The term epigenetics describes the study of mechanisms that lead to heritable changes in phenotypes and gene expression without any interference with the nucleotide sequence of a gene. The mechanisms of epigenetics can change the genome function due to exogenous (genetic or environmental) factors, but at the same time provide a platform for the stable passage of gene expression states from parent cells to daughter cells. The most common epigenetics mechanisms include DNA methylation, histone acetylation, histone methylation, histone ubiquitination etc. These mechanisms affect the histones leaving the nucleotide sequence unchanged. These modifications change DNA interactions with other nuclear proteins (histones) inducing either repression or inactivation of transcription of critical genes.
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All the cells of an individual have identical DNA sequence since they originate from the same embryo during early development. This also applies to identical twins whose genome is exactly the same. However, the embryo divides into different cell lines which lead to different organs. As the identical twins grow, they acquire different characteristics from each other. One of the identical twins may develop cancer in their lifetime but the other may not. These observations are brought about by the mechanisms of epigenetics whose function is to silence some genes. Different factors and lifestyles affect DNA expression due to alterations of the epigenome. The epigenome comprises of the proteins (histones and other proteins) onto which DNA duplexes bind enabling packaging of DNA.
Characteristics arising from epigenetics are heritable. For example, a gene controlling obesity in mice can be silenced by feeding the mice with a diet of high methyl content. The offspring of later generations will not be obese and their skin color is grey.
Laboratory research findings confirm that DNA methylation, an epigenetic mechanism, is a heritable trait, but age must be taken into account when studying epigenetics (Belland Spector, 2011). To investigate how epigenetic traits are inherited, twin or individuals sharing a family history are examined. Twins are preferred due to their identical genomes. They are also born almost at the same time. Twin studies will establish whether certain genes are affected more than others by epigenetic changes and how this affects their heritability.
Twin studies have been carried out to examine how methyl groups attach to DNA packaging proteins (Bell and Spector, 2011). Examination of epigenetics activity on the X-chromosome reveals that some genes are silenced and the attachment of methyl groups on the histone proteins keeps the silenced genes inactive. This observation was believed to be more frequent as the individual grows. The silenced genes on the X-chromosome are passed on to daughter cells in the same state after fertilization leading to offspring with similar characteristics. A study in Spain involving several sets of identical twins of different ages indicated that their epigenetic patterns are identical but usually change greatly proportionally with growth and lifestyles.
To comprehend the role of epigenetic variations in complex traits, timing of their expression is very important. Epigenetics profiles in multiple tissues obtained at birth or at the onset of adulthood can provide crucial information about the onset of disease. Data from analysis of DNA methylation of tissues from newborn twins indicates the role of both genetic and intrauterine environment on epigenetics. Observed changes in birth weight and other early development effects have been attributed to epigenetics whereby epigenetic marks are introduced following disturbances in the intrauterine environment associated with Assisted Reproduction Technologies (ARTs).
Epigenetic differences characteristic of MZ twins can be applied in forensics and tissue transplantation. Although the genetic identity of MZ twins can allow twins to give each other alibis in criminal cases, this can be reversed using their differences in epigenetic profiles which replicate continually with age. The knowledge of a baseline of ‘normal’ epigenetic differences between MZ twins at different ages could prevent rejection of transplants in humans. If well studied, small subtle epigenetic differences of immune genes in the host or in the transplants could be managed to improve transplantation results (Belland Spector, 2011).
Applying the concept of epigenetics, it is credible to conclude that we could easily have inherited some characteristics or traits from our family line (from grandparents through our parents). A genomic research carried out by Dr Stefanie Seisenberger reveals the important role played by DNA methylation during the early development of the male and female cells of reproduction system. Results identified regions of DNA that avoid demethylation and serve as candidates for how environmental information can be passed on from parent to offspring. Type 2 diabetes is a common phenomenon tracing back to family history. Health issue related to our family history can now be managed clinically, hence prolonging life.
Understanding epigenetics is crucial because it enlightens us to realize that our lifestyles could result in aberrations in our genomic makeup which could be passed on to our future generations. We have a responsibility to our future children’s children. Careless lifestyles like smoking, heavy drinking or unhealthy diet intake could cause epigenetic variations which are not only detrimental to us but also to our children when passed on at birth. Individuals that expose themselves to agents that cause cancer like UV light risk propagating a family line that is susceptible to cancers.
With a clear understanding of epigenetics, you can improve your health and longevity. Whilst epigenetic changes are marked mainly by aging, the food we take greatly contributes to the same effects. Some compounds found in the food could lead to increased epigenetic alterations which bring about dire health conditions such as uncontrolled weight gain. Specific methyl group binding on histone proteins only silences genes or activates their expression while the nucleotide sequence remains unchanged. This situation can be passed on to daughter cells after cell division, which is the basis of some cancers. It is crucial to avoid obesity by taking proper diet and important supplements. Moderate and regular body exercises are useful in maintaining proper body weight. Compounds present in preparations of garlic, teas, soya products, herbs, grapes and cruciferous vegetables have been effective defense agents against different tumors. These agents also act as epigenetic modulators that impact on both the initiation and progression of oncogenesis.
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