An evolutionary perspective on Elovl5 fatty acid elongase: comparison of Northern pike and duplicated paralogs from Atlantic salmon

Abstract

BackgroundThe ability to produce physiologically critical LC-PUFA from dietary fatty acids differs greatly among teleost species, and is dependent on the possession and expression of fatty acyl desaturase and elongase genes. Atlantic salmon, as a result of a recently duplicated genome, have more of these enzymes than other fish. Recent phylogenetic studies show that Northern pike represents the closest extant relative of the preduplicated ancestral salmonid. Here we characterise a pike fatty acyl elongase, elovl5, and compare it to Atlantic salmon elovl5a and elovl5b duplicates.ResultsPhylogenetic analyses show that Atlantic salmon paralogs are evolving symmetrically, and they have been retained in the genome by purifying selection. Heterologous expression in yeast showed that Northern pike Elovl5 activity is indistinguishable from that of the salmon paralogs, efficiently elongating C18 and C20 substrates. However, in contrast to salmon, pike elovl5 was predominantly expressed in brain with negligible expression in liver and intestine.ConclusionsWe suggest that the predominant expression of Elovl5b in salmon liver and Elovl5a in salmon intestine is an adaptation, enabled by genome duplication, to a diet rich in terrestrial invertebrates which are relatively poor in LC-PUFA. Pike have retained an ancestral expression profile which supports the maintenance of PUFA in the brain but, due to a highly piscivorous LC-PUFA-rich diet, is not required in liver and intestine. Thus, the characterisation of elovl5 in Northern pike provides insights into the evolutionary divergence of duplicated genes, and the ecological adaptations of salmonids which have enabled colonisation of nutrient poor freshwaters.

Molecular cloning, tissue distribution and nutritional regulation of a Δ6-fatty acyl desaturase-like enzyme in large yellow croaker (Larimichthys crocea)

“…; Hastings, Agaba, Tocher, Zheng, Dickson, Dick & Teale ; Morais, Monroig, Zheng, Leaver & Tocher ; Zheng, Ding et al . ; Gregory, See, Gibson & Schuller ; Carmona‐Antoñanzas, Tocher, Taggart & Leaver ). This further verified that low LC‐PUFA biosynthesis could not be due to deficiencies in these steps (desaturasion and elongation).…”

Omega-3 long-chain polyunsaturated fatty acids and aquaculture in perspective

“…This is entirely expected as metabolic pathways such as LC-PUFA have evolved to satisfy the requirements of the fish, not of human beings. Therefore, the differences between freshwater/salmonid and marine species in the EPA pathway are probably a consequence of the differing levels of LC-PUFA in the respective environments (higher in marine) leading to different evolutionary pressures, and are reflected in their qualitative EFA requirements (Leaver et al, 2008b;Carmona-Antoñanzas et al, 2013). DHA production from EPA is more conserved although there are few data, but this pathway is likely important particularly for brain development and function and, again, an evolutionary adaptation (Zheng et al, 2009).…”

Diversification of substrate specificities in teleostei Fads2: characterization of Δ4 and Δ6Δ5 desaturases of Chirostoma estor

“…This was hypothesized to be a consequence of marine fi sh having evolved in an LC-PUFA-rich environment; and thus, there was low evolutionary pressure to retain the ability to desaturate and elongate C 18 PUFA . In contrast, lower levels of LC-PUFAs in the food chain meant freshwater species retained the ability to biosynthesize LC-PUFAs from C 18 PUFAs ( 8,32,33 ). This hypothesis was based upon fi sh that were largely carnivorous in the case of marine species and detritivorous/herbivorous in freshwater species ( 34 ).…”