“Junk DNA” behind the difference between humans and chimpanzees

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Published 13 October 2021 at 10.13

Domestic. Human DNA is very similar to that of the chimpanzee, which is evolutionarily our closest living relative. Now, stem cell researchers in Lund have found a previously overlooked part of our DNA, so-called non-coded DNA, which seems to contribute to a difference that, despite all our similarities, can explain why our brains function differently.

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The chimpanzee is our closest living relative evolutionarily and research believes that our relationship is based on a common ancestor. About five to six million years ago, our developmental pathways were divided into what is today the modern chimpanzee and Homo Sapiens, man in the twenty-first century

Stem cell researchers in Lund have in a new study investigated what it is in our DNA which causes the brains of humans and chimpanzees to differ and find answers.

– Instead of studying living humans and chimpanzees, we have used stem cells grown in our cell culture laboratory. The stem cells have been reprogrammed from skin cells by our partners in Germany, the USA and Japan. After that, we examined the stem cells that we cultured into brain cells, says Johan Jakobsson, professor of neuroscience at Lund University, who led the study in Lund.

From the stem cells, the researchers have specifically grown human and chimpanzee brain cells and compared the two cell types. The researchers then found that humans and chimpanzees use some of their DNA in different ways, which seems to play a major role in the development of our brains.

According to the researchers, this indicates that what is the basis of the human brain evolution is probably much more complicated genetic mechanisms than previously thought, when it was thought that the answers were in the two percent genetic DNA.

– The part that differs in our DNA was unexpected, these are so-called structural variants of DNA that were previously referred to as “junk DNA”, a long DNA strand that repeats itself and which has long been judged to be without function. Usually, we researchers have searched for answers in the part of DNA where the protein-producing genes are located – which only makes up about two percent of our entire DNA – and examined the proteins themselves to find examples of differences, says Johan Jakobsson.

The new findings thus suggest that the differences seem to lie outside the protein-coding genes in what has been termed “junk DNA”, which is thought to be dysfunctional and which makes up the majority of all our DNA.

– This may explain that what underlies the evolution of the human brain is probably much more complicated genetic mechanisms than previously thought, when it was thought that the answers were in the two percent genetic DNA. Our results indicate that what has been important for brain development may instead be hidden in the overlooked 98 percent, which seem to be important. This is a surprising result.

Johan Jakobsson believes that the new findings in the future may also contribute to genetically based answers to questions about psychiatric diseases, such as schizophrenia, a disease that seems to be unique to humans.

– But the road there can be long, as instead of researching further on the two percent encoded DNA, you may now have to dig deeper into all the 100 percent, a considerably much more complicated task for the research.