How human are you? Maybe not as much as you thought

Think all your DNA is all human? Think again.

Nineteen new pieces of DNA — left by viruses that first infected our ancestors hundreds of thousands of years ago — have been found lurking between our genes. One stretch of this newfound DNA, found in about 50 of the people studied, contains an intact, full genetic recipe for an entire virus.

The findings, published in the Proceedings of the National Academy of Sciences, add to what science already knows about human endogenous retroviruses (HERVs) — ancient infectious viruses that inserted a DNA-based copy of their own RNA genetic material into our ancestors’ genomes. Over generations, the virus-generated DNA kept getting copied and handed down when humans reproduced. That’s how we’ve reached the stage we’re at today — with about 8% of what we think of as our ‘human’ DNA actually coming from viruses.

The study was conducted by researchers from Tufts University and the University of Michigan (U-M) Medical School, who examined the genomes of 2500 people from around the world. Some came from the 1000 Genomes Project, an international collaboration, while another set came from the Human Genome Diversity Project, with a focus on DNA samples from African volunteers. The latter samples showed more signs of HERVs, in line with the high level of genetic diversity in African populations.

The new HERVs are part of the family called HERV-K. The intact whole viral genome, or provirus, recently found was on the X chromosome. Dubbed Xq21, it’s only the second intact provirus found to be hiding in human DNA.

“This one looks like it is capable of making [an] infectious virus, which would be very exciting if true, as it would allow us to study a viral epidemic that took place long ago,” said senior author and virologist Dr John Coffin, from the Tufts University School of Medicine. “This research provides important information necessary for understanding how retroviruses and humans have evolved together in relatively recent times.”

“This is a thrilling discovery,” said co-first author Dr Julia Wildschutte, who began the work as a PhD student in Coffin’s lab at Tufts. “It will open up many doors to research. What’s more, we have confirmed in this paper that we can use genomic data from multiple individuals compared to the reference human genome to detect new HERVs. But this has also shown us that some people carry insertions that we can’t map back to the reference.”

“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,” added U-M genetics researcher Dr Jeffrey Kidd. “There have been a number of examples of other HERVs that insert themselves next to human genes or near them, and have impact on their expression. We’re interested in applying these methods to find other types of viral or mobile element insertions.”

Cataloguing all the HERV insertions in humans will require even more scanning of whole human genomes, which are becoming easier to come by as technology improves and becomes less expensive.

This is a modified version of an article published by the University of Michigan under a Creative Commons Attribution 3.0 licence.

Originally published here.