Background Chromosomes are subdivided spatially to delimit long-range interactions into topologically associating domains (TADs). TADs are often flanked by chromatin insulators and transcription units that may participate in such demarcation. Remarkably, single-cell Drosophila TAD units correspond to dynamic heterochromatin nano-compartments that can self-assemble. The influence of insulators on such dynamic compartmentalization remains unclear. Moreover, to what extent heterochromatin domains are fully compartmentalized away from active genes remains unclear from Drosophila to human. Results Here, we identify H3K27me3 micro-domains genome-wide in Drosophila, which are attributed to the three-dimensional spreading of heterochromatin marks into euchromatin. Whereas depletion of insulator proteins increases H3K27me3 spreading locally, across heterochromatin borders, it concomitantly decreases H3K27me3 levels at distant micro-domains discrete sites. Quantifying long-range interactions suggests that random interactions between heterochromatin TADs and neighbor euchromatin cannot predict the presence of micro-domains, arguing against the hypothesis that they reflect defects in self-folding or in insulating repressive TADs. Rather, micro-domains are predicted by specific long-range interactions with the TAD borders bound by insulator proteins and co-factors required for looping. Accordingly, H3K27me3 spreading to distant sites is impaired by insulator mutants that compromise recruitment of looping co-factors. Both depletions and insulator mutants significantly reduce H3K27me3 micro-domains, deregulating the flanking genes. Conclusions Our data highlight a new regulatory mode of H3K27me3 by insulator-based long-range interactions controlling distant euchromatic genes.

中文翻译：

---

基于绝缘体的环介导 H3K27me3 在抑制常染色质基因的远处微域上的扩散

背景 染色体在空间上被细分以将远程相互作用划分为拓扑关联域 (TAD)。TAD 的两侧通常是染色质绝缘体和可能参与这种划分的转录单位。值得注意的是，单细胞果蝇 TAD 单元对应于可以自组装的动态异染色质纳米隔室。绝缘体对这种动态划分的影响仍不清楚。此外，从果蝇到人类，异染色质域在多大程度上与活性基因完全区分开来仍不清楚。结果在这里，我们在果蝇中鉴定了全基因组的 H3K27me3 微域，这归因于异染色质标记向常染色质的三维扩散。而绝缘体蛋白的消耗会增加 H3K27me3 的局部扩散，跨越异染色质边界，它同时降低了远处微域离散位点的 H3K27me3 水平。量化长程相互作用表明，异染色质 TAD 和相邻常染色质之间的随机相互作用无法预测微域的存在，这与它们反映自折叠或绝缘抑制性 TAD 中的缺陷的假设相反。相反，微域是通过与由绝缘体蛋白和循环所需的辅助因子结合的 TAD 边界的特定远程相互作用来预测的。因此，H3K27me3 扩散到远处站点会受到损害循环辅助因子募集的绝缘子突变体的影响。耗尽和绝缘子突变体都显着减少了 H3K27me3 微结构域，从而解除了对侧翼基因的调控。