Our understanding of heterochromatin nanostructure and its capacity to mediate gene silencing in a living cell has been prevented by the diffraction limit of optical microscopy. Thus, here to overcome this technical hurdle, and directly measure the nucleosome arrangement that underpins this dense chromatin state, we coupled fluorescence lifetime imaging microscopy (FLIM) of Förster resonance energy transfer (FRET) between histones core to the nucleosome, with molecular editing of heterochromatin protein 1 alpha (HP1α). Intriguingly, this super-resolved readout of nanoscale chromatin structure, alongside fluorescence fluctuation spectroscopy (FFS) and FLIM-FRET analysis of HP1α protein-protein interaction, revealed nucleosome arrangement to be differentially regulated by HP1α oligomeric state. Specifically, we found HP1α monomers to impart a previously undescribed global nucleosome spacing throughout genome architecture that is mediated by trimethylation on lysine 9 of histone H3 (H3K9me3) and locally reduced upon HP1α dimerisation. Collectively, these results demonstrate HP1α to impart a dual action on chromatin that increases the dynamic range of nucleosome proximity. We anticipate that this finding will have important implications for our understanding of how live cell heterochromatin structure regulates genome function.

中文翻译：

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异染色质蛋白 1 α （HP1α） 经历单体到二聚体的转变，打开并压缩活细胞基因组结构


我们对异染色质纳米结构及其介导活细胞中基因沉默的能力的理解被光学显微镜的衍射极限所阻止。因此，为了克服这一技术障碍，并直接测量支撑这种致密染色质状态的核小体排列，我们将核小体核心组蛋白之间 Förster 共振能量转移 （FRET） 的荧光寿命成像显微镜 （FLIM） 与异染色质蛋白 1 α （HP1α） 的分子编辑相结合。有趣的是，纳米级染色质结构的超分辨读数，以及 HP1α 蛋白-蛋白质相互作用的荧光波动光谱 （FFS） 和 FLIM-FRET 分析，揭示了核小体排列受 HP1α 寡聚状态的差异调节。具体来说，我们发现 HP1α 单体在整个基因组结构中赋予以前未描述的全局核小体间距，该间距由组蛋白 H3 赖氨酸 9 （H3K9me3） 上的三甲基化介导，并在 HP1α 二聚化时局部减少。总的来说，这些结果表明 HP1α 对染色质具有双重作用，从而增加了核小体邻近的动态范围。我们预计这一发现将对我们理解活细胞异染色质结构如何调节基因组功能产生重要影响。