Fig. 1.

Insulator elements mechanism of action. a Insulator flanking a transgene and an enhancer element generates an insulated neighborhood via CTCF-loop formation, favoring enhancer–promoter interactions within the DNA loop. b Enhancer-blocking elements result from insulators between a transgene and an enhancer, leaving the enhancer outside the DNA loop, blocking its interaction with the transgene promoter. c Insulators acting as barrier elements prevent the spread of heterochromatin by recruiting histone-modifying enzymes (HME) to preserve a transcriptionally active euchromatin state