Acute and chronic hypoxia affects HIF-1α mRNA levels in sea bass (Dicentrarchus labrax)

Aquatic hypoxia is a frequent event and in fish a complex set of physiological and biochemical alterations are employed to cope with this environmental stress. Many of these adjustments depend to a large extent on changes in the expression of genes that encode for physiologically relevant proteins. Genes that are induced by hypoxia appear to share a common mode of transcriptional regulation. This induction depends upon activation of a transcription factor, the hypoxia-inducible factor-1 (HIF-1), which is composed of α and β subunits. In this study we report first on the molecular cloning and characterization of HIF-1α in sea bass (Dicentrarchus labrax). The full-length sea bass cDNA for HIF-1α was isolated and deposited in the GenBank with accession no. DQ171936. It consists of 3317 base pairs (bp) carrying a single open-reading frame that encompasses 2265 bp of the coding region and 1052 bp of the 3′ UTR. The predicted sea bass HIF-1α protein (755 amino acids) shows a high level of conservation at the bHLH (basic helix–loop–helix domain), PAS A/B (Per-ARNT-Sim A/B domain), N-TAD (N-terminal transactivation domain), and C-TAD (C-terminal transactivation domain), whereas only few variations are found at the ODD (oxygen-dependent degradation domain) regions among vertebrates.We then utilized the real-time PCR technology to monitor dynamic changes in levels of HIF-1α mRNA in response to acute and chronic hypoxic stress. The number of HIF-1α mRNA copies was significantly increased in liver tissue in response to both acute (1.9 mg/L, dissolved oxygen for 4 h) and chronic (4.3 mg/l, DO for 15 days) hypoxia in sea bass whereas it remained unchanged in fish exposed to hyperoxic (DO 13.5 ± 1.2 mg/L, 155% saturation) conditions. This is the first study to investigate the behaviour of HIF-1α gene transcripts during hypoxia in a representative of marine, hypoxia-sensitive species.