DNMT1-depletion caused cell growth delay. A) Morphology of IMR90 and HCT116 cells 24 and 72 hours post-transfection of siDNMT1 or siGFP. There are only slight differences between cells untreated (wt) and transfected with control siRNA (siGFP), on the contrary the treatment with siDNMT1 altered cell density/dish. B) Pictures and histogram showing the effects of siRNAs targeting DNMT1 and controls (wt and siGFP) in IMR90 and HCT116 cells on proliferation. Human fibroblasts slowed down proliferation in comparison to control cells at 72 h; however they resumed proliferation at 144 h. HCT116 cells growth was less affected by DNMT1 silencing. C) Real Time RT-PCR analysis of IMR90 and HCT116 cells showing decrease of DNMT1 transcriptional reduction after 72 hours from transfection of siRNAs targeting DNMT1. D) Western Blot showing the reduction of DNMT1 protein in both IMR90 and HCT116 cells treated with siDNMT1, consistent with Real Time RT-PCR results (see Additional file 1 for the densitometric analysis) E) Cytofluorimetric profiles of IMR90 and HCT116 cells pulsed with BrdU for 1 h, and stained with anti-BrdU antibody FITC-conjugated and propidium iodide. Following DNMT1 silencing IMR90 cells arrested in G1, while HCT116 cells slightly accumulated in S phase.