Functional characterisation of a Fads2 fatty acyl desaturase with delta6/delta8 activity and an Elovl5 with C16, C18 and C20 elongase activity in the anadromous teleost meagre (Argyrosomus regius)

The meagre, Argyrosomus regius, is a carnivorous fish with great potential to diversify finfish aquaculture in the Mediterranean. However, currently nothing is known about their essential fatty acid requirements. Meagres are marine fish but also display anadromous behaviour migrating to river estuaries to spawn, and thus may provide an insight to the influence of diadromy on biosynthetic ability for long-chain polyunsaturated fatty acid (LC-PUFA). Our primary aim was to characterise key cDNAs (fatty acyl desaturases and elongases) of the biosynthetic pathway as a key step to establish the capacity of meagre for LC-PUFA biosynthesis from shorter chain PUFA. The cDNA sequences of a fatty acyl desaturase (Fads) and elongase of very long-chain fatty acids (Elovl) were obtained using PCR-based methodologies, and function of the proteins was investigated by expression of the coding sequences of the putative desaturase and elongase in the yeast Saccharomyces cerevisiae. The tissue distribution of both cDNAs was studied by reverse transcription PCR. Our results demonstrated that meagre possesses at least one fatty acyl desaturase and one elongase involved in the endogenous production of LC-PUFA. The meagre desaturase and elongase were identified as orthologues of Fads2 and Elovl5, respectively. Functionally, the desaturase had dual Δ6/Δ8 activity, whereas the elongase exhibited high elongation efficiency for C18 and C20 PUFA with low activity towards C22 PUFA. However, we also showed that the meagre Elovl5 elongated 16:3n - 3 to 18:3n - 3, the first time that C16 elongation activity had been demonstrated for a fish elongase. Similar to other marine teleosts, expression of fads2 and elovl5 transcripts was highest in brain. The functions and expression of the meagre Fads2 and Elovl5 proteins suggest that the meagre has a ‘marine type' LC-PUFA biosynthetic pathway, and that its anadromous behaviour has no major influence.