Transcriptional Architecture and Chromatin Landscape of the Core Circadian Clock in Mammals

Transcription Around the Clock The biological clock that controls daily rhythms in mammalian physiology and behavior is thought to be regulated in large part by transcriptional events (see the Perspective by Doherty and Kay ). Koike et al. (p. 349 ; published online 30 August) produced a comprehensive analysis of these transcriptional events across the entire mouse liver genome over a 24-hour period. Only ∼22% of cycling messenger RNA transcripts were driven by de novo transcription, suggesting that posttranscriptional events also play an important regulatory role in the mammalian clock. Biological timing in organisms can also respond to rhythmic cues from the environment. Morf et al. (p. 379 , published online 23 August) explored how one such cue, cycles in ambient temperature, influence circadian timing in mammalian cells. Cold-inducible RNA–binding protein (CIRP) accumulates when body temperature is low. A systematic search for binding partners of CIRP identified RNA encoding core components of the circadian clock. Loss of CIRP decreased the amplitude of circadian gene expression and cells lacking CIRP adapted more quickly to temperature cycles.