What about people who separate us from inhuman prime ministers, our closest relatives? One of the biggest differences, scientifically speaking, is the size of our much larger brains – and now, we’ve discovered a key secret behind that unparalleled growth.
In new research comparing different types of brain organoids – small masses of brain material grown from gas cells – scientists found a key developmental difference in neural gas cell development between human brain bones, gorilla, and chimpanzee.
Neural stem cells (also called neuroepithelial cells) are a type of proliferating cells, which cause the neurons and glial cells that make up the central nervous system. But the way this shift occurs during early brain development is not the same in all primates, the new research shows.
As neural stem cells move into specific brain cell types, they change their shape, which in turn affects the rate at which they can divide and eventually form neurons. In mice, such a shape change was known to occur in just a few hours, ultimately limiting the amount of brain cells the animals produce.
(S.Benito-Kwiecinski / MRC LMB / Cell)
Above: Cloud cells at five days, of different shape, unchanged in humans (left) compared to apes (right).
Now, scientists from the Molecular Biology Laboratory (LMB) of the UK Medical Research Council have shown that the process takes much longer in primates, lasting several days, in fact. For gorillas and chimpanzees, the delayed shape change takes about five days to continue generating new neurons.
Human neuroepithelial cells take even longer to transition – even a whole week, allowing neurogenesis processes to run for longer, which itself produces more brain cells, more brain tension, and at the eventually producing larger brains (or, as seen here, larger organoids sitting in a basin).
“We have found that a delayed change in the shape of early cells in the brain is sufficient to alter the course of development, helping to determine the numbers of neurons produced,” bio- LMB development expert and lead researcher Madeline Lancaster explains.
“Surprisingly, a simple evolutionary change in cell shape could have a major impact on brain evolution.”
In addition to highlighting the difference in transition, however, analysis of the organs has also revealed what makes the developmental changes possible.
According to the researchers, a gene called ZEB2 plays a key role in regulating the process, causing the neural stem cells to change shape and mature effectively earlier, which shortening the time they can multiply before they become progenitor cells that eventually form into neurons. .
(S.Benito-Kwiecinski / MRC LMB / Cell)
Above: Human brain organoids at five weeks of age, much larger than gorilla and chimpanzee organoids (left to right, respectively).
Not only that, but in experiments in which ZEB2 expression dynamics were handled, the researchers showed that the organs could also be manipulated – with human brain organoids becoming smaller when strengthen the gene, and gorilla organoid more similar to the size of a human brain when ZEB2 was blocked.
The researchers confirm that organoid tissue is never a perfect representation of true animal organs, so we cannot conclude that ZEB2 activity and inactivity would work in the same way in real brain human or non-human prime.
Nevertheless, the researchers say that this is a true idea of what is likely to account for much of the difference in brain size between humans and other large onions – and future studies, including experimentation with transgenic mice or images of ape embryos, may shed even more light.
“This provides some first-hand insight into what’s different about the developing human brain that separates us from our closest relatives, the other great apes,” says Lancaster.
“I feel like we’ve learned something fundamental about the issues I’ve been interested in for as long as I can remember – what makes us human.”
The results are reported in Cell.