Fig. 2. Upregulation of hypoxia-inducible factor (HIF) expression in Tibetan chickens (TBCs) compared with Arbor Acres chickens (AACs) reared at high altitude. Protein expression level of HIF-1α (A) was determined by western blotting; RNA expression levels of HIF-1α (B), HIF-2α (C), and HIF-3α (D) were determined by quantitative reverse transcriptase polymerase chain reaction. RNA levels from the normoxia group were normalized to a value of 1. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was used as the loading control. The results are representative of at least three independent experiments run in triplicate and expressed as means ± SD (n = 3). ^*p < 0.05, ^**p < 0.01, ^***p < 0.001.