Everyone knows that DNA is the code that makes you, well, you. But did you know that that code can be used by your body in different ways?
How your genes are actually used is called gene expression. Gene expression acts as both an on/off switch to control when proteins are made and also a volume control that increases or decreases the amount of proteins made. Gene expression is controlled by a number of factors, including methylation, which is used to lock genes in the “off” position. So what, exactly, is methylation, how does it happen, and what are the consequences of methylation?
Methylation: What is it?
DNA consists of a double strand of four different main nucleotides: cytosine, adenine, guanine, and thymine. When a process called methylation occurs, a small chemical group called a methyl group—CH, is added at a particular location along the strand of DNA. In humans, this mostly occurs where a cytosine base pair is found next to a guanine nucleotide—this is called a CpG site.
Methylation: When does it occur?
DNA methylation is a part of normal cell function: it is necessary for cell differentiation and embryonic development. While patterns of DNA methylation are normally stable, lifestyle changes can affect where and when it occurs. For example, studies show that acute sleep deprivation can increase methylation—twins with different sleep/wake cycles have distinct methylation patterns despite having identical DNA.
Methylation: What does it tell us?
In the 1990s, geneticist Jean-Pierre Issa found that an increase in methylation at CpG sequences changed with aging, and that this is a much more precise measure of age than telomere length, the previous biomarker of aging.