染色质根据紧致程度通常被分为常染色质和异染色质。异染色质是高度紧缩，常常伴随着组蛋白的修饰H3K9me3或H3K27me3。愈来愈的证据表明异染色质通过HP1介导的相分离形成。但是表观修饰是如何在活细胞中调节异染色质形成，维持和动态变化至今仍不清楚。我们前期工作中开发了CRISPRainbow和CRISPR-Sirius用于在活细胞中观察基因组DNA，并且示踪它们的动态变化。本申请项目将利用这些系统示踪在改变表观修饰过程中，三维基因组的重构和异染色质的形成。将主要集中在下面三个方面：1）建立染色质表观修饰干扰和活细胞示踪一体系统(Perturb-Imaging)；2）示踪H3K9三甲基修饰之后异染色质的形成过程；3）揭示HP1在介导异染色质形成和维持过程中的作用。这些研究将揭示染色质在细胞内动态组织结构，并且可以帮助了解和分析异染色质动态变化在细胞命运决定中的作用。

Interphase chromatin is typically classified as euchromatin or heterochromatin, depending on the degree of its compaction. Heterochromatin is highly condensed, with the signatures of H3K9me3 or H3K27me3. It has been proposed that the heterochromatin formation is mediated by liquid-liquid phase separation. How the epigenetic modifications regulate heterochromatin formation, maintenance and dynamics in living cells is still unclear? Previously we have developed CRISPRainbow and CRISPR-Sirius to visualize genomic DNA and track their dynamics in live cells (Ma et al., Nat Biotechnol 2016; Ma et al., Nat Methods 2018). Here we will harness these platforms to track the reorganization of the 3D genome and heterochromatin formation upon the change of epigenetic state. Three aspects will be focused: 1) Establishing a system for changing epigenetic modification and tracking the genome dynamics; 2) Live cell tracking heterochromatin formation when subjected to H3K9 trimethylation; 3) The role of HP1 during heterochromatin formation and maintenance. The proposed study will reveal how heterochromatin is organized in live cells and might facilitate to dissect the role of heterochromatin dynamics in cell fate decision.