8% of your genome is a virus, and some of it may be the key to your existence.

The human genome has some kind of virus in your DNA, as if it were a fossil from a past more distant than humanity itself. This has been known for many years. Instructions for life are written in the form of these DNA chains, in cells. “Phrases” which are genes and sometimes include “words” that are alien to him.

Since the time of the first creatures that had more than one cell (multicellular), viruses have been hidden to cause infections. They are specialists in “hacking” cells in order to spread them. Along the way they leave trace in the form of one’s own genetic material, which is sometimes integrated into the host genome. And this is passed on from generation to generation, so that an animal species can integrate parts of the “source code” of viral origin. In the human genome up to 8% of its DNA may come from viruses.

These viral remnants, integrated into our DNA, were considered irrelevant for decades. But recently it has been noticed that They may have certain functions. Now researchers from the National Center for Cancer Research (CNIO) have found: Science achievements the role that these viruses play in the absolutely vital process of embryonic development.

A few hours after fertilization, a unique phenomenon occurs: transition to pluripotency, when the egg changes from two to four cells. Before this stage, each of the two cells of the embryo is totipotent, that is, capable of giving birth to a new independent organism that directs the embryonic process, which has the potential to become any cell of the human body. In the next stage, these two cells become four, but these four cells are no longer totipotent, but pluripotent.

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Pluripotent stem cells no longer manage or initiate the initial process; However, they are also necessary. They can specialize in different tissues. And at this stage from “totipotency” to “pluripotency” the hereditary genetic remains of the individual come into play. an endogenous retrovirus called MERLV. At least in laboratory mice, where this was observed.

A retrovirus His genome is written in RNA language, but he is able to use it to generate DNA letters in the cells he infects. Thus, it effectively integrates and camouflages itself within its host. be elusivesuch as the human immunodeficiency virus (HIV), which integrates into the genome of an infected cell.

A fossil virus from the Cambrian period that you “carry” in your genome.

Research shows that the endogenous retrovirus MERVL sets the pace of embryonic development mice, especially at a certain stage of the transition from totipotency to pluripotency, and explains the mechanism by which this occurs.

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“This is a completely new role for endogenous retroviruses,” Dr. Juder told Newtral.es. “We have discovered a new mechanism that explains how an endogenous retrovirus directly controls pluripotency factors.”

Endogenous retroviruses appear to have played a key role in the explosion of life during the Cambrian period.

“That doesn’t necessarily mean it’s an exceptional case. Other endogenous retroviruses may have specific functions in different contexts or at different stages of development. Continued research in this area could reveal more information about the diverse functions of endogenous retroviruses in various biological processes beyond mice, including humans.

The genetic material of so-called “endogenous retroviruses” has been integrated into the genomes of organisms. causes of the Cambrian explosion; During that period, more than 500 million years ago, the world’s seas experienced a boom in biodiversity. Over the past decade, the genetic sequences of these viruses have been discovered to comprise at least 8% to 10% of the human genome.

“Until recently, these viral remains were consideredjunk DNAunusable or even harmful genetic material,” explains Sergio De la Rosa, co-author of the study from the CNIO. “Intuitively, it was believed that the presence of viruses in the genome could not be good. However, in recent years we are beginning to understand that these retroviruses, which have evolved with us over millions of years, They have important functions, as well as the regulation of other genes. “This is an extremely active area of ​​research.” In 2018, for example, it was observed that some genes thought to be useless were important in the immune system of mouse models.

Hereditary viruses in our DNA, relevant to regenerative medicine and artificial embryos

According to Sergio de la Rosa and co-author Nabil Juder, this discovery is relevant for the field of regenerative medicine and the creation of artificial embryos. Open a new path for generate stable cell lines in the totipotency phase. Cell lines are cultures of identical cells created to grow, usually in laboratory dishes; They are used for experiments outside of living beings.

This new mechanism of action includes another gene, called URI, a gene that Juder’s group is studying in depth. Many years ago it was discovered that if ARVI is eliminated from laboratory animals, the embryos do not even develop. De la Rosa wanted to know why and how its association with the MERVL retrovirus was discovered in mice.

Nabil Jouder (CNIO) has already discovered that by eliminating another gene now associated with this ancestral virus, an embryo is not formed.

The results indicate that one of the functions of URI is to mediate the action of molecules necessary for the acquisition of pluripotency; If the URI does not work, then the pluripotency factors do not work, and the cell remains in its previous state, useless for creating a viable embryo. What is the relationship between the DNA of the MERVL virus embedded in the genome (in this particular case, the genome is not human, but mouse) and the URI gene? The protein is one of the first, called MARVL-gag. This protein binds to the URI and works like turning the thread of a faucet.

As De la Rosa explains: “This smooth transition. When viral protein expression is high, there are fewer pluripotency factors; “As ERV expression decreases, URI stabilizes these factors.” Thus, it allows the embryo to adapt and coordinate its actions during development. Remnants of this ancestral DNA in our genome show that the MERVL virus evolved into symbiosis with the cells he infected. These two have “benefited” and evolved over millions of years “to ensure the smooth and timely progression of early embryonic development,” the authors conclude in Science achievements.