FIGURE 2.

Mechanism of loop extrusion. Cohesin acts as a molecular motor in the “loop extrusion” model: After binding to chromosomes, cohesin moves in two opposite directions along chromatin fibers and extrudes DNA loops until it contacts the target CTCF site in the converging direction. During TAD formation, cohesin undergoes functional changes by interacting with various regulatory factors. The cohesin loading factor, NIPBL, loads cohesin at specific DNA sites and facilitates cohesin's translocation on chromosomal fibers. Cohesin's release from chromosomes requires the PDS5 subunit to recruit the cohesin‐releasing factor, WAPL. The unloading efficiency of WAPL is stronger than that of PDS5, and both participate in the cohesin release process. Finally, cohesin ensures its smooth arrival at the target CTCF site through direct interaction with CTCF.