The DNA of our bodies predetermines a lot of things about us before we are even born- from our looks to what kind of diseases we might be susceptible to. Some even say that the contents of our DNA are our biological destiny of sorts.
But it’s not all our DNA. Otherwise, how could different cells in our body behave differently when provided with the same set of instructions in the DNA sequence? Changes in gene expression are caused by heritable factors, as well as elements of the internal and external environment of an organism.
This is why the study of epigenetics is relevant and why there is much to be learned about the potential that lies in examining and manipulating our epigenome.
Epigenetics is a field of study that deals with changes in gene activity caused due to behavioural and environmental factors. The origins of the word- epi, which means in addition to or above- tell us that epigenetics is about things that are beyond the scope of genetics.
The history of epigenetics stretches back to 1942 when British embryologist C H Waddington first coined the term to describe cell differentiation during embryonic development. The term has broadened since then, to now describe how all changes in an organism that results from gene expression vary without there being any change in the source DNA sequences.
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Gene expression is when DNA codes ultimately get translated into proteins, but the how of this is not exactly dictated by the DNA. The phenotype- the characteristics that an organism exhibits- varies from the genotype, the genes it carries. This is where epigenetics comes in.
Epigenetics is the study of mechanisms that are behind changes in gene expression that are not caused by changes in DNA. These changes are called epigenetic variations. These epigenetic variations are either hereditary or a result of the environment within and surrounding an organism.
This is why identical DNA or identical genes don’t always result in identical outcomes.
All the cells in our body typically have the same DNA sequences, so there must be something else that decides what phenotype is expressed in each part of our body. Epigenetic variations can turn genes on and off, and therefore affect the protein production in cells.
This makes sure that different cells in our body produce only the proteins that are in accordance with their corresponding functions. Even though bone cells and muscle cells carry the same DNA sequence, proteins for muscle growth are not produced in bone cells.
Beyond localized production of proteins suitable for specific cell functions, epigenetic variations are important because it allows our fixed DNA to adapt dynamically to different environments that we find ourselves in.
There are different mechanisms that drive epigenetic variations and control gene expression. Three of the most important of them are DNA methylation, histone modification, and non-coding RNA.
DNA Methylation is the process by which methyl groups are transferred to the DNA molecule, and this mechanism can modify or repress genes. They typically trigger genes to the off position, so to speak. Demethylation, similarly, can cause genes to become activated.
Histones are proteins that help DNA to form nucleosomes, which in turn become chromatin. Since it forms structural support to the chromatin, it determines how accessible parts of the DNA is. So modification to histones can affect gene expression. A common type of histone modification is histone acetylation. In it, the addition of acetyl groups to histone tails makes the DNA more accessible and thus activates certain genes.
RNA is an important part of the gene expression machinery of organisms. RNA molecules that are not translated into proteins are called non-coding RNAs. These are significant in causing epigenetic variations.
We are now acquainted with the mechanisms of epigenetic variation, but what causes epigenetic changes- especially with respect to humans?
Development: Epigenetic variations cause the cells of an embryo to develop and differentiate into cells having different specific functions.
Age: Throughout the natural course of a person’s life, epigenetic changes occur.
Lifestyle: Changes in a person’s behaviour or surrounding environment can result in epigenetic changes.
Disease: Infections can cause epigenetic variations in your body. Certain epigenetic factors can increase susceptibility to diseases like cancer. Cancer can also cause epigenetic abnormalities.
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So aside from hereditary changes that accumulate over generations, genes are affected by our environment, and in particular the environments we may be exposed to early in life. This idea has a significant impact on not just science, but on our social and personal worlds. Although the exact impact the environment has on our genes- human genes- are not established yet.
A TEDx talk by Moshe Szyf, one of the pioneers in the field of epigenetics, describes geneticists vs epigeneticists argument behind social structures- “Geneticists will try to tell you that poor people are poor because their genes made them poor. Epigenecisits will tell you poor people are in a bad environment or impoverished environment that creates that phenotype, that property.”
Experiments have shown that the conditions that a person is exposed to, beginning from the early stages of foetal development, can have a significant impact on epigenetic variations. It has been shown that there is an entire rearrangement of the genome in response to the stress faced in early life, caused due to DNA methylation.
Although epigenetic variations are thought to become more stable in adulthood, they are still dynamic enough for a person’s lifestyle to have an impact on them. The extent of these impacts is still being studied. But it is apparent that our habits like our diet, stress levels, addictive behaviours, and our external environment, do cause changes in gene expression.
Epigenetics gives way to the conclusion that if genes can be programmed by the environment, then they could also be potentially reprogrammed.
This has implications that would result in being able to undo unfavourable epigenetic variations, control diseases like cancer, reduce susceptibility to addictions, encourage healthy behaviours, etc.
Epigenetics in cancer research is one area of increased interest in the scientific community. Cancer has been linked to the presence of epigenetic abnormalities. Reprogramming epigenetic factors could thus result in a way to treat, prevent and cure cancer effectively.
Epigenetic drugs can treat not just cancer but also cardiovascular, neurological, and metabolic disorders.
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The study of epigenetics has the potential to give us valuable insights into how the genetic mechanisms of our body operate. From this, we can diagnose and treat diseases, improve ourselves, and develop better habits.
The epigenetics market is projected to value at 35 billion US dollars by 2028. Beyond human health, epigenetics research now also finds applications in agriculture and other fields.
The advancements in technology in recent times make it a prime time for exploring the epigenome, and there is a long way to go before the opportunity is fully realized and utilized.
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