The chimpanzee is, in evolutionary terms, our closest living relative: around five or six million years ago, our paths parted from the common ancestor and we became the distinct species that we are today. Now, a team of scientists from the University of Lund (Sweden) has investigated our DNA to find out why our brains work in such a different way.
The results, published in the journal Cell Stem Cell , reveal that there is a previously overlooked part of our genome, so-called non-coding DNA, that could contribute to a crucial difference that, despite all our similarities to chimpanzees, it makes us so different.
To do this, the researchers changed the traditional approach: “Instead of studying humans and living chimpanzees, we use stem cells grown in a laboratory. Stem cells were reprogrammed from skin cells by our partners in Germany, the United States, and Japan. Then we looked at the stem cells that we had turned into brain cells, ”explains Johan Jakobsson, professor of neuroscience at Lund University, who led the study. Using the stem cells, the researchers specifically grew human and chimpanzee brain cells and compared the two types of cells.
The technique used by the researchers was developed by the Japanese Shinya Yamanaka and recognized with the Nobel Prize in Physiology or Medicine in 2012. The scientist discovered that specialized cells can be reprogrammed and developed in all types of body tissue, something that opens the door to carry out many studies that were previously not possible for ethical reasons. For example, this one, in which Lund’s team has been able to study the differences between the brain cells of humans and chimpanzees.
98% hidden
Upon analysis, the researchers found that humans and chimpanzees use a part of their DNA in different ways, which appears to play a considerable role in the development of our brains.
The differences between both genomes were found in a totally unexpected region. It was the structural variant of DNA that was previously called ‘junk DNA’, a long, repetitive strand of DNA that was long considered to have no function but to make up most of the genome. Traditionally, scientists have focused on looking for answers in the area of DNA where the genes that code for proteins are found and that only constitute 2% of all our DNA.
“This suggests that the basis for the evolution of the human brain must be found in much more complex genetic mechanisms than previously believed, since the answer was supposed to lie in that 2% of genetic DNA”, explains the author. “Our results indicate that, however, what has been significant for the development of the human mind must be hidden in that 98% of DNA that we have overlooked until now. It is a surprising find ”.
Jakobsson thinks that, in the future, these findings may also contribute to genetic responses to the origin of psychiatric disorders such as schizophrenia, a disease that appears to be unique to humans. “But there is a long way to go before we get to that point, since instead of carrying out more research on the 2% of the encoded DNA, we are now forced to delve into the remaining 98%,” he concludes.
Referencia: Johansson et al. 2021. A cis-acting structural variation at the ZNF558 locus controls a gene regulatory network in human brain development. Cell Stem Cell. DOI: https://doi.org/10.1016/j.stem.2021.09.008
