A new study has found evidence of molecular changes contributing to human brain development and evolution from chimpanzees.
This new study was published in the journal Cell on 7th February 2019.
The study is grounded on a discovery made by Arnold Kriegstein, the John Bowes Distinguished Professor in Stem Cell and Tissue Biology, and his collaborators. It says that Kriegstein and his group has created chimpanzee brain ‘organoids’ that may reveal the secrets of human evolution.
“Organoids” are small clusters of brain cells grown from stem cells in a laboratory dish that mimic the development and organization of full-size brains. These are produced from so-called induced pluripotent stem cells (iPSCs). iPSCs are adult cells, usually, skin cells, reprogrammed into stem cells that have the capability of becoming any tissue in the body.
Aparna Bhaduri, a postdoctoral researcher in the Kriegstein lab, diagnosed human and chimpanzee organoids at various development stages that helped her in comparing the growth of brain cells of the two through cell type and genetic programs.
Bhaduri later found that there occurred several hundred changes in humans but not in chimps. She deduced that these changes could help her in explaining the evolutionary origin and growing size of distinct human brains.
Kriegstein‘s group is one of the first groups to work on this project. Also, this new study with 56 organoids from stem cells derived from the skin of 8 chimpanzees and 10 human is the latest.
Arnold Kriegstein said, “By birth, the human cortex is already twice as large as in the chimpanzee, so we need to go back much earlier into embryonic development to understand the events that drive this incredible growth.”
Study’s co-first author Alex Pollen, an assistant professor of neurology and former Kriegstein lab postdoctoral researcher said, “These chimpanzee organoids give us an otherwise inaccessible window to six million years of our evolution. They let us ask new questions about what makes us human”.
Pollen also added, “Being so close to wild chimpanzees made me want to ask questions about our own species’ evolution.”
In earlier studies, some genetic changes caused up to the threefold expansion of the human brain’s neocortex. The neocortex is that part of the brain that is responsible for everything from language to self-awareness to abstract thought. But due to ethical restrictions, it was not possible for scientists to conduct this study then.
There has been evidence of autism and other uniquely human neurodevelopmental disorders due to the signaling of mTOR. mTOR links other proteins and serves as a core component of two distinct protein complexes.
Scientists wonder if the recent evolution of unusually large brains has some role to play in presence of these disorders.
As Bhaduri says, the discovery of this molecular pathway in cells seems to be targeted during evolution. And this might help in explaining the specialized role in generating advanced human cortex.