Molecular and functional characterisation of two elovl4 elongases involved in the biosynthesis of very long-chain (> C 24 ) polyunsaturated fatty acids in black seabream Acanthopagrus schlegelii

A complete biosynthetic pathway of the long-chain polyunsaturated fatty acids in an amphidromous fish, ayu sweetfish Plecoglossus altivelis (Stomiati; Osmeriformes)

The biosynthetic capability of the long-chain polyunsaturated fatty acids (LC-PUFA) in teleosts are highly diversified due to evolutionary events such as gene loss and subsequent neo- and/or sub-functionalisation of enzymes encoded by existing genes. In the present study, we have comprehensively characterised genes potentially involved in LC-PUFA biosynthesis, namely one front-end desaturase (fads2) and eight fatty acid elongases (elovl1a, elovl1b, elovl4a, elovl4b, elovl5, elovl7, elovl8a and elovl8b) from an amphidromous teleost, Ayu sweetfish, Plecoglossus altivelis. Functional analysis confirmed Fads2 with Δ6, Δ5 and Δ8 desaturase activities towards multiple PUFA substrates and several Elovl enzymes exhibited elongation capacities towards C18-20 or C18-22 PUFA substrates. Consequently, P. altivelis possesses a complete enzymatic capability to synthesise physiologically important LC-PUFA including arachidonic acid (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) from their C18 precursors. Interestingly, the loss of elovl2 gene in P. altivelis was corroborated by genomic and phylogenetic analyses. However, this constraint would possibly be overcome by the function of alternative Elovl enzymes, such as Elovl1b, which has not hitherto been functionally characterised in teleosts. The present study contributes novel insights into LC-PUFA biosynthesis in the relatively understudied teleost group, Osmeriformes (Stomiati), thereby enhancing our understanding of the complement of LC-PUFA biosynthetic genes within teleosts.

Determination of dietary essential fatty acids in a deep-sea fish, the splendid alfonsino Beryx splendens: functional characterization of enzymes involved in long-chain polyunsaturated fatty acid biosynthesis

The splendid alfonsino Beryx splendens is a commercially important deep-sea fish in East Asian countries. Because the wild stock of this species has been declining, there is an urgent need to develop aquaculture systems. In the present study, we investigated the long-chain polyunsaturated fatty acid (LC-PUFA) requirements of B. splendens, which are known as essential dietary components in many carnivorous marine fish species. The fatty acid profiles of the muscles, liver, and stomach contents of B. splendens suggested that it acquires substantial levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from its natural diet. The functional characterization of a fatty acid desaturase (Fads2) and three elongases (Elovl5, Elovl4a, and Elovl4b) from B. splendens confirmed their enzymatic capabilities in LC-PUFA biosynthesis. Fads2 showed Δ6 and Δ8 bifunctional desaturase activities. Elovl5 showed preferential elongase activities toward C₁₈ and C₂₀ PUFA substrates, whereas Elovl4a and Elovl4b showed activities toward various C_18-22 substrates. Given that Fads2 showed no Δ5 desaturase activity and no other fads-like sequence was found in the B. splendens genome, EPA and arachidonic acid cannot be synthesized from C₁₈ precursors; hence, they can be categorized as dietary essential fatty acids in B. splendens. EPA can be converted into DHA in B. splendens via the so-called Sprecher pathway. However, given that fads2 is only expressed in the brain, it is unlikely that the capacity of B. splendens to biosynthesize DHA from EPA can fulfill its physiological requirements. These results will be useful to researchers developing B. splendens aquaculture methods.

The repertoire of the elongation of very long-chain fatty acids (Elovl) protein family is conserved in tambaqui (Colossoma macropomum): Gene expression profiles offer insights into the sexual differentiation process

Elongation of very long-chain fatty acids (Elovl) proteins are critical players in the regulation of the length of a fatty acid. At present, eight members of the Elovl family (Elovl1-8), displaying a characteristic fatty acid substrate specificity, have been identified in vertebrates, including teleost fish. In general, Elovl1, Elovl3, Elovl6 and Elovl7 exhibit a substrate preference for saturated and monounsaturated fatty acids, while Elovl2, Elovl4, Elovl5 and Elovl8 use polyunsaturated fatty acids (PUFA) as substrates. PUFA elongases have received considerable attention in aquatic animals due to their involvement in the conversion of C₁₈ PUFAs to long-chain polyunsaturated fatty acids (LC-PUFA). Here, we identified the full repertoire of elovl genes in the tambaqui Colossoma macropomum genome. A detailed phylogenetic and synteny analysis suggests a conservation of these genes among teleosts. Furthermore, based on RNAseq gene expression data, we discovered a gender bias expression of elovl genes during sex differentiation of tambaqui, toward future males. Our findings suggest a role of Elovl enzymes and fatty acid metabolism in tambaqui sexual differentiation.

Determination of very long-chain polyunsaturated fatty acids from 24 to 44 carbons in eye, brain and gonads of wild and cultured gilthead sea bream (Sparus aurata)

Very long-chain (> C24) polyunsaturated fatty acids (VLC-PUFA) play an important role in the development of nervous system, retinal function and reproductive processes in vertebrates. Their presence in very small amounts in specific lipid classes, the lack of reference standards and their late elution in chromatographic analyses render their identification and, most important, their quantification, still a challenge. Consequently, a sensitive and feasible analytical methodology is needed. In this work, we have studied the effect of chain length, as well as the number and position of unsaturations (or double bonds) on the response of GC-APCI-(Q)TOF MS, to establish an analytical method for VLC-PUFA quantification. The developed methodology allows the quantification of these compounds down to 2.5 × 10^–3 pmol/mg lipid. The reduction of VLC-PUFA levels in lipid fractions of the organs from the herein sampled farmed fish suggesting a yet undetected effect on these compounds of high vegetable oil aquafeed formulations, that currently dominate the market.

Association Analysis between Genetic Variants of elovl5a and elovl5b and Poly-Unsaturated Fatty Acids in Common Carp (Cyprinus carpio)

Simple Summary

PUFAs have an essential impact on human health, but their availability constitutes a critical bottleneck in food production. Although fish is the traditional source of PUFAs, it is limited by the stagnation of fisheries. Many studies aim to increase the PUFA products of fish. Genetic markers are efficient in aquaculture breeding. Fatty acid desaturase 2 (fads2) and elongase 5 (elovl5) are the rate-limiting enzymes in the synthesis of PUFAs. The allo-tetraploid common carp is able to biosynthesize endogenous PUFAs. However, selective breeding common carp with high PUFA contents was hindered due to a lack of effective molecular markers. For future breeding common carp capable of producing endogenous PUFAs more effectively, we previously identified the polymorphisms in the coding regions of two duplicated fads2, fads2a and fads2b. However, the polymorphisms in the duplicated elovl5, elovl5a and elovl5b, were not detected. This study screened the genetic variants in the coding regions of elovl5a and elovl5b. Moreover, the joint effects of multiple coding SNPs in fads2b and elovl5b, two major genes regulating the PUFA biosynthesis, were evidenced with the increased explained percentages of the PUFA contents. These polymorphisms in these two genes were used to evaluate the breeding values of PUFAs. These SNPs would be potential markers for future selection to improve the PUFA contents in common carp.

Abstract

The allo-tetraploid common carp, one widely cultured food fish, is able to produce poly-unsaturated fatty acids (PUFAs). The genetic markers on the PUFA contents for breeding was limited. The polymorphisms in elovl5a and elovl5b, the rate-limiting enzymes in the PUFA biosynthesis, have not been investigated yet. Herein, we identified one coding SNP (cSNP) in elovl5a associated with the content of one PUFA and two cSNPs in elovl5b with the contents of eight PUFAs. The heterozygous genotypes in these three loci were associated with higher contents than the homozygotes. Together with previously identified two associated cSNPs in fads2b, we found the joint effect of these four cSNPs in fads2b and elovl5b on the PUFA contents with the increased explained percentages of PUFA contents. The genotype combinations of more heterozygotes were associated with higher PUFA contents than the other combinations. Using ten genomic selection programs with all cSNPs in fads2b and elovl5b, we obtained the high and positive correlations between the phenotypes and the estimated breeding values of eight PUFAs. These results suggested that elovl5b might be the major gene corresponding to common carp PUFA contents compared with elovl5a. The cSNP combinations in fads2b and elovl5b and the optimal genomic selection program will be used in the future selection breeding to improve the PUFA contents of common carp.

Cloning and characterisation of a Δ9 fatty acyl desaturase-like gene from the red claw crayfish (Cherax quadricarinatus) and its expression analysis under cold stress

Desaturase is one of the key enzymes in the unsaturated fatty acid synthesis pathway. Δ9 desaturase catalyzes the synthesis of oleic acid from stearic acid by introducing double bonds in the 9th and 10th carbon chains, thereby increasing the content of MUFAs in the body. In order to explore the main function of the Δ9 desaturase gene under low temperature stress, RACE-PCR technology was used in this study to clone the full-length sequence of the CqFAD9-like from the hepatopancreas of red claw crayfish, Cherax quadricarinatus. The full length of the sequence is 1236 bp, and the open reading frame is 1041 bp, encoding 346 amino acid residues. The 5 'UTR is 116 bp, the 3' UTR is 79 bp, and the 3 'UTR contains a PloyA tail. The predicted theoretical isoelectric point and molecular weight are 8.68 and 40.28 kDa, respectively. Homology analysis showed that the sequence had the highest similarity with FAD9 from crustaceans. The results of real-time PCR showed that the expression level of this gene was highest in the hepatopancreas, which was significantly higher than other tissues, followed by the ovaries, brain ganglion and stomach. At the same time, the expression of the CqFAD9-like in hepatopancreas of crayfish cultured at 25, 20, 15 and 9 °C for four weeks was detected. The results showed that expression of the FAD9 gene increased gradually with decreasing temperature, indicating that metabolic desaturation might play a regulatory role during cold stress.

Lack of ∆5 Desaturase Activity Impairs EPA and DHA Synthesis in Fish Cells from Red Sea Bream and Japanese Flounder

Long-chain (≥ C₂₀) polyunsaturated fatty acids (LC-PUFA), such as eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA), are necessary for human health and are obtained from marine fish-derived oils. Marine fish are LC-PUFA-rich animals; however, many of them require LC-PUFA for growth. Therefore, it is suggested that they do not have sufficient ability to biosynthesize LC-PUFA. To evaluate in vivo LC-PUFA synthetic activity in fish cells, fish-derived cell lines from red sea bream (Pagrus major, PMS and PMF), Japanese flounder (Paralichthys olivaceus, HINAE), and zebrafish (Danio rerio, BRF41) were incubated with n-3 fatty acids labeled by radioisotopes or stable isotopes, and then, n-3 PUFA were analyzed by thin-layer chromatography or liquid chromatography-mass spectrometry. Labeled EPA and DHA were biosynthesized from labeled α-linolenic acid (18:3n-3) in BRF41, whereas they were not detected in PMS, PMF, or HINAE cells. We next cloned the fatty acid desaturase 2 (Fads2) cDNAs from PMF cells and zebrafish, expressed in budding yeasts, and then analyzed the substrate specificities of enzymes. As a result, we found that Fads2 from PMF cells was a ∆6/∆8 desaturase. Collectively, our study indicates that cell lines from red sea bream and Japanese flounder were not able to synthesize EPA or DHA by themselves, possibly due to the lack of ∆5 desaturase activity. Furthermore, this study provides a sensitive and reproducible non-radioactive method for evaluating LC-PUFA synthesis in fish cells using a stable isotope and liquid chromatography-mass spectrometry.

Biosynthesis of Long-Chain Polyunsaturated Fatty Acids in Marine Gammarids: Molecular Cloning and Functional Characterisation of Three Fatty Acyl Elongases

Long-chain (C20-24) polyunsaturated fatty acids (LC-PUFAs) are essential nutrients that are mostly produced in marine ecosystems. Previous studies suggested that gammarids have some capacity to endogenously produce LC-PUFAs. This study aimed to investigate the repertoire and functions of elongation of very long-chain fatty acid (Elovl) proteins in gammarids. Our results show that gammarids have, at least, three distinct elovl genes with putative roles in LC-PUFA biosynthesis. Phylogenetics allowed us to classify two elongases as Elovl4 and Elovl6, as they were bona fide orthologues of vertebrate Elovl4 and Elovl6. Moreover, a third elongase was named as "Elovl1/7-like" since it grouped closely to the Elovl1 and Elovl7 found in vertebrates. Molecular analysis of the deduced protein sequences indicated that the gammarid Elovl4 and Elovl1/7-like were indeed polyunsaturated fatty acid (PUFA) elongases, whereas Elovl6 had molecular features typically found in non-PUFA elongases. This was partly confirmed in the functional assays performed on the marine gammarid Echinogammarus marinus Elovl, which showed that both Elovl4 and Elovl1/7-like elongated PUFA substrates ranging from C18 to C22. E. marinus Elovl6 was only able to elongate C18 PUFA substrates, suggesting that this enzyme does not play major roles in the LC-PUFA biosynthesis of gammarids.

Regulation of long-chain polyunsaturated fatty acid biosynthesis in teleost fish

Omega-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFA, C_20-24), including eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), are involved in numerous biological processes and have a range of health benefits. Fish have long been considered as the main source of n-3 LC-PUFA in human diets. However, the capacity for endogenous biosynthesis of LC-PUFA from C₁₈ PUFA varies in fish species based on the presence, expression and activity of key enzymes including fatty acyl desaturases (Fads) and elongation of very long-chain fatty acids (Elovl) proteins. In this article, we review progress on the identified Fads and Elovl, as well as the regulatory mechanisms of LC-PUFA biosynthesis both at transcriptional and post-transcriptional levels in teleosts. The most comprehensive advances have been obtained in rabbitfish Siganus canaliculatus, a marine teleost demonstrated to have the entire pathway for LC-PUFA biosynthesis, including the roles of transcription factors hepatocyte nuclear factor 4α (Hnf4α), liver X receptor alpha (Lxrα), sterol regulatory element-binding protein 1 (Srebp-1), peroxisome proliferator-activated receptor gamma (Pparγ) and stimulatory protein 1 (Sp1), as well as post-transcriptional regulation by individual microRNA (miRNA) or clusters. This research has, for the first time, demonstrated the involvement of Hnf4α, Pparγ and miRNA in the regulation of LC-PUFA biosynthesis in vertebrates. The present review provides readers with a relatively comprehensive overview of the progress made into understanding LC-PUFA biosynthetic systems in teleosts, and some insights into improving endogenous LC-PUFA biosynthesis capacity aimed at reducing the dependence of aquafeeds on fish oil while maintaining or increasing flesh LC-PUFA content and the nutritional quality of farmed fish.

Biosynthesis of LC-PUFAs and VLC-PUFAs in Pampus argenteus: Characterization of Elovl4 Elongases and Regulation under Acute Salinity

Salinity has been demonstrated to influence the biosynthesis of long-chain (C_20-24) polyunsaturated fatty acids (LC-PUFAs) in teleost fish. Since LC-PUFAs are essential nutrients for vertebrates, it is central to understand how fish cope with an acute change in salinity associated with natural events. We herein report on the cloning and functional characterization of two elongation of very-long-chain fatty acid (Elovl)4 proteins, namely, Elovl4a and Elovl4b, and study the roles that these enzymes play in the biosynthesis of LC-PUFAs and very-long-chain (>C₂₄) polyunsaturated fatty acids (VLC-PUFAs) in marine teleost Pampus argenteus. The P. argenteus Elovl4 displayed all of the typical features of Elovl-like enzymes and have eyes and brain as major sites through which they exert their functions. Moreover, functional studies showed that the P. argenteus Elovl4 can effectively elongate C_18-22 substrates to C₃₆ VLC-PUFA. Because both P. argenteus Elovl4 are able to produce 24:5n - 3 from shorter precursors, we tested whether the previously reported Δ6 Fads2 from P. argenteus was able to desaturate 24:5n - 3 to 24:6n - 3, a key step for docosahexaenoic acid (DHA) synthesis. Our results showed that P. argenteus can indeed bioconvert 24:5n - 3 into 24:6n - 3, suggesting that P. argenteus has the enzymatic capacity required for DHA biosynthesis through the coordinated action of both Elovl4 and Fads2. Furthermore, an acute salinity test indicated that low-salinity stress (12 ppt) upregulated genes involved in LC-PUFA biosynthesis, with 12 ppt salinity treatment showing the highest hepatic LC-PUFA content. Overall, our results unveiled that the newly characterized Elovl4 enzymes have indispensable functions in LC- and VLC-PUFA biosynthesis. Moreover, acute salinity change influenced the biosynthesis of LC-PUFA in P. argenteus. This study provided new insight into the biosynthesis of LC- and VLC-PUFAs in vertebrates and the physiological responses that teleosts have under acute salinity stress.

Functional characterization, tissue distribution and nutritional regulation of the Elovl4 gene in golden pompano, Trachinotus ovatus (Linnaeus, 1758)

The elongases of very long-chain fatty acids (Elovls) are involved in the rate-limiting of the carbon chain elongation reaction in fatty acid (FA) biosynthesis in vertebrates. One member of the Elovls family, Elovl4, has been regarded as a critical enzyme involved in the biosynthesis pathway of polyunsaturated fatty acids (PUFAs). To explore the role of Elovl4 in PUFA synthesis in Trachinotus ovatus, the cDNA of the Elovl4b gene is cloned from T. ovatus (ToElovl4b). The ORF of ToElovl4b was 918 bp and encoded 305 amino acid (aa) protein sequences. Sequence alignment showed that the deduced amino acids contained significant structural features of the Elovl4 family, such as a histidine box motif (HXXHH), multiple transmembrane domains and an endoplasmic reticulum (ER) retention signal. Moreover, phylogenetic analysis revealed that ToElovl4b was highly conserved with that of Rachycentron canadum Elovl4b. Moreover, heterologous expression in yeast demonstrated that ToElovl4b could efficiently elongate 18:2n-6, 18:3n-6 and 20:5n-3 FAs up to 20:2n-6, 20:3n-6 and 22:5n-3, respectively. Furthermore, the tissue expression profile indicated that mRNA expression of ToElovl4b was higher in the gonads and brain than in other tissues. Additionally, nutritional regulation suggested the highest mRNA levels of ToElovl4b in liver and brain were under feeding with 1:1 FO-SO (fish oil, FO; soybean oil, SO) and 1:1 FO-CO (corn oil, CO)), respectively. These new insights were useful for understanding the molecular basis and regulation of LC-PUFA biosynthesis in fish.

Molecular and Functional Characterization of Elovl4 Genes in Sparus aurata and Solea senegalensis Pointing to a Critical Role in Very Long-Chain (>C24) Fatty Acid Synthesis during Early Neural Development of Fish

Very long-chain fatty acids (VLC-FA) play critical roles in neural tissues during the early development of vertebrates. However, studies on VLC-FA in fish are scarce. The biosynthesis of VLC-FA is mediated by elongation of very long-chain fatty acid 4 (Elovl4) proteins and, consequently, the complement and activity of these enzymes determines the capacity that a given species has for satisfying its physiological demands, in particular for the correct development of neurophysiological functions. The present study aimed to characterize and localize the expression of elovl4 genes from Sparus aurata and Solea senegalensis, as well as to determine the function of their encoded proteins. The results confirmed that both fish possess two distinct elovl4 genes, named elovl4a and elovl4b. Functional assays demonstrated that both Elovl4 isoforms had the capability to elongate long-chain (C_20–24), both saturated (SFA) and polyunsaturated (PUFA), fatty acid precursors to VLC-FA. In spite of their overlapping activity, Elovl4a was more active in VLC-SFA elongation, while Elovl4b had a preponderant elongation activity towards n-3 PUFA substrates, particularly in S. aurata, being additionally the only isoform that is capable of elongating docosahexaenoic acid (DHA). A preferential expression of elovl4 genes was measured in neural tissues, being elovl4a and elovl4b mRNAs mostly found in brain and eyes, respectively.

The fatty acid elongation genes elovl4a and elovl4b are present and functional in the genome of tambaqui (Colossoma macropomum)

Long-chain (C_20-24) polyunsaturated fatty acids (LC-PUFA) are physiologically important nutrients for vertebrates including fish. Previous studies have addressed the metabolism of LC-PUFA in the Amazonian teleost tambaqui (Colossoma macropomum), an emerging species in Brazilian aquaculture, showing that all the desaturase and elongase activities required to convert C₁₈ polyunsaturated fatty acids (PUFA) into LC-PUFA are present in tambaqui. Yet, elongation of very long-chain fatty acid 4 (Elovl4) proteins, which participate in the biosynthesis of very long-chain (>C₂₄) saturated fatty acids (VLC-SFA) and very long-chain polyunsaturated fatty acids (VLC-PUFA), had not been characterized in this species. Here, we investigate the repertoire and function of two Elovl4 in tambaqui. Furthermore, we present the first draft genome assembly from tambaqui, and demonstrated the usefulness of this resource in nutritional physiology studies by isolating one of the tambaqui elovl4 genes. Our results showed that, similarly to other teleost species, two elovl4 gene paralogs termed as elovl4a and elovl4b, are present in tambaqui. Tambaqui elovl4a and elovl4b have open reading frames (ORF) of 948 and 912 base pairs, encoding putative proteins of 315 and 303 amino acids, respectively. Functional characterization in yeast showed that both Elovl4 enzymes have activity toward all the PUFA substrates assayed (18:3n-3, 18:2n-6, 18:4n-3, 18:3n-6, 20:5n-3, 20:4n-6, 22:5n-3, 22:4n-6 and 22:6n-3), producing elongated products of up to C₃₆. Moreover, both Elovl4 were able to elongate 22:5n-3 to 24:5n-3, a key elongation step required for the synthesis of docosahexaenoic acid via the Sprecher pathway.

Cloning and functional characterization of an elovl4-like gene involved in the biosynthesis of long-chain polyunsaturated fatty acids in the swimming crab Portunus trituberculatus

Elongation of very long-chain fatty acid 4 (Elovl4) proteins participate in the biosynthesis of long-chain and very long-chain polyunsaturated fatty acids (LC-PUFA and VLC-PUFA). In the present study, an elovl4 cDNA was cloned from the swimming crab Portunus trituberculatus by PCR techniques and functionally characterized using recombinant expression in yeast Saccharomyces cerevisiae. The elovl4 cDNA sequence contained an open reading frame of 1038 base pairs, encoding a protein of 346 amino acids. The elovl4 has typical Elovl structures, with transmembrane domains (6) and a histidine box. The elovl4 was expressed in various tissues analyzed, with the highest expression found in intestine and hepatopancreas, followed by stomach and eyestalk. The functional characterization of Elovl4 yeast showed that the P. trituberculatus Elovl4 can elongate C_18-22 polyunsaturated fatty acids (PUFA), reaching in some cases products of C₂₄ and C₂₆. Along its ability to elongate PUFA, the P. trituberculatus Elovl4 was also efficient in the elongation of saturated fatty acids, with 28:0 and 30:0 being prominent elongation products. These results provide insight into the LC-PUFA biosynthetic capability of commercially important species of crustaceans.

Elovl4a participates in LC-PUFA biosynthesis and is regulated by PPARαβ in golden pompano Trachinotus ovatus (Linnaeus 1758)

The elongases of very long-chain fatty acids (Elovls) are responsible for the rate-limiting elongation process in long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis. The transcription factor, PPARα, regulates lipid metabolism in mammals; however, the detailed mechanism whereby PPARαb regulates Elovls remains largely unknown in fish. In the present study, we report the full length cDNA sequence of Trachinotus ovatus Elovl4a (ToElovl4a), which encodes a 320 amino acid polypeptide that possesses five putative membrane-spanning domains, a conserved HXXHH histidine motif and an ER retrieval signal. Phylogenetic analysis revealed that the deduced protein of ToElovl4a is highly conserved with the Oreochromis niloticus corresponding homologue. Moreover, functional characterization by heterologous expression in yeast indicated that ToElovl4a can elongate C18 up to C20 polyunsaturated fatty acids. A nutritional study showed that the protein expressions of ToElovl4a in the brain and liver were not significantly affected among the different treatments. The region from PGL3-basic-Elovl4a-5 (−148 bp to +258 bp) is defined as the core promoter via a progressive deletion mutation of ToElovl4a. The results from promoter activity assays suggest that ToElovl4a transcription is positively regulated by PPARαb. Mutation analyses indicated that the M2 binding site of PPARαb is functionally important for protein binding, and transcriptional activity of the ToElovl4a promoter significantly decreased after targeted mutation. Furthermore, PPARαb RNA interference reduced ToPPARαb and ToElovl4a expression at the protein levels in a time-dependent manner. In summary, PPARαb may promote the biosynthesis of LC-PUFA by regulating ToElovl4a expression in fish.

New Insights on Intermediary Metabolism for a Better Understanding of Nutrition in Teleosts

The rapid development of aquaculture production throughout the world over the past few decades has led to the emergence of new scientific challenges to improve fish nutrition. The diet formulations used for farmed fish have been largely modified in the past few years. However, bottlenecks still exist in being able to suppress totally marine resources (fish meal and fish oil) in diets without negatively affecting growth performance and flesh quality. A better understanding of fish metabolism and its regulation by nutrients is thus mandatory. In this review, we discuss four fields of research that are highly important for improving fish nutrition in the future: ( a) fish genome complexity and subsequent consequences for metabolism, ( b) microRNAs (miRNAs) as new actors in regulation of fish metabolism, ( c) the role of autophagy in regulation of fish metabolism, and ( d) the nutritional programming of metabolism linked to the early life of fish.

The elongation of very long-chain fatty acid 6 gene product catalyses elongation of n-13 : 0 and n-15 : 0 odd-chain SFA in human cells

Normal odd-chain SFA (OCSFA), particularly tridecanoic acid (n-13 : 0), pentadecanoic acid (n-15 : 0) and heptadecanoic acid (n-17 : 0), are normal components of dairy products, beef and seafood. The ratio of n-15 : 0:n-17 : 0 in ruminant foods (dairy products and beef) is 2:1, while in seafood and human tissues it is 1:2, and their appearance in plasma is often used as a marker for ruminant fat intake. Human elongases encoded by elongation of very long-chain fatty acid (ELOVL)1, ELOVL3, ELOVL6 and ELOVL7 catalyse biosynthesis of the dominant even-chain SFA; however, there are no reports of elongase function on OCSFA. ELOVL transfected MCF7 cells were treated with n-13 : 0, n-15 : 0 or n-17 : 0 (80 µm) and products analysed. ELOVL6 catalysed elongation of n-13 : 0→n-15 : 0 and n-15 : 0→n-17 : 0; and ELOVL7 had modest activity toward n-15 : 0 (n-15 : 0→n-17 : 0). No elongation activity was detected for n-17 : 0→n-19 : 0. Our data expand ELOVL specificity to OCSFA, providing the first molecular evidence demonstrating ELOVL6 as the major elongase acting on OCSFA n-13 : 0 and n-15 : 0 fatty acids. Studies of food intake relying on OCSFA as a biomarker should consider endogenous human metabolism when relying on OCSFA ratios to indicate specific food intake.

Cloning, tissue distribution and nutritional regulation of a fatty acyl Elovl4-like elongase in mud crab, Scylla paramamosain (Estampador, 1949)

In this report, the full-length cDNA of fatty acyl Elovl4-like elongase was cloned from the hepatopancreas of Scylla paramamosain by rapid-amplification of cDNA ends (RACE). To the best of our knowledge, this is the first report of Elovl4-like elongase in crustaceans. The full-length cDNA of Elovl4-like was 1119bp, which included a 5'-terminal untranslated region (UTR) of 58bp, a 3'-terminal UTR of 44bp and an open reading frame (ORF) of 1017bp encoding a polypeptide of 338 amino acids. Tissue distribution analysis revealed that Elovl4-like transcripts are widely distributed in various organs, with high mRNA levels in the hepatopancreas and cranial ganglia. Further, Elovl4-like transcriptional levels in hepatopancreas were up-regulated in proportion to the replacement of dietary fish oil (FO) with soybean oil (SO). The result showed that Elovl4-like transcripts increased about 0.83 and 1.12-fold respectively when SO constituted 80% and 100% of total oil (P<0.05). These results may contribute to better understanding of the long-chain polyunsaturated fatty acids (LC-PUFA) biosynthetic pathway and regulation mechanism in this species.