Molecular characterization of prepro-orexin in Atlantic cod (Gadus morhua): cloning, localization, developmental profile and role in food intake regulation.

A full-length cDNA encoding for prepro-orexin (prepro-OX) was cloned from Atlantic cod (Gadus morhua) hypothalamus using reverse transcription and rapid amplification of cDNA ends (RACE). The 143 amino acids (aa) prepro-OX contains a 38 aa signal peptide, a 50 aa orexin-A peptide and a 29 aa orexin-B peptide. Semi-quantitative RT-PCR shows that prepro-OX mRNA is present in brain and pituitary and in peripheral tissues, including gill, spleen, stomach and gut. Within the brain, high expression levels are seen in the hypothalamus. During development, prepro-OX is expressed from the cleavage stage up to the hatched larvae. Slot blot analysis shows that prepro-OX expression levels are higher in fish fed low (0.2% BW) and medium (0.8% BW) rations than in fish fed high rations (1.5% BW). Fish fed low and medium rations also display periprandial changes in prepro-OX expression, with higher expression levels at meal time (0 h) compared to 2h before and 2h after feeding. Our results suggest that orexins might be involved in development and feeding regulation in Atlantic cod.