Most of us probably have a bit of an idea of what genetics is: Inside our cells, we have DNA that contains the instructions to build and run everything in our body. The parts of DNA that could make different things (such as creating enzymes like lactase for breaking down the sugar in milk) are called genes. Mutations occur when mistakes are made when DNA is copied during cell replication, or when DNA is damaged. Some mutations can be beneficial – the lactase gene I mentioned earlier arose thanks to a mutation several thousand years ago; while some mutations can be extremely negative – the skin cancer melanoma is the result of UV radiation damaging the DNA.
So if that’s genetics, what is epigenetics? Well, gene expression can also be changed in response to environmental factors like disease and diet. This is precisely what epigenetics is: a mechanism that changes the final output of genes without changing the DNA molecule itself. Epigenetic changes can even be inherited just like DNA changes. While the DNA has not been changed, the expression of those genes and the final result has been altered.
Examples of epigenetic mechanisms
- DNA methylation: Methyl groups can be added to regions of the DNA, which prevents genes from being expressed. The addition or removal of these groups can change the expression of the gene in the cell.
- Chromatin structure and histone acetylation: In the cell, DNA is folded (when stretched out, your DNA totals about 2-3 meters in length!). How DNA is folded can influence the expression levels of genes. Some enzymes could change the folding structure, which make genes easier or harder to access. This is another way the cell can regulate gene expression.
- Non-coding RNAs: Before a gene can become a protein, it has to go through a middle step where it becomes a molecule similar to DNA called RNA. However, some RNA will never reach this final step and will instead regulate other RNA or the chromosomes themselves. A couple of types of non-coding RNA include:
- microRNAs (miRNAs)
- PiwiRNAs (piRNAs)
- Long non-coding RNAs (lncRNAs)
While the field of epigenetics is still relatively young, more and more clinical trials are being conducted into drugs that can utilise one of the epigenetic mechanisms above to help diagnose and treat disease. A couple of applications include:
- Diagnosing prostate cancer by identifying DNA methylation markers associated with the disease
- Diagnosing and treating cancers and heart disease with microRNAs