Is hair in the genome

Gene switch discovered for blonde hair

Stanford (USA) - The vast majority of people are dark-haired. So far, eight genes are known that influence pigment production in skin cells and thus also hair color. American researchers have now identified a genetic trait that is responsible for the high proportion of blond people in Northern Europe. In their genome, they found a minimal change in a section of DNA that regulates the activity of several genes. Replacing a single DNA building block inhibits a specific gene in skin cells by 20 percent. This is enough, as experiments with mice have shown, to significantly reduce the pigment content of the hair, the scientists report in the journal "Nature Genetics". The gene switch did not affect eye color at the same time.

"We looked for general mechanisms by which external features such as the color of skin and hair develop in the course of evolution," says David Kingsley of Stanford University. His working group first researched how sticklebacks adapt their skin color to a changed environment. In doing so, they identified a DNA region in the genome of the fish that does not itself code a protein, but rather regulates the activity of protein-coding genes. One of them controlled the skin color of the sticklebacks. The researchers also found a very similar section of DNA in the genes of mice and humans. It controls the activity of the KITLG gene, which is required for the development of various cell types - including pigment-forming skin cells. DNA analyzes had shown that this region of the genome differs very slightly in blond and dark-haired people: in blondes, the DNA building block A is exchanged for another (G) at one point.

Experiments with cultures of human skin cells showed that this exchange reduced the activity of the KITLG gene by 20 percent. Mice, to which the “blonde version” of the DNA segment had been transferred into the genome, developed a lighter coat than the normal, dark-haired animals. The genetic change apparently only affected the hair color and did not at the same time affect the color of the eyes. There is also no evidence, according to the researchers, that blonde hair color in people could be linked to special personality traits.

This result is a good example of how a conspicuous physical trait can change very easily by only slightly reducing the activity of a gene, says Kingsley. There would probably be numerous as yet unknown DNA segments distributed throughout the genome that function in a similar way as gene switches for various genes. These genetic control elements could be responsible not only for the variation in external traits, but also for different susceptibility to disease and other properties.

The hair color is determined by the type and amount of melanin pigments deposited in the hair. If the black-brown eumelanin is mainly produced, the result is a dark hair color. If, on the other hand, the red-yellow pheomelanin predominates, the result is reddish hues. A low production of both pigment types leads to blonde hair. The respective underlying genetic characteristics are not yet fully known. In people with albinism, a genetic defect disrupts the formation of melanin, which results in the lack of color in the skin, hair and eyes.

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