Fig. 2: Hierarchical order of the 3D genome.
From: Regulating epithelial-mesenchymal plasticity from 3D genome organization
The 3D genome in the nucleus is organized into hierarchical units of chromatin, with the formation of chromosomal territories (CTs) at the chromosomal resolution, where each chromosome occupies a distinct and non-overlapping area. Within CTs, there are chromatin compartments, comprising A compartments with open euchromatin enriched in highly expressed genes, and B compartments with closed heterochromatin associated with repressed transcription regions. Further organization within the compartments involves topologically associated domains (TADs), stable units guiding genome folding and long-range regulation. The finest level, often involving kilobases resolution, consists of chromatin loops which establish interactions between distant promoters and enhancers, playing a pivotal role in directly regulating gene expression.
