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

Endogenous LC-PUFA biosynthetic capability in dwarf surf clam Mulinia lateralis: characterization and functional analysis of fatty acyl elongases and a desaturase

Elongases of very long-chain fatty acids (Elovls) and fatty acyl desaturases (Fads) are two key enzymes in the biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFAs). Here, we identified and characterized five Elovl genes (MulElovl2/5, MulElovl4, MulElovlc, MulElovl7a, and MulElovl7b) from the genome of Mulinia lateralis, a potential model bivalve. Expression analysis revealed that MulElovl2/5, MulElovl4 and MulElovlc were highly expressed during the middle stage of embryonic development, whereas MulElovl7a and MulElovl7b peaked in mid-to-late development before declining. Tissue-specific expression showed that MulElovl2/5 and MulElovl4 were predominantly expressed in the digestive gland. Additionally, we examined the effects of dietary LC-PUFA composition on MulElovls expression by feeding M. lateralis two unialgal diets: Chlorella pyrenoidosa (Cp), rich in linoleic acid (LA, C18:2n-6) and α-linolenic acid (ALA, C18:3n-3), and Platymonas helgolandica (Ph), rich in eicosapentaenoic acid (EPA, C20:5n-3). Notably, MulElovls were significantly upregulated in most tissues of the Cp group, suggesting a compensatory mechanism under LC-PUFA-deficient conditions. Functional assays revealed distinct substrate specificities: MulElovl2/5 elongated C18 and C20 PUFAs, while MulElovl4 and MulElovlc efficiently converted C20 to C22 PUFAs. Additionally, MulFadsB exhibited Δ6 desaturase activity, enabling the conversion of C18 PUFAs. These findings demonstrate that M. lateralis possesses endogenous biosynthetic pathways for arachidonic acid (ARA) from LA via Δ6 desaturation, elongation, and Δ5 desaturation, as well as partial elongation of EPA to C22:5n-3. Our findings provide new insights into a comparison of endogenous LC-PUFAs synthetic capabilities in mollusks and highlight M. lateralis as a valuable model for investigating lipid metabolism in marine bivalves.

Omega-3 polyunsaturated fatty acids in the brain and visual system: Focus on invertebrates

A critical role of omega-3 polyunsaturated fatty acids (PUFA), mainly docosahexaenoic acid 22:6ω3 (DHA), in the development and function of the brain and visual system is well established. DHA, the most abundant omega-3 PUFA in the vertebrate brain, contributes to neuro- and synaptogenesis, neuronal differentiation, synaptic transmission and plasticity, neuronal network formation, memory and behaviour formation. Based on these data, the unique importance of DHA and its irreplaceability in neural and retinal tissues has been postulated. In this review, we consider omega-3 PUFA composition in the brain and retina of various invertebrates, and show that DHA has only been found in marine mollusks and crustaceans. A gradual decrease in the DHA content until its disappearance can be observed in the brain lipids of the series marine-freshwater-terrestrial crustaceans and marine-terrestrial mollusks, suggesting that the transition to the land lifestyle in the evolution of invertebrates, but not vertebrates, was accompanied by a loss of DHA. As with terrestrial crustaceans and mollusks, DHA was not found in insects, either terrestrial or aquatic, or in nematodes. We show that the nervous and visual systems of various DHA-free invertebrates can be highly enriched in alpha-linolenic acid 18:3ω3 or eicosapentaenoic acid 20:5ω3, which affect neurological and visual function, stimulating synaptogenesis, synaptic transmission, visual processing, learning and even cognition. The review data show that, in animals at different levels of organization, omega-3 PUFA are required for the functioning of the nervous and visual systems and that their specific needs can be met by various omega-3 PUFA.

FoodAtlas: Automated knowledge extraction of food and chemicals from literature

Automated generation of knowledge graphs that accurately capture published information can help with knowledge organization and access, which have the potential to accelerate discovery and innovation. Here, we present an integrated pipeline to construct a large-scale knowledge graph using large language models in an active learning setting. We apply our pipeline to the association of raw food, ingredients, and chemicals, a domain that lacks such knowledge resources. By using an iterative active learning approach of 4120 manually curated premise-hypothesis pairs as training data for ten consecutive cycles, the entailment model extracted 230,848 food-chemical composition relationships from 155,260 scientific papers, with 106,082 (46.0 %) of them never been reported in any published database. To augment the knowledge incorporated in the knowledge graph, we further incorporated information from 5 external databases and ontology sources. We then applied a link prediction model to identify putative food-chemical relationships that were not part of the constructed knowledge graph. Validation of the 443 hypotheses generated by the link prediction model resulted in 355 new food-chemical relationships, while results show that the model score correlates well (R2 = 0.70) with the probability of a novel finding. This work demonstrates how automated learning from literature at scale can accelerate discovery and support practical applications through reproducible, evidence-based capture of latent interactions of diverse entities, such as food and chemicals.

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.

Sensing and regulation of long-chain polyunsaturated fatty acids pool in marine mollusks: Characterization of UBXD8 from the razor clam Sinonovacula constricta

The razor clam Sinonovacula constricta is known for its richness in long-chain polyunsaturated fatty acids (LC-PUFA, C ≥ 20). Previously, we demonstrated that it possesses a complete LC-PUFA biosynthetic pathway. However, the mechanisms by which it senses the LC-PUFA pool to regulate their biosynthesis remain unclear. Here, we presented the LC-PUFA sensor UBXD8 as a critical molecule in this intriguing process. The S. constricta UBXD8 (ScUBXD8) shared all characteristic features of its mammalian counterpart and exhibited high mRNA levels in digestive tissues, suggesting its functional role in this bivalve species. By purification of ScUBXD8 protein in vitro, we discovered its ability to sense unsaturated fatty acids (UFA, C ≥ 14) but not saturated ones, as evidenced by polymerization detection. Furthermore, the intensity of ScUBXD8 polymerization increased progressively with longer acyl chain lengths, greater unsaturation degrees, and higher UFA concentrations. Exceptionally, for those located at the same node in LC-PUFA biosynthetic pathway, ScUBXD8 displayed a stronger sensitivity to n-6 UFA compared to n-3 UFA. These results suggested a critical role for ScUBXD8 in balancing fatty acids composition and ratio of n-6/n-3 UFA in S. constricta. Moreover, the UAS domain was confirmed essential for ScUBXD8 polymerization. Through knockdown of ScUbxd8 gene in vivo, there were significant shifts in expression patterns of genes related to LC-PUFA biosynthesis, concurrently influencing fatty acids compositions. These results suggested that ScUBXD8 likely plays a regulatory role in LC-PUFA biosynthesis, possibly through the INSIG-SREBP pathway. Collectively, this study proposed that S. constricta might maintain LC-PUFA homeostasis through UBXD8 to regulate their biosynthesis.

Long-chain polyunsaturated fatty acid biosynthesis in a land-crab with advanced terrestrial adaptations: Molecular cloning and functional characterization of two fatty acyl elongases

Depending on the presence and activities of the front-end fatty acyl desaturases and elongation of very long-chain fatty acid (Elovl) enzymes, animals have different capacities for long-chain (≥C₂₀) polyunsaturated fatty acids (LC-PUFA) biosynthesis. Successful land colonisation in brachyuran crabs requires a shift towards terrestrial food chain with limited LC-PUFA availability. We cloned and functionally characterised two elovl genes from the purple land crab Gecarcoidea lalandii. The two Elovl contained all the necessary motifs of a typical polyunsaturated fatty acids (PUFA) Elovl and phylogenetically clustered in the Elovl1 and Elovl6 clades, respectively. The G. lalandii Elovl1 elongated saturated fatty acids, with low activities towards C20 and C22 PUFA substrates. Moreover, the G. lalandii Elovl6 was particularly active in the elongation of C18 PUFA, although it also recognised monounsaturated fatty acids as substrates for elongation. Collectively, the herein characterised G. lalandii elovl paralogues fulfil all the elongation steps involved in the LC-PUFA biosynthetic pathways. Tissue distribution of the G. lalandii elovl genes, along with the FA composition analyses, suggest the hepatopancreas and gill as key metabolic sites for fatty acid elongation. However, current data suggest that G. lalandii is unable to rely solely on biosynthesis to fulfil LC-PUFA requirements, since front-end desaturase appears to be absent in this species and other decapods.

The features of the fatty acid composition of Pyrus L. total lipids are determined by mountain ecosystem conditions

The composition of fatty acids (FAs) of total lipids of pericarp, seeds, and leaves of Pyrus caucasica Fed. and Pyrus communis L. growing in mountain ecosystems at different altitudes (300, 700 and 1200 m) was studied. It was found that the greatest differences in the relative content of FAs within a species, depending on the altitudes above sea level, were characteristic of the outer tissues of the pericarp (peel) and leaves, which were in direct contact with the external environment. Pericarp parenchyma to a lesser extent, and seeds practically did not differ in FA composition at different heights. At altitudes with increased UV radiation, conjugated octadecadienoates: rumenic acid (9,11-18:2) and 10,12-18:2 were registered in the pericarp and leaf of Purys L., the functions of which in plants were practically not studied. The wild P. caucasica at all growing altitudes was characterized by more very-long-chain FAs (VLCFAs) than the P. communis cultivar. At 700 m, most likely when exposed to fungal infections, the relative number of VLCFAs increased significantly, and new species of individual odd-chaine FAs appeared in their composition in both representatives. It was especially worth noting the appearance in peel and leaf melissic acid (30:0), which was rarely recorded in the plant. A characteristic feature of only P. communis at an altitude of 700 m was the large number of unsaturated individual VLCFAs. Based on the data obtained, a scheme of possible pathways for VLCFA biosynthesis in P. communis were proposed.

Molecular and functional characterization of a SCD 1b from European sea bass (Dicentrarchus labrax L.)

Fatty acid desaturation is a highly complex and regulated process involving different molecular and genetic actors. Ultimally, the fatty acid desaturase enzymes are responsible for the introduction of double bonds at different positions of specific substrates, resulting in a wide variety of mono- and poly-unsaturated fatty acids. This substrate-specificity makes it possible to meet all the functional needs of the different tissues against a wide variety of internal and external conditions, giving rise to a varied profile of expression and functionality of the different desaturases in the body. Being our main interest to study and characterize at the molecular level the fatty acid desaturation process in fishes, we have focused our effort on characterizing SCD 1b from European sea bass (Dicentrarchus labrax, L.). In this work, we have characterized a tearoyl-CoA Desaturase cDNA that codes a protein of 334 amino acids, which shares the greatest homology to marine fish SCD 1b. Northern blot analysis showed two transcripts of 3.5 kb and 1.4 kb. Two putative cis-acting conserved motifs are localized in the cDNA 5'-end: a polypyrimidine CT dinucleotide repeat tract and two non-palindromic putative NRL-response elements (NREs). The deduced protein presents two Δ9 FADs like domain, three His-rich motifs, a total of nine His residues acting as di‑iron coordination ligands. The SCD 1b 3D protein modelling shows a structure made up primarily of α-helices, four of which could be transmembrane helices. The catalytic region is oriented to the cytosolic side of the Endoplasmic Reticulum membrane, where the 9-histidine residues are arranged coordinated to two non-heme Fe²⁺ ions. A new His-containing motif NX₃H-like includes an Asn residue that participates in the coordination of Fe²⁺1 through a water molecule. The protein has a large pocket with a large opening to the outside. It includes a tunnel in which the substrate-binding site is located. The external shape is reminiscent of a boathook. It shows group specificity, although a greater preference for 18C substrates. The length of the tunnel, delimited by seven amino acids that forms a pocket at the end of the tunnel, the possibility that the substrates adopt different conformations inside the tunnel as well as and the movement of acyl chain inside the tunnel, could explain the high preference for 18C fatty acids and the group specificity of the enzyme. The cDNA encodes a functional SCD enzyme, whose subcellular localization is the Endoplasmic Reticulum, which complements the ole1Δ gene-disrupted gene in DTY-11A Saccharomyces cerevisiae strain and produces an increment of palmitoleic and oleic acids. The scd 1b gene is expressed in all tested tissues, showing the liver and adipose tissue a higher level of expression against the brain, heart, gonad and intestine. Scd 1b expression was always bigger than those of the Δ6 fad gene, being especially significant in adipose tissue and liver. From our data, we conclude that, in contrast to the functional significance of SCD 1b in adipose tissue, liver and heart, Δ6 FAD seems to play a more determining role in the biosynthesis of unsaturated fatty acids in the intestine, brain and gonad in fish.

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.

Endogenous LC-PUFA biosynthesis capability in commercially important mollusks

Mollusks are excellent dietary sources for LC-PUFA. However, the main challenge limiting mollusk production is the high mortality rate of molluskan larvae in early life cycle stages. This paper reviews scientific evidences on molecular and biochemical studies of LC-PUFA biosynthesis in commercially important molluskan species. It carefully summarizes the pertinent data published on specific research questions to improve the understanding of the diverse evidences. It is helpful to clarify the current state of research and determine topics for future studies on LC-PUFA biosynthesis in mollusks. From the analysis of published data, mollusks have the ability to biosynthesis LC-PUFA to a certain extent. LC-PUFA biosynthesis information of commercially important molluskan species can be useful to determine the fatty acids essential for their diet. Therefore, specific management strategies or feeds can be developed to strengthen the industry by improving the health and survival rate of molluskan larvae.

An improved genome assembly and annotation of the Antarctic copepod Tigriopus kingsejongensis and comparison of fatty acid metabolism between T. kingsejongensis and the temperate copepod T. japonicus

Copepods in the genus Tigriopus are widely distributed in the intertidal zone worldwide. To assess differences in fatty acid (FA) metabolism among congeneric species in this genus inhabiting polar and temperate environments, we analyzed and compared FA profiles of the Antarctic copepod Tigriopus kingsejongensis and the temperate copepod T. japonicus. Higher amounts of total FAs were found in the Antarctic copepod T. kingsejongensis than the temperate copepod T. japonicus under administration of the identical amount of Tetraselmis suecica. To determine the genomic basis for this, we identified fatty acid metabolism-related genes in an improved genome of T. kingsejongensis. The total length of the assembled genome was approximately 338 Mb with N50 = 1.473 Mb, 938 scaffolds, and a complete Benchmarking Universal Single-Copy Orthologs value of 95.8%. A total of 25,470 genes were annotated using newly established pipeline. We identified eight elongation of very long-chain fatty acid protein (Elovl) genes and nine fatty acid desaturase (Fad) genes in the genome of T. kingsejongensis. In addition, fatty acid profiling suggested that the duplicated Δ5/6 desaturase gene in T. kingsejongensis is likely to play an essential role in synthesis of different FAs in T. kingsejongensis to those in T. japonicus. However, further experimental research is required to validate our in silico findings. This study provides a better understanding of fatty acid metabolism in the Antarctic copepod T. kingsejongensis.

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.

Two Elongases, Elovl4 and Elovl6, Fulfill the Elongation Routes of the LC-PUFA Biosynthesis Pathway in the Orange Mud Crab (Scylla olivacea)

While the capacity for long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis has been elucidated in vertebrates and several invertebrate phyla, the comparative knowledge in crustaceans remains vague. A key obstacle in mapping the full spectrum of LC-PUFA biosynthesis in crustacean is the limited evidence of the functional activities of enzymes involved in desaturation or elongation of polyunsaturated fatty acid substrates. In this present study, we report on the cloning and functional characterization of two Elovl elongases from the orange mud crab, Scylla olivacea. Sequence and phylogenetic analysis suggest these two Elovl as putative Elovl4 and Elovl6, respectively. Using the recombinant expression system in Saccharomyces cerevisiae, we demonstrate the elongation capacity for C18-C22 PUFA substrates in the S. olivacea Elovl4. The S. olivacea Elovl6 elongated saturated fatty acids, monounsaturated fatty acids, and interestingly, C18-C20 PUFA. Taken together, both Elovl fulfill the elongation steps required for conversion of C18 PUFA to their respective LC-PUFA products. Elovl4 is expressed mainly in the hepatopancreas and gill tissues, while Elovl6 is predominant in digestive tissues. The mRNA expression of both enzymes was higher in mud crabs fed with vegetable oil-based diets. Tissue fatty acid composition also showed the existence of LC-PUFA biosynthesis intermediate products in tissues expressing these two elongases. In summary, we report here two novel Elovl with PUFA elongating activities in a marine brachyuran. This will contribute significantly to the understanding of the LC-PUFA biosynthesis pathway in crustaceans and advance the development of aquafeed for intensive farming of the mud crab.

Cadmium transcriptionally regulates Scd1 expression in silver pomfret

Cadmium (Cd) is one of the major contaminants in aquatic ecosystem. Stearoyl-coenzyme A desaturase 1 (Scd1) has been implicated in adaptive responses to environmental stressors. The objectives of this study are (a) to characterize scd1 mRNA from silver pomfret (Pampus argenteus); (b) to investigate the expression and activity of Scd1 in silver pomfret exposed to Cd; and (c) to investigate how Cd modifies scd1 gene transcription in silver pomfret. Results indicated that Scd1 was generally conserved across fish species and scd1 mRNA level was higher by far in the brain and liver, followed by the kidney and intestine. Exposure to Cd led to significant changes of the expression and activity of Scd1 in in the liver and intestine. The liver mRNA abundance of scd1 was significantly lower in the Cd-treated groups than in the control group. The 10 days treatment with 1 mg/L Cd significantly upregulated the intestinal scd1 mRNA level, an approximately 9-fold higher in the 1 mg/L Cd-treated group as compared with the control group. Accordingly, Scd1 activity indices (18:1n-9/18:0) in the liver were significantly decreased in the 0.5 mg/L group compared with the control group, while Scd1 activity indices in the intestine were significantly increased in the 1 mg/L group compared with the control group. Moreover, overexpression of sterol regulatory element binding transcription factor 1 (Srebp1) and peroxisome proliferator-activated receptor γ (Pparγ )in HEK 293T cells produced a 2-fold increment in the activity of the scd1 promoter. Furthermore, srebp1 had a similar expression pattern to scd1 in the liver and intestine of silver pomfret exposed to Cd. These results indicated that Cd could regulate scd1 expression, possibly through the transcriptional factor Srebp1.

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.

Methyl-end desaturases with ∆12 and ω3 regioselectivities enable the de novo PUFA biosynthesis in the cephalopod Octopus vulgaris

The interest in understanding the capacity of aquatic invertebrates to biosynthesise omega-3 (ω3) long-chain (≥C₂₀) polyunsaturated fatty acids (LC-PUFA) has increased in recent years. Using the common octopus Octopus vulgaris as a model species, we previously characterised a ∆5 desaturase and two elongases (i.e. Elovl2/5 and Elovl4) involved in the biosynthesis of LC-PUFA in molluscs. The aim of this study was to characterise both molecularly and functionally, two methyl-end (or ωx) desaturases that have been long regarded to be absent in most animals. O. vulgaris possess two ωx desaturase genes encoding enzymes with ∆12 and ω3 regioselectivities enabling the de novo biosynthesis of the C₁₈ PUFA 18:2ω6 (LA, linoleic acid) and 18:3ω3 (ALA, α-linolenic acid), generally regarded as dietary essential for animals. The O. vulgaris ∆12 desaturase ("ωx2") mediates the conversion of 18:1ω9 (oleic acid) into LA, and subsequently, the ω3 desaturase ("ωx1") catalyses the ∆15 desaturation from LA to ALA. Additionally, the O. vulgaris ω3 desaturase has ∆17 capacity towards a variety of C₂₀ ω6 PUFA that are converted to their ω3 PUFA products. Particularly relevant was the affinity of the ω3 desaturase towards 20:4ω6 (ARA, arachidonic acid) to produce 20:5ω3 (EPA, eicosapentaenoic acid), as supported by yeast heterologous expression, and enzymatic activity exhibited in vivo when paralarvae were incubated in the presence of [1-¹⁴C]20:4ω6. These results confirmed that several routes enabling EPA biosynthesis are operative in O. vulgaris whereas ARA and docosahexaenoic acid (DHA, 22:6ω3) should be considered essential fatty acids since endogenous production appears to be limited.

Marine natural products

Covering: January to December 2017This review covers the literature published in 2017 for marine natural products (MNPs), with 740 citations (723 for the period January to December 2017) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 477 papers for 2017), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Geographic distributions of MNPs at a phylogenetic level are reported.

Trace elements in wild edible Aplysia species: Relationship with the desaturation-elongation indexes of fatty acids

The profile of essential and non-essential elements was traced in the edible sea hares Aplysia depilans Gmelin, Aplysia fasciata Poiret and Aplysia punctata Cuvier. Manganese (Mn), iron (Fe), zinc (Zn), copper (Cu) and selenium (Se) were identified as the major essential elements. Risk assessment evidenced that the levels of cadmium (Cd) and lead (Pb) did not exceed the maximum limit value established by the European Regulation, the contents of chromium (Cr), nickel (Ni) and arsenic (As) being also below the levels established by the FDA guide. A correlation between trace elements levels and desaturation-elongation indexes of fatty acids was found. While Cd, Se and molybdenum (Mo) seem to promote the desaturation-elongation process involved on the production of C20:4n-6c, Ni, Cr and Fe may potentiate the conversion of C18:3n-3c to C20:5n-3c. Furthermore, cobalt (Co), Ni and Cu appear to decrease Δ9 desaturation index. Besides the suggested biosynthetic switch modulated by trace elements, the nutritional value of the species is further strengthened.

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.

Biosynthesis of Polyunsaturated Fatty Acids in the Razor Clam Sinonovacula constricta: Characterization of Δ5 and Δ6 Fatty Acid Desaturases

To investigate the endogenous long-chain polyunsaturated fatty acid (LC-PUFA) biosynthetic ability in Sinonovacula constricta, fatty acid desaturases (Fads) of this bivalve, namely, Scfad5a, Scfad5b, and Scfad6, were cloned and characterized in the current study. Meanwhile, the tissue distributions of S. constricta Fads and fatty acids (FAs) were examined. Heterologous expression in yeasts confirmed that Scfad5a and Scfad5b were both Δ5 Fads, while Scfad6 was a Δ6 Fad. However, compared with Fads in other organisms, the desaturation activities of S. constricta Fads were relatively low (especially for Scfad6), indicating an adaptation to living conditions. S. constricta Fads were expressed in all tissues examined, and particularly high expressions were found in intestine and gonad. Moreover, FAs were differently distributed among tissues, which might be correlated with their corresponding physiological roles. Taken together, the results provided an insight into LC-PUFA biosynthesis in S. constricta. Notably, Scfad6 was the first functionally characterized Δ6 Fad in marine molluscs to date.