Cloning and nutritional regulation of a Δ6-desaturase-like enzyme in the marine teleost gilthead seabream ( Sparus aurata)

Abstract

Marine fish are presumed to have a lower capacity than freshwater fish for the bioconvertion of 18C fatty acids into 20–22C highly unsaturated fatty acids (HUFA). The present work investigated the first step of this pathway, the Δ6-desaturation, in gilthead seabream. A full-length desaturase-like cDNA was identified from total RNA extracted from viscera of juvenile fish fed for 96 days on an experimental HUFA-free diet containing olive oil as the sole lipid source. The open reading frame encodes a 445-amino acid peptide that contains two membrane-spanning domains, three histidine-rich regions, and a cytochrome b 5 domain, which are characteristic of Δ6- and Δ5-desaturases. Predicted protein sequence of seabream desaturase-like indicated a high percentage of identity with mammalian Δ6-desaturases (approx. 65%). Northern analysis showed two transcripts of approximately 3.7 and 1.8 kb which were highly expressed in fish fed on HUFA-free diet and slightly expressed in fish fed on HUFA-rich diet. The fatty acid profile of the former group was characterized by high levels of Δ6-desaturation products (18:2 n-9 and 20:2 n-9) with no detectable levels of Δ5-desaturation product (20:3n-9). These results demonstrate for the first time the presence and nutritional modulation of a Δ6-desaturase-like cDNA in a marine fish.