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. The experiment involves sequencing of ChIP-seq samples from skeletal muscle tissue under different conditions and marks (EZH1, H3K27me3, Suz12)

基因表达的昼夜节律性是细胞生理学的保守特征。该过程涉及转录与转录后分子机制间的精细调控，其高度依赖细胞的代谢状态，而代谢状态可保障组织特异性基因程序的内在可塑性。表观基因组结构及其调控因子的动态变化，在维持这种可塑性方面发挥关键作用。本研究探究了多梳细胞记忆复合体PRC2-EZH1（Polycomb Repressive Complex 2-EZH1）在有丝分裂后骨骼肌细胞的转录节律调控中所扮演的角色。我们发现，PRC2-EZH1的核心组分受BMAL1的直接调控，呈现振荡表达特性，并同时调控靶基因的沉默与激活。完全组装的PRC2-EZH1复合体通过调控周期性H3K27me3（组蛋白H3赖氨酸27三甲基化）的修饰状态，对直接靶基因的周期性表达产生负向调控作用。与之相反，本研究证实EZH1可通过稳定RNA聚合酶II（RNA Pol II）复合体、维持转录过程的保真度，调控组成型昼夜节律基因的表达。综上，本研究揭示了多梳蛋白家族（PcG）在成年骨骼肌细胞昼夜节律基因调控中的双重多效性作用，以及PcG细胞记忆系统在体细胞中的可塑性本质。本实验包含对不同条件下骨骼肌组织的ChIP-seq（染色质免疫共沉淀测序）样本进行测序，检测的靶点包括EZH1、H3K27me3与Suz12。