What is epigenetics? Keys to understanding it
Jul 16, 2021
How important is DNA. The genetic code is the linchpin of life, which in the case of humans stores the information that allows the organism to develop among the nearly 20,000 genes that make up the genome. All cells of the same body have the same DNA.
So how is it possible that they act differently? Rather, how does one neuron is it a neuron and not a hepatocyte, if they have the same DNA? The answer lies in epigenetics.
- Related article: "Genetics and behavior: do genes decide how we act?”
What is epigenetics?
Although it contains the information, the deoxyribonucleic acid chain is not everything, since there is an important component that is the environment. Here comes the term epigenetics, "about genetics" or "in addition to genetics."
There are factors external to the genetic code that regulate the expression of the different genes, but always keeping the DNA sequence intact. It is a mechanism that has its relevance: if all the genes were active at the same time it would not be a good thing, for which a control over the expression is necessary.
The term epigenetics was coined by Scottish geneticist Conrad Hal Waddington in 1942 to refer to the study of the relationship of genes and environment.
A simple way to understand epigenesis was given to me by a good friend with this example: yes we think that DNA is a library, genes are books, and gene expression is the librarian. But the libraries themselves, the dust, the bookshelves, the fires... everything that prevents or helps the librarian to access books would be epigenetics.
The truth is that the human genome consists of more than 20,000 genes, but these are not always active at the same time. Depending on the type of cell it is, at what stage of development the organism is, or even the environment itself where the individual lives, there will be some active genes and others not. The presence of a group of proteins that is responsible for controlling gene expression without modify the DNA sequence, that is, without causing mutations or translocations, for example, allow this.
Knowing the epigenome
The concept of epigenome was born as a consequence of the appearance of epigenetics, and it is only all the components that are part of this regulation of gene expression.
Unlike the genome, which remains stable and unchanging from birth to old age (or so it should be), the epigenome is dynamic and variable. Throughout development it changes, can be affected by the environment, and it is not the same according to the type of cell. To put an environmental effect, it has been seen that consuming tobacco it has a negative impact on the epigenome, which favors the appearance of cancer.
Before continuing, a brief review of genetics is advisable to understand the purpose of DNA. The genetic code contains genes, but for that very reason this would have no consequences. In general, it is necessary that a protein complex called RNA polymerase "reads" this gene and transcribes it to another type of nucleic acid chain called "messenger RNA" (mRNA), which only consists of the gene fragment read.
It is necessary that this RNA obtained is translated into the final product, which is none other than a protein, formed by another molecular complex known as ribosome, which synthesizes protein from mRNA. Being clear about how it works, I continue.
DNA is a very large structure, which in the case of humans is almost two meters long, much greater than the diameter of any cell.
Nature is wise and found a method to drastically reduce the size and pack it inside the cell nucleus: thanks to structural proteins called "histones", which are grouped in groups of eight to form the nucleosome, support the DNA strand to wrap around it and facilitate folding.
The DNA strand is not completely compacted, leaving parts freer for the cell to carry out its functions. The truth is that folding makes it difficult for RNA polymerase to read genes, which is why it is not always folded in the same way in different cells. By not allowing access to RNA polymerase, it is already exerting control over gene expression without modifying the sequence.
It would be very simple if it were only this, but the epigenome also makes use of chemical markers. The best known is DNA methylation, which consists of the attachment of a methyl group (-CH3) to deoxyribonucleic acid. This mark, depending on its placement, can both stimulate the reading of a gene and prevent it from being reached by RNA polymerase.
Is the epigenome inherited?
The genome, which is invariable, is inherited of each of the parents of an individual. But, does the same thing happen with the epigenome? This issue has brought a lot of controversy and doubts.
Remember that, unlike the genetic code, the epigenome is dynamic. There are scientific groups that are convinced that it is also inherited, and the most frequently used example is a case of a village in Sweden where the grandchildren of grandparents who experienced famine live longer, as if it were a consequence of the epigenetics.
The main problem with these types of studies is that they do not describe the process, but are only conjectures without a demonstration that resolves the doubt.
As for those who believe that the epigenome is not inherited, they are based on a study that reveals a family of genes whose main function is restart the epigenome in the zygote. However, the same study makes it clear that the epigenome does not restart completely, but that 5% of genes escape from this process, leaving a small door open.
The importance of epigenetics
The importance that is being given to the study of epigenetics is that it may be the way to investigate and understand life processes As the aging, mental processes or stem cells.
The field in which more results are being obtained is in the understanding of the biology of the Cancer, looking for targets to generate new drug therapies to fight this disease.
As mentioned earlier in the text, the epigenome in each cell changes according to the stage of development in which the person is.
Studies have proven this. For example, it has been observed that the genome varies in the human brain from birth to maturity, while in adulthood until well into old age it remains stable. During aging there are changes again, but this time down instead of up.
For this study they focused on DNA methylations, seeing that more were generated during adolescence and decreased in old age. In this case, lack of methylation hinders the work of RNA polymerase, which leads to a decrease in efficiency by neurons.
As an application for understanding aging, there is a study that makes use of DNA methylation patterns in bloodline cells as indicators of biological age. Sometimes, the chronological age does not coincide with the biological age, and with the use of this pattern it is possible to know the health status and mortality of the patient in a more concrete way.
Cancer and pathologies
Cancer consists of a cell that for some reason ceases to be specialized in its tissue of origin and begins to behave as if it were an undifferentiated cell, without limiting its proliferation or displacing others tissues.
Logically, it is normal to think that changes in the epigenome can cause a cell to become cancerous by affecting gene expression.
In DNA there are genes known as "cancer suppressors"; its own name indicates what its function is. Well, in some cases of cancer it has been seen that these genes are methylated in such a way that they inactivate the gene.
It is currently being sought to study whether epigenetics affects other types of pathologies. There is evidence to suggest that it is also involved in arteriosclerosis and some types of mental illness.
The pharmaceutical industry has its sights set on the epigenome, which thanks to its dynamism is a feasible target for future therapies. They are already being put into practice treatments for some types of cancer, mainly in leukemias and lymphomas, where the drug targets DNA methylation.
It should be noted that this is effective as long as the origin of the cancer is epigenetic and not another, such as a mutation.
However, the biggest challenge is to obtain all the information about the human epigenome, by way of sequencing the human genome. With broader knowledge, in the future more personalized treatments could be devised and individualized, to be able to know the needs of the cells of the damaged area in a specific patient.
Science needs more time
Epigenetics is a fairly recent field of research and further study is needed to further understand the subject.
What does have to be clear is that epigenetics consists of gene expression regulations They do not modify the DNA sequence. It is not uncommon to find erroneous mentions of epigenetics in cases of mutations, for example.