Chimpanzees Carry Viral DNA That Shuts off a Gene Active in Human Brain Development

A team at Lund University in Sweden reports that ancient viral DNA carried by chimpanzees, but absent from humans, switches off a gene that is active while the human brain is forming, and that cutting the viral sequence out of chimpanzee cells switches the gene back on.

Humans and chimpanzees have diverged in brain size, structure and cognition over the past 5 to 7 million years even though their protein-coding genes are highly conserved, so the differences between the two brains are sought in how genes are switched on and off. The study, published Oct. 23, 2026, in Science Advances, describes one such difference.

Chimpanzees carry a family of ancient viral sequences lodged in their genome, called PTERV1, that humans do not have, and their role in brain evolution had not been established. Patricia Gerdes, Johan Jakobsson and colleagues at Lund University examined those insertions in chimpanzee neural organoids, small clusters of brain cells grown in a dish. The insertions were heavily marked by DNA methylation, the chemical tags that switch DNA off, and formed more than 150 species-specific stretches of tightly packed DNA with the potential to influence how nearby genes are regulated.

One chimpanzee-specific insertion, on chromosome 19, switches off a gene called LINC00662 by spreading those tags along the surrounding DNA. When the team deleted that insertion with CRISPR, LINC00662 became active again in chimpanzee induced pluripotent stem cells, reprogrammed cells grown in culture. LINC00662 makes RNA rather than a protein. The paper describes it as a human-specific transcript expressed during brain development, with a role in the maturation of neurons, the outgrowth of axons and the development of neural organoids.

The authors conclude that retroviral insertions contributed to the divergence of human and chimpanzee brains, on evidence from organoids and cultured cells rather than from brain tissue.

The paper lists co-authors at the University of Washington, the University of Minnesota, the University of Gothenburg and Uppsala University, and funding from the US National Institutes of Health and the Swedish Research Council.