How important is DNA. The genetic code is the key to 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 in the same body have the same DNA.
So how is it possible that they act differently? Better said, how is a neuron a neuron and not a hepatocyte, if they have the same DNA? The answer lies in epigenetics
Although it contains information, the deoxyribonucleic acid chain is not everything, since there is an important component that is the environment. This is where the term epigenetics comes in, “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 good at all, which is why control over expression is necessary.
The term epigenetics was coined by the 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: if we think that DNA is a library, genes are the books and genetic expression is the librarian. But the libraries themselves, the dust, the shelves, the fires… everything that prevents or helps the librarian from being able 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, what stage of development the organism is in or even the environment where the individual lives, there will be some genes active and others not. The presence of a group of proteins that is responsible for controlling genetic expression without modifying the DNA sequence, that is, without causing mutations or translocations, for example, allows this.
Knowing the epigenome
The concept of epigenome was born as a consequence of the appearance of epigenetics, and is nothing more than all the components that are part of this regulation of genetic expression.
Unlike the genome, which remains stable and immutable 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 is not the same depending on the cell type. To put an environmental effect, it has been seen that consuming tobacco has a negative impact on the epigenome, which favors the appearance of cancer.
Before continuing, a brief review of genetics is in order to understand the purpose of DNA. The genetic code contains genes, but for that 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 read gene fragment.
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 the ribosome, which synthesizes the protein from the mRNA. Being clear about how it works, I continue.
Epigenetic mechanisms
DNA is a very large structure, which in the case of humans is almost two meters long, much larger 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 group together in groups of eight to form the nucleosome, provide support for the DNA chain to coil around it and facilitate folding.
The DNA strand is not compacted completely, leaving freer parts 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 they are not always folded in the same way in different cells. By not allowing access to RNA polymerase, it is already exerting control over genetic expression without modifying the sequence.
It would be very simple if it were just this, but the epigenome also uses 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.
The genome, which is invariant, is inherited of each of the parents of an individual. But does the same happen with the epigenome? This topic 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 common example they present is a case of a town in Sweden where the grandchildren of grandparents who went through famine live longer, as if it were a consequence of epigenetics.
The main problem with this type 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 reset the epigenome in the zygote However, the same study makes it clear that the epigenome is not completely reset, but rather that 5% of genes escape 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 can be the way to investigate and understand vital processes such as aging, mental processes or stem cells.
The field in which the most results are being obtained is in the understanding of cancer biology, searching for targets to generate new pharmacological therapies to fight this disease.
Aging
As mentioned previously in the text, the epigenome in each cell changes depending on the stage of development in which the person is.
There are studies that have proven this. For example, it has been observed that the genome varies in the human brain from birth until maturity, while in adulthood until well into old age it remains stable. During aging there are changes again, but this time downwards instead of upwards.
For this study they focused on DNA methylations, seeing that they were generated more during adolescence and decreased in old age. In this case, the lack of methylation makes the work of RNA polymerase difficult which leads to a decrease in efficiency on the part of the neurons.
As an application to understanding aging, there is a study that uses DNA methylation patterns in bloodline cells as indicators of biological age. Sometimes, chronological age does not coincide with biological age, and with the use of this pattern, the patient’s health status and mortality could be known in a more concrete way.
Cancer consists of a cell that for some reason stops being specialized in its tissue of origin and begins to behave as if it were an undifferentiated cell, without limiting its proliferation or moving to other tissues.
Logically, it is normal to think that changes in the epigenome can cause a cell to become cancerous by affecting genetic expression.
In the DNA there are Genes known as “cancer suppressors” ; Its name itself indicates what its function is. Well, in some cases of cancer it has been seen that these genes are methylated in a way that inactivates the gene.
Currently, efforts are being made 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.
medical applications
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 in 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 due to a mutation.
However, the greatest challenge is to obtain all the information about the human epigenome, in the manner of sequencing the human genome. With broader knowledge, in the future more personalized treatments could be devised and individualized, by being able to know the needs of the cells in 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 better understand the subject.
What must be clear is that epigenetics consists of regulations of genetic expression They do not modify the DNA sequence. It is not uncommon to find erroneous mentions of epigenetics in cases of mutations, for example.
