Human pigmentation depends on genes
Last reviewed: 07.06.2024
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More than one hundred and sixty genes are responsible for skin tone, eye color and hair color.
Pigmentation is provided by melanocytes, which produce the pigment substance melanin. It is produced in two variants: red-yellow pheomelanin and brown-black eumelanin. The color of hair and eyes depends not only on their presence and amount, but also on the ratio. For example, people with brown eyes have eumelanin predominant in the iris pigment epithelium, while people with blue or green eyes have pheomelanin predominant.
All quantities and ratios of melanin cells are determined by genes, and there are many more such responsible genes than previously thought. Thus, scientists have found 169 gene carriers of information, of which 135 were not previously considered as involved in pigment formation.
A new optical technique allowed to detect the connection of genes with melanin, thanks to which it was possible to determine the number and concentration of pigment in a single structure. The researchers changed gene activity in pigment cells using the CRISPR-Cas9 genetic editor. After turning off a particular gene using this editor, the amount of melanin was measured in the cells, which allowed them to understand what the "turned off" gene affects. As a result, the scientists counted 169 newly discovered implicated genes. Functionally, they were divided into two categories. The first category directly controls melanin production by ensuring appropriate enzyme activity, encoding regulatory proteins that control gene enzyme activity. The second category influences the transport of pigment through the cellular structure and the maturation processes of melanosomes, the specific cytoplasmic organelles that synthesize and store melanin. In addition, there are genes that regulate the degree of acidity of the internal environment of melanosomes. The function of pigment-producing enzymes is largely dependent on the pH of the environment. The influence of the discovered genes on pigmentation was tested not only on individual cellular structures, but also directly on the human body. Gene-melanin activity was analyzed in children with different skin tones.
Eye and hair color and skin tone are genetically important and complex traits that require much deeper study. Melanin is present in a wide variety of living organisms: for example, the famous cuttlefish ink also contains this pigment.
Eumelanin gives a dark, brown hue, while pheomelanin provides a pinkish, reddish color. The important ability of eumelanin is to absorb and scatter ultraviolet and visible light.
Interestingly, melanosomes in dark-skinned people are larger and do not form clusters. In light-skinned people, melanosomes are relatively small and often form clusters surrounded by a membrane. There is also such a phenomenon as albinism, an inherited pigmentation disorder in which the skin, eyes and hair are partially or completely devoid of melanin.
Full details are published at SCIENCE