Search

Long‐chain (≥C20) polyunsaturated fatty acids (LC‐PUFAs) are physiologically important fatty acids for most animals, including humans. Although most LC‐PUFA production occurs in aquatic primary producers such as microalgae, recent research indicates the ability of certain groups of (mainly marine) invertebrates for endogenous LC‐PUFA biosynthesis and/or bioconversion from dietary precursors. The genetic pathways for and mechanisms behind LC‐PUFA biosynthesis remain unknown in many invertebrates to date, especially in non‐model species. However, the numerous genomic and transcriptomic resources currently available can contribute to our knowledge of the LC‐PUFA biosynthetic capabilities of metazoans. Within our previously generated transcriptome of the benthic harpacticoid copepod Platychelipus littoralis, we detected expression of one methyl‐end desaturase, one front‐end desaturase, and seven elongases, key enzymes responsible for LC‐PUFA biosynthesis. To demonstrate their functionality, we characterized eight of them using heterologous expression in yeast. The P. littoralis methyl‐end desaturase has Δ15/17/19 desaturation activity, enabling biosynthesis of α‐linolenic acid, eicosapentaenoic acid and docosahexaenoic acid (DHA) from 18:2 n−6, 20:4 n−6 and 22:5 n−6, respectively. Its front‐end desaturase has Δ4 desaturation activity from 22:5 n−3 to DHA, implying that P. littoralis has multiple pathways to produce this physiologically important fatty acid. All studied P. littoralis elongases possess varying degrees of elongation activity for saturated and unsaturated fatty acids, producing aliphatic hydrocarbon chains with lengths of up to 30 carbons. Our investigation revealed a functionally diverse range of fatty acid biosynthesis genes in copepods, which highlights the need to scrutinize the role that primary consumers could perform in providing essential nutrients to upper trophic levels. [ABSTRACT FROM AUTHOR]

The nutritional diversity of resources can affect the adaptive evolution of consumer metabolism and consumer diversification. The omega‐3 long‐chain polyunsaturated fatty acids eicosapentaenoic acid (EPA; 20:5n‐3) and docosahexaenoic acid (DHA; 22:6n‐3) have a high potential to affect consumer fitness, through their widespread effects on reproduction, growth and survival. However, few studies consider the evolution of fatty acid metabolism within an ecological context. In this review, we first document the extensive diversity in both primary producer and consumer fatty acid distributions amongst major ecosystems, between habitats and amongst species within habitats. We highlight some of the key nutritional contrasts that can shape behavioural and/or metabolic adaptation in consumers, discussing how consumers can evolve in response to the spatial, seasonal and community‐level variation of resource quality. We propose a hierarchical trait‐based approach for studying the evolution of consumers' metabolic networks and review the evolutionary genetic mechanisms underpinning consumer adaptation to EPA and DHA distributions. In doing so, we consider how the metabolic traits of consumers are hierarchically structured, from cell membrane function to maternal investment, and have strongly environment‐dependent expression. Finally, we conclude with an outlook on how studying the metabolic adaptation of consumers within the context of nutritional landscapes can open up new opportunities for understanding evolutionary diversification. [ABSTRACT FROM AUTHOR]

Omega-3 (ω3 or n-3) long-chain polyunsaturated fatty acids (PUFA), including eicosapentaenoic acid and docosahexaenoic acid (DHA), play physiologically important roles in vertebrates. These compounds have long been believed to have originated almost exclusively from aquatic (mostly marine) single-cell organisms. Yet, a recent study has discovered that many invertebrates possess a type of enzymes called methyl-end desaturases (ωx) that enables them to endogenously produce n-3 long-chain PUFA and could make a significant contribution to production of these compounds in the marine environment. Polychaetes aremajor componentsofbenthic fauna andthusimportant tomaintain a robust foodweb as a recycler of organic matter and a prey item for higher trophic level species like fish. In the present study, we investigated the ωx enzymes fromthe common ragworm, Hediste diversicolor, a common inhabitant in sedimentary littoral ecosystemsof theNorthAtlantic. Functional assays of the H. diversicolor ωx demonstrated unique desaturation capacities. An ω3 desaturasemediated the conversion of n-6 fatty acid substrates into their corresponding n-3products includingDHA.Afurther enzymepossessedunique regioselectivities combining both ω6 andω3 desaturase activities. These results illustrate that the long-chainPUFAbiosynthetic enzymaticmachineryof aquatic invertebrates such as polychaetes is highly diverse and clarify that invertebrates can be major contributors to fatty acid trophic upgrading in aquatic food webs. [ABSTRACT FROM AUTHOR]

Colonization of new ecological niches has triggered large adaptive radiations. Although some lineages have made use of such opportunities, not all do so. The factors causing this variation among lineages are largely unknown. Here, we show that deficiency in docosahexaenoic acid (DHA), an essential w-3 fatty acid, can constrain freshwater colonization by marine fishes. Our genomic analyses revealed multiple independent duplications of the fatty acid desaturase gene Fads2 in stickleback lineages that subsequently colonized and radiated in freshwater habitats, but not in close relatives that failed to colonize. Transgenic manipulation of Fads2 in marine stickleback increased their ability to synthesize DHA and survive on DHA-deficient diets. Multiple freshwater ray-finned fishes also show a convergent increase in Fads2 copies, indicating its key role in freshwater colonization. [ABSTRACT FROM AUTHOR]

To reduce the requirement for fish oil in marine aquaculture, it would be advantageous to endow marine fish species with the capability for the endogenous biosynthesis of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). For this purpose, we have previously produced transgenic Nibe croaker ( Nibea mitsukurii ) carrying an elongase of very-long-chain fatty acids 2 ( elovl2 ) gene isolated from Masu salmon ( Oncorhynchus masou ). However, fatty acid analysis revealed that 24:5n-3 accumulated in the liver of the transgenic fish, whereas the DHA level did not differ between non-transgenic and transgenic fish. Therefore, to select more effective enzymes for successful transgenic synthesis of DHA, understanding the endogenous DHA biosynthetic pathway in the Nibe croaker is considered to be important. The present study aimed to investigate the biochemical functions of the Elovl5, Elovl4 and Fads2 enzymes involved in the DHA biosynthetic pathway in the Nibe croaker. The results showed that both Elovl5 and Elovl4 were able to elongate C18 fatty acids to C22 fatty acids and that Fads2 had Δ6 desaturase activity toward C18 fatty acids and weak Δ8 desaturase activity toward C20 fatty acids. On the other hand, Fads2 was found to lack the ability to convert 24:5n-3 to 24:6n-3, a fatty acid that can directly be converted to DHA via β-oxidation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 C 18–20 or C 18–22 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 C 18 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. • A complete biosynthetic capability of LC-PUFA is present in an amphidromous fish, Plecoglossus altivelis. • Fads2 desaturase showed Δ6, Δ5 and Δ8 desaturase activities. • Varied elongation activities towards C 18 through C 22 PUFA were detected in each of the eight elongases. • Interestingly, Elovl1b and Elovl7 could be involved in the LC-PUFA biosynthesis in Plecoglossus altivelis. [ABSTRACT FROM AUTHOR]

Long-chain (≥C 20) 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, fads 1, fads 2 and elovl 2 showed a higher expression in intestine, while elovl 5 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. [Display omitted] • fads and elovl are expressed from embryo, increasing from 15 days after hatching. • fads and elovl expression is regulated by organogenesis and diet on larvae ontogeny. • fads 1, fads 2 and elovl 2 are mainly expressed in intestine, while elovl 5 in liver. • A. tropicus possess the enzymatic machinery to synthetize LC-PUFA from PUFA. [ABSTRACT FROM AUTHOR]