Components of DNA that do not encode protein sequences, known as non-coding DNA, may hold the answers to why human brains work so differently to those of other primate species, according to a new study published in early October in the peer-reviewed scientific journal Stem Cell, a broad-spectrum journal that covers stem cell biology.
Stem cell researchers at Lund University in Sweden discovered that such DNA shows differences in the brains of humans and nonhuman primates. Non-coding DNA was previously believed to have no practical function – even being deemed “junk DNA” in scientific circles – making the discovery of particular interest to researchers.
The findings open a realm of possibilities for what makes humans different from other species, a subject which particularly fascinates the study’s author Johan Jakobsson, a professor of neuroscience at Lund.
“I believe that the brain is the key to understanding what it is that makes humans human,” he said. “How did it come about that humans can use their brains in such a way that they can build societies, educate their children and develop advanced technology?”
Researchers grew brain cells from humans and chimpanzees using stem cells and compared the two cell types, finding that they use the non-coded part of their DNA in different ways, which appears to play a considerable role in the development of human brains.
“The part of our DNA identified as different was unexpected,” declared Jakobsson. “It was a so-called structural variant of DNA that was previously called ‘junk DNA,’ a long repetitive DNA string which has long been deemed to have no function.”
The so-called “junk DNA” comprises over 98% of DNA matter in human and primate brains.
“Previously, researchers have looked for answers in the part of the DNA where the protein-producing genes are – which only makes up about 2% of our entire DNA – and examined the proteins themselves to find examples of differences,” explained Jakobsson. “Our results indicate that what has been significant for the brain’s development is instead perhaps hidden in the overlooked 98%.”
Perhaps the reason this new evidence came to light was the use of stem cells in the research. Stem cells are unique in their ability to take the form of various types of cells, as well as reproduce and proliferate without limits, and are crucial to various forms of scientific research.
This novel stem cell research technique was developed by John B. Gurdon and Shinya Yamanaka, the 2012 Nobel Prize laureates in Physiology or Medicine. Studying the differences between humans and chimpanzees, using ethically defensible methods, would not have been possible if this revolutionary technique had not been available, according to the researchers.
“Instead of studying living humans and chimpanzees, we used stem cells grown in a lab,” Jakobsson said.
The new findings will potentially contribute to genetic research regarding psychiatric disorders, such as schizophrenia, a disorder that appears to be unique to humans.
“But there is a long way to go before we reach that point,” Jakobsson says, because “instead of carrying out further research on the 2% of coded DNA, we may now be forced to delve deeper into all 100% – a considerably more complicated task for research.”