It’s all in our genes, or so we thought… On a genetic level, almost all the cells in our bodies are the same and yet we are all vastly different from one another. Genetically speaking, the cells which form our kidneys and those that form our livers are exactly the same, but they make two hugely different, vital organs. So how does one single genome (our sequence of genes) have so many various outcomes, and what is the benefit of knowing this?
Take two creatures which have an identical genetic code (inbred mice, a maggot and a fly, both male and female crocodiles). They should look exactly the same as one another, but they don’t. They may vary in weight for example, and this is due to epigenetics. From the Greek epi = “as well as”, epigenetics literally means “as well as genetics”; an additional layer of instructions to our genetics.
Nessa Carey, a molecular biologist, has wonderful ways of explaining this topic. She imagines DNA as a script, not a template; like a script, it can be altered and deviated from. We all have the same basic starting script and yet, we all perform our own interpretation of the film in the end.
The phenomenon of epigenetics is demonstrated as the body switches genes on and off depending on if they are being used. For example, if on a Friday you come home and think “a glass of wine would be great”, but then a couple of Friday’s in and that one glass has become a few more to achieve the same effect. Well, that’s because your body is breaking down the alcohol faster. This happens as a gene that controls the breakdown of alcohol is modified as more alcohol is consumed. These epigenetic modifications are added to tails which protrude from proteins, making it easier for the gene controlling alcohol breakdown to be switched on. When (if) you decide to lower your alcohol consumption again, these modifications switch the alcohol breakdown gene off again, but the modifications are always there.
These changes can be permanent. If the modifications are present on a lot of the protein tails, the change can transfer onto the DNA itself. In some cases, this can turn a gene off permanently with no ability to switch on again. Hence, kidney cells are kidney cells and heart cells are heart cells forever (this is cell differentiation). The epigenetic modifications alter the likelihood of gene being expressed but never change the DNA code. So what happens when these epigenetic modifications go awry?
Some epigenetic modifications go wrong during development or cell division, resulting in numerous diseases. Cancer is the most well-known condition linked to epigenetic fault. The over expression of cell regulatory genes (control how quickly a cell divides) can lead to cancer; fundamentally just cells which are dividing too rapidly.
Epigenetics is not purely hereditary either, diet and other external influences (such as stress, cigarette smoke etc.) have been shown to play a role in causing epigenetic modifications. As children, identical twins have exactly the same epigenome (same script of epigenetic modifications). However, in adulthood, the same identical twins will have differences in their epigenomes. This is purely due to environmental factors.
We now know that not only our genes cause some diseases/conditions but other epigenetic factors have a role too, and this is revolutionary. This finding makes it possible to start predicting which environmental factors lead to epigenetic modifications, and also which changes could be prevented/controlled for future generations. The knowledge of our genetic sequence could one day lead to personalised medicine. The identification of epigenetic modifications would enable research into personalised medicine to target even more conditions and hopefully, treat us as individuals in the future.
*Side Note: If this subject interests you, I implore you to watch the video below at some point, presented by Nessa Carey. She explains it so very well, and is the reason I started following this topic. Her two books (Junk DNA and The Epigenetics Revolution) are also brilliant reads and accessible to everyone.