From reading, I know that epigenome has to do with gene expression, which itself is when a cell reads a gene to create a protein
Epigenetics is interesting because even though two individuals may have the same DNA(twins) but due to environmental factors, etc , their epigenome may be different.
Can someone give an explanation for how DNA methylation fits into the picture? Is methylation a technique for influencing gene expression?
In: Biology
Essentially, Epigenetics refers to changes in gene expression, involving no changes in actual gene sequence.
Very generally speaking, there are 2 (of 5+) noteworthy ways in which expression of genes can change without changing the genome:
1. Histone modification: DNA in its typical state is wound up in chromosomes and is called chromatin, in which the DNA strands are convoluted and tied up around proteins called histones. Changes to the histones via enzymes result in loosening/tightening of DNA with respect to the histones, affecting the way that the gene is expressed; i.e, changing the production of the protein coded by that gene.
2. DNA methylation: This method involves the addition of CH3 methyl groups to the promoter region of DNA, whereby the promoter region is the area in which the expression of a gene in the form the production of a protein begins. Methylation will generally repress this region, meaning that this gene will not be expressed, and there will be no protein product.
As a result, even identical twins that have the exact same genetic sequence can express different protein products, resulting in different phenotypical expression (that is, observable characteristics).
The reason I brought up histone modification in addition to DNA methylation is just to highlight how epigenetics is determined by more than just changes to the DNA strand itself, but even changes to the DNA’s environment.
Apologies if i’ve delved into too much detail or used too much jargon; this topic is the type of thing you’d be learning in a university biology course, so it’s difficult to condense into a simpler format.
P.S a really good example of epigenetics and its effect on a population can be seen in th Dutch Famine population study, where it was found that offspring of mothers exposed to famine born into a post-famine environemnt with plenty of food and nutrients were mal-adapted to the environment they were living in, resulting in a higher incidence of metabolic disease (diabetes, cardiovascular disease etc) due to epigenetic programming in the fetus in the mother during nutritional stress.
You have it right. All nucleated cells have the same DNA sequence (assuming no retro virus and the like), but what makes cells different in functionality is which of the thousands of genes they actually express. This is dictated by which transcription factors are present which themselves need to be expressed, and the picture gets more complex. But another way of regulation is the epigenome, this is basically like you described, a way to affect the expression of a gene either by directly modifying the DNA sequence covalently or by modifying the histoens covalently. Such covalent modifications include methylation, hydroxymethylation, acetylation, phosphorylation, ubiquitination and sumoylation. These are just chemical groups or proteins added covalently to the DNA bases or the amino acids making up histones. Not all of these apply to both DNA and histones, some to both some to one or the other. And of course there are sooooo many other things in epigenetic regarding many types of RNA and such, but let’s not get too complex. Btw, histones are proteins that the DNA wraps around in many layers of organization to condense it (since it’s extremely long), and when you transcribe a gene you usually loosen this binding a bit to make it accessible, so if you modify those histones you may either reduce or enhance the tightness of the wrapping, thereby affecting gene expression. For methylation, since you’re interested in it, when it happens on DNA it is thought to recruit some proteins that repress gene expression or it directly inhibits the binding of transcription factors. When it’s on histones, it functions to wrap the tail of the histones tighter around the DNA to restrict access of transcription factors that can facilitate the expression of the gene. And methylation is not permanent, it can be written and erased, but it does play a role in genomic imprinting where your parent can transmit their DNA methylation to their offspring, that’s how x chromsome silencing works (women have two and one is silenced).
Latest Answers