Just one gene
People's self-domestication was explained by a change in the work of one gene
Polina Loseva, N+1
Scientists have calculated a gene that played an important role in the process of human self–domestication - the acquisition of prosocial behavior and softened facial features. This is the BAZ1B gene: it regulates the packaging of DNA and the work of other genes, including those that have been subjected to positive selection in modern humans compared to Neanderthals. The work is published in the journal Science Advances.
Domestication led to the formation of a similar set of signs in different mammalian species: softened facial features, reduced aggressiveness and increased friendliness. Moreover, in some species this happened without the active participation of humans, that is, in the process of self-domestication (self-domestication). For example, in cats or dogs, it went on regardless of breeding – people did not always choose which of the animals would interbreed with each other, and sometimes those who got along better with humans turned out to be more prolific.
The effect of this mechanism can be extended to the person himself. Thus, the hypothesis of self-domestication suggests that many traits of modern humans arose as a result of selection for the same traits as in domestic animals. Some researchers associate these changes with the work of the neural crest – this is the germ tissue that forms next to the neural tube, and then its cells spread throughout the body and are part of the peripheral nervous system, skin and facial skeleton. A violation of the activity of these cells could explain the whole complex of signs – from non-aggressive behavior to altered facial features.
The genes that determine these signs in humans are still unknown, but patients with Williams syndrome, a hereditary disease caused by the absence of one of the sections of the seventh chromosome, are usually considered as a model.
People with Williams syndrome are also extremely friendly and not aggressive, but suffer from mental retardation. Many scientists therefore believe that the genetic engine of self-domestication may be located somewhere in the genes missing from these patients.
Matteo Zanella from the University of Milan and his colleagues drew attention to the BAZ1B gene – it is located on the same part of the seventh chromosome, which is absent in people with Williams syndrome. This gene is responsible for packing DNA in the nucleus and is involved in the migration of neural crest cells in frogs. Mutations in this gene cause deformations of the muzzle in mice, and in modern humans it bears traces of selection compared to ancestral variants that can be found in Neanderthals and Denisovans.
To test what the disruption of this gene in humans will lead to, scientists decided to turn it off in the culture of neural crest stem cells. As cell donors, the researchers took four healthy people, four patients with Williams syndrome and four patients with autism spectrum disorder caused by the doubling of the examined section of the seventh chromosome. Then the donor cells were reprogrammed into pluripotent cells and neural crest cells were grown from them.
In these cells, scientists blocked the work of BAZ1B using RNA interference and estimated the rate at which the cells tightened the hole in the culture - this indicator indicates the ability of cells to migrate in principle. The researchers noticed that cells with a doubled BAZ1B gene crawled worse than in the control condition when this gene was blocked, and cells with a missing BAZ1B – on the contrary, better. The fact that two opposite states of the gene (lack and excess) cause opposite changes when this gene is blocked, allowed scientists to conclude that BAZ1B really affects the mobility of nerve crest cells.
The researchers then compared the expression of genes in cells with different BAZ1B activity (normal operation of the gene, shortage and excess), as well as the state of chromatin (location of epigenetic labels) to determine the target genes for which it is responsible for packaging, and which will respond most strongly to changes in its amount in the cell. Then they compared a set of these target genes with paleogenetic data to check whether there are differences in their sequence in modern humans, Neanderthals and Denisovans.
It turned out that among the 10 percent of genes that bear the strongest imprint of positive selection in modern humans – that is, minimal diversity and a well–established set of mutations compared to ancient humans - 82 genes overlap with a set of BAZ1B target genes. There are many of them who are responsible for the morphogenesis of the human head and the work of nerve crest cells. Finally, among them there are three genes that are associated with the shape of the lower part of the human face – namely, it is stronger in Neanderthals and smoothed in patients with Williams syndrome.
Apparently, the BAZ1B gene turned out to be a link between human facial features and self-domestication: it controls the work of nerve crest cells and at the same time regulates the activity of genes on which the expression of facial features depends. In addition, it is these target genes that have been subjected to particularly harsh selection during human evolution. Apparently, changes in the work of BAZ1B could lead to a softening of facial features in people and, probably, to an increase in friendliness.
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