Methylation of CpG dinucleotides in the lacI gene of the Big Blue® transgenic mouse

摘要: Abstract Cytosine residues at CpG dinucleotides can be methylated by endogenous methyltransferases in mammalian cells. The resulting 5-methylcytosine base may undergo spontaneous deamination to form thymine causing G/C A/T transition mutations. Methylated CpGs also preferential targets for environmental mutagens and carcinogens. Big Blue® transgenic mouse has been used investigate tissue organ specificity of mutations deduce mutational mechanisms a mammal vivo. contains approximately 40 concatenated lambda-like shuttle vectors, each which one copy an Escherichia coli lac I gene as target. lambda mice are characterized high frequency targeted suggesting important contribution from methylation-mediated events. To study the methylation status gene, we have mapped distribution 5-methylcytosines along DNA-binding domain flanking sequences mice. We analyzed genomic DNA various tissues including thymus, liver, testis, derived two thymic lymphomas. DNAs unmethylated control were chemically cleaved, then positions ligation-mediated PCR distinguish cytosines. Our data show that most binding extent (>98%) all tested; only few sites partially (70–90%) methylated. conclude tissue-specific is unlikely contribute significantly patterns, occurrence common mutation specific not related selective these sequences. confirm previous suggestions transgenes presence bases.