EPIGENETICS

 In an earlier post “From DNA to chromosomes: connecting the dots”, I explained the terminology used in genetics including gene expression and DNA mutations. I stated that genetic mutations are irreversible which is why they are transmitted from the parents to the offspring from one generation to the next.

Genes play a very important role in our health. Genetic mutations that we have inherited from our parents can predispose humans to certain conditions such as heart disease, diabetes or breast cancer.

It is not only the genetic mutations that we have inherited that play a role in our health. Our behaviours and environment, what we eat and how active we are can also influence our health by affecting our genes. EPIGENETICS is the study of how our behaviours and environment affect the way our genes work. The prefix epi- in epigenetics comes from the Greek language and implies features that are "on top of" or "in addition to changes in genetic sequence.”

Unlike genetic mutations that are irreversible, epigenetic alterations are reversible, the DNA sequence does not change. Genetic mutations change gene expression i.e. instructions on which protein is to be produced and when whereas epigenetic changes act as a switch to turn genes “on” or “off”. 

Even though epigenetics is reversible, it can be inherited. An example of epigenetic inheritance, discovered about 10 years ago in mammals, is parental imprinting. In parental imprinting, certain autosomal genes have seemingly unusual inheritance patterns. For example, the mouse Igf2 gene is expressed in a mouse only if it was inherited from the mouse's father (https://www.ncbi.nlm.nih.gov/books/NBK21276/). It has been suggested that certain foods can turn a gene “on” or “off” implying that they van greatly influence our health and well-being.

Examples of epigenetics are:

• DNA methylation. A methyl (-CH3) group adds itself to a DNA like a cap and prevents gene expression. In other words, the gene is switched off and cannot produce the protein it is programmed to do. If demethylation occurs, i.e. removal of the methyl group, the gene will be turned on again.
• Another example is histone modification. Histones are important because very long DNA molecules wrap around histone proteins and give chromosomes a compact structure so that they can fit in the cell’s nucleus; they also regulate gene expression. In this case of epigenetics, DNA wraps around histones in such a way that they cannot be accessed by proteins that read and copy them. They are effectively turned off. Chemical groups can be added or removed from histones and turn them on again..
• Non-coding RNA: We have seen in my earlier post that DNA produces coding RNA that then leaves the nucleus and is used to make proteins. DNA also produces non-coding RNA that attaches itself to coding RNA along with certain proteins and helps to control gene expression. It can, however, also break down the coding RNA and prevent it from making proteins. It can also instruct proteins to modify histones to switch genes “on” or “off”.

According to the National Center for Biotechnology Information NCBI, lifestyle factors such as diet, obesity, physical activity, tobacco smoking, alcohol consumption, environmental pollutants, psychological stress and working on night shifts have been found to modify epigenetic patterns.  Other scientic articles link epigenetic mechanisms to various diseases including cancers of almost all types, cognitive dysfunction, and respiratory, cardiovascular, reproductive, autoimmune, and neurobehavioral illnesses. Known or suspected drivers behind epigenetic processes include many agents, including heavy metals, pesticides, diesel exhaust, tobacco smoke, polycyclic aromatic hydrocarbons, hormones, radioactivity, viruses, bacteria, and basic nutrients. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1392256/)

Studies of identical twins who have been reared apart show the effects that epigenetics can have on the siblings (https://www.theatlantic.com/science/archive/2018/05/twin-epigenetics/560189/).

Even though genetics has been the major focus of scientists upto now, epigenetics will increasingly dominate scientific interest in the future.