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Koala Virus Gives Researchers a Live Look at the Evolution of Junk DNA in Humans

An international team of researchers believes that a virus infecting koalas could demonstrate how viruses have altered the DNA of humans and other species throughout history.

“Retroviruses insert their genome into their host’s chromosome, from where they make more copies of themselves,” explained Prof Paul Young of The University of Queensland. “Some can also infect what are known as germline cells, which alters the host genetic code and that of all their descendants.”

Retrovirus insertions in humans date back more than five million years, so it’s difficult to know what happened when the first interactions took place. “About a decade ago, we discovered that the wild koala population was being invaded by a retrovirus,” Young said. “This isn’t great news for the koala, but it has provided us with an opportunity to study what’s happening to these retroviral genomes early in their association with a new host.”

He said new retroviruses within a species could continue to replicate with disastrous consequences but, over time, their disease-causing effects usually stopped and either took on new functions or became inert junk DNA. “Until now, scientists could only guess at why and how this happened,” Young said.

“Because the koala retrovirus is still relatively young – less than 50,000 years old – and not yet ‘fixed’ in a certain location within the koala genome, scientists can monitor this early engagement between a retrovirus and its host,” added Prof Joanne Meers of UQ.

“This means that the koala, a species not usually associated with biomedical breakthroughs, is providing key insights into a process that has shaped 8% of the human genome, and will likely show us what happened millions of years ago when retroviruses first invaded the human genome,” said Prof Alex Greenwood of the Leibniz Institute for Zoo and Wildlife Research.

The research has been published in the Proceedings of the National Academy of Sciences (https://goo.gl/Vk42XX).