Like the real brain, the organoids of the human brain have grown much larger than the organoids of other brains
In the early stages of brain development, neurons are composedfrom stem cells - neural precursors. These cells are initially cylindrical in shape, which allows them to easily divide into identical daughter cells. The more often they multiply at this stage, the more neurons there will be in the brain in the future. As the cells mature and their reproduction slows down, they lengthen, forming the shape of an extended cone.
Earlier studies in mice have shown that theirnerve progenitor cells mature, acquire a conical shape and slow down their reproduction for several hours. Now brain organelles have helped scientists figure out how this process develops in humans, gorillas and chimpanzees.
They found that gorillas and chimpanzees take much longer to make the transition than humans. The entire process takes approximately five days.
After just 5 days, progenitor cellsgorilla neurons mature and take on a conical shape (right), while human cells (left) remain cylindrical. Credit: S. Benito-Kwiecinski / MRC LMB / Cell.
Human progenitor cells are even largerstayed at this stage of growth - about seven days. They retained their cylindrical shape longer than other great apes. The difference in the speed of transition from neural progenitors to neurons means that human cells have more time to reproduce. Scientists suggest that this process is responsible for more neurons in the human brain compared to the brain of a gorilla or chimpanzee.
A relatively simple evolutionary change in the shape of cells could have major implications for brain evolution.
To uncover the genetic mechanism that controlsWith these differences, the researchers compared the expression of genes that turn on and off in human brain organoids with other monkeys. They identified differences in a gene called ZEB2, which was activated in gorilla brain organoids earlier than in human organelles.
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