Ancient Viral DNA in Chimp Genome Tied to Brain Gene Control
Researchers report that retroviral DNA present at 158 chimp genome sites but absent in humans may influence gene networks tied to neuron development.
The story in focus
Science News reports that researchers led by Johan Jakobsson at Lund University found ancient retroviral DNA at 158 sites in chimpanzee genomes but absent in humans. Removing it from chimp stem cells with CRISPR reactivated LINC00662, a gene active in human brain cells. The team reports in Science Advances that the remnant may influence neuron-related gene networks.
- The viral DNA entered an ancestral African ape genome between 5 million and 7 million years ago and is absent in humans.
- CRISPR removal of the viral DNA in chimp stem cells turned on LINC00662, matching its active state in human brain cells.
- Outside researchers say the neuronal effect is shown, but its evolutionary reach is not yet established.
What the team found
The study, reported October 23 in Science Advances, examined endogenous retroviruses, viral DNA left after infection that can be inherited if it lands in reproductive cells. Such remnants make up at least 8 percent of human and chimp genomes, the researchers note.
The specific vestige studied entered an ancestral African ape genome between 5 million and 7 million years ago, according to the team. In chimpanzees it sits at 158 genome locations; humans carry none, and why is unknown.
Editing experiments
Working with chimpanzee stem cells, the researchers used CRISPR to delete the viral DNA. LINC00662, normally silenced in chimpanzees, switched on and produced detectable RNA, matching its normal activity in human brain cells. The team also used CRISPR to silence LINC00662 in human cells, reproducing the chimpanzee condition.
With LINC00662 active in either chimp or human cells, the researchers observed increased activity in other genes potentially important for brain development, including genes involved in neuron development and maturation and in forming new neural connections. Exactly how the viral shutdown affected chimpanzee brain biology remains unclear, the team says.
Caution from outside scientists
Giorgia Modenini, an evolutionary biologist at the University of Padua who was not involved, said the work highlights that genomes can change through means other than single-letter DNA swaps.
Ravinder Kanda, an evolutionary geneticist at Oxford Brookes University, said the researchers convincingly showed the viral remnants influence developmental differences between human and chimp neurons, but how far that extends is not yet clear. Kanda suggested other gene controls may be involved and that many more retroviruses likely remain undiscovered.
Did the study show the viral DNA caused human and chimp brain differences?
No. The team reports the remnant may have contributed to divergence in brain evolution, while outside researchers say the neuronal effect is convincing but its broader evolutionary reach is not yet established.
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