Strong resetting of the mammalian clock by constant light followed by constant darkness.
The mammalian molecular circadian clock in the suprachiasmatic nuclei (SCN) regulates locomotor activity rhythms as well as clocks in peripheral tissues (Reppert and Weaver, 2002; Ko and Takahashi, 2006). Constant light (LL) can induce behavioral and physiological arrhythmicity by desynchronizing clock cells in the SCN (Ohta et al., 2005). We examined how the disordered clock cells resynchronize by probing the molecular clock and measuring behavior in mice transferred from LL to constant darkness (DD). The circadian locomotor activity rhythms disrupted in LL become robustly rhythmic again from the beginning of DD, and the starting phase of the rhythm in DD is specific, not random, suggesting that the desynchronized clock cells are quickly reset in an unconventional manner by the L/D transition. By measuring mPERIOD protein rhythms, we showed that the SCN and peripheral tissue clocks quickly become rhythmic again in phase with the behavioral rhythms. We propose that this resetting mechanism may be different from conventional phase shifting, which involves light induction of Period genes (Albrecht et al., 1997; Shearman et al., 1997; Shigeyoshi et al., 1997). Using our functional insights, we could shift the circadian phase of locomotor activity rhythms by 12 h using a 15 h LL treatment: essentially producing phase reversal by a single light pulse, a feat that has not been reported previously in wild-type mice and that has potential clinical utility.
Chen
Rongmin
R
Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida 32306, USA.
Seo
Dong-Oh
DO
Bell
Elijah
E
von Gall
Charlotte
C
Lee
Choogon
C
D000818:Animals; D001683:Biological Clocks / Q000502:physiology* / Q000528:radiation effects; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology* / Q000528:radiation effects; D003624:Darkness; D008027:Light; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009043:Motor Activity / Q000502:physiology / Q000528:radiation effects; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D056950:Period Circadian Proteins; D010775:Photic Stimulation; D013493:Suprachiasmatic Nucleus / Q000378:metabolism* / Q000528:radiation effects; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; C539023:Per1 protein, mouse; C513312:Per2 protein, mouse; D056950:Period Circadian Proteins; D014157:Transcription Factors