Epigenetic mechanisms
Just a short description so that people will understand that it’s not just about genes!
Up until recently it was thought that mammalian blue print, in this case human, consisted of the genome (the total collection of our genes) i.e. characteristics inherited from our parents which is fixed. Increasingly it is understood that these genes can be altered by the environment, that is, what we are exposed to e.g. our diet, exercise, chemicals and even our behaviour.
The ENCODE human genome project revealed that “junk DNA” is no longer a fact and that although only about 20% of DNA encodes for proteins the rest encodes for many types of regulatory RNAs, histone modification, gene modification such as methylation etc. (1, 2)
There are several different ways that a genome can be changed or modified by epigenetic mechanisms (3). There is complex cross-talk between these modifications so that everything we encounter is transcribed and translated into our bodies. The main mechanisms are: methylation, acetylation and microRNA (miRNA) control (4-6).
1. Methylation 2
DNA Methylation (Fig 1) is mainly an inhibitory mechanism where a methyl group is added reducing a gene’s function. The opposite is also used to reinstate a gene’s function (demethylation).
Histone Acetylation (Fig 1) usually enhances gene activity through various mechanisms including triggering the removal of a methyl group.
3. MiRNA control (2+5)
MicroRNAs (MiRNA) are small non-coding RNA molecules which attach themselves to sections of mRNA (messenger RNA) to block translation of the underlying DNA to proteins (Fig 2). There is an feedback relationship between MiRNA control and the epigenetic modifications shown above (7). This is essential to the normal functioning of cells. When this is faulty it can lead to serious diseases such as cancer, cardiovascular disease and schizophrenia.