Epigenetics | New Scientist

By Alice Klein

Epigenetics is the study of how genes are influenced by the environment.

Every person is born with a fixed set of genes, but they can be switched on or off in different cells and in response to lifestyle factors like diet, exercise and stress.

Genes, which are sequences of DNA, are turned on and off by small chemical tags called epigenetic marks (epigenetics literally means on top of genetics). The best-known epigenetic marks are called methyl groups.

Epigenetics explains how cells in the body can perform different functions, even though they carry the same DNA instruction manuals. For example, the liver and brain cells of an individual contain exactly the same DNA, but they behave differently because they have different epigenetic marks controlling the genes they can switch on and off.

Research over the last two decades has revealed that epigenetic marks can be altered by lifestyle and environmental factors like drinking coffee, folic acid intake, obesity, exercise, anxiety, smoking, and exposure to air pollution. This may help to explain why lifestyle factors affect our chances of developing certain conditions like cancer and diabetes, because epigenetic marks can activate or silence certain genes involved in disease progression.

There is some evidence that epigenetic changes can be passed down to subsequent generations.

For example, when male mice are trained to associate a cherry blossom smell with an electric shock, epigenetic changes occur in their sperm. These changes seem to be passed to their pups and their grand-pups, meaning they too show signs of fear when exposed to cherry blossom smells.

This cross-generational epigenetic effect is harder to prove in humans, but there are some hints that it occurs. For example, one study found that grandchildren of Swedish men who experienced famine had lower rates of diabetes, whereas grandchildren of well-fed men had higher rates. Another study found that sons of US Civil War soldiers who spent time in prisoner-of-war camps were more likely to die young than sons of non-imprisoned soldiers, possibly because they inherited epigenetic elements of their fathers trauma.

Some scientists are sceptical about whether epigenetic changes can be passed down in families because epigenetic marks are erased when sperm and eggs form embryos. Others, however, believe that some epigenetic marks are able to slip through this reprogramming process, or that there are mechanisms of epigenetic inheritance we havent discovered yet.

Because epigenetic changes are common in cancer, drugs have been developed to try to treat cancer by reversing these changes.

The first approved epigenetic cancer drug was azacytidine, which is used to treat leukaemia. It works by removing methyl groups from DNA in order to re-activate tumour suppressor genes that stop cancer cells from growing and dividing.

Since the approval of azacytidine in 2004, five more epigenetic cancer drugs have been approved, and several more are being evaluated in clinical trials.

One drawback of current epigenetic cancer drugs is that they alter the expression of many different genes, not just those involved in cancer, which can lead to side-effects. Research is currently underway to try to target them more precisely to relevant genes.

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Epigenetics | New Scientist