By Dr Ananya Mandal, MD
DNA contains combinations of four nucleotides which include cytosine, guanine, thymine and adenine. DNA methylation refers to the addition of a methyl (CH3) group to the cytosine or guanine nucleotides. This methyl group may be added to the fifth carbon atom of the cytosine base or the sixth nitrogen atom of the adenine base.
This modification of the DNA alters the genes expressed in cells when they divide and differentiate from embryonic stem cells into cells of a particular tissue. The change in gene expression is stable and the cell does not revert back to a stem cell or another type of cell. The process of DNA methylation is stopped when a zygote is being formed but is restored as cell division occurs during development.
Importance of DNA methylation
DNA methylation is vital to healthy growth and development and is linked to various processes such as genomic imprinting, carcinogenesis and the suppression of repetitive elements. DNA methylation also enables the expression of retroviral genes to be suppressed, along with other potentially dangerous sequences of DNA that have entered and may damage the host.
Another important purpose of DNA methylation is the formation of the chromatin structure, which enables a single cell to grow into a complex multicellular organism made up of different tissues and organs.
In addition, DNA methylation plays an important part in the development of cancer and is a key regulator of gene transcription. Studies have shown that genes with a promoter region that contains a high concentration of 5-methylcytosine are transcriptionally silent. Aberrant methylation of DNA has been associated with an increased rate of malignancy. DNA hypermethylation is linked to the activation of genes and DNA hypomethylation has been associated with the development of cancer through various mechanisms.
Reviewed by Sally Robertson, BSc
Last Updated: Oct 8, 2014