Gene-endogenous retrovirus confrontation. (A) Cartoon showing spreading of H3K4me3 euchromatin from the gene promoter towards the ERV sequence. The ERV becomes unmethylated and is able to act as an alternative promoter, potentially increasing expression of the gene. (B) ERV domination and heterochromatin spreading with consequent silencing of the nearby gene. (C) Equilibrium state where both euchromatin and heterochromatin form a boundary that may contain CTCF and allows for the ERV to be methylated while the gene is in an open chromatin conformation and is transcribed. CGI: CpG Island; CTCF: CCCTC-binding factor; ERV: endogenous retrovirus; LTR: long terminal repeat.
Rebollo et al. Genome Biology 2012 13:R89 doi:10.1186/gb-2012-13-10-r89