EPIGENETICS: AN OVERVIEW
By Farhia Rashid
What is Epigenetics?
Epigenetics is the study of heritable changes in gene expression that do not involve changes to underlying DNA sequence (a change in phenotype without a change in genotype). This later affects how cells read the genes. Changes in epigenetics are natural, but can also be affected by factors such as age, lifestyle and disease. While epigenetic changes are usually not harmful, they can occasionally have damaging effects, which can result in diseases such as cancer.
Epigenetic Research: the History
Epigenetics began as broad-based research, focused on combining genetics and developmental biology, during the mid-20th century. The term ‘epigenetics’ originally referred to the influence of genetic processes on development. Later, as more research was put into the molecular basis of observations found that environmental stress caused genetic assimilation of phenotypes in Drosophila fruit flies. Since then, much research has gone into unravelling the epigenetic mechanisms relating to phenotypic changes.
Some major epigenetic modifications that are currently being researched include: DNA methylation, chromatin remodelling, histone modifications, and non-coding RNA mechanisms.
Epigenetics and the Environment: How can lifestyle affect epigenetics?
Both the environment and individual lifestyle can directly interact with the genome to influence epigenetic change. For example, studies have shown that prenatal and early postnatal environmental factors influence the foetus’ adult risk of developing various disorders. One study showed that children born during the Dutch famine (1944-1945) have increased rates of coronary heart disease and obesity after the mother’s exposure to famine during pregnancy, compared to those not exposed to famine. Less DNA Methylation of a particular gene was found to be associated with this.
The environment has a very powerful affect on epigenetic tags. One focus of this research area is pollution; it has been found that air pollution can alter methyl tags on DNA and increase a person’s risk of neurodegenerative disease. However, it is believed that Vitamin B could protect against harmful epigenetic effects of air pollution.
Diet has also been proven to have an effect on epigenetic tags. For example, it has been found that the ketogenic diet (high fat and low carb diet) can open up chromatin and improve mental ability. Some studies have also found that certain foods could make changes to methyl marks on oncogenes or tumour suppressor genes.
Studies performed by Feinberg and Vogelstein in 1983, using human tumour tissues, found that the genes in cancer cells were significantly more hypo-methylated compared to normal tissues. DNA hypo-methylation activates oncogenes, which also leads to chromosome instability. The building up of genetic errors can transform normal cells into an invasive tumour. Subsequently, epigenetic changes can be used as biomarkers for diagnosis of early stage cancer.
Genetic assimilation: A process in which an environmentally induced phenotype becomes genetically fixed.
DNA methylation: An epigenetic mechanism that occurs through the addition of a CH3 group cytosine (one of 4 DNA bases), therefore modifying the function of genes.
Oncogenes: A gene that, in certain circumstances, can transform a cell into a tumour cell.
Hypo-Methylated: Decrease in the epigenetic DNA methylation.
Chromosome instability: When chromosomes in the genome are unstable; chromosomes are either wholly or partially duplicated or deleted.