Abstract: Objective To study the change and significance of DNA methylation pattern and DNA methyltransferase (DNMT1)protein in ⁶⁰Co γ-ray irradiated mice tissues.Methods Twelve SPF C57BL/6J mice were randomly divided intocontrol group and radiation group.The radiation group were exposed to 4Gy-single whole body radiation.All mice were sacrificed 3 days after the radiation.The total number of peripheral white blood cells and the frequencies of micronucleated polychromatic erythocytes(fMNPCE)were measured.Methylated DNA immunoprecipitation-chip(MeDIP-chip)was adopted to investigate the differentially expressed CpG islands methylation profiles in mouse liver genome promoter.The immunohistochemical(SP method)and western blot method were used to check the expression of DNMT1 protein in tissues.Results Compared with the control group,the promoter methylation profiles of irradiated mice changed obviously,with 1300 genes methylated and 660 genes demethylated.With the improvement of the screening criteria,the obviously methylated genes were Trim71,Sema3f,Pcdh8,Sox4,1110034A24Rik,Limk1,Nefl,and Xpr1 and the demethylated genes were Sfrs18,Dr1, Ankrd42,Nae1,Sfi1,Accn1,Srd5a1,Nsun2,Eif1a,and Dusp5.Except in the lung,the expression of DNMT1 protein in liver, kidney,testicle,and brain tissues were all increased(P<0.05).Conclusion There are methylation changes of gene promoter in ionizing radiation injury and the increased expression of DNMT1 may be the reason of gene promoter methylation.