Viruses known to our ancestors millions of years ago left a large number of viral genetic sequences in our genome. This heritage would allow us today to avoid certain infections at key times in our development.
- The study authors speculate that other proteins of viral origin could also provide us with protection against certain infections.
- According to them, discovering them could open a door to the creation of new antiviral treatments.
Viruses have not only brought misfortune to mankind. By dint of infecting us for millions of years, they have left a substantial genetic heritage during our evolution: today, nearly 10% of our genetic information is actually DNA of viral origin. We owe it above all to a family of viruses, the retroviruses (including HIV, which causes AIDS) because they have a special power: that of producing DNA from the RNA containing their genetic information, a process called “reverse transcription”.
How human DNA got filled with bits of virus genes
These bits of viral genes can then be introduced into the genome of the infected cell. And if the latter is a germ cell (at the origin of ovules and spermatozoa), the viral genetic sequence is transmitted to future generations, settling definitively in the genome of individuals from this line.
This phenomenon has occurred many, many times in the history of the evolution of the genre. homo, so much so that our current DNA is packed with pieces of virus genes. And they are of great use to us: this genetic heritage allows us to avoid certain infections by other viruses. This is revealed a studypublished on October 27 in the journal Science.
A team of scientists from Cornell University in the United States has analyzed the human genome to identify genetic relics that come from viruses. They found 1,507 bits of sequences that previously coded for viral envelopes, twenty of which have integrated into human genes. About half of these 1,507 genes were expressed at a specific time, notably in the human embryo or in cells of the immune system.
Embryos are protected against certain infections thanks to viruses
They then focused on one gene in particular, coding for suppressin. This protein of viral origin is produced in the placenta and throughout the development of the embryo and the fetus, according to the authors of the study. In their in vitro experiments, they discovered that the cells which produce it are protected against infections by retroviruses. This protection disappeared when the suppresin was eliminated. And cells that usually don’t produce this protein get this protection as soon as they are forced to make suppresin.
The virus that transmitted this ability to produce supressin to us would be a retrovirus present in the genomes of all great apes, according to the researchers. It would have infected a common ancestor of our line, about thirty million years ago. Since it has been so well conserved in all of these species, it is likely that it had an important role in the survival or reproduction of these species, having led to selection pressure. This brings points to the researchers’ hypothesis that it would offer viral protection during embryonic development, when an infection could have very serious consequences for survival.