Epigenetics is the study of how environmental factors and behaviour can alter the function of genes. Epigenetics is the process where genes are altered without modifying the DNA coding itself. It explains how experiences in a person’s lifetime can change how their DNA is expressed and how that change can be passed on to the next generation.
The term epigenetics became popular in the early 1940s when British embryologist Conrad Waddington used it to explain the connections between genes and gene products. The Greek word “epi” means “over, on top of.” As a result, epigenetics examines the extra set of instructions that sit above DNA and regulate how genes are expressed. While epigenetic alterations can alter how your body interprets a DNA sequence, they are reversible and do not alter your DNA sequence like genetic changes do[1].
Our DNA receives tiny chemical tags that are either added to or removed in response to alterations in the environment we are living in[2]. These tags play a role in deciding whether to turn genes on or off and thus affect protein synthesis, which is necessary to construct the various types of functional cells that our bodies require.
Even though all of our cells share the same DNA, there are numerous different cell types in our body because of the expression or inhibition of particular gene sets. Epigenetic silencing is one method of turning genes off, and it can contribute to differential expression. Silencing could also explain why genetic twins do not have identical phenotypes[3].
Throughout your life, your epigenetics alter. Your epigenetics at birth are not the same as those in adolescence or old age. Some research states; that the degree of DNA methylation declines with age.
Most epigenetic changes occur only during the individual organism’s lifetime, and environmental factors such as diet, stress, exercise, and exposure to pollutants (heavy metals, pesticides, diesel exhaust, tobacco smoke, radioactivity, bacteria, and viruses) can influence certain epigenetic modifications.
Epigenetics and inheritance:
Some epigenetic changes can be passed down over generations (meiotic inheritance) and between mother and daughter cells (mitotic inheritance)[4]. One reason for the striking phenotypic changes that can exist between cells and organisms with identical DNA is epigenetics.
Epigenetic information is not transmitted using the same process as traditional genetic information since it isn’t contained in the DNA sequence. In fact, many epigenetic alterations are “erased” or “reset” spontaneously when cells divide (whether through meiosis or mitosis), preventing their inheritance[5].
One consequence of epigenetic inheritance is that your experiences, particularly the traumatic experiences, might have a long-term impact on your family. Errors in the epigenetic process, such as incorrect gene modification or inability to add a chemical group to a specific gene or histone, can result in abnormal gene activity or inactivity, resulting in genetic diseases.
Prader-Willi syndrome, for example, occurs when a group of paternal genes on one chromosome is missing and the silent copies on the other chromosome are unable to compensate for the absence[6].
Epigenetic modifications
DNA Methylation
DNA methylation is a common type of epigenetic alteration. DNA methylation is the process by which tiny chemical groups – methyl groups (containing of one carbon atom and three hydrogen atoms) are attached to DNA. This is extremely specific and always occurs in a CpG site (a region in which a cytosine nucleotide is connected by a phosphate to a guanine nucleotide)[3].
When methyl groups are present on a gene, it is switched off or silenced by preventing the proteins that connect to DNA to “reading” the gene from doing so. Demethylation is a procedure that can reverse this process[7].
Histone modification
Histone modification is a typical epigenetic modification. In the cell nucleus, histones are structural proteins that are chromatin’s main building block[3].
After being transformed into proteins, histones can undergo post-translational modifications that affect how chromatin is organized, which in turn affects whether the linked chromosomal DNA will be expressed.
More DNA is exposed and the gene is activated if histones are not tightly packed. On the other hand, if the chromatin is closely packed together, proteins that read genes are unable to reach the DNA as quickly, turning the gene “off.”
Genes can be turned “on” or “off” by adding or removing chemical groups from histones, such as methyl or acetyl groups (each consisting of two carbon, three hydrogen, and one oxygen atom). These changes influence how tightly the DNA is wrapped around histones[8].
Both DNA methylation and histone modification are common cellular processes that play a part in development by giving instructions to stem cells, or cells with the potential to differentiate into other types of cells.
Non-coding RNA
Your DNA serves as a blueprint for the production of both coding and non-coding RNA. Non-coding RNA regulates gene expression by binding to coding RNA and degrading (breaking down) the coding RNA so that it cannot be used to produce proteins. Non-coding RNA may also recruit proteins to change histones, allowing genes to be turned “on” or “off.”
Epigenetics and Cancer
Cancer was the first human disease to be linked to epigenetics in 1983.
Researchers discovered that sick tissue from colorectal cancer patients had less DNA methylation than normal tissue from the same patients[9]. They discovered that hypermethylation inhibited tumour suppressor genes in particular.
While cancer cells exhibit higher DNA methylation at specific genes, DNA methylation levels in cancer cells are overall lower than in normal cells. Because methylated genes are generally switched off, lack of DNA methylation can result in abnormally high gene activation, causing cells to grow uncontrollably and eventually leading to cancer. On the other side, excessive methylation can undo the action of tumour suppressor genes.
Most cancers display different epigenetic patterns than those of healthy cells, and these patterns can be important for the development of the disease[10]. Epigenetics alone cannot diagnose cancer, and cancers would need to be confirmed with further screening tests[7].
Epigenetics is a developing field with enormous promise for understanding the complex relationship between genes and the environment. By studying epigenetics further, we can investigate the possibility of using epigenetic markers as diagnostic tools for illness detection and learn how changes in epigenetic patterns can contribute to the development of various diseases.
Reference:
- C, B.G. (2023). Epigenetics: How It Shapes Gene Expression and Development. [online] The Science Notes. Available at: https://thesciencenotes.com/epigenetics-gene-expression-development/ [Accessed 24 Sep. 2023].
- Henriques, M. (2019). Can the legacy of trauma be passed down the generations? [online] Bbc.com. Available at: https://www.bbc.com/future/article/20190326-what-is-epigenetics [Accessed 24 Sep. 2023].
- Simmons, D. (2014). Epigenetic Influences and Disease | Learn Science at Scitable. [online] Nature.com. Available at: https://www.nature.com/scitable/topicpage/epigenetic-influences-and-disease-895/ [Accessed 24 Sep. 2023].
- Hamilton, J.P. (2011). Epigenetics: Principles and Practice. Digestive Diseases, [online] 29(2), pp.130–135. doi:https://doi.org/10.1159/000323874.
- Rogers, K. and Fridovich-Keil, J.L. (2018). epigenetics | Definition, Inheritance, & Disease. In: Encyclopædia Britannica. [online] Available at: https://www.britannica.com/science/epigenetics [Accessed 24 Sep. 2023].
- Genomics Education Programme. (n.d.). What is epigenetics? [online] Available at: https://www.genomicseducation.hee.nhs.uk/education/core-concepts/what-is-epigenetics/ [Accessed 24 Sep. 2023].
- CDC (2022). What is Epigenetics? [online] Centers for Disease Control and Prevention. Available at: https://www.cdc.gov/genomics/disease/epigenetics.htm [Accessed 24 Sep. 2023].
- MedlinePlus (2021). What is epigenetics?: MedlinePlus Genetics. [online] medlineplus.gov. Available at: https://medlineplus.gov/genetics/understanding/howgeneswork/epigenome/ [Accessed 24 Sep. 2023].
- Simmons, D. (2014). Epigenetic Influences and Disease | Learn Science at Scitable. [online] Nature.com. Available at: https://www.nature.com/scitable/topicpage/epigenetic-influences-and-disease-895/ [Accessed 24 Sep. 2023].
