An article published in the journal “Proceedings of the National Academy of Sciences” describes the discovery of 19 new pieces of DNA (image ©Michael Ströck) found in the human genome that originated from viruses. One of those pieces even contains all the DNA generated by a retrovirus. This research also confirms the presence of 17 pieces of DNA of viral origin discovered in recent years by other scientists.
It’s long been known that many animals, including humans, have acquired genes from microorganisms existing in their environment in ancient times. This occurred through horizontal gene transfer, which transfers genetic material to not descendant cells. A research published about a year ago indicated that many pieces of human DNA derived from various types of microorganisms, not only of viruses.
A team from Tufts University and the University of Michigan Medical School focused on the study of DNA of people from around the world that included many from Africa, where the human species originated. Sophisticated techniques were used to compare key areas of the genome of each of these people with a human “reference” genome.
The result was the discovery of many traces of retroviruses the type called HERV (human endogenous retroviruses), which are exactly retroviruses absorbed in the past in the DNA of human beings or their ancestors. This family of the same kind that includes HIV is composed of a number of retroviruses, which are viruses composed of RNA.
When they attack an animal, retroviruses try to insert a DNA version of their genetic material in their target’s cells but sometimes things go wrong. When the infection is not successful, it may happen that pieces of that DNA end up in the genome of what was supposed to be the victim and are inherited by its descendants.
In the case of the 2500 people studied, it was found that 50 of them contain in their DNA the entire genome necessary to recreate one of these retroviruses. This DNA, along with pieces of DNA inserted by 19 other retroviruses, have become part of humans’ genome. The same thing happened for pieces of DNA from other 17 retroviruses discovered in recent years in the course of other research. According to the latest estimates, approximately 8% of the DNA of Homo sapiens is derived from retroviruses.
The results of this type of acquisition are variable. In some cases, those pieces of DNA are not active but in others they have a function. One of the pieces helps to create a cell layer around the fetus during its developement to protect it from toxins present in the mother’s body.
Advances in genetic analysis techniques are helping scientists to more thoroughly analyze human DNA and that of other organisms. This also allows research on HERVs to better understand how our genome has been modified by the action of foreign microorganisms and how this might have influenced our evolution.
