Overview of 3D genome folding. (A) The higher order structure of the 3D genome is organized in the hierarchical order, starting with nucleosome fiber that forms the loops, and Topologically Aassociating Domains (TADs), compartments A/B (green/red, respectively) in alternating globular structures, and chromosomes. (B) Loop extyrusion as the working model for loop formation, in which DNA is extruded through the hallow of the cohesin. Extrusion stops as cohesin meets at the CTCF dimer with the antiparallel orientation.
