Genome-wide profiles of RNA polymerase II (Pol 2) DNA occupancy and the histone modifications H3K4me3 and H3K36me3 around the circadian cycle. Mus musculus

To understand the transcriptional basis of circadian rhythms in mouse liver, we generated genome-wide profiles of RNA polymerase II (Pol 2) DNA occupancy and the histone modifications H3K4me3 and H3K36me3 around the circadian cycle. We found that Pol 2 occupancy at promoters and in gene bodies cycle in synchrony, suggesting that Pol 2 recruitment at promoters underlies circadian gene transcription. On average, Pol 2 occupancy precedes mRNA accumulation by about three hours. Promoters of transcribed genes have tri-methylated H3K4 residues even at their trough activity times, and the tri-methylation levels increase in phase with Pol 2 loading. In contrast, the tri-methylation of H3K36 residues lags transcription by three hours with amplitudes that are markedly shallower, indicating that this mark is less dynamic on the circadian time scale. The comparison of Pol 2 occupancy and mRNA accumulation revealed that both transcriptional and post-transcriptional regulatory mechanisms can account for diurnal mRNA profiles. Additional processed data and visualization tools are available at http://cyclix.vital-it.ch/ Contributed by members of CycliX consortium (http://cyclix.vital-it.ch/) Overall design: 28 samples examinded, 7 Polr2b, 7 H3K4me3, 7 H3k36me3, 7 input samples.