Fig. 2
From: Getting the genome in shape: the formation of loops, domains and compartments
Convergent CTCF sites at topologically associated domain (TAD) boundaries. The linear distribution of CTCF binding sites and regulatory elements across a hypothetical chromosomal segment (top) results in three-dimensional looped configurations (bottom) that will differ between cells and change over time. CTCF-mediated loops can create TADs, within which enhancer-promoter loops are formed. Loops preferentially occur between convergent CTCF sites, which predicts that a TAD boundary needs to have divergent CTCF sites to accommodate looping with its neighboring boundaries. Note that not all CTCF sites form loops, even when associated with CTCF