Evolution of the human brain was determined by only one mutant gene

(ORDO NEWS) — As a group of German scientists found out, a human-specific gene turned out to be the main factor in the expansion of the new cerebral cortex.

This means that the action of this gene, which appeared as a result of just a couple of mutations, could help a person develop unique cognitive abilities in the course of evolution.

The new cortex, or neocortex, is the evolutionarily youngest area of ​​the cerebral cortex. It is isolated from all mammalian species, but it is in humans that the neocortex makes up the bulk of the cortex, even when compared with the higher great apes.

It is this region of the brain that is responsible for higher cognitive abilities such as conscious thinking, speech, learning, and reasoning.

It is believed that the increase in the volume of the cortex observed in humans is associated with a higher proliferative capacity (that is, the ability to reproduce by cell division and subsequent tissue growth) of the progenitor cells of the cerebral cortex neurons.

And although the genes responsible for this increased proliferation seem to have already been found in previous studies, no one has yet studied their influence on the development of the brain of great apes.

This was noticed by a group of scientists from the Max Planck Institute for Molecular Cell Biology and Genetics (Germany) and decided to find out how the activity of a gene that increases the proliferation of neuron precursors in humans would act in the brain of a chimpanzee, a characteristic representative of great apes.

However, earlier studies on great apes were not carried out for a reason, because they are banned in Europe for ethical reasons.

The authors of the new work found a way out – they conducted experiments with the so-called brain organoids. Organoids are model three-dimensional cellular structures a few millimeters in diameter that can be grown from chimpanzee or human induced pluripotent stem cells (iPSCs).

Evolution of the human brain was determined by only one mutant gene 1
Brief description of the main results of the study

ISPCs are obtained by reprogramming ordinary differentiated cells with a given function so that they become stem cells again.

Further, almost any other cells can be obtained from them, including organelles that mimic brain tissue and even the cerebral cortex separately. Moreover, it was previously shown that studies on such organoids are identical to experiments on a real brain.

The scientists chose the previously known human-specific ARHGAP11B gene, which is active primarily in neuronal progenitor cells in the human fetal neocortex, and forced it to be expressed in chimpanzee brain organoid cells.

This led to a doubling of the number of neuronal precursors, which play a key role in the expansion of the neocortex.

Evolution of the human brain was determined by only one mutant gene 2
Section of a human brain organoid. Purple color shows actively proliferating brain stem cells

On the other hand, by blocking the expression of this gene in human brain organoid cells, the researchers reduced the number of neocortical neuron precursors to the level of chimpanzees.

Moreover, blocking a similar but not identical ARHGAP11A gene, which is much more common among many animal species, does not lead to such drastic changes.

It is assumed that the ARHGAP11B gene appeared as a result of a partial duplication (doubling) of the ARHGAP11A gene about 5 million years ago and a further mutation of this copy.

It is these mutations and the subsequent expression of ARHGAP11B that may have played a key role in increasing cognitive abilities and human evolution.

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