A difference between humans and apes has been defined on a genetic level *
Vi News * American scientists have increased the brain size of mice by transplanting to rodents a fragment of human DNA that controls gene activity
This experiment has clearly demonstrated at the genetic level the difference of the human brain from the brain of chimpanzees. The results of the study have been published in the magazine Current Biology, and you can also read the summary of it on Science News.
Scientists have been arguing for several millennia about the reasons for human uniqueness. Ever since they managed to decode the genomes of humans and chimpanzees (our closest relatives among the apes), biologists began looking for the molecular basis of a large brain, bipedalism, language and other features that have brought evolutionary success of the genus of Homo. By2008, scientists have identified several hundred potentially important DNA fragments.
Greg Wray and his colleagues at Duke University have selected about a hundred enhancers – DNA fragments that control the activity of neighboring genes associated with brain activity and that also differ in humans and chimpanzees. Then they chose HARE5, the most active enhancer in the region of the cerebral cortex, and produced mini-genes containing human and chimpanzee versions of the enhancers related to the informant gene which forces a mouse embryo to turn blue in color.
It turned out that when making a human version of the enhancer, the brain of mouse embryos have turned blue faster and on a larger area.
Scientists believe that HARE5 controls the gene Frizzled 8 – an important element for the development of the brain’s molecular signaling pathway. It was later found that the human version of the enhancer makes future nerve cells divide more frequently, which increases the reservoir of the cells for the cerebral cortex. As a result, the embryos with HARE5 from humans, the brain was 12 per cent bigger. Now scientists are planning to examine whether such a large brain made mice smarter.
Other scientists have positively assessed the work by Ray and the fact that he has found a specific area of the human genome responsible for brain size. However, researchers fear that the effect of HARE5 may be only a matter of chance.