CpG islands present in putative promoter regions of the two genes of interest. A. Promoter structure of NDRG2 gene (the sequence are shown in Additional file 2). The black arrows correspond to NDRG2 primers for BSA assay, the grey arrows correspond to NDRG2_M_2 and NDRG2_M primers for MSP assays. B. CpG islands present in NDRG2 (numbered from 1 to 16) and PRDX6 (numbered from 1 to 26) genes obtained by MethPrimer software. Methylation status of CpG sites in vitro methylated DNA (IVD), normal lymphocytes (NL), three colon cancer cell lines, and in normal (N) and tumor (T) tissue of one patient with colorectal cancer. Methylated and unmethylated cytosine residues are indicated with filled and small circles while open circles denote partially methylated sites.