An international team of researchers led by Lanzhou University, China, has completed the genomic sequence of a female domestic yak.
Yak near the sacred Yundrok Yumtso Lake in Tibet (Dennis Jarvis)
As an iconic symbol of Tibet, the yak, Bos grunniens, is the most important domesticated species for Tibetans living at high altitude in China’s Qinghai Province, which could provide meat and other basic resources, such as milk, transportation, dried dung for fuel, and hides for tented accommodation.
Yaks have many anatomical and physiological traits that enable them live at high altitude, including high metabolism, acute senses, impressive foraging ability, enlarged hearts and lungs, and a lack of blood vessel constriction in the lungs when faced with relatively low oxygen conditions.
The researchers sequenced the genome of a female domestic yak using high-throughput sequencing technology. The genomic data yielded 2,657Mb draft yak genome assembly that had 65-fold coverage. They also conducted transcriptome sequencing on RNA samples derived from fresh heart, liver, brain, stomach, and lung tissues collected from the same yak. Based on the transcriptome data, researchers estimated that the yak genome contains 22,282 protein-coding genes and 2.2 million heterozygous SNPs. The results were published in Nature Genetics.
In order to understand evolutionary adaptation of yak to the high-altitude, the team conducted the comparative genomic analyses between yak and cattle, a closely related animal that typically lives at much lower altitudes. Although the yak and cattle were estimated to have diverged around 4.9 million years ago, many of the yak and cattle genes have remained very similar, with the two animals sharing 45 percent protein identity and 99.5 percent protein similarity.
However, they identified distinct gene expansions related to sensory perception and energy metabolism-related in yak.
The researchers also found an enrichment of protein domains related to the extracellular environment and hypoxic stress. Especially, they found the orthologous genes in yak related to hypoxia and nutrition metabolism had undergone positively selected and rapid evolution.
The study on high-altitude adaptation of yaks may help to improve current understanding, treatment, and prevention of altitude sickness and other hypoxia-related diseases in humans. Moreover, the yak genome provided a valuable resource for accelerating the genetic improvement of milk and meat production of this important animal.
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Bibliographic information: Qiu Q et al. 2012. The yak genome and adaptation to life at high altitude. Nature Genetics, published online 01 July 2012; doi:10.1038/ng.2343
