A new study has shown that mice genetically enhanced to carry the human enhancer HARE5 had brains that developed more quickly and grew 12 percent larger than mice with a chimpanzee version of the DNA.
With the research, scientists from Duke University scanned the human genome for sequences known as “human accelerated regions” that differ between people and chimpanzees. According to The Washington Post, one of the sequences discovered was HARE5. This is a so-termed enhancer that regulates gene expression.
To determine the functional differences between human and chimp HARE5, which only vary at 16 locations in over 1,200 bases of DNA, the researchers engineered two sets of mice, each with a reporter gene under the control of either the human or the chimp version of the enhancer. The reporter made cells in which HARE5 was activated turn blue.
When they examined the mouse embryo, the scientists found that the human version of HARE5 was expressed in the brain beginning around day nine, slightly earlier and in more parts of the brain than the chimp sequence. The scientists also found that the enhancer was active in neural stem cells, where it likely controls the nearby brain development gene FZD8. The mouse brains with the human gene had stem cells that divided more frequently, making more neurons and leading to an increased brain size compared to the mice with the chimp enhancer.
Discussing the consequences, lead researcher Debra Silver told National Geographic’s Not Exactly Rocket Science: “It shows that just having a few changes to our DNA can have a big impact on how the brain is built. It is probably one of many regions that explain why our brains are bigger than those of chimps.”
For the next phase of the research, the scientists plan to study how the larger, more quickly developing brains influence mouse memory and social behaviour.
The strange findings have been published in the journal Current Biology. The research is titled “Human-Chimpanzee Differences in a FZD8 Enhancer Alter Cell-Cycle Dynamics in the Developing Neocortex.”
