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February 19, 2020
Science

Epigenome Explained: An Introduction

An introduction to epigenome and what it is.
By
Tomohiro Takano

We all know that DNA is a molecule that carries information. It is basically a blueprint of all the different proteins your cells can produce. Each gene within the DNA carries the information to build a specific protein. In all, you have over 20,000 different genes in your DNA. Plus, every cell in your body has that exact same copy of DNA. 

However, if every cell in your body expressed every single protein, your body would not be functional. The different cells and tissues within your body have different functions. Muscle cells and liver cells cannot be the same, because they have vastly different functions. Since proteins cause function, these cells must express different sets of proteins to fulfill their function. 

But, how does a cell know which proteins to express? And, what happens when a cell expresses the wrong proteins?

Well, to understand these complex questions, you must first understand the epigenome


What is the Epigenome?

DNA is simply a molecule made of many smaller molecules. These molecules, called nucleotides, store information based on a three-nucleotide system. Each set of 3 nucleotides is called a codon, and each codon tells the cell to add a specific part of each new protein created. Each gene contains thousands or millions of codons, and in your DNA there are tens of thousands of genes. 

In order to express the right set of genes in each cell, cells use a “machine” of proteins and other molecules to maintain the DNA and express only the genes that are needed. This cellular machine uses a number of tools to change the DNA so that only a certain subset of genes is expressed. 

To do this, the epigenome does many things. It uses proteins to add chemicals to the DNA molecule, which can block other proteins from expressing the DNA and creating protein. It can also change how DNA is stored if it interacts with histones. Histones are large proteins that the DNA wraps around to be stored. You also may have heard of DNA Methylation, when a protein adds a methyl molecule (CH3) to a site in the DNA. These are just a few of the many changes that the epigenome can make to stop certain genes from being turned into proteins. 

In other words, if each cell was a horse and carriage the epigenome would be like the driver. The driver pulls on the reins and directs were the carriage goes. Likewise, the epigenome blocks or promotes certain genes to change the function of a cell.


How does the Epigenome Work?


Without going into detailed specifics, we can get a general overview of how the epigenome functions. The proteins, chemicals, and structures of the epigenome are influenced by their environment. At a cellular level, this environment includes hormones, cellular signals, and any molecules or influences that have come from outside of the body.

At a fundamental level, the epigenome controls cellular differentiation. This is simply a fancy phrase that describes the process of cells changing as they progress from a single cell into an entire organism. After the first few cellular divisions, the epigenome starts changing what DNA is expressed in each cell. 

For example, the first epigenomic changes may create a line of cells that can go on to become many different cell types. In the next division, more epigenetic changes will shut off more genes, and the cells will become more specific. Eventually, these changes pile up until cells only express a very specific and limited range of genes. These cells are very specific, such as a heart muscle cell, a liver cell, or a nerve cell. Together, all of these specific cells function together to create you - a multicellular organism!

But, epigenetic changes do not stop when cells are done differentiating. In fact, the epigenome is constantly making changes to your genes based on your environment, your diet, how much you exercise, and many other factors. Here’s some proof of how important the epigenome is:


These mice are clones. That means they have exactly the same DNA sequence. Researchers simply altered the epigenome of the top mouse. While these changes were small, they resulted in a crooked tail, folded ears, and probably a high number of other changes within the mouse!


Your Actions Affect the Epigenome!

The epigenome is highly sensitive to changes in your environment. What you eat, how much you exercise, your local environment, and many other things can send chemical signals to the epigenome causing it to change the way your DNA is expressed!

To see this in action, let’s consider smoking. Tobacco contains thousands of chemicals (both natural and artificial), which get into your lungs when you smoke the plant. In your lungs, these chemicals transfer to your bloodstream and are carried to every cell in your body. Some of these chemicals can change the function of the epigenome and cause it to block or promote certain genes. Some of these chemicals are also mutagens, which can cause damage to the DNA itself.

Between these two processes, your risk of cancer becomes much higher. Not only is the DNA mutating into a non-functional form, but changes to your epigenome can completely change how a cell functions. Instead of a functional lung cell, for instance, it will produce a completely different set of proteins. Once a cell has been changed, it may start to divide rapidly - leading to a cancerous tumor. Tumors are bad because the tissue itself is no longer functional and the mass of extra cells can block important pathways, nerves, and vessels within your body.

More than that, scientists have found that the epigenome can be inherited. That means that regardless of your DNA, you can pass on a malfunctioning epigenome. For example, scientists have found that women who smoke pass on certain epigenetic changes to their babies that may lead to health conditions later in the baby’s life!

But, it’s not just the bad things you do that can change your epigenome. Exercise and a healthy diet can improve the expression of your epigenome, whereas a lack of exercise and a poor diet can introduce bad changes to your epigenome. 


So, What Does This Mean for Me?

While DNA can only be modified by mutations, the epigenome can change with every action you take. Some actions may even cause your epigenome to go haywire and help promote cancer and other diseases. 

So, in order to live the happiest and healthiest life, you must consider that every action you take contributes to how your DNA is expressed. 

But, there is good news! Good decisions, like exercising and eating a healthy diet, can help your epigenome express the appropriate genes in every cell. This means that your health is less a function of your DNA, and more a function of your epigenome.


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Tomohiro Takano
Tomohiro Takano
Co-Founder and CEO