Human DNA Can Cause Bigger Brains In Mice
We knew that chimpanzees were closely related to humans in terms of the brain matter, though chimpanzees’ brains weigh three times less than ours.
So when you hear about mice being injected with human DNA to increase the size of their brain, it only sends a shiver down our spine. Researchers at Duke University have now discovered the DNA sequence which might help in identifying the main reasons behind human intelligence. And they hope to accomplish that by injecting the DNA sequence into mice embryos.
The DNA sequence is called HARE5, and is a gene activity regulator which tends to show a marked increase in the size of a mouse embryo’s brain when exposed to it. As a control experiment, some embryos were also injected with Chimpanzee HARE5. Consequently, the mouse embryo’s brain grew 12 percent larger when injected with human HARE5, as compared to chimpanzee HARE5.
“I think we’ve just scratched the surface, in terms of what we can gain from this sort of study,” said Debra Silver, assistant professor of molecular genetics and microbiology in the Duke University Medical School. “There are some other really compelling candidates that we found that may also lead us to a better understanding of the uniqueness of the human brain.”
HARE5 is a genetic enhancer, which is a piece of the DNA that can be bound with proteins to activate the transcription of the genes. It is a part of the group of Human Accelerated Regulatory Enhancers, which is run through HARE1 to HARE6.
So to find the exact region in the DNA which could enhance brain growth, the researches screened the databases of the human and chimpanzee DNA and genomic information to find enhancers which were activated mainly during brain development. Out of the 106 candidates, the HARE group was found to be nearest to the genes which were involved in brain development.
Out of the HARE group, Hare5 was the closest and strongest candidate, which is located near the Frizzled8, a molecular pathway often linked with brain development and disease. It was also discovered that HARE5 and Frizzled8 also have a physical connection in the brain tissue.
Even though human and chimpanzee HARE5 are very similar in chemistry, they both reacted differently in mouse embryos. Human HARE5 rapidly produced neuron progenitor cells, which results in more neurons, affecting the region of the brain involved in higher functions, such as language and reasoning
“What’s really exciting about this was that the activity differences were detected at a critical time in brain development: when neural progenitor cells are proliferating and expanding in number, just prior to producing neurons,” Silver said.
Source: Current Biology