Mice grow bigger brains when given this stretch of human DNA

Summary

Researchers have identified a genetic dial in the human brain that, when inserted in mice, boosts their brain size by about 6.5%.Credit: Sergey Bezgodov/ShutterstockTaking a snippet of genetic code that is unique to humans and inserting it into mice helps the animals to grow bigger brains than usual, according to a report out in Nature today1.The slice of code — a stretch of DNA that acts like a dial to turn up the expression of certain genes — expanded the outer layer of the mouse brain by increasing the production of cells that become neurons. The finding could partially explain how humans evolved such large brains compared with their primate relatives.This study goes deeper than previous work that attempted to unpick the genetic mechanisms behind human brain development, says Katherine Pollard, a bioinformatics researcher at the Gladstone Institute of Data Science and Biotechnology in San Francisco, California. “The story is much more complete and convincing,” she says.The brain expanderHow the human brain grew to be so big and complex remains a mystery, says Gabriel Santpere Baró, a neuroscientist who studies genomics at the Hospital del Mar Medical Research Institute in Barcelona, Spain. “We still do not have a definitive answer to how the human brain has tripled in size since our split from chimpanzees” during evolution, he says.How human brains got so big: our cells learned to handle the stress that comes with sizePrevious studies2,3 have hinted that human accelerated regions (HARs) — short snippets of the genome that are conserved across mammals, but which underwent rapid change in humans after they evolutionarily diverged from chimpanzees — could be key contributors to brain development and size. But the exact mechanisms that underlie the brain-building effects of HARs are yet to be uncovered, says study co-author Debra Silver, a developmental neurobiologist at Duke University in Durham, North Carolina.To build a clearer picture, Silver and her colleagues z...