More ancient viruses may be present in human DNAAmy Walsh (Author) Published Date : Mar 23, 2016 09:18 IST
Scientists have found that non-human DNA lurks within us, left by viruses that first infected our ancestors hundreds of thousands of years ago. And the new discovery suggests it's even less human than scientists previously thought.
Nineteen new pieces of non-human DNA -- left by viruses that first infected our ancestors hundreds of thousands of years ago -- have just been found, lurking between our own genes.
In this latest study, the researchers looked at the entire genomes of people from around the world. This included people from Africa, where the ancestors of modern humans originated before traveling around the world. The scientists used sophisticated techniques in order to compare key areas of each person's genome to a reference human genome.
In this case, the researchers found 19 new pieces of non-human DNA that were left by viruses that infected our ancestors. In addition, one piece of newfound DNA contained an intact, full genetic code for an entire virus.
But how did this foreign DNA end up in humans in the first place These viruses are called human endogenous retroviruses (HERVs). These ancient infectious viruses inserted a DNA-based copy of their RNA genetic material into our ancestors' genomes. They're actually part of the same type of virus that includes modern human immunodeficiency virus, which cause AIDS.
Whether or not it can replicate, or reproduce, it isn't yet known. But other studies of ancient virus DNA have shown it can affect the humans who carry it.
In addition to finding these new stretches, the scientists also confirmed 17 other pieces of virus DNA found in human genomes by other scientists in recent years.
Working at Tufts University and the University of Michigan Medical School, the researchers made the findings with funding from the National Institutes of Health.
The findings add to what science already knows about human endogenous retroviruses, or HERVs. That's the name for the ancient infectious viruses that inserted a DNA-based copy of their own RNA genetic material into our ancestors' genomes. They're part of the same type of virus that includes the modern human immunodeficiency virus, which causes AIDS.
Over generations, the virus-generated DNA kept getting copied and handed down when humans reproduced.
This one looks like it is capable of making infectious virus, which would be very exciting if true, as it would allow us to study a viral epidemic that took place long ago, John Coffin, one of the researchers, said. This research provides important information necessary for understanding how retroviruses and humans have evolved together in relatively recent times.
The findings reveal a bit more about these viruses, and possibly show researchers a bit more about human evolution.
This is a thrilling discovery, Julia Wildschutte, co-first author of the new study, said. It will open up many doors to research.
The new HERVs are part of the family called HERV-K. The intact whole viral genome, or provirus, just found was on the X chromosome; it's been dubbed Xq21. It's only the second intact provirus found to be hiding in human DNA.
Many studies have tried to link these endogenous viral elements to cancer and other diseases, but a major difficulty has been that we haven't actually found all of them yet, says co-first author Zachary H. Williams, a Ph.D. student at the Sackler School of Graduate Biomedical Sciences at Tufts University in Boston. A lot of the most interesting elements are only found in a small percentage of people, which means you have to screen a large number of people to find them.
U-M genetics researcher Jeffrey Kidd, Ph.D., worked with Wildschutte when she was a member of his laboratory team. These are remnants of ancient events that have not been fixed in the population as a whole, but rather happened in the ancestors of some people alive today, Kidd says.
The findings are published in the March 2016 journal Proceedings of the National Academy of Sciences.
More ancient viruses may be present in human DNA