Dual Role of PRC2-EZH1 in Orchestrating Rhythmicity of Circadian Transcriptional Program in Post-mitotic Skeletal Muscle Cells

Circadian rhythmicity of gene expression is a conserved feature of cell physiology. This involves the fine tuning between transcriptional and post-transcriptional molecular mechanisms, strongly dependent on the metabolic state of the cell that guarantees intrinsic plasticity of tissue specific genetic programs. To support the plastic properties a key role is played by the dynamics of epigenome structure and its regulators. Here we investigate the role of the Polycomb cell memory complex PRC2-EZH1 in regulating transcriptional rhythmicity in post-mitotic skeletal muscle cells. We show that PRC2-EZH1 core components are under direct regulation of BMAL1, show an oscillatory behavior and control both silencing and activation of target genes. Fully assembled PRC2-EZH1 complex negatively regulates cyclic expression of direct targets through modulation of cyclic H3K27me3 status. Conversely, we show that EZH1 regulates constitutive circadian genes expression, through stabilization of RNA Pol II machinery and maintenance of transcription process fidelity. Collectively, these findings unveil the dual and multi role of PcG in circadian gene regulation in adult skeletal muscle cells, and the plastic nature of PcG cell memory system in somatic cells.