A non-circadian role for clock-genes in sleep homeostasis: a strain comparison.
BACKGROUND
We have previously reported that the expression of circadian clock-genes increases in the cerebral cortex after sleep deprivation (SD) and that the sleep rebound following SD is attenuated in mice deficient for one or more clock-genes. We hypothesized that besides generating circadian rhythms, clock-genes also play a role in the homeostatic regulation of sleep. Here we follow the time course of the forebrain changes in the expression of the clock-genes period (per)-1, per2, and of the clock-controlled gene albumin D-binding protein (dbp) during a 6 h SD and subsequent recovery sleep in three inbred strains of mice for which the homeostatic sleep rebound following SD differs. We reasoned that if clock genes are functionally implicated in sleep homeostasis then the SD-induced changes in gene expression should vary according to the genotypic differences in the sleep rebound.


RESULTS
In all three strains per expression was increased when animals were kept awake but the rate of increase during the SD as well as the relative increase in per after 6 h SD were highest in the strain for which the sleep rebound was smallest; i.e., DBA/2J (D2). Moreover, whereas in the other two strains per1 and per2 reverted to control levels with recovery sleep, per2 expression specifically, remained elevated in D2 mice. dbp expression increased during the light period both during baseline and during SD although levels were reduced during the latter condition compared to baseline. In contrast to per2, dbp expression reverted to control levels with recovery sleep in D2 only, whereas in the two other strains expression remained decreased.


CONCLUSIONS
These findings support and extend our previous findings that clock genes in the forebrain are implicated in the homeostatic regulation of sleep and suggest that sustained, high levels of per2 expression may negatively impact recovery sleep.
Franken
Paul
P
Department of Biological Sciences, Stanford University, Stanford, CA, USA. Paul.Franken@unil.ch
Thomason
Ryan
R
Heller
H Craig
HC
O'Hara
Bruce F
BF
D000704:Analysis of Variance; D000818:Animals; D056926:CLOCK Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology*; D006706:Homeostasis / Q000235:genetics*; D017403:In Situ Hybridization; D051379:Mice; D008815:Mice, Inbred Strains; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D056950:Period Circadian Proteins; D016548:Prosencephalon / Q000378:metabolism; D012890:Sleep / Q000235:genetics*; D012892:Sleep Deprivation; D013045:Species Specificity; D013997:Time Factors; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D014851:Wakefulness / Q000235:genetics
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C498260:Dbp protein, mouse; D009687:Nuclear Proteins; C539023:Per1 protein, mouse; C513312:Per2 protein, mouse; D056950:Period Circadian Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D056926:CLOCK Proteins; C538944:Clock protein, mouse