DNA Methylation: How it works

DNA methylation is one of the ways your cells control which genes to express. It is an example of epigenetic modification. Epigenetics mechanisms like this do not change the DNA sequence, only the way the genes are expressed. Whether or not DNA methylation is heritable is not clear.

This is how DNA methylation works:

  • Cytosine is a nucleotide, a DNA building block.
  • Through the action of an enzyme called methyltransferase, a methyl group is added to cytosine.
  • This is one of the ways your cells know which genes to express.
  • Cytosine is often found next to guanine, another building block. This is sometimes shown in literature as “CG.”
  • Cytosine and guanine are connected by a phosphate group. This is sometimes shown in literature as “CpG.”
  • A bunch of CpG sites together is called a CpG island. These islands are found in front of genes on DNA.
  • Special molecules called transcription factors land on CpG islands. When they do, the cell expresses the gene.
  • But when the cytosine on CpG islands is methylated, the transcription factor cannot bind. The gene is not expressed.

See pictures below.

Methylation is known to have an important role in cancer biology. Methylation of tumor suppressor genes causes the tumor suppressors not to be expressed, resulting in cancer.

Methylation 1Methylation 2Methylation 3

3 Responses

  1. Yvonne November 24, 2014 / 6:19 pm

    Wonderful explanation. But still yearning for how methylation of genes can lead to Mast Cell disease and if companies like 23 and me can be used to diagnose this. .. You’re such a info temptress! 😉
    I would really love it if we could just be (one day) diagnosed by a cheek swab to measure the DNA methylation of Mast cell related genes. Trying to get diagnosed/proof of illness Is a bit of a no man’s land.

    Thanks again so very much!

    • Lisa Klimas November 25, 2014 / 12:00 am

      Somehow hit edit instead of reply for your comment – I didn’t edit anything, just wanted to mention it. 🙂

      I also would love if we all had a quick diagnostic for mast cell disease. I am not convinced that methylation is the key in mast cell disease, there is significant evidence that all forms of MCD are due to mutations, not epigenetic changes. People ask me a lot about 23andme and I don’t personally feel it is useful for diagnosing mast cell disease. I do think there are some rare diseases with specific mutations that can identified by this test, but it is my opinion that it is not very helpful for mast cell disease particularly.

  2. Fussy Bug January 24, 2015 / 5:08 pm

    Your time and energy put into this topic is appreciated by me.
    Way above my head, but will continue to chew on it until I can digest it.
    I guess my big take away is that mutations and epigenetics are different.

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