Molecular cloning and nutritional regulation of putative ∆6 desaturase mRNA from striped catfish (Pangasianodon hypophthalmus)

Abstract

Here we report the full-length cDNA cloning and nutritional regulation of a putative Δ6 fatty acyl desaturase (Δ6 fads) gene from striped catfish, Pangasianodon hypophthalmus. The 5′ and 3′ RACE analysis revealed a cDNA sequence of 1896 base pairs (bp) comprising a 5′ UTR of 49bp, 3′ UTR of 509bp and an open reading frame (ORF) of 1338bp specifying a protein of 445 amino acids. Bioinformatics analysis showed that the deduced peptide sequence included all the characteristic features of microsomal fatty acyl desaturases, including N-terminal cytochrome b5 domain containing the haem binding motif H-P-G-G, fatty acyl (FA) desaturase domain, three histidine boxes and transmembrane regions. P. hypophthalmus ∆6 desaturase peptide sequence shares high similarity with Pangasius larnaudii (95%) and Clarias macrocephalus (90%). The predicted secondary and tertiary protein structures revealed that desaturase protein contains mostly α-helix followed by random coils and strands. Tissue distribution analysis showed that Δ6 fads is mainly expressed in brain followed by liver, heart, gill and muscle. Since α-linolenic acid is a substrate for the Δ6 FADS enzyme, various concentrations of this fatty acid (0.5, 1, 1.5 and 2gkg−1) were administered to experimental fish through feed to find out its effect on the expression of Δ6 fads. Results showed that the liver Δ6 fads gene expression is up-regulated in fish fed with experimental diets (p<0.05). Statement of relevanceThe fatty acid composition of fish depends on both dietary fatty acid input and endogenous HUFA biosynthesis capacity. Fatty acyl desaturases (fads) introduce double bonds in selected positions of the acyl chains. Particularly, Δ6 FADS are the first enzymes involved in the biosynthesis of long-chain HUFA from the C18 n-3 and n-6 precursors, which is a rate limiting step. The extent to which fish can desaturate/elongate C18 FAs to HUFAs varies with species. Hence it is important to study the relationships between LC-PUFA biosynthesis pathways and the habitat and feeding habit of fish species, which will provide the basis for understanding the regulatory mechanisms controlling LC-PUFA biosynthesis pathways. The present study reports the full-length cDNA cloning, tissue distribution and nutritional regulation of Δ6 fads-like gene from freshwater catfish, P. hypophthalmus. This is the first report on cloning and expression analysis of Δ6 fads-like gene from any freshwater catfish.