Evolutionary functional elaboration of the Elovl2/5 gene family in chordates

Studies on the characteristics of polycyclic aromatic hydrocarbons accumulation in lipids and the disturbance of lipid metabolism of Ruditapes philippinarum

Polycyclic aromatic hydrocarbons (PAHs) constitute a class of persistent organic pollutants with strong lipophilicity, which readily accumulate within organisms and have the effect to induce disorders in lipid metabolism. The present study aimed to investigate the accumulation localization and pattern of PAHs in Ruditapes philippinarum, and to reveal the association between PAHs and lipids metabolism. The 21-day exposure experiment was conducted using a mixture of phenanthrene, chrysene, and benzo[a]pyrene (the proportion is 1:1:1) at concentrations of 0.4 μg/L, 2 μg/L, and 10 μg/L. The tissue distribution of PAHs indicated that the digestive gland was the primary site of PAHs accumulation. Meanwhile, fluorescence colocalization suggested that PAHs primarily accumulated within the lipid droplets of digestive gland cells. This study further determined the transcriptomic and lipidomic profiles of the digestive gland to analyze the key genes involved in disrupted lipid metabolism and the major lipids affected. Lipidomic analysis identified the key differential metabolites as triglycerides (TGs). Furthermore, TGs were upregulated in the digestive gland had a total carbon atom number of 50-64 and a total number of 3-9 double bonds in the acyl side chains. Biochemical analysis experiments and oil red O stained frozen sections confirmed that the content of TGs steadily increased in various tissues during the experiment, leading to an elevated digestive gland index. Changes of lipid metabolism associated genes expression level also indicated that the synthesis of lipid in digestive gland were up-regulated while the decomposition was down-regulated. This study is the first to demonstrate the cellular localization of PAHs accumulation in bivalves and confirms the pattern of variation in TGs, providing new insights into the mechanisms of PAHs bioaccumulation and lipid metabolism disruption.

Molecular Identification and Functional Characterization of LC-PUFA Biosynthesis Elongase (elovl2) Gene in Chinese Sturgeon (Acipenser sinensis)

Elongases of very-long-chain fatty acids (Elovls) are critical rate-limiting enzymes that are involved in LC-PUFA biosynthesis through catalyzing the two-carbon elongation of a pre-existing fatty acyl chain. Thus far, several Elovls have been extensively studied in teleost. However, the functional and physiological roles of Elovls in chondrichthyans have rarely been reported. In this study, we identified and characterized elovl2 from the endangered Chinese sturgeon (Acipenser sinensis) by whole genome scanning. The results show that the coding sequence of elovl2 was 894 bp in length, for a putative protein of 297 amnio acids. Comparative genomic analyses indicated that Chinese sturgeon elovl2 was evolutionarily conserved. Functional characterization in yeast demonstrated that the Chinese sturgeon Elovl2 could efficiently elongate C20 (ARA and EPA) and C22 (22:4n-6 and 22:5n-3) substrates, confirming its critical roles in LC-PUFA biosynthesis. Spatial and temporal expression analyses showed high elovl2 mRNA levels were detected in the liver and brain and showed an increase trend both in embryonic and post-hatching stages. Interestingly, diets with vegetable oils as lipid sources could significantly induce the high expression of elovl2 in Chinese sturgeon, implying that the endogenous LC-PUFA biosynthesis pathway was stimulated by lack of LC-PUFA in their diets. Our findings will enhance our understanding about the evolutionary and functional roles of elovl2 and provide novel insights into the LC-PUFA biosynthesis mechanism in vertebrates.

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.

Elongation capacity of polyunsaturated fatty acids in the annelid Platynereis dumerilii

Elongation of very long-chain fatty acid (Elovl) proteins plays pivotal functions in the biosynthesis of the physiologically essential long-chain polyunsaturated fatty acids (LC-PUFA). Polychaetes have important roles in marine ecosystems, contributing not only to nutrient recycling but also exhibiting a distinctive capacity for biosynthesizing LC-PUFA. To expand our understanding of the LC-PUFA biosynthesis in polychaetes, this study conducted a thorough molecular and functional characterization of Elovl occurring in the model organism Platynereis dumerilii. We identify six Elovl in the genome of P. dumerilii. The sequence and phylogenetic analyses established that four Elovl, identified as Elovl2/5, Elovl4 (two genes) and Elovl1/7, have putative functions in LC-PUFA biosynthesis. Functional characterization confirmed the roles of these elongases in LC-PUFA biosynthesis, demonstrating that P. dumerilii possesses a varied and functionally diverse complement of Elovl that, along with the enzymatic specificities of previously characterized desaturases, enables P. dumerilii to perform all the reactions required for the biosynthesis of the LC-PUFA. Importantly, we uncovered that one of the two Elovl4-encoding genes is remarkably long in comparison with any other animals' Elovl, which contains a C terminal KH domain unique among Elovl. The distinctive expression pattern of this protein in photoreceptors strongly suggests a central role in vision.

Spinocerebellar ataxia 38: structure-function analysis shows ELOVL5 G230V is proteotoxic, conformationally altered and a mutational hotspot

Fatty acid elongase ELOVL5 is part of a protein family of multipass transmembrane proteins that reside in the endoplasmic reticulum where they regulate long-chain fatty acid elongation. A missense variant (c.689G>T p.Gly230Val) in ELOVL5 causes Spinocerebellar Ataxia subtype 38 (SCA38), a neurodegenerative disorder characterized by autosomal dominant inheritance, cerebellar Purkinje cell demise and adult-onset ataxia. Having previously showed aberrant accumulation of p.G230V in the Golgi complex, here we further investigated the pathogenic mechanisms triggered by p.G230V, integrating functional studies with bioinformatic analyses of protein sequence and structure. Biochemical analysis showed that p.G230V enzymatic activity was normal. In contrast, SCA38-derived fibroblasts showed reduced expression of ELOVL5, Golgi complex enlargement and increased proteasomal degradation with respect to controls. By heterologous overexpression, p.G230V was significantly more active than wild-type ELOVL5 in triggering the unfolded protein response and in decreasing viability in mouse cortical neurons. By homology modelling, we generated native and p.G230V protein structures whose superposition revealed a shift in Loop 6 in p.G230V that altered a highly conserved intramolecular disulphide bond. The conformation of this bond, connecting Loop 2 and Loop 6, appears to be elongase-specific. Alteration of this intramolecular interaction was also observed when comparing wild-type ELOVL4 and the p.W246G variant which causes SCA34. We demonstrate by sequence and structure analyses that ELOVL5 p.G230V and ELOVL4 p.W246G are position-equivalent missense variants. We conclude that SCA38 is a conformational disease and propose combined loss of function by mislocalization and gain of toxic function by ER/Golgi stress as early events in SCA38 pathogenesis.

Integrated lipidomics and transcriptomics analysis reveal lipid metabolism disturbance in scallop (Chlamys farreri) exposure to benzo[a]pyrene

Benzo[a]pyrene (B[a]P) commonly bioaccumulates in lipid-rich tissues due to its lipophilicity and further affects lipid metabolism. The present study systematically investigated the lipid metabolism disturbance in digestive glands of scallops (Chlamys farreri) exposure to B[a]P, based on lipidomics, transcriptomics, molecular and biochemical analysis. We exposed the scallops to environmentally relevant concentrations of B[a]P for 21 days. The bioaccumulation of B[a]P, lipid content and lipid peroxidation in digestive glands were measured. Integrated lipidomics and transcriptomics analysis, the differential lipid species were identified and key genes based on the pathways in which genes and lipid species involved together were selected in scallop exposure to 10 μg/L B[a]P. The changes of lipid profile showed that triglycerides (TGs) were accumulated after 21 days exposure, while the phospholipids (PLs) decreased demonstrated membrane structures were disrupted by B[a]P. In combination with the change of gene expression, we speculated that B[a]P could induce lipids accumulation by up-regulating lipid synthesis-related genes expression, down-regulating lipolysis-related genes expression and interfering with lipid transport. Overall, this study provides new insights into the mechanisms of lipid metabolism disturbance in bivalves exposed to PAHs, and establishes a foundation for understanding the bioaccumulation mechanism of B[a]P in aquatic organisms, which is of great importance for further ecotoxicological study.

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.

Comparative analysis of nutritional and transcriptional regulation of hacd1 in large yellow croaker (Larimichthys crocea) and rainbow trout (Oncorhynchus mykiss)

3-hydroxyacyl-CoA dehydratases 1 (Hacd1) is a critical enzyme in long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis. The difference in expression of hacd1 might account for the stronger capacity of LC-PUFA biosynthesis in freshwater fish than in marine fish, but little is known about fish hacd1. Therefore, this study compared the responses of large yellow croaker and rainbow trout hacd1 to different oil sources or fatty acids, and also examined transcriptional regulation of this gene. In this study, hacd1 was highly expressed in the liver of large yellow croaker and rainbow trout, which is the main organ for LC-PUFA biosynthesis. Therefore, we cloned the hacd1 coding sequence, with a phylogenetic analysis showing that this gene is evolutionarily conserved. Its localization to the endoplasmic reticulum (ER), likely also indicates a conserved structure and function. The expression of hacd1 in the liver was significantly decreased after the substitution of soybean oil (SO) for fish oil but was not significantly affected after palm oil (PO) substitution. Linoleic acid (LA) incubation significantly promoted hacd1 expression in primary hepatocytes of large yellow croaker and eicosapentaenoic acid (EPA) incubation significantly promoted hacd1 expression in primary hepatocytes of rainbow trout. Transcription factors STAT4, C/EBPα, C/EBPβ, HNF1, HSF3 and FOXP3 were identified in both large yellow croaker and rainbow trout. HNF1 had a stronger activation effect in rainbow trout than in large yellow croaker. FOXP3 inhibited hacd1 promoter activity in large yellow croaker but had no effect in rainbow trout. Therefore, the differences between HNF1 and FOXP3 affected the expression of hacd1 in the liver thus being responsible for the high capacity of LC-PUFA biosynthesis in rainbow trout.

A complete inventory of long-chain polyunsaturated fatty acid biosynthesis pathway enzymes in the miniaturized cyprinid Paedocypris micromegethes

The capacity for long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis activity in a species depends on the enzymatic activities of fatty acyl desaturase (Fads) and elongation of very long-chain fatty acid (Elovl). The miniaturized fish Paedocypris micromegethes is a developmentally truncated cyprinid living in highly acidic water conditions in tropical peat swamps. The capacity for LC-PUFA biosynthesis in this species, which has a reduced genome size, is unknown. A high-quality de novo transcriptome assembly enabled the identification of a putative Fads2 and four Elovl. The Fads2 was verified as a P. micromegethes Fads2 ortholog with in vitro Δ5 and Δ6 activities. The Elovl sequences were established as an Elovl5, Elovl2, and two Elovl4 paralogs, namely Elovl4a and Elovl4b. These Elovl enzymes, mainly Elovl5 and Elovl2, fulfill the necessary C18, C20, and C22 PUFA elongation steps for LC-PUFA biosynthesis. Collectively, these results validate the presence of a complete repertoire of LC-PUFA biosynthesis enzymes in a peat swamp miniatured freshwater fish.

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.

Genome-wide characterization of the Elovl gene family in Gymnocypris przewalskii and their potential roles in adaptation to cold temperature

The elongase of the very long-chain fatty acids (Elovls) gene family in fish has more diversity than in other vertebrates, which plays several critical roles in fatty acid synthesis and low-temperature stress adaptation. Gymnocypris przewalskii settles in plateau lakes with cold and resource-poor settings, and the evolution and function of Elovl genes in this fish are unknown. In the study, to identify the Elovl genes in G. przewalskii, the genome-wide identification and phylogenetic analysis of the gene members have been conducted with the expression profile of different tissues under cold stress. Fatty acid compositions, meanwhile, were detected in both the hepatopancreas and skeletal muscle during cold adaptation. A total of 21 Elovl members have been identified from the genome of G. przewalskii, belonging to Elovl1, Elovl2, Elovl4, Elovl5, Elovl6, Elovl7, and Elovl8 subgroups, with conserved ELO domain and four common motifs. Phylogenetic analysis revealed that subfamilies Elovl1 and Elovl7, Elov2, and Elovl5 have a closer genetic relationship, while the Elovl6 class was classed into an independent clade. Synteny analysis showed that whole-genome duplication, tandem duplicates, and gene conversion could drive the Elovls family expansion in G. przewalskii. The Ka/Ks and RELAX analysis showed distinguishing positive selection traces in ORF sequences of gpElovl2. Transcriptional data showed that different gpElovl subtypes exhibited a tissue-specific expression. Subtypes gpElovl1a, gpElovl2 and gpElovl6l were highly expressed induced by cold stress, as well as fatty acid metabolism-related genes, including Acyl-CoA synthetase long-chain gene (Ascl1a-1) and Stearyl-CoA desaturase gene (Scd1a-1). In addition, monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) contents of the hepatopancreas and skeletal muscle were significantly increased under 15-day cold stress. These results provide a better understanding of fish Elovl genes and their roles in cold adaptation.

Effect of Lemna minor supplemented diets on growth, digestive physiology and expression of fatty acids biosynthesis genes of Cyprinus carpio

The potential nutritional value of duckweed Lemna minor (Lemnaceae) was evaluated for common carp Cyprinus carpio fry. Fish were fed diets containing five graded levels of duckweed: 0% (LM0, control), 5% (LM5), 10% (LM10), 15% (LM15) and 20% (LM20). The final weight and specific growth rate were significantly higher in LM15 and LM20 diets fed fish compared to others. Feed conversion ratio was minimum in fish fed diet LM20. Amylase activity was significantly higher in LM0 treatment. Total protease, trypsin and chymotrypsin activities showed linear relationships with the increased level of duckweed in the diet. Protein and essential amino acids contents were significantly higher in carp fed diets LM15 and LM20 compared to others. Lipid content was significantly higher in fish fed duckweed-based diets compared to control. A direct relationship was found between the inclusion level of duckweed in the diet and n-3 long-chain polyunsaturated fatty acid (LC-PUFA) content of carp. Contents of desaturated and elongated products of dietary linolenic acid (18:3n-3) including 20:4n-3, 20:5n-3, 22:5n-3 and 22:6n-3 increased in a graded manner with increasing dietary duckweed. The monounsaturated fatty acids and n-6 PUFA contents reduced significantly in fish fed duckweed. Expression of fads2d6, elovl2, elovl5 and fas were higher in carp fed diets LM10, LM15 and LM20 compared to control fish. The inclusion of L. minor in diet enhanced the nutritional value of carp by increasing protein, lipid, amino acids and n-3 PUFA contents.

Environmental adaptation in fish induced changes in the regulatory region of fatty acid elongase gene, elovl5, involved in long-chain polyunsaturated fatty acid biosynthesis

Fish are the main source of long-chain polyunsaturated fatty acids (LC-PUFA) for human consumption. In the process of evolution via natural selection, adaptation to distinct environments has likely driven changes in the endogenous capacity for LC-PUFA biosynthesis between marine and freshwater fishes. However, the molecular mechanisms underlying adaptive changes in this metabolic pathway are poorly understood. Here, we compared the transcriptional regulation of elongation of very long chain fatty acids protein 5 (Elovl5), which is one of the critical enzymes in LC-PUFA biosynthesis pathway, in marine large yellow croaker (Larimichthys crocea) and freshwater rainbow trout (Oncorhynchus mykiss). Comparative transcriptomic and absolute mRNA quantification analyses revealed that the expression of elovl5 in rainbow trout was markedly higher than that in large yellow croaker. Correspondingly, the number of chromatin accessible areas in the regulatory region of elovl5 in rainbow trout was higher than in large yellow croaker, which revealed that chromatin accessibility in the regulatory region of elovl5 in rainbow trout was higher. Furthermore, the differences in sequence and activity of the elovl5 promoter were observed between rainbow trout and large yellow croaker, and transcription factors including CCAAT/enhancer-binding protein β (CEBPβ), GATA binding protein 3 (GATA3) and upstream stimulatory factor 2 (USF2) displayed different regulatory roles on elovl5 expression between the two species. We propose that changes in the gene regulatory region driven by natural selection likely play a key role in differences in elovl5 expression and the activity of Elovl5, which may influence the LC-PUFA biosynthesis capacities of rainbow trout and large yellow croaker. These findings may also provide opportunities to improve the quality of aquatic products and, consequently, human health.

Molecular Characterization, Tissue Distribution and Differential Nutritional Regulation of Three n-3 LC-PUFA Biosynthesis-Related Genes in Hybrid Grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

Elongases of very long-chain fatty acids (Elovls) and fatty acid desaturases (Fads) are crucial enzymes involved in the biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFAs). In this paper, we report the molecular cloning and characterization of three genes from the marine teleost Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂, and analyzed tissue distribution and their expression in response to dietary n-3 LC-PUFA levels after a 42-day feeding experiment. The elovl5, elovl8 and fads2 genes encoded 294, 263 and 445 amino acids, respectively, which exhibited all the characteristics of the Elovl and Fads family. Tissue distribution analysis revealed that elovl5, elovl8 and fads2 were widely transcribed in various tissues, with the highest level in the brain, as described in other carnivorous marine teleosts. The transcript levels of elovl5, elovl8 and fads2 in the liver were significantly affected by dietary n-3 LC-PUFA, and higher LC-PUFA levels repressed their expression. These results demonstrated, for the first time, the presence and nutritional modulation of elovl5, elovl8 and fads2 cDNA in the juvenile hybrid grouper. Further studies are needed to determine the functional characterization of these genes and explore the mechanism of these genes when regulated by dietary fatty lipid profiles in this species.

circ01592 regulates unsaturated fatty acid metabolism through adsorbing miR-218 in bovine mammary epithelial cells

The composition of fatty acids plays a key role in regulating milk flavor and quality. Therefore, to improve the quality of milk, it is particularly important to study the regulatory mechanism of fatty acid metabolism in dairy cows. In this study, the expression profiles at non-lactation, peak-lactation, mid-lactation and late-lactation were constructed by high-throughput sequencing. Considering non-lactation as the control group and the other points as the experimental groups, the differentially expressed genes were screened. ELOVL5 was significantly upregulated and was selected for subsequent analyses. Bioinformatics prediction, a dual-luciferase assay, qPCR analysis and western blot analysis were used for verification. The results showed that ELOVL5 was a downstream target gene of miR-218 that regulated milk fat metabolism. A dual-luciferase assay and expression level analysis showed that circ01592 can directly bind to miR-218 and that overexpression of circ01592 (pcDNA-circ01592) significantly reduced the expression of miR-218 and enhanced the expression of ELOVL5, the target gene of miR-218 in BMECs. A functional study of BMECs showed that circ01592 promoted the synthesis of TAG and increased the content of UFA. The function of miR-218 was opposite to that of circ01592. Overall, the data showed that circ01592 promoted TAG synthesis and fatty acid composition by binding miR-218, alleviating the inhibitory effect of miR-218 on ELOVL5 expression. These mechanisms provide a new research approach and theoretical basis for improving milk quality.

Composition of uterine milk and its changes with gestational period in red stingrays (Hemitrygon akajei)

Uterine milk is secreted in the uterus for embryo nutrition in several elasmobranch species and may contribute to rapid embryonic growth, but the details of its composition and its functions are poorly understood. In this study, to explore the roles of uterine milk for embryos, its components throughout the gestational period were analysed in detail. Uterine milk was collected from pregnant red stingrays (Hemitrygon akajei) in the early, middle and late gestational periods, respectively (n= 3 for each period). The crude composition, constituent proteins and fatty acids in the milk were analysed. The uterine milk was rich in proteins throughout the gestational period, whereas lipids dramatically increased in the middle period and reduced slightly towards the late period. Some proteins potentially associated with nutrition, cartilage growth and embryonic immunity were found. Several enzymes related to central metabolism were also detected. The constituent fatty acids in the middle and late periods were similar to those in the egg yolks of elasmobranchs, except for C18:2, which was rich only in the uterine milk. The most abundant fatty acid in the milk was C16:1, which could function as a lipokine to promote lipid metabolism in the embryo. This study's data suggest that uterine milk may be secreted in addition to the egg yolk in elasmobranchs to support rapid and healthy embryonic growth.

Expression of long-chain polyunsaturated fatty acids biosynthesis genes during the early life-cycle stages of the tropical gar Atractosteus tropicus

Long-chain (≥C₂₀) polyunsaturated fatty acids (LC-PUFA), including eicosapentaenoic acid (EPA, 20:5n-3), arachidonic acid (ARA, 20:4n-6) and docosahexaenoic acid (DHA, 22:6n-3), are essential in multiple physiological processes, especially during early development of vertebrates. LC-PUFA biosynthesis is achieved by two key families of enzymes, fatty acyl desaturases (Fads) and elongation of very long-chain fatty acid (Elovl). The present study determined the expression patterns of genes encoding desaturases (fads1 and fads2) and elongases (elovl2 and elovl5) involved in the LC-PUFA biosynthesis during early life-stages of the tropical gar Atractosteus tropicus. We further analyzed the fatty acid profiles during early development of A. tropicus to evaluate the impact of Fads and Elovl enzymatic activities. Specific oligonucleotides were designed from A. tropicus transcriptome to perform qPCR (quantitative polymerase chain reaction) on embryonic and larval stages, along with several organs (intestine, white muscle, brain, liver, heart, mesenteric adipose, kidney, gill, swim bladder, stomach, and spleen) collected from juvenile specimens. Fatty acid content of feeds and embryonic and larval stages were analyzed. Results show that fads1, fads2, elovl2 and elovl5 expression was detected from embryonic stages with expression peaks from day 15 post hatching, which could be related to transcriptional and dietary factors. Moreover, fads1, fads2 and elovl2 showed a higher expression in intestine, while elovl5 showed a higher expression in liver, suggesting that the tropical gar activates its LC-PUFA biosynthetic machinery to produce ARA, EPA and DHA to satisfy physiological demands at crucial developmental milestones during early development.

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.

Elovl2 But Not Elovl5 Is Essential for the Biosynthesis of Docosahexaenoic Acid (DHA) in Zebrafish: Insight from a Comparative Gene Knockout Study

Teleost fish can synthesize one of the major omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs), docosahexaenoic acid (DHA, 22:6n-3), from dietary α-linolenic acid (ALA; 18:3n-3), via elongase of very long-chain fatty acid (Elovl) and fatty acid desaturase (Fads). However, it remains unclear which elongase is primarily responsible for the endogenous synthesis of DHA. Here, in this study, the knockout models of the two major elongases, Elovl2 and Elovl5, were generated by CRISPR/Cas9 approach in zebrafish and comparatively analyzed. The homozygous mutants were validated by Sanger sequencing, mutation-mediated PCR, and whole-mount in situ hybridization analysis of the endogenous target genes. Compared with wild-type (WT) counterparts, the content of DHA was significantly reduced by 67.1% (P < 0.05) in the adult liver and by 91.7% (P < 0.01) in the embryo at 3-day post-fertilization (dpf) of the elovl2 mutant, but not of the elovl5 mutant. Further study revealed that elovl2 and fads2 was upregulated by 9.9-fold (P < 0.01) and 9.7-fold (P < 0.01) in the elovl5 mutant, and elovl5 and fads2 were upregulated by 15.1-fold (P < 0.01) and 21.5-fold (P < 0.01) in the elovl2 mutant. Our study indicates that although both Elovl2 and Elovl5 have the elongase activity toward C20, the upregulation of elovl2 could completely replace the genetic depletion of elovl5, but upregulation of elovl5 could not compensate the endogenous deficiency of elovl2 in mediating DHA synthesis. In conclusion, the endogenous synthesis of DHA in is mediated by Elovl2 but not Elovl5 in zebrafish and a DHA-deficient genetic model of zebrafish has been generated.

Flatfishes colonised freshwater environments by acquisition of various DHA biosynthetic pathways

The colonisation of freshwater environments by marine fishes has historically been considered a result of adaptation to low osmolality. However, most marine fishes cannot synthesise the physiologically indispensable fatty acid, docosahexaenoic acid (DHA), due to incomplete DHA biosynthetic pathways, which must be adapted to survive in freshwater environments where DHA is poor relative to marine environments. By analysing DHA biosynthetic pathways of one marine and three freshwater-dependent species from the flatfish family Achiridae, we revealed that functions of fatty acid metabolising enzymes have uniquely and independently evolved by multi-functionalisation or neofunctionalisation in each freshwater species, such that every functional combination of the enzymes has converged to generate complete and functional DHA biosynthetic pathways. Our results demonstrate the elaborate patchwork of fatty acid metabolism and the importance of acquiring DHA biosynthetic function in order for fish to cross the nutritional barrier at the mouth of rivers and colonise freshwater environments.

Matsushita et al. demonstrate the evolution of DHA biosynthetic mechanisms in four species of flatfish as some of them colonised freshwater environments. Their analyses show independent changes to the biosynthetic pathways as a way to overcome the lack of exogenous DHA that would typically be available from prey in the marine environment.

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.

Functional characterisation of fatty acyl desaturase, Fads2, and elongase, Elovl5, in the Boddart's goggle-eyed goby Boleophthalmus boddarti (Gobiidae) suggests an incapacity for long-chain polyunsaturated fatty acid biosynthesis

The biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFA), a process to convert C18 polyunsaturated fatty acids into eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) or arachidonic acid (ARA), requires the concerted activities of two enzymes, the fatty acyl desaturase (Fads) and elongase (Elovl). This study highlights the cloning, functional characterisation and tissue expression pattern of a Fads and an Elovl from the Boddart's goggle-eyed goby (Boleophthalmus boddarti), a mudskipper species widely distributed in the Indo-Pacific region. Phylogenetic analysis revealed that the cloned fads and elovl are clustered with other teleost orthologs, respectively. The investigation of the genome of several mudskipper species, namely Boleophthalmus pectinirostris, Periophthalmus schlosseri and Periophthalmus magnuspinnatus, revealed a single Fads2 and two elongases, Elovl5 and Elovl4 for each respective species. A heterologous yeast assay indicated that the B. boddarti Fads2 possessed low desaturation activity on C18 PUFA and no desaturation on C20 and C22 PUFA substrates. In comparison, the Elovl5 showed a wide range of substrate specificity, with a capacity to elongate C18, C20 and C22 PUFA substrates. An amino acid residue that affects the capacity to elongate C22:5n-3 was identified in the B. boddarti Elovl5. Both genes are highly expressed in brain tissue. Among all tissues, DHA is highly concentrated in neuron-rich tissues, whereas EPA is highly deposited in gills. Taken together, the results showed that due to the inability to perform desaturation steps, B. boddarti is unable to biosynthesise LC-PUFA, relying on dietary intake to acquire these nutrients.

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.

A comparative metabolomics study on anadromous clupeid Tenualosa ilisha for better understanding the influence of habitat on nutritional composition

INTRODUCTION

Fish inhabiting different aquatic habitats adapts to the environment by metabolomic readjustments. Understanding the combined activities of all the metabolic pathways (metabolome) helps in better understanding the complex interactions between gene and environment.

OBJECTIVES

The anadromous migratory Tenualosa ilisha is a high value food fish comprising the dominant fishery of the rivers Padma and Hooghly. The present study aimed at understanding the influence of the two habitats on the nutritional composition of hilsa.

METHODS

Metabolite profiling was carried out by GC/MS. De novo assembly of hilsa liver transcriptome was generated under Illumina HiSeq platform and multivariate analysis was employed for correlation and comparison.

RESULTS

GC/MS fingerprinting showed C16:0, C18:1, C20:5 and C22:6 to be the predominant fatty acids present in hilsa liver, which were also found to be significantly higher in Hooghly hilsa. Comparative transcriptome analysis revealed that the differentially expressed genes were mainly associated with 'lipid metabolism' and 'amino acid metabolism' pathways. Multivariate analysis between the metabolites amino acid, fatty acid and corresponding gene expression showed that few genes of amino acid metabolism (EZH1, ALAS2 and ALDH4A1) positively correlated with individual amino acids (lysine, glycine and glutamate) in Hooghly hilsa. Similarly, the key genes for LC-PUFA biosynthesis (ELOVL5, FADS2, CPT1) showed positive correlation with individual LC-PUFAs (C18:3, C20:4, C20:5, C22:6), indicating higher LC-PUFA biosynthesis potential in Hooghly hilsa.

CONCLUSION

Comparative metabolomic study in hilsa from the two different habitats showed that the habitats influence the nutritional composition as evidenced by high abundance of amino acids lysine, leucine and arginine and LC-PUFAs C18:3, C20:4, C20:5, C22:6 in Hooghly hilsa.

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.

Molecular cloning and 3D model of a fatty-acid elongase in a carnivorous freshwater teleost, the European perch (Perca fluviatilis)

The European perch (Perca fluviatilis) is a carnivorous freshwater fish able to metabolise polyunsaturated fatty acids (PUFA) into highly unsaturated fatty acids (HUFA). This makes it a potential candidate for sustainable aquaculture development. In this study, special attention is given to the fatty-acid elongase (ELOVL) family, one of the two enzymatic systems implied in the HUFA biosynthesis. Structural information on European perch enzyme converting PUFA into HUFA is obtained by both molecular cloning and in silico characterization of an ELOVL5-like elongase from P. fluviatilis (pfELOVL). The full-length cDNA sequence consists of a 885-base pair Open Reading Frame coding for a 294-amino acid protein. Phylogenetic analysis and sequence alignment with fish elongases predict the pfELOVL clusters within the ELOVL5 sub-group. The amino-acid sequence displays the typical ELOVL features: several transmembrane α helices (TMH), an endoplasmic reticulum (ER) retention signal, and four "conserved boxes" involved in the catalytic site. In addition, the topology analysis predicts a 7-TMH structure addressed in the ER membrane. A 3D model of the protein embedded in an ER-like membrane environment is also provided using de novo modelling and molecular dynamics. From docking studies, two putative enzyme-substrate-binding modes, including H bonds and CH-π interactions, emphasize the role of specific residues in the "conserved boxes".

Genome-wide characterization and expression of the elongation of very long chain fatty acid (Elovl) genes and fatty acid profiles in the alga (Tetraselmis suecica) fed marine rotifer Brachionus koreanus

To understand the lipid metabolism in invertebrate species, identification of the fatty acid (FA) synthesis gene families in invertebrate species is important, since some FA are unable to be synthesized in the organisms by themselves. In the study, to identify the elongation of very long chain fatty acid (Elovl) genes in the marine rotifer Brachionus koreanus, the genome-wide identification and phylogenetic analysis of Elovl genes have been conducted with the expression profile of Elovl genes on the alga Tetraslemis suecica-fed B. koreanus. A total 10 Elovl genes have been identified from the genome of B. koreanus, with conserved HXXHH motif. Synteny analysis showed that tandem duplication event has occurred (Elovl3/6a and b, Elovl9a and b, and Elovl9c and d) in the ancestor. Phylogenetic analysis have clearly revealed that Brachionus spp. has only 2/5 and 3/6 subfamilies, and two novel Elovl classes have been revealed, namely Elovl9 and 10. Transcriptional data showed that the 10 Elovl genes were differently expressed and their expression could be regulated by feeding the alga T. suecica. From fatty acid (FA) profile data of the alga Tetraslemis suecica-fed B. koreanus, we revealed that the marine rotifer B. koreanus may synthesize very long chain fatty acid (VLCFA; >22 carbons) by themselves, as VLCFA was hardly detected in the alga T. suecica. The study provides a better understanding of FA metabolism of the marine rotifer B. koreanus after feeding the T. suecica.

Retention of fatty acyl desaturase 1 (fads1) in Elopomorpha and Cyclostomata provides novel insights into the evolution of long-chain polyunsaturated fatty acid biosynthesis in vertebrates

Background

Provision of long-chain polyunsaturated fatty acids (LC-PUFA) in vertebrates occurs through the diet or via endogenous production from C₁₈ precursors through consecutive elongations and desaturations. It has been postulated that the abundance of LC-PUFA in the marine environment has remarkably modulated the gene complement and function of Fads in marine teleosts. In vertebrates two fatty acyl desaturases, namely Fads1 and Fads2, encode ∆5 and ∆6 desaturases, respectively. To fully clarify the evolutionary history of LC-PUFA biosynthesis in vertebrates, we investigated the gene repertoire and function of Fads from species placed at key evolutionary nodes.

Results

We demonstrate that functional Fads1Δ5 and Fads2∆6 arose from a tandem gene duplication in the ancestor of vertebrates, since they are present in the Arctic lamprey. Additionally, we show that a similar condition was retained in ray-finned fish such as the Senegal bichir and spotted gar, with the identification of fads1 genes in these lineages. Functional characterisation of the isolated desaturases reveals the first case of a Fads1 enzyme with ∆5 desaturase activity in the Teleostei lineage, the Elopomorpha. In contrast, in Osteoglossomorpha genomes, while no fads1 was identified, two separate fads2 duplicates with ∆6 and ∆5 desaturase activities respectively were uncovered.

Conclusions

We conclude that, while the essential genetic components involved LC-PUFA biosynthesis evolved in the vertebrate ancestor, the full completion of the LC-PUFA biosynthesis pathway arose uniquely in gnathostomes.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1271-5) contains supplementary material, which is available to authorized users.

"Out of the Can": A Draft Genome Assembly, Liver Transcriptome, and Nutrigenomics of the European Sardine, Sardina pilchardus

Clupeiformes, such as sardines and herrings, represent an important share of worldwide fisheries. Among those, the European sardine (Sardina pilchardus, Walbaum 1792) exhibits significant commercial relevance. While the last decade showed a steady and sharp decline in capture levels, recent advances in culture husbandry represent promising research avenues. Yet, the complete absence of genomic resources from sardine imposes a severe bottleneck to understand its physiological and ecological requirements. We generated 69 Gbp of paired-end reads using Illumina HiSeq X Ten and assembled a draft genome assembly with an N50 scaffold length of 25,579 bp and BUSCO completeness of 82.1% (Actinopterygii). The estimated size of the genome ranges between 655 and 850 Mb. Additionally, we generated a relatively high-level liver transcriptome. To deliver a proof of principle of the value of this dataset, we established the presence and function of enzymes (Elovl2, Elovl5, and Fads2) that have pivotal roles in the biosynthesis of long chain polyunsaturated fatty acids, essential nutrients particularly abundant in oily fish such as sardines. Our study provides the first omics dataset from a valuable economic marine teleost species, the European sardine, representing an essential resource for their effective conservation, management, and sustainable exploitation.

Insights into the phylogenetic and molecular evolutionary histories of Fad and Elovl gene families in Actiniaria

The biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFAs, ≥ C20) is reliant on the action of desaturase and elongase enzymes, which are encoded by the fatty acyl desaturase (Fad) and elongation of very long-chain fatty acid (Elovl) gene families, respectively. In Metazoa, research investigating the distribution and evolution of these gene families has been restricted largely to Bilateria. Here, we provide insights into the phylogenetic and molecular evolutionary histories of the Fad and Elovl gene families in Cnidaria, the sister phylum to Bilateria. Four model cnidarian genomes and six actiniarian transcriptomes were interrogated. Analysis of the fatty acid composition of a candidate cnidarian species, Actinia tenebrosa, was performed to determine the baseline profile of this species. Phylogenetic analysis revealed lineage-specific gene duplication in actiniarians for both the Fad and Elovl gene families. Two distinct cnidarian Fad clades clustered with functionally characterized Δ5 and Δ6 proteins from fungal and plant species, respectively. Alternatively, only a single cnidarian Elovl clade clustered with functionally characterized Elovl proteins (Elovl4), while two additional clades were identified, one actiniarian-specific (Novel ElovlA) and the another cnidarian-specific (Novel ElovlB). In actiniarians, selection analyses revealed pervasive purifying selection acting on both gene families. However, codons in the Elovl gene family show patterns of nucleotide variation consistent with the action of episodic diversifying selection following gene duplication events. Significantly, these codons may encode amino acid residues that are functionally important for Elovl proteins to target and elongate different precursor fatty acids. In A. tenebrosa, the fatty acid analysis revealed an absence of LC-PUFAs > C20 molecules and implies that the Elovl enzymes are not actively contributing to the elongation of these LC-PUFAs. Overall, this study has revealed that actiniarians possess Fad and Elovl genes required for the biosynthesis of some LC-PUFAs, and that these genes appear to be distinct from bilaterians.

Elongation of very Long-Chain (>C24) Fatty Acids in Clarias gariepinus: Cloning, Functional Characterization and Tissue Expression of elovl4 Elongases

Elongation of very long-chain fatty acid 4 (Elovl4) proteins participate in the biosynthesis of very long-chain (>C₂₄) saturated and polyunsaturated fatty acids (FA). Previous studies have shown that fish possess two different forms of Elovl4, termed Elovl4a and Elovl4b. The present study aimed to characterize both molecularly and functionally two elovl4 cDNA from the African catfish Clarias gariepinus. The results confirmed that C. gariepinus possessed two elovl4-like elongases with high homology to two previously characterized Elovl4 from Danio rerio, and thus they were termed accordingly as Elovl4a and Elovl4b. The C. gariepinus Elovl4a and Elovl4b have open reading frames (ORF) of 945 and 915 base pairs, respectively, encoding putative proteins of 314 and 304 amino acids, respectively. Functional characterization in yeast showed both Elovl4 enzymes have activity towards all the PUFA substrates assayed (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, the C. gariepinus Elovl4a and Elovl4b were able to elongate very long-chain saturated FA (VLC-SFA) as denoted by increased levels of 28:0 and longer FA in yeast transformed with elovl4 ORF compared to control yeast. These results confirmed that C. gariepinus Elovl4 play important roles in the biosynthesis of very long-chain FA. Tissue distribution analysis of elovl4 mRNAs showed both genes were widely expressed in all tissues analyzed, with high expression of elovl4a in pituitary and brain, whereas female gonad and pituitary had the highest expression levels for elovl4b.

Functional characterization and differential nutritional regulation of putative Elovl5 and Elovl4 elongases in large yellow croaker (Larimichthys crocea)

In the present study, two elongases, Elovl4 and Elovl5, were functionally characterized and their transcriptional regulation in response to n-3 LC-PUFA administration were investigated in vivo and in vitro. We previously described the molecular characterization of croaker elovl5. Here, we report the full-length cDNA sequence of croaker elovl4, which contained 1794 bp (excluding the polyA tail), including 909 bp of coding region that encoded a polypeptide of 302 amino acids possessing all the characteristic features of Elovl proteins. Functional studies showed that croaker Elovl5, displayed high elongation activity towards C₁₈ and C₂₀ PUFA, with only low activity towards C₂₂ PUFA. In contrast, croaker Elovl4 could effectively convert both C₂₀ and C₂₂ PUFA to longer polyenoic products up to C₃₄. n-3 LC-PUFA suppressed transcription of the two elongase genes, as well as srebp-1 and lxrα, major regulators of hepatic lipid metabolism. The results of dual-luciferase reporter assays and in vitro studies both indicated that the transcriptions of elovl5 and elovl4 elongases could be regulated by Lxrα. Moreover, Lxrα could mediate the transcription of elovl4 directly or indirectly through regulating the transcription of srebp-1. The above findings contribute further insight and understanding of the mechanisms regulating LC-PUFA biosynthesis in marine fish species.

Biosynthesis of Polyunsaturated Fatty Acids in Octopus vulgaris: Molecular Cloning and Functional Characterisation of a Stearoyl-CoA Desaturase and an Elongation of Very Long-Chain Fatty Acid 4 Protein

Polyunsaturated fatty acids (PUFAs) have been acknowledged as essential nutrients for cephalopods but the specific PUFAs that satisfy the physiological requirements are unknown. To expand our previous investigations on characterisation of desaturases and elongases involved in the biosynthesis of PUFAs and hence determine the dietary PUFA requirements in cephalopods, this study aimed to investigate the roles that a stearoyl-CoA desaturase (Scd) and an elongation of very long-chain fatty acid 4 (Elovl4) protein play in the biosynthesis of essential fatty acids (FAs). Our results confirmed the Octopus vulgaris Scd is a ∆9 desaturase with relatively high affinity towards saturated FAs with ≥ C₁₈ chain lengths. Scd was unable to desaturate 20:1n-15 (^∆520:1) suggesting that its role in the biosynthesis of non-methylene interrupted FAs (NMI FAs) is limited to the introduction of the first unsaturation at ∆9 position. Interestingly, the previously characterised ∆5 fatty acyl desaturase was indeed able to convert 20:1n-9 (^∆1120:1) to ^∆5,1120:2, an NMI FA previously detected in octopus nephridium. Additionally, Elovl4 was able to mediate the production of 24:5n-3 and thus can contribute to docosahexaenoic acid (DHA) biosynthesis through the Sprecher pathway. Moreover, the octopus Elovl4 was confirmed to play a key role in the biosynthesis of very long-chain (>C₂₄) PUFAs.