Schematic representation of the 11p15 mucin gene cluster regulation by epigenetics. Sense of transcription is indicated by the broken arrow situated at the transcriptional start site of each mucin gene. CpG islands are represented by open circles. Relevant methylated (m) CpG sites (black circles) or region (black square for MUC5B) implicated in the silencing are indicated. For MUC2, site-specific methylation is associated with the establishment of a repressive histone code. Silencing of MUC5AC is most probably due to indirect mechanisms or methylation of other regions. MUC6 regulation is not influenced by epigenetics.