We all have a daily routine. For much of the EpiGenie office staff, that includes getting out of bed, brushing our teeth, going to work, grabbing a coffee, clocking a few hours on Facebook and complaining that there aren’t enough hours in the day. Now, researchers say that transcription and epigenetic modifications in mouse liver cells also have a daily rhythm too, but it’s a bit more dynamic. It turns out that Pol II transcription has two main activity peaks—once during the morning and once in the evening—and that the epigenetic landscape can change throughout the day.
The Swiss team looked at ChIP-Seq profiles for Pol II, and histone modifications like H3K4me3, and H3K36me3, as well as mRNA accumulation, at six time points during a 24-hour cycle. Here’s what they found:
- Rhythmic recruitment of Pol II onto gene promoters (not a transition from a paused state to elongation) was the likely cause of the two main transcription peaks, in the morning and in the evening.
- H3K4me3 (at promoters) lagged Pol II occupancy by an hour, and H3K36me3 (in gene bodies) lagged Pol II by three hours, as did mRNA accumulation. This indicates a dynamic chromatin remodeling.
- They found three different classes of mRNA accumulation patterns.
- Posttranslational mechanisms, such as degradation, may contribute to a rhythmic accumulation of mRNA.
The researchers say that although their analysis didn’t include proteins, similar mechanisms may hold true for protein accumulation in cells throughout the day.
Fit this into your routine and read the details at PLOS Biology, November 2012.