Fig. 1.

Three major epigenetic modification mechanisms. A) DNA methylation. DNA methylation is mediated by DNA methyltransferase enzymes at CpG sites. It can also decrease gene expression by reducing the binding of transcription factors or increasing the binding of methyl-CpG binding proteins[11,12,59,100]. B) Histone modification. Histone acetylation, particularly in lysine residues of histone tails, is an important histone modification that can accelerate binding transcription factors and then gene expression beside DNA demethylation[18,59]. C) miRNA. The formation of miRNA begins in nucleus and continues in cytosol that can perform a mechanism to regulate gene expression in mRNA level[101].