The transcriptomic landscape of yaks reveals molecular pathways for high altitude adaptation

Yak is one of the largest native mammalian species at the Himalayas, the highest plateau area in the world with an average elevation of >4,000 m above the sea level. Yak is well adapted to high altitude environment with a set of physiological features for a more efficient blood flow for oxygen delivery under hypobaric hypoxia. Yet, the genetic mechanism underlying its adaptation remains elusive. We conducted a cross-tissue, cross-altitude, and cross-species study to characterize the transcriptomic landscape of domestic yaks. The generated multi-tissue transcriptomic data greatly improved the current yak genome annotation by identifying tens of thousands novel transcripts. We found that among the eight tested tissues (lung, heart, kidney, liver, spleen, muscle, testis, and brain), lung and heart are two key organs showing adaptive transcriptional changes and >90% of the cross-altitude differentially expressed genes in lung display a nonlinear regulation. Pathways related to cell survival and proliferation are enriched, including PI3K-Akt, HIF-1, focal adhesion, and ECM-receptor interaction. These findings, in combination with the comprehensive transcriptome data set, are valuable to understanding the genetic mechanism of hypoxic adaptation in yak.