[Improvement and Evaluation on Bisulfite Modification of DNA for DNA Methylation Detection].

OBJECTIVE: To establish a rapid and convenient method of DNA modification by bisulfite sodium for the detection of DNA methylation. METHODS: Through increasing the bisulfite sodium concentration and the temperature of treatment, cutting down the modification time, besides using glassmilk to adsorb the DNA in the purification and recovery, to improve the methods of DNA modification. Efficiency of cytosine converted to thymine in MAGE-A3 gene and DAP-K gene fragments were analyzed by bisulfite sequencing PCR in order to evaluate the DNA modification effect among the improved method, traditional method and kit method. RESULTS: The operating time of test was shortened to about 3 hours by the improved method; conversion rate of unmethylated cytosine to thymine was over 99%; compared with the traditional method and kit method, there was no significant difference (χ(2) = 0.0564, P > 0.05); the improved method was only for the unmethylated cytosine conversion modification, and there was no significant difference in process of methylated cytosine converted to thymine comparing with the traditional method (χ(2) = 0.0149, P > 0.05). CONCLUSION: The improved method has high efficiency of DNA modification and has no significant effect on excessive modification;meanwhile, it has many advantages such as time-saving and easy to operate etc.

[Value of DAPK Gene Methylation Patterns in the Diagnosis of Leukemia].

OBJECTIVE: To screen the differential methylation patterns of tumor suppressor gene DAPK and evaluate its value as a biomarker for the diagnosis of leukemia. METHODS: The methylation status of DAPK gene promoter's CpG island was analyzed in the genomes of normal human white blood cells and HL-60, U937 and Jurkat cell lines by bisulfite sequencing PCR (BSP). The effectiveness of differential methylation patterns of DAPK gene for diagnosis of leukemia was verified in the leukemia cell lines and peripheral blood samples by methylation specific PCR (MSP). RESULTS: The methylation pattern of DAPK gene in different cell genomes displayed that the degree of unmethylation in normal cell genome was higher than that of leukemia cell lines. The differential CpG sites were found and could be used to differentiate HL-60 and the other 3 cell lines by MSP. Meanwhile, the differential methylation patterns in clinical specimens could distinguish acute non-lymphocytic leukemia (ANLL) and other types of leukemia by MSP. The diagnostic sensitivity, specificity and accuracy were 59.1%, 100% and 82.7% respectively. No relationship was found between MSP diagnosis results and clinical pathological typing. CONCLUSION: The differential methylation patterns of DAPK gene as potential tumor biomarker for diagnosis of leukemia can enrich the means of diagnosis of leukemia, provide idea and basis for finding all kinds of tumor's DNA methylation biomarkers in the future.