Biosynthesis of long-chain polyunsaturated fatty acids in marine fish: Characterization of an Elovl4-like elongase from cobia Rachycentron canadum and activation of the pathway during early life stages

Abstract

Marine fish, unlike freshwater species, have been generally considered to have a limited ability to biosynthesize long-chain polyunsaturated fatty acids (LC-PUFA) from C18 precursors due to apparent limited enzymatic activities involved in the pathway. Although LC-PUFA play important physiological roles throughout the entire life cycle, requirements for early life stages are especially high and provision of preformed LC-PUFA in egg lipids appears critical to support the formation of developing tissues where these compounds accumulate. No studies, however, have been conducted to explore the capability of marine fish embryos (here referring to life stages from zygote to the oesophagus opening) for de novo synthesis of the LC-PUFA required for normal growth and development. The present study aimed to investigate the activation of the LC-PUFA biosynthetic pathway during embryogenesis of the marine teleost cobia (Rachycentron canadum). First, a fatty acyl elongase with sequence similarity to mammalian elongase of very long-chain fatty acids 4 (Elovl4) was isolated, and its biochemical function characterized showing that it catalyzed the production of very long-chain fatty acids (VLC-FA) including both saturated and polyunsaturated fatty acids with chain lenghts ≥ 24 carbons. Notably, cobia Elovl4 was able to elongate 22:5n-3 to 24:5n-3 and thus could play a key role in the biosynthesis of docosahexaenoic acid (22:6n-3), a critical fatty acid in neural tissues. Subsequently, the fatty acid dynamics of embryos at different developmental stages and the temporal expression patterns of target genes including elovl4, and the formerly characterized elovl5 elongase and ∆6 fatty acyl desaturase, were analyzed in order to elucidate the overall activation of the LC-PUFA biosynthetic pathway in cobia embryos. Our results indicated that expression of the LC-PUFA biosynthetic pathway in cobia embryos is initiated at 12-18 hours post-fertilization

Biosynthesis of very long-chain fatty acids (C>24) in Atlantic salmon: Cloning, functional characterisation, and tissue distribution of an Elovl4 elongase

“…The ER retrieval signal of salmon Elovl4 contains an arginine residue in position -5 from the Cterminus of the protein, and conserves one lysine residue in the position -3 (RXKXX), the latter regarded as a critical residue for ER retrieval signal function (Jackson et al, 1990). The RXKXX pattern is common to other teleostei Elovl4 including the puffer fish T. rubripes and T. nigroviridis, the D. rerio Elovl4_a, and cobia R. canadum (Zhang et al, 2003;Monroig et al, 2010aMonroig et al, , 2011. Elovl4 proteins are highly conserved through evolution (Leonard et al, 2004).…”

“…Whereas zebrafish Elovl4_a was only able to produce saturated VLC-FA, the b isoform was efficient in the synthesis of both saturated VLC-FA and VLC-PUFA up to C36. The other members of the same phylogenetic cluster, cobia (Monroig et al, 2011) In addition to a role in the biosynthesis of saturated VLC-FA, salmon Elovl4, as with zebrafish Elovl4_b (Monroig et al, 2010a) and cobia Elovl4 (Monroig et al, 2011), also appears to be a critical enzyme required for the biosynthesis of VLC-PUFA. Salmon Elovl4 showed high efficiency in the elongation of C20 and C22 PUFA substrates that led to the production of n-3 and n-6 polyenes containing up to C36.…”

“…Recently, we isolated and characterised elovl4 cDNAs from zebrafish Danio rerio (Monroig et al, 2010a) and cobia Rachycentron canadum (Monroig et al, 2011). These investigations have demonstrated that, similarly to mammals, teleostei Elovl4 are key enzymes in the biosynthesis of both saturated and polyunsaturated VLC-FAs up to C36.…”

Biosynthesis of essential fatty acids in Octopus vulgaris (Cuvier, 1797): Molecular cloning, functional characterisation and tissue distribution of a fatty acyl elongase

“…More distantly, the other elongase identified in the L. gigantea genome (transcript 2) and also other Elovl-like proteins from A. californica and M. galloprovincialis grouped together with vertebrate Elovl4 elongases, another type of elongase involved in the biosynthesis of very long-chain FA (C>24) including both saturates and polyenes (Agbaga et al, 2008;Monroig et al, 2010bMonroig et al, , 2011bMonroig et al, , 2012b. While these results suggest that another elongase with similarity to Elovl4 might also be present in the common octopus, the functional characterisation of the present Elovl cDNA confirmed, not only its participation in the PUFA elongation pathway, but also that it has substrate specificities more similar to Elovl5 than Elovl2.…”

Investigating the essential fatty acids in the common cuttlefish Sepia officinalis (Mollusca, Cephalopoda): Molecular cloning and functional characterisation of fatty acyl desaturase and elongase

“…3). The deduced aa sequence of the cuttlefish Elovl showed 77.7 % identity to the common octopus Elovl previously characterised (Monroig et al, 2012b), with lower identity scores to homologues from the bivalve C. nobilis (noble scallop) (49.5 %) (Liu et al, 2013) (Agbaga et al, 2008;Monroig et al, 2010Monroig et al, , 2011b. The cuttlefish Elovl sequence was deposited in the GenBank database with accession number KP260646.…”