New genetic research has revealed the existence of certain regions in the human genome that have changed or mutated more rapidly than most others, resulting in differences that make us human among our primate cousins.
By using the latest sequencing and bioinformatics tools, scientists at the Gadstone Institutes were able to identify certain genomic regions that guide the development of human-specific characteristics.
“Advances in DNA sequencing and supercomputing have given us the power to understand evolution at a level of detail that just a few years ago would have been impossible,” said Gladstone Laboratory Investigator Katherine Pollard, who is also a professor of epidemiology and biostatistics at the University of California, San Francisco’s (UCSF’s) Institute for Human Genetics. “In this study, we found stretches of DNA that evolved much more quickly than others. We believe that these fast-evolving stretches were crucial to our human ancestors becoming distinct from our closest primate relatives.”
Called “human accelerated regions”, or HARs, they were found to mutate at a relatively fast rate. Specifically, HARs act as “enhancers,” controlling when and for how long certain genes are “switched on” or activated during embryonic development. This was revealed through experiments in embryonic animal models and the use of supercomputers to conduct powerful computational genomics analyses. The research team identified more than 2,600 HARs. Then, using a machine-learning algorithm called EnhancerFinder and genetic information input they were able to reduce the list to those HARs they predicted to be likely enhancers. “We predicted that nearly eight hundred HARs act as enhancers at a specific point during embryonic development,” explained Tony Capra, PhD, the study’s lead author. “Confirming this prediction for several dozen HARs, our next goal was to see whether any of these HARs enhanced patterns of gene activation that were uniquely human.”
Five such HARs were identified, active in both human and chimpanzee genomes, but which activated genes in different embryonic regions. For example, the human versions of HARs 2xHAR.164 and 2xHAR.170 are active in a region of the brain between the midbrain and hindbrain, while the chimp versions are not. This so-called “gain of function” of these two HARs in human embryos may point to differences in the development of key brain regions such as the cerebellum, which is known to regulate not only motor control but may also regulate higher cognitive functions, such as language, fear and pleasure.
“These results, while preliminary, offer an unprecedented glimpse into how very recent changes to the human genome have modified the genetic programs that control embryonic development to potentially yield different results,” said Capra. “We anticipate that if we were to look at the activity of HARs that are enhancers during later developmental stages, we would see even more differences between humans and chimpanzees.”
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Source: Adapted and edited from a Gladstone Institutes press release.
Gladstone is an independent and nonprofit biomedical-research organization dedicated to accelerating the pace of scientific discovery and innovation to prevent, treat and cure cardiovascular, viral and neurological diseases. Gladstone is affiliated with the University of California, San Francisco.
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