Nature meets Nurture – it ’ s epigenetics Written by Joe Sheppard
Our genes are the ultimate blueprint for who we are and how we look . They decide simple characteristics of our appearance like hair or eye colour as well as more complex traits such as height or even intelligence which no single gene encodes . These complex traits arise from the highly coordinated expression of multiple genes that work together in ensembles to produce the range of heights and appearances that we see in our population .
But what influences which genes are expressed in which cell , or how strong of an effect any given gene should be ? Despite having the same DNA in a neuron in your brain and in a white blood cell in your bloodstream , these two cells are vastly different in shape and function and use different , specialised subsets of genes that give them their unique cellular identities . To achieve this , cells restrict or facilitate access to genes through chemical alterations to DNA that change its shape .
This is a process known as epigenetics , an additional layer of control over our DNA that chooses which parts of the genetic blueprint are used in different tissues of our body , thus guiding our development from embryos all the way into adulthood , a process from which epigenetics gets its name : epigenesis .
To understand epigenetics a knowledge of chromatin structure is needed . You see , the DNA in the nucleus of a single cell isn ’ t free-floating , but is instead wrapped around proteins called histones that bind along the length of
DNA . Once DNA has bound to histones forming a nucleosome , many histones can bind to each other thus condensing the DNA into a small area . Most of the DNA in our cells exists in this form , highly condensed unreadable chromatin , called heterochromatin .
Cells achieve subtle control over which genes are read , or how often , through the covalent modification of DNA and histones that alter its readability , these are called epigenetic markers and they come in two broad forms :
1 . DNA methylation on cytosine residues in the DNA . Methylcytosine binding proteins recognise this marker and promote the condensation of DNA into silent heterochromatin .
2 . Histone modifications can take a variety of forms , most notably , histone acetylation reduces the charge attraction between histones and DNA favouring chromatin decondensing and active transcription .
20 | NEUROMAG | November 2017