The Psychotherapist’s Essential Guide to the Brain Part 9
Epigenetics

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There was a time when we used to think the brain was immutable, until we discovered that it was quite malleable and now the remarkable plasticity of the brain is common knowledge. There is a similar paradigm shift in our thinking about DNA—it’s not fixed, it’s actually malleable as well— genes are as capable of modification as the brain. Both have some level of fixation along with plasticity that allows wiring pathways and gene expression to change with experience over time. It can be seen quite pointedly in genetically identical twins who have common DNA-driven similarities, yet differences develop over time in response to their personal experience (Kaminsky et al., 2009).
DNA, the molecule that acts as long-term storage for our genetic information, is also capable of regulating its own use. The vast majority of our DNA is not dedicated to protein production and much of this was know as “junk DNA”. We are now discovering non-protein coding DNA gives rise to various factors and RNA strands acting to regulate, stimulate, and disrupt the activity of protein production. Much of this is an epigenetic response, or a response that is specific to the nature of the individual’s experience within the context of environmental conditions. This represents an enormous breakthrough in the understanding of our malleable biology.

Epigenetics (literally “above the genes”) is the study of how environmental factors influence gene expression both within and through heritable changes in DNA (also known as behavioural epigenetics). The environment can “mark” genes, dramatically or subtly, changing levels of expression either transiently or for a lifetime and beyond to the following generations (Peckham, 2013). It is the mechanism by which genes adapt to the environment, shaping gene expression to best adapt to whatever circumstances confront us.

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When the environment prompts heritable changes in gene expression there are no changes made in the underlying DNA sequence (Levenson & Sweatt, 2005). In any strand of DNA only a well-defined portion of the genetic possibilities within the DNA are expressed and the rest are permanently, temporarily or semi-permanently turned off. In the language of geneticists, the universal DNA genotype is epigenetically changed to a cell-specific phenotype. The detail of epigenetic action is complex, but the principles are quite straightforward. By adding or subtracting chemicals, it is possible to “silence” a gene or make it impossible for that gene to be expressed in that cell or any of its daughter cells. This is not exactly the same process we talk about when referring to turning genes on and off, which is more about utilising genes that are readily available only in relation to particular needs at the time. Genes that are epigenetically silenced are taken completely out of the picture (Hill, 2013).

One way that a gene is silenced is when chemical alterations are made to tiny chemical tails that emerge from each of the eight histones. Addition or subtraction of these chemicals allows or disallows the transcription factors to attach to the promoter region, the most discussed process being acetylation. If we just look at the acetylation process, we see that when a histone tail is acetylated, the difference in ionic (electrochemical) charge between the histone and the section of DNA wrapped around it is neutralised. The larger the difference in charge between objects, the stronger the electromagnetic attraction. The effect of acetylation in neutralising this difference is that the DNA is looser and therefore accessible to transcription factors. When the histone tail is deacetylised, the difference in charge increases, which causes the DNA to wrap tightly around the histone, making it impossible for transcription to occur (Grunstein, 1997; for a general discussion of DNA methylation and histone modification see Peckham, 2013)…

This has been an excerpt from The Psychotherapist’s Essential Guide To The Brain (Part 9): Epigenetics. To read the full article, and more excellent material for the psychotherapist, please subscribe to our monthly magazine.

 

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