A virus that disappeared millions of years ago may have contributed to a difference between the human brain and the chimpanzee brain.
We share almost all of our genes with chimpanzees. Yet our brains do not develop in exactly the same way. To understand why, researchers are trying to determine which genes are activated or remain switched off during growth.
Representation of human evolution.
Pixabay
A team from Lund University in Sweden has discovered that an ancient viral infection left an important trace in chimpanzee DNA. The virus, called PTERV1, belonged to a family capable of inserting its own genetic material into that of the cells it infects. These pieces of DNA can then be passed on to subsequent generations.
In chimpanzees, one of these ancient viral sequences is located near a gene called LINC00662. This gene is active during the early stages of human brain development, but remains silent in chimpanzees. The researchers wondered whether the sequence left by the virus prevented its activation.
To find out, they created tiny models of brain tissue in the laboratory using human and chimpanzee cells. These structures, called organoids, make it possible to study certain aspects of brain development without working directly on a living brain.
The team then removed the viral sequence from chimpanzee cells using the CRISPR tool. The result was immediate for the aspect being studied: the previously silent gene started functioning again. The viral trace therefore did play a role in switching it off in chimpanzees.
The researchers carried out the opposite experiment in human brain models: they deactivated LINC00662. The activity of several genes involved in the formation of nerve cells and their connections then decreased. This indicates that LINC00662 contributes to brain development, although its exact role remains to be understood.
Caution: the study does not show that a virus alone is responsible for human intelligence. The brain evolved under the influence of many genetic and biological changes. Here, the researchers identified a specific mechanism observed in cells and brain tissue models, not a general explanation for all our differences.
This discovery is a reminder that an ancient infection can leave traces far beyond the animals it affected. Fragments of viruses integrated into DNA millions of years ago could still influence how genes function today.