Sea Bass Hypoxia Inducible Factor (HIF)-1alpha : molecular cloning and mRNA quantification during acute and chronic hypoxia exposure

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 a heterodimer composed of two subunits: a and b. In this study we report first on the molecular cloning and characterization of HIF-1a in sea bass (Dicentrarchus labrax). The full-length sea bass cDNA for HIF-1a 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. We then utilized the real-time PCR technology to monitor dynamic 2010 Fish Biology Congress Abstracts changes in levels of HIF-1a transcripts, in response to acute and chronic hypoxic stress. The number of HIF-1a mRNA copies were significantly increased in response to both acute (1.9 mg/L, dissolved oxygen for 4 hours) 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-1a gene transcripts during hypoxia in a representative of marine, hypoxia-sensitive species.