Bioruptor® in Action Video

Expertise

Expertise | DNA Methylation

DNA Methylation

DNA methylation is the first discovered epigenetic mark, and remains the most studied. DNA is methylated following DNA replication and is involved in a number of biological processes including; regulation of imprinted genes, X chromosome inactivation and tumor suppressor gene silencing in cancer cells. Methylation often occurs in cytosine-guanine rich regions of DNA (CpG islands), which are commonly upstream of promoter regions. Here at Diagenode we have developed a variety of assays and kits to facilitate the research of DNA methylation.

DNA methylation and CpG islands

DNA methylation is an epigenetic event that affects cell function by altering gene expression. It involves the addition of a methyl group to cytosine residues at CpG dinucleotides, a reaction that is catalyzed by DNA methyltransferase (DNMT) enzymes. The DNMT enzymes (DNMT 1, 3a or 3b) catalyses the transfer of a methyl group (CH3) from S-adenosylmethionine (SAM) to the carbon-5 position of cytosine generating 5-methyl cytosine. There are about 45,000 CpG islands in the human genome, and these are mostly located at promoters within first exons of genes. CpG islands are unmethylated in normal cells and their methylation has been associated with human disorders and epigenetic diseases. CpG islands located in the 5’ region of a gene are known as molecular switches that can turn-off or turn-on the expression of the downstream gene. For the majority of genes, the CpG islands in their 5’ regions are not methylated and they are ready to be expressed. In some cancers, CpG islands in the 5’ regions of tumorsuppressor genes are methylated and their expressions are switched-off. For example the methylation of CpGs near tumor suppressor genes (p53 or p16) has been linked to their transcriptional silencing and can result in canerous tumors. This mechanism of gene silencing is known to be one of the major mechanisms of tumorsuppressor gene inactivation.

What is the role of DNA methylation?

In higher organisms from plants to humans, methylation protects DNA from endonuclease degradation and plays a critical role in regulating gene expression, making it essential for normal development and function.

DNA methylation, Epigenetics and cancer

The pattern of DNA methylation and histone modification(s) is critical for genome stability and controlling gene expression in the cell and plays an essential role in maintaining cellular function. The formation of cancer cells can be driven by the alteration of the DNA methylation pattern leading to the silencing of tumor suppressor genes. For example hyper-methylation at the promoter regions of BRCA1, hMLH1, p16INK4a and VHL lead to gene silencing and catastrophic consequences. On the other hand, global hypo-methylation, which can lead to chromosome instability, has also been recognized as a cause of oncogenesis. This is because it is often accompanied by region-specific hyper-methylation and therefore disrupts the balance of the cells gene expression.