Due to one amino acid substitution, our brains have more neurons than Neanderthals had

(ORDO NEWS) — The Neanderthal brain is no different in size from the brain of a reasonable person, but it turned out that our new cortex contains more nerve cells.

This is due to a single amino acid change in the TKTL1 protein that increased the number of radial glial cells from which neurons are formed during embryonic development and contributed to the evolution of human cognitive abilities.

The change in the structure of the brain is considered the main factor in the development of cognitive abilities that occurred during the evolution of Homo sapiens.

At the same time, a comparison of the brain sizes of our closest extinct relatives of Neanderthals ( Homo neanderthalensis ) and modern humans did not reveal any differences.

However, the difference in the number of neurons, which also contributes to cognition, has not yet been known.

Now, researchers from the Max Planck Institute for Molecular Cell Biology and Genetics (Germany) have found that the TKTL1 protein, which differs in just one amino acid between us and Neanderthals, affects the amount of radial glia.

These cells are the precursors of neurons in the developing neocortex (the upper and most “evolutionarily new” layer of the cerebral cortex).

The activity of the catalytic enzyme TKTL1, a transketolase-like protein 1, was found to be especially high in the frontal lobe of the human fetal cortex, where it contributes to the formation of more radial glia cells.

We have this protein contains the amino acid arginine, instead of which the Neanderthals had lysine. The results of the study are published in the journal Science.

During the experiments, the scientists compared how the two versions of TKTL1 affected the production of neurons in the neocortex of the mouse embryo.

They noticed that the number of radial glial cells increased in fetuses with Homo sapiens TKTL1, but not with the Neanderthal version of the protein. As a consequence, the brains of adult mice with arginine-containing TKTL1 had more neurons.

The researchers then examined the relevance of these effects to human brain development. To this end, they replaced arginine with lysine in TKTL1 human brain organelles, miniature structures that mimic the structure of various organs. On this model, scientists were able to once again confirm their hypothesis.

Although we cannot know exactly how many neurons were in the Neanderthal brain, based on the data obtained, we can conclude that Homo sapiens probably has more neurons in the frontal lobe of the brain, where TKTL1 activity is highest.

This protein affects cell metabolism, in particular, stimulates the pentose phosphate pathway of glucose oxidation and enhances the synthesis of fatty acids, which in turn increases the production of certain membrane lipids necessary for the division and growth of radial glia cells.

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