The catadromous teleost Anguilla japonica has a complete enzymatic repertoire for the biosynthesis of docosahexaenoic acid from alpha-linolenic acid: Cloning and functional characterization of an Elovl2 elongase

Abstract

The Japanese eel Anguilla japonica is a catadromous fish species with considerable farming scale. Previous studies showed that dietary α-linolenic acid (18:3n-3) and linoleic acid (18:2n-6) satisfied essential fatty acid requirements in eel, which suggested that Japanese eel should have a complete pathway for the biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFA). However, existing knowledge was insufficient to explain the molecular basis of LC-PUFA biosynthetic capacity in eel. In order to further characterize this pathway in eel, a full-length cDNA of a putative fatty acyl elongase was isolated, with the ORF encoding a protein with 294 amino acids. The putative elongase displayed high homology to Elovl2 of other teleosts. Functional characterization by heterologous expression in yeast showed the protein product of the cDNA had high activity towards C20 and C22 PUFA substrates and low activity towards C18 PUFA substrates, characteristic of Elovl2 elongases. Tissue distribution of the elovl2 mRNA showed highest expression in brain and eyes, which was different from freshwater and anadromous species. This may reflect an important role for this enzyme in the in situ endogenous biosynthesis of docosahexaenoic acid (DHA) in neural tissues in eel. This is the first report of an Elovl2 in a catadromous teleost and demonstrates that Japanese eel has a complete enzyme repertoire required for the endogenous biosynthesis of DHA via the Sprecher pathway. These data have increased our knowledge of the diversity of LC-PUFA biosynthesis in vertebrates, and provided further insight into the regulatory mechanisms of LC-PUFA biosynthesis in teleost fish.