Jakarta –
About 30 million years ago, virus it infected our primate ancestors and one of its genes got stuck in its genome. Over time, viral genes become “tame” and territorial.
Later, the virus was found to help primates fight off other viruses by preventing them from entering cells. That virus, known as Suppressyn (SUPYN), is still around today and still helping us.
Quoted from Science.orga new study reveals that this ‘restrictor’ virus may help the placenta protect the embryo from viral infection.
“This is a very robust experimentally supported story,” said Giulia Pasquesi, an evolutionary biologist at the University of Colorado, Boulder, who was not involved in the study.
Discovering more such viral genes, he said, could help us harness or enhance our innate antiviral properties without needing to develop new drugs or vaccines. “There are all the elements that we already have in our genome,” she said.
The virus process becomes protective
Viruses that incorporate their genetic material into our genome are known as retroviruses. HIV is perhaps the best known example. Once integrated into our genes, it hijacks our body’s cellular machinery to produce more viruses. If they infect sperm or oocytes, precursors of eggs, their genes become part of our DNA and can be passed on to our offspring.
Once a piece of viral DNA is incorporated into our genome, it is known as an endogenous retrovirus (ERV). About 8% of the human genome consists of ERV sequences that have been trapped in our DNA since they infected our human ancestors millions of years ago. These genes have lost their original viral function over time, but that doesn’t mean they’re useless.
To find out which ERVs might still be active in the human body, molecular biologist Cedric Feschotte of Cornell University and his colleagues scanned the human genome for ERV sequences they thought might encode proteins. They found 1507 sequences and about half appeared to be doing something in human tissue.
An ERV appears in a human gene known as Suppressyn (SUPYN), which codes for a protein produced in the placenta and early human embryos. SUPYN binds to a cell-surface receptor known as ASCT2, the same receptor used by another ERV-derived protein called syncytin to form connections between cells.
In its former life as a retrovirus, Syncytin was able to combine with the cell membrane to enter cells. Its modern shape allows the placenta to form during fetal development by holding cells together. Placental evolution would not have been possible without it.
“You could say that without retroviruses there would be no mammals. It’s almost as if life wouldn’t have evolved that way,” said Welkin Johnson, a virologist at Boston College.
But ASCT2 is also a weak point for mammals. Viruses called D-type retroviruses use them to bypass cellular defenses to sneak into cells and cause various diseases in many animals, including non-human primates.
Feschotte said this could present a major challenge for ancient animals if they didn’t have a way to protect themselves from this retrovirus. Preserving the placenta will be key, because retroviruses that infect embryos early enough in their development can enter sperm and eggs.
Viruses are natural antiviruses
When Feschotte and his colleagues experimentally infected human placental cells with a retrovirus, they found that SUPYN competes against the pathogen by blocking the ASCT2 receptor, making it impossible for the virus to enter the cells.
The cells appeared to activate SUPYN when they detected the virus, indicating that it encodes an antiviral protein.
Johnson noted that it’s not known for certain whether SUPYN actually blocks virus anything in humans. Although type D retroviruses can infect monkeys and other primates, none of them appear to infect humans.
Still, Johnson praised the research. He notes that it’s possible that SUPYN evolved to block the now-extinct virus, or perhaps that SUPYN is so good at its job that it prevents enemy viruses from gaining a foothold to thrive in our bodies.
Pasquesi added: “It is technically impressive that the authors managed to figure out which receptor this retrovirus uses to enter cells. He is currently working on a similar study mapping domesticated ERVs in the human genome and has found about 30 ERVs that appear to be important for the human immune system.
“It’s amazing how our bodies do everything antivirus so small,” he said.
Feschotte’s team now plans to treat the dozens of other active retroviruses they’ve identified. He pointed out that while Suppressyn is known to be a functional human gene, the other 99% of active ERVs who found it looked like meaningless junk DNA may, in fact, be deceptive.
“There’s a potential protein treasure here. At least there’s the potential for this treasure to have interesting assets for medicine or physiology or development,” he said.
Watch a video “Regarding the finding of a virus similar to Covid-19 in bats in southern China“
[Gambas:Video 20detik]
(rns/rns)
