To correctly read the information stored in our DNA genomes (the genetic code), cells must read another language that overlays it – the epigenetic code – which controls access to that information. A process such as transcription can only retrieve this information according to the access granted by the epigenome.
The term epigenetics was coined in the 1940s by British embryologist and geneticist Conrad Waddington to describe “the interaction of genes with their environment….which bring the phenotype into being”. Now the term epigenetics (literally over or above genetics) refers to the extra layers of instructions that influence gene activity without altering the DNA sequence.
There are three main components to the epigenetic code:
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Methylated cytosine residues in DNA
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The range of post-translational modifications to the core histone proteins within the nucleosomes (referred to as the histone code)
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RNA molecules, often non-coding RNA
The epigenomes change and diverge, strongly implicating an epigenetic basis controlling the development of diseases. Our chromosomes adopt higher order structures, for example an enhancer promoter interaction over tens of kilobases, which can be revealed by techniques such as chromosome conformation capture (3C). 3C identifies the DNA involved in these interactions, and as the epigenome changes the 3C interactions change. These ‘epigenetic switches’ can be used to diagnose a cancer long before other symptoms are evident.
Reference. Jane Mellor, The Biochemist, Volume 32, NO 5, October 2010
