Epigenetics

What Is Epigenetics?

Epigenetics is the study of heritable changes in gene expression that do not involve changes to the underlying DNA sequence which in turn affects how cells read the genes. Genetic changes do not only occur due to changes in DNA sequence. Environmental factors such as lifestyle, diet, exercise habits may also affect the activity of genes and these changes can increase the predisposition to various diseases. Epigenetics studies the conditions caused by the fact that genes do not work more or less without changing the DNA sequence. The term is defined as changes in gene function that cannot be explained by changes in DNA sequence, which can be inherited by mitosis and/or meiosis division. Studies have conducted that several changes in the epigenetic properties of the cell nucleus may occur during development and there is a significant relationship between the loss of cellular potential and irreversible gene silencing. Our body contains more than 250 cells. Even though these cells have exactly the same DNA, liver and nerve cells have quite different structures and tasks from each other. However, this differentiation was achieved by epigenetic mechanisms, as it was performed without causing a change in our gene coding.

Thanks to the advances in genetic science, some areas of the DNA can be activated or silent with epigenetic. But, in addition to identified cellular differences, these epigenetic signs, depending on environmental conditions and our lifestyle, become open to change throughout our lives. For example, smoking changes the epigenetic structure in lung cells and causes cancer over time. In the epigenetic memory of cells, factors such as stress, disease and diet are also stored and cause long-term negative consequences. For example, fruit flies were found to be exposed to certain chemicals, causing spiny bumps to form over the eyes for at least 13 generations. According to another study, applying a chemical that affects reproductive hormones to pregnant rats resulted in generations of sick offspring. Studies in humans have demonstrated that children, malnourished adults and grandchildren have a higher rate of heart disease and diabetes. Considering all these, it is observed that there is also a close relationship between epigenetics and nutrition.

Epigenetic changes can also occur over generations along psychological factors. For example, in a research carried out at Emory University School of Medicine in the United States, male mice were given an electric shock from their feet at the same time with a chemical that smelled like almonds.  When this practice was repeated in the same way, the mice began to show signs of fear as soon as they smelled it. It was later revealed that, although they were not given an electric shock when they first smelled it, the offspring and even grandchildren of these mice also showed the same fear. All these examples reveal how our gene expression is affected by external factors, even without a change in DNA sequencing.

Although it is believed that epigenetic changes cannot be transferred to the next generations and it’s thought that epigenetic memory will be erased during the development of sperm and egg cells, recent studies have shown that this is not the case. The study published in the journal Science by researchers from the Max Planck Institute has shown that epigenetic changes are transferred from mother to embryo. In the study that used fruit flies as models, H3K27me3 DNA methylation observed in humans was targeted. (DNA methylation causes the relevant gene’s expression to change by adding a methyl group to the DNA, and usually suppresses the active gene.) During the study, it’s been observed that the methylated DNA kept the methyl group after fertilization while the other epigenetic markers in the mother’s egg cell were erased. When the enzyme that put the mark “H3K27me3” was removed with genetic processes in order to understand the importance of this transfer in the embryo, it was observed that the embryo could not develop. In other words, the unknown importance of epigenetic heritage in embryo development was also revealed by this study. The fact that normally suppressed genes becoming active prematurely when methylation disappears and causing the death of the embryo showed the vital importance of genetic heritage in the definition of the genetic code.

Another research examined 94 healthy babies and reported how long babies were exposed to physical interactions such as hugging and holding them from 5 weeks old to 4.5 years old. Methylation differences were found in five different regions in the DNA of children who were less exposed to physical interaction (especially those who had stressful infancy). One of these five regions was close to a gene that plays an important role in the immune system, while another was close to a gene that is important for metabolism.

It is possible to say that the transmission of epigenetic changes across generations is possible, in the light of all these studies. In the field of Preventive Medicine, it is possible to ensure that holistic assessment of nutrition, exercise, lifestyle, psychological factors protect these epigenetic changes, these epigenetic changes, without being exposed to these risks.

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