Mammalian PERIOD2 regulates H2A.Z incorporation in chromatin to orchestrate circadian negative feedback

Area of Science:

• Molecular Biology
• Chronobiology
• Epigenetics

Background:

• Mammalian circadian oscillators are regulated by a transcriptional-translational feedback loop.
• The PER-CRY complex represses the activity of the CLOCK-BMAL1 transcription factor.

Purpose of the Study:

• To investigate the role of histone variant H2A.Z in regulating circadian gene expression and chromatin organization.
• To elucidate the mechanism by which PER2 influences H2A.Z deposition and its impact on circadian rhythms.

Main Methods:

• Analysis of nucleosome occupancy in Per knockout fibroblasts.
• Assessment of circadian period length in cells with altered H2A.Z levels or YL1 depletion.
• ChIP-seq to examine BMAL1 chromatin recruitment.
• Immunoprecipitation to identify PER2-interacting proteins.

Main Results:

• Per null fibroblasts exhibit altered nucleosome occupancy and impaired H2A.Z deposition.
• H2A.Z knockout mimics the Per null chromatin state and disrupts cellular rhythms.
• PER2 interacts with the H2A.Z chaperone YL1.
• Perturbing H2A.Z deposition or binding sites lengthens the circadian period.
• H2A.Z deletion impairs BMAL1 recruitment and promotes its degradation.

Conclusions:

• A PER2-mediated pathway for H2A.Z deposition is crucial for circadian clock function.
• This pathway compacts CLOCK-BMAL1 binding sites, organizes circadian chromatin landscapes via CTCF, and bookmarks genomic loci for BMAL1 binding.
• H2A.Z acts as a key epigenetic regulator in the mammalian circadian system.