The mouse Clock mutation reduces circadian pacemaker amplitude and enhances efficacy of resetting stimuli and phase-response curve amplitude.
The mouse Clock gene encodes a basic helix-loop-helix-PAS transcription factor, CLOCK, that acts in concert with BMAL1 to form the positive elements of the circadian clock mechanism in mammals. The original Clock mutant allele is a dominant negative (antimorphic) mutation that deletes exon 19 and causes an internal deletion of 51 aa in the C-terminal activation domain of the CLOCK protein. Here we report that heterozygous Clock/+ mice exhibit high-amplitude phase-resetting responses to 6-h light pulses (Type 0 resetting) as compared with wild-type mice that have low amplitude (Type 1) phase resetting. The magnitude and time course of acute light induction in the suprachiasmatic nuclei of the only known light-induced core clock genes, Per1 and Per2, are not affected by the Clock/+ mutation. However, the amplitude of the circadian rhythms of Per gene expression are significantly reduced in Clock homozygous and heterozygous mutants. Rhythms of PER2::LUCIFERASE expression in suprachiasmatic nuclei explant cultures also are reduced in amplitude in Clock heterozygotes. The phase-response curves to changes in culture medium are Type 0 in Clock heterozygotes, but Type 1 in wild types, similar to that seen for light in vivo. The increased efficacy of resetting stimuli and decreased PER expression amplitude can be explained in a unified manner by a model in which the Clock mutation reduces circadian pacemaker amplitude in the suprachiasmatic nuclei.
Vitaterna
Martha Hotz
MH
Center for Functional Genomics, Center for Sleep and Circadian Biology and Department of Neurobiology and Physiology, Northwestern University, 2205 Tech Drive, Evanston, IL 60208-3520, USA.
Ko
Caroline H
CH
Chang
Anne-Marie
AM
Buhr
Ethan D
ED
Fruechte
Ethan M
EM
Schook
Andrew
A
Antoch
Marina P
MP
Turek
Fred W
FW
Takahashi
Joseph S
JS
D000818:Animals; D001683:Biological Clocks / Q000502:physiology*; D056926:CLOCK Proteins; D018797:Cell Cycle Proteins; D002940:Circadian Rhythm / Q000502:physiology*; D005786:Gene Expression Regulation; D008027:Light; D051379:Mice; D008815:Mice, Inbred Strains; D009043:Motor Activity / Q000502:physiology; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D056950:Period Circadian Proteins; D017440:Photoperiod; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013493:Suprachiasmatic Nucleus / Q000502:physiology; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; C513312:Per2 protein, mouse; D056950:Period Circadian Proteins; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D056926:CLOCK Proteins; C538944:Clock protein, mouse