Fig. 6

Models of TET-dependent regulation of TEs. a TE-derived ESC enhancers interact with highly expressed genes; TET binding is associated with lower 5mC levels, increased NOS binding and higher gene expression, which could have played a role in the exaptation of these TEs by the host genome. b L1 elements bound by KRAB-ZFP/KAP1 do not bind TETs and have high 5mC levels; loss of KAP1 binding (in currently active L1s or at different points during L1 evolution) would allow for TET binding, which would drive DNA demethylation and promote LINE-1 expression and expansion; upon TET binding, recruitment of other TET-dependent epigenetic modifiers (e.g. SIN3A) ensure that L1 expression is kept under control, constituting host defence strategies that could partly have evolved from the need to maintain genome stability