Researchers from several US institutions, coordinated by the Gladstone Institutes, have determined that a chance event of reorganization of large portions of the genome of human ancestors, which occurred more than a million years ago, triggered a cascade of rapid changes in DNA that would be the basis of unique human characteristics, such as the highly developed brain. The researchers analyzed stretches of DNA called ‘human accelerated regions’ (HARs), many of which control brain development. They found that HARs are almost identical among all humans but differ between humans and all other mammals. It is unknown why these sequences remained stable in mammals for millennia only to suddenly change in early humans.
The study of 241 mammalian genomes allowed us to conclude that HARs tend to be located in areas of the human genome that have large structural differences compared to other mammals. This suggests that human-specific structural changes may have created the right environment for HARs to rapidly evolve in the human ancestor after remaining roughly the same for millions of years of mammalian evolution.
Using a machine learning model to compare DNA sequences and identify regions of the genome that fold differently, the researchers predicted that nearly 30% of HARs were in areas of the genome that fold differently in humans compared to chimpanzees. This differential folding in humans brought different genes closer to the HARs, which could have drastic consequences for our ancestors.
The director of the Gladstone Institute for Data Science and Biotechnology, Katie Pollard, explained that the way the genome folds into three-dimensional space is particularly important for enhancers. This is because enhancers can affect the activity of any gene that ends up nearby, which can vary depending on how the DNA is folded. Pollard also highlighted that this structural change in the human genome had a significant impact on the evolution of the human brain.
Leave a Reply