Epigenetics

Epigenetics is the study of external modifications to the genetic code, as well as their impacts and affects. It is “the study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself.”

Epigenetic processes such as methylation change the expression of genes, which changes the phenotype. When a methyl group is added, it causes the DNA to become very tightly coiled, and therefore that section cannot be copied and passed on to daughter cells. Other epigenetic modifications include acetylation (the addition of an acetyl group) and histones, which are protein markers that also alter gene expression.

An experiment conducted by John Gurdon, where he transplanted nuclei from an adult toad into an egg to see if the egg and adult cells are genetically identical. The results of the experiment showed that, in fact, they were, and the egg developed into a foetus, and was born alive and reasonably healthy. This shows that the nucleus of an adult cell and a zygote are genetically identical. So what causes adult cells to become so specifically programmed, where an embryonic stem cell stays pluripotent?

The answer is epigenetic modifications: Certain factors, which were isolated by Shinya Yamanaka, are introduced into the nucleus of an adult fibroblast to strip away all the epigenetic modifications and return the fibroblast to its totipotent state. However underneath all the modifications, both cells are genetically identical. As a foetus develops, different modifications are added to different cells, and they become more and more specialised, until they end up as heart cells, or neurons or skin cells. Conrad Waddington proposed that as cells differentiate, they roll further and further down a trough, and have less and less options for differentiation. A totipotent cell is at the very top of the hill, able to roll into any trough, but a cardiomyocyte would be towards the bottom, unable to roll back up the hill without first removing the epigenetic modifications.

Understanding epigenetic processes could be the key to curing metabolic diseases like diabetes, as well as providing blood for those who need regular transplants. If cells can be returned to a pluripotent state, and then programmed into a different cell, organs can simply be grown from a sample of skin cells taken from the person who needs the donation, this means that organs will never be in short supply, and there won’t be the risk of rejection. This is just one of the reasons that the study of epigenetics is quickly becoming one of the most important areas of medical science, and could be the key to curing almost every inherited/chromosomal disorder by altering the genome during development.

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