Promoter methylation negatively correlated with mRNA expression but not tissue differential expression after heat stress

DNA methylation plays a central role in gene expression. In this study, we detected the promoter methylation pattern of the chicken heat shock protein 70 (HSP70) gene and its association with messenger RNA (mRNA) expression before and after heat shock. The results showed that mRNA expression increased in response to heat stress and peaked at 3 h before dropping. Hypomethylation of the HSP70 promoter occurred in all of the groups studied, but the difference between groups within tissue type was not significant. The DNA methylation level of the control and the 6-h treatment groups was slightly higher than that of the 3-h treatment group in brain tissue and leg muscle. Correlation analysis between mRNA expression and DNA methylation of HSP70 showed that DNA methylation was negatively associated with mRNA expression in leg muscle (P = 0.0124), indicating that DNA methylation may be negatively associated with the expression of HSP70, although the difference was not significant. We concluded that the expression of HSP70 is heat inducible and tissue dependent and that heat induction may correlate with DNA methylation pattern in the HSP70 promoter, whereas tissue dependence is unrelated to DNA methylation pattern.