Ancient Virus Switched Off a Chimp Brain Gene Humans Still Use

An ancient virus may have left chimpanzees with a quieter version of a gene that helps human brain cells mature. According to ScienceAlert, a new study in Science Advances reports that a retrovirus called PTERV1 inserted DNA into the chimpanzee genome that switches off a gene known as LINC00662. The findings come from lab experiments on cells, not from studies of living animals or people.

What did the researchers want to know?

Humans and chimpanzees diverged from a common ancestor after about 5-6 million years of evolution, and only 1.2 percent of our DNA differs. Lead author Patricia Gerdes, a molecular neurogeneticist at Lund University in Sweden, told ScienceAlert the team wanted to understand how brains could evolve differently when so many protein-making genes are similar.

She said ancient viruses can leave DNA behind in the genome, and those remnants can affect nearby genes. PTERV1 was a strong candidate because it is found in chimpanzees and other African apes but not in humans. ScienceAlert says the virus infected chimpanzees about 4 million years ago.

What did the study find?

LINC00662 is a molecule made from DNA that gives cells instructions for building a particular protein. Both humans and chimpanzees have it. Gerdes said the team found it active during early human brain development, and its experiments suggest it helps brain cells mature and grow extensions.

In chimpanzees, the virus’s DNA insertion switches the gene off. In human brain organoids, which are tiny clusters of cells grown in a lab, switching off LINC00662 meant neurons and their extensions did not mature and grow as prolifically. In chimpanzee stem cells, removing the insertion restored the gene’s activity.

Does this explain why human brains are bigger?

Not on its own. Human brains are about three times larger than chimpanzee brains, but Gerdes cautioned that the work does not show removing the insertion would transform brain development. She said brain differences arise from many genetic and developmental influences, and that removing the insertion from an adult brain would not undo earlier development.

She also said that if humans had the same insertion, it probably would have switched off LINC00662 and altered brain cell development. But she said the team cannot predict a particular brain shape, ability or behavior, since the effect could depend on the surrounding human DNA and other genes. The researchers do not yet know all of the gene’s roles in the human body, or what its loss means for chimpanzees as a whole.

Why didn’t humans catch the virus?

That is unclear, and the study does not try to answer it. ScienceAlert reports a few theories: an antiviral protein called TRIM5α may have protected humans, or the ancestors of chimps and humans may have lived in different places when the infection spread.

Why does it matter?

The study adds evidence that insertions of viral DNA contributed to differences between humans and chimpanzees, and it points to one specific gene affected. For general readers, it shows how much ancient infections can shape evolution. It does not suggest any change to chimpanzees today, and it offers no immediate medical use.

Around Prague, based on reporting by ScienceAlert