Figure 3.
DNA methylation schematic. Addition of a methyl (CH3) group to cytosine residues on CpG islands effectively silences gene expression. Methylation of CpG islands is regulated by S-adenosylmethionine (SAM) and activity of DNA methyltransferase (DNMT). The methyl group derived from methylated tetrahydrofolate (THF) is donated to SAM and SAM then transfers the methyl group to cytosine nitrogenous bases in the DNA sequence. The ApoE (apolipoprotein E) gene (allele ϵ3, site A) is an example of where methylation silences (downregulates) ApoE and Aβ accumulates as a result of inhibiting Aβ processing [36].