Role of chromatin modifier enzymes (DNMT1, HDAC1, HDAC2 and HDAC3) in the silencing of MUC2 and MUC5B. siRNA experiments were carried out as described in the Materials and methods section. MUC2, MUC5B and GAPDH mRNA levels were assessed by RT–PCR. PCR products (10 μl for MUC2 and MUC5B, 6 μl for GAPDH) were analysed on a 1.5% agarose gel. (a) Diagram showing data expressed as MUC2/GAPDH ratio. (b) Diagram showing data expressed as MUC5B/GAPDH ratio. Control corresponds to the means value from mock cells and cells transfected with non-targeting siRNA. *P⩽0.05; **P⩽0.005; ***P⩽0.0005.