Hypoxia-inducible factors (HIFs) are transcription factors that respond to changes in oxygen tension in the cellular environment. In this study, we identified full-length cDNAs of HIF-1α, HIF-2α and HIF-3α in an endangered hypoxia-sensitive fish species, Chinese sucker. The HIF-1α/2α/3α cDNAs are 3890, 3230 and 3374 bp in length, encoding 780, 782 and 632 amino acid residues, respectively. The real-time PCR results suggested that HIF-1α and HIF-3α mRNAs were highly expressed in liver and gonads, followed by spleen and muscle. Moreover, HIF-1α and HIF-3α transcription factors revealed similar developmental expression patterns, with the lowest expression at 48h post-fertilization, and reaching the highest expression level at 360 h post-fertilization. Short-term hypoxia exposure (2.2, 2.8 and 3.2mg/L dissolved oxygen for 24h) increased mRNA levels of HIF-1α and HIF-3α. HIF-2α mRNA showed similar expression patterns with that of HIF-1α and HIF-3α, however, its expression was extremely low in the spatio-temporal expression patterns and hypoxia treatment. This is the first report describing the potential to identify hypoxia-sensitive/tolerant fishes according to the number of the serine residues of fish oxygen-dependent degradation (ODD) domain. It was suggested that Cyprinomorpha fishes, with less than 40 serine residues in fish ODD domain were hypoxia-sensitive fishes and more than 40 serine residues in this domain were hypoxia-tolerant fishes.
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