25/05/2023
Although viruses are commonly associated with disease-causing and sometimes devastating epidemics, they have also played a significant role in human evolution because without their support, you wouldn't be here at all.
The maboya lizards found in the Andes mountains of Colombia are not like other reptiles. Although the majority of reptiles lay hard-shelled eggs, some maboya species give birth to live young. It is very important that such mothers have umbilical cords, which are specialized organs for feeding the babies growing inside their bodies.
Placentas or placentas are commonly associated with mammals such as mice and humans, and we are placental mammals. But the placenta is found in other types of organisms too.
In 2001, zoologists Martha Patricia Ramírez-Penilla and Adriana Jerez of the Industrial University of Santander in Bucaramanga, Colombia, revealed that maboya lizards have highly developed placentas, not too different from those of us humans.
the placenta after acquiring ERV from the virus. This suggests that this may have been the case in the ancestor of all placental mammals. Hedman said: 'This showed a link between placental acquisition and syncytin acquisition.'
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The story of syncytons and the placenta is one of the most dramatic examples of viral DNA influencing evolution. This is particularly noteworthy because a complete viral gene survives in the human genome and encodes a protein. Many other ERVs do not encode proteins, but still have their own functions.
Some ERVs play a role in stem cells, and such multipurpose cells are found in developing embryos. Some stem cells are pluripotent, meaning they can turn into any type of cell in the body, from neurons to muscle fibers.
A family of retroviruses, called HERV-H, are essential for multivalent competence. However, they do not code for proteins. Instead, HERV-H sequences are transcribed onto molecules called RNAs and make the cell pluripotent. Virologist Christine Kozak of the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, says: 'If they are suppressed, the cell changes shape and loses its ability to maintain its non-differentiating state. '
Other ERVs control the activity of genes, and thus they control physiological processes. For example, our bodies use an enzyme called amylase to break down starch-like carbohydrates in our food. 'We have amylase in our pancreas and we have amylase in our saliva,' Grandi says. The amylase gene is activated in the salivary gland by a sequence of DNA called a promoter and comes from ERV.
Viruses that keep us healthy
Not surprisingly, ERVs come from viruses and many scientists are interested in their role in health and disease. One such example was presented in a 2022 study led by molecular biologist and geneticist Cedric Feshotte of Cornell University in Ithaca, New York. The team was trying to find an example of a phenomenon in humans that is already known in other animals.
Sometimes ERV genes code for proteins that the immune system adapts to and can then use to fight other viruses. The target virus may be closely related to, or distantly related to, the virus that gave rise to ERV in the first place. Antiviral proteins from ERVs have been studied in mice, chickens and cats, Feschute says. However, he says that 'to my knowledge, no example of this has been found in the human genome.'
The team scanned the known ERVs in the human genome and identified hundreds of sequences that could potentially encode antiviral proteins. They then focused on a gene called suppressin, which encodes a protein similar to the virus's outer coat protein. The suppressin protein prevents retroviruses from entering cells, because it binds to receptors on the outer membrane of the cell that the virus uses to enter the cell itself. Feshotte compares this to putting a broken key in a lock that prevents someone from opening the door.
Suppressin is found mostly in the placenta and the developing embryo or fetus. It turns out that its original use was to prevent retroviruses from infecting fetuses with very weak immune systems. "It protects the offense line rather than the organism as a whole," Feschute says.
But they think ERVs probably do a lot more in our immune system. "We have 1500 candidates," he says. That's a lot of genes.' Although many geneticists still consider ERVs to be dysfunctional or defective, this is a misguided idea. 'They're degenerating but they still make RNA and they still make a lot of protein,' he says. We need to keep a close eye on it.' And the picture is just emerging. A study published in April 2023 found that certain ERVs help the immune system target cancer cells.
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Do ERVs make us sick?
While they may protect us from disease, it should come as no surprise that some of these ERVs may be responsible for causing adverse health effects in us humans. "There is a lot of interest right now in the possibility that human ERVs may be linked to disease," Kozak says. At this point there is a lot of suggestive evidence but no proof.'
Feshotte believes it's important to consider what ERVs actually do. And we haven't always got it right. "Ever since endogenous retroviruses were discovered, people have been trying to link them to cancer. This is because they were found to cause cancer in animals when they were first discovered," he says. have been. Funders poured tons of money into the discovery of ERVs in the hope that it would uncover the mechanisms of cancer and thus lead to possible cures, but many came away empty-handed.
The important point is that human ERVs are not capable of making viruses, which can infect other cells.
"They are abundant in rats and chickens," says Feshotte. They can cause all kinds of diseases.'
However, EVRs found in humans are under control of the genome and therefore do not cause viral infections.
"I think it probably has to do with genetic surveillance or lack of surveillance," Feshotte said. Because ERVs are widely distributed throughout the human genome, they can establish connections between multiple genes located at sequence (sequence) distances.
Genes must be switched on or off in sequence for many body systems to function. It is controlled by ERV. "We are now rethinking its role in disease, but its mechanism is different."
The role of ERV in disease is currently shrouded in mystery. But it is clear that they are the engine of evolution. Viruses cause major changes in genetic structure by adding new DNA segments to our genome.
ERVs can cause duplications and deletions in DNA while in situ. These are the changes that are actually useful and spread. No animal including humans can survive without them.
The final lesson is that man is truly an evolved being. Some of us have as much as two percent Neanderthal DNA in our genomes. Some populations have some DNA from Denisovans, another extinct human group. About eight percent of our genome comes from viruses.
"If you look at the detailed list of human genes, this becomes a very important question," says Feshotte.
About 20,000 protein-coding genes are known, while part of the DNA comes from viruses. '
