926:CLOCK Proteins; D018797:Cell Cycle Proteins; D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology; D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005246:Feedback / Q000502:physiology; D005420:Flavoproteins / Q000235:genetics; D005786:Gene Expression Regulation / Q000502:physiology*; D008297:Male; D051379:Mice; D008954:Models, Biological; D009687:Nuclear Proteins / Q000235:genetics; D056950:Period Circadian Proteins; D017956:Photoreceptor Cells, Invertebrate; D043562:Receptors, G-Protein-Coupled; D013493:Suprachiasmatic Nucleus / Q000502:physiology*; D013995:Time; D015534:Trans-Activators / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic / Q000502:physiology
D056930:ARNTL Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D056926:CLOCK Proteins; D018797:Cell Cycle Proteins; D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins; D009687:Nuclear Proteins; D056950:Period Circadian Proteins; D043562:Receptors, G-Protein-Coupled; D015534:Trans-Activators; D014157:Transcription Factors; C538961:Bmal1 protein, mouse; C539023:Per1 protein, mouse; C513312:Per2 protein, mouse; C119828:cry protein, Drosophila; C538944:Clock protein, mouse