Rhythms of mammalian body temperature can sustain peripheral circadian clocks.
BACKGROUND
Low-amplitude temperature oscillations can entrain the phase of circadian rhythms in several unicellular and multicellular organisms, including Neurospora and Drosophila. Because mammalian body temperature is subject to circadian variations of 1 degrees C-4 degrees C, we wished to determine whether these temperature cycles could serve as a Zeitgeber for circadian gene expression in peripheral cell types.


RESULTS
In RAT1 fibroblasts cultured in vitro, circadian gene expression could be established by a square wave temperature rhythm with a (Delta)T of 4 degrees C (12 hr 37 degrees C/12 hr 33 degrees C). To examine whether natural body temperature rhythms can also affect circadian gene expression, we first measured core body temperature cycles in the peritoneal cavities of mice by radiotelemetry. We then reproduced these rhythms with high precision in the liquid medium of cultured fibroblasts for several days by means of a homemade computer-driven incubator. While these "in vivo" temperature rhythms were incapable of establishing circadian gene expression de novo, they could maintain previously induced rhythms for multiple days; by contrast, the rhythms of control cells kept at constant temperature rapidly dampened. Moreover, circadian oscillations of environmental temperature could reentrain circadian clocks in the livers of mice, probably via the changes they imposed upon both body temperature and feeding behavior. Interestingly, these changes in ambient temperature did not affect the phase of the central circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus.


CONCLUSIONS
We postulate that both endogenous and environmental temperature cycles can participate in the synchronization of peripheral clocks in mammals.
Brown
Steven A
SA
Department of Molecular Biology, University of Geneva, Sciences II, 30, Quai Ernest Ansermet, CH-1211 Geneva, Switzerland.
Zumbrunn
Gottlieb
G
Fleury-Olela
Fabienne
F
Preitner
Nicolas
N
Schibler
Ueli
U
D000818:Animals; D001831:Body Temperature / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology*; D004268:DNA-Binding Proteins; D005347:Fibroblasts / Q000502:physiology; D015870:Gene Expression; D008099:Liver / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008954:Models, Biological; D051381:Rats; D013493:Suprachiasmatic Nucleus / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics
C485975:DBP protein, rat; D004268:DNA-Binding Proteins; C498260:Dbp protein, mouse; D014157:Transcription Factors