Adaptation to the highlands at the genetic level
Genome analysis told about the adaptations of Tibetans to life in the mountains
Oleg Lischuk, N+1
Tibetans.
India Illustrated, 1905 / Special Collections, University of Houston Libraries
Genetic analysis conducted by Australian and Chinese scientists revealed a set of adaptations that allowed Tibetans to settle the high-altitude plateau, and also allowed to clarify their origin. The results of Yang et al. Genetic signatures of high-altitude adaptation in Tibetans are published in the journal Proceedings of the National Academy of Sciences.
Tibetans are of great interest to science because they serve as an example of a relatively recent adaptation of people to new conditions. They live on the Tibetan plateau with an average altitude of about 4,000 meters above sea level, where the oxygen content in the air is about 40 percent lower and ultraviolet radiation is about 30 percent more intense than at sea level. Previous genetic studies with a relatively small number of participants (less than 150 people) revealed single gene variants that contribute to adaptation to these conditions, but these data cannot explain all the physiological features observed in Tibetans.
The staff of the University of Queensland and Wenzhou Medical University conducted a high-quality genomic DNA analysis of 3381 residents of Sertar and Litang counties in Gardze-Tibet Autonomous Region of Sichuan Province, as well as 7287 representatives of other nationalities of East Asian origin. The processing of the obtained data by the principal component method did not reveal fundamental genetic differences between the two populations, although in Sertare biological samples were taken mainly from students and staff of the local Buddhist institute who came from different regions of the Tibetan Plateau, and in Litang – from the indigenous nomadic population who lived in this area for centuries. Comparison of samples with the database of the 1000 Genomes project showed that all participants from Tibetan counties are of East Asian origin, and 3008 of them are Tibetans, and 373 are representatives of the Han Chinese ethnic majority.
Further analysis showed that the closest genetic relatives of the Tibetans are the peoples inhabiting the regions adjacent to the Tibetan Plateau: Nakhi and Yi, who live mainly in Yunnan and Sichuan, as well as Mongols, most of whom live in Qinghai Province. It also turned out that the divergence of Tibetans and Han occurred about 4,725 years ago – about 2,000 years earlier than expected by the results of a full-exome analysis.
Also, a comparison of the genomes of Tibetans and other East Asians revealed nine significantly different loci. Seven of them were associated with known physiological mechanisms of adaptation to high-altitude conditions. In particular, Tibetans have a variant of the methylenetetrahydrofolate reductase (MTHFR) gene, which provides increased levels of folate and homocysteine in the blood, which provides additional protection from ultraviolet radiation. The available data also confirmed that they have a variant of the EPAS1 gene encoding the HIF transcription factor subunit, which is responsible for the reaction to hypoxia (oxygen starvation) and is associated with hemoglobin, erythrocyte and hematocrit levels (an indicator of erythrocyte saturation with hemoglobin).
Earlier, an international group of scientists found out that the EPAS1 variant, which helps to adapt to hypoxia, was inherited by Tibetans from Denisov people and is practically not found in other ethnic groups.
Portal "Eternal youth" http://vechnayamolodost.ru
05.04.2017