Changing a single amino acid in a protein can have significant effects. By this means, the production of neurons would be more important in the frontal lobe during the development of the brain in modern humans than in Neanderthals.
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What makes modern humans unique? The answer lies partly in the frontal lobe from neocortex (an area of brain), according to a new study appeared in Science. Admittedly, the volume endocranial structure of modern humans and Neanderthals was no different, suggesting a similar size of the brain and the neocortex. But it was unknown until now whether an identical size of the neocortex implied the same production of neurons.
Few proteins show differences in the sequence of their amino acids between Homo sapiens and our ancestors. Neanderthals. However, this is the case with TKTL1, which differs from only one amino acid of the Neanderthal variant. Institute researchers Max Planck of cellular biology molecular and genetic from Dresden (Germany) found that this protein increased a type of brain progenitor cells called basal radial glial cells, which generate the majority of neurons in the developing neocortex.
More neurons formed with the modern human variant of TKTL1
Next, the study authors wanted to know the significance of this amino acid modification for the development of the neocortex. They introduced the modern human variant or the Neanderthal variant of TKTL1 into the neocortex ofembryos of mouse. Result: basal radial glial cells increased with the modern human variant of TKTL1, but not with the variant of Neanderthal. Thus, the brains of mouse embryos with the modern human variant of TKTL1 contained more neurons.
In order to know if these same effects were found for the development of brain human, the researchers used human brain organoids – miniature structures mimicking the main structure and functions of the brain and cultured in the laboratory from stem cells human. They thus replaced thearginine of the TKTL1 of modern man by the lysine of Neanderthal TKTL1 and they found that fewer basal radial glial cells were produced and therefore also fewer neurons.
In more detail, Homo sapiens TKTL1 acts through modifications of the metabolismby one stimulation of the pentose pathway phosphates followed by an increase in the synthesis of Fatty acids. In fact, the modern human TKTL1 increases the synthesis of certain lipids membranes, which are necessary to generate the long process of basal radial glial cells, and therefore to increase the production of neurons.
An impact on the cognitive abilities associated with the frontal lobe?
If the study implies that neocortical neurogenesis in modern humans was greater than in Neanderthals (particularly in the frontal lobe), the authors speculate that this may have favored the cognitive abilities of modern humans associated with the frontal lobe. Thus, the genetic evolution of our species probably contributed to the development of language and voluntary motor coordination.
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