Molecular characterization and expression analysis of three hypoxia-inducible factor alpha subunits, HIF-1α/2α/3α of the hypoxia-sensitive freshwater species, Chinese sucker

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-1 alpha, HIF-2 alpha and HIF-3 alpha in an endangered hypoxia-sensitive fish species, Chinese sucker. The HIF-1 alpha/2 alpha/3 alpha 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-1 alpha and HIF-3 alpha mRNAs were highly expressed in liver and gonads, followed by spleen and muscle. Moreover, HIF-1 alpha and HIF-3 alpha transcription factors revealed similar developmental expression patterns, with the lowest expression at 48 h post-fertilization, and reaching the highest expression level at 360 h post-fertilization. Short-term hypoxia exposure (2.2, 2.8 and 3.2 mg/L dissolved oxygen for 24 h) increased mRNA levels of HIF-1 alpha and HIF-3 alpha. HIF-2 alpha mRNA showed similar expression patterns with that of HIF-1 alpha and HIF-3 alpha, 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. (C) 2012 Elsevier B.V. All rights reserved.