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

First neurotranscriptome of adults Tambaquis (Colossoma macropomum) with characterization and differential expression between males and females

The Tambaqui is one of the most representative Amazon fish species, being highly exploited in fisheries, aquaculture and as a research model. Nonetheless, data about functional genome are still required to evaluate reproductive and nutrition parameters as well as resistance to pathogens. The of next-generation sequencing has allows assessing the transcriptional processes in non-model species by providing comprehensive gene collections to be used as a database in further genomic applications and increased performance of captive populations. In this study, we relied on RNAseq approach to generate the first transcriptome of the telencephalon from adult males and females of Colossoma macropomum, resulting in a reference dataset for future functional studies. We retrieved 896,238 transcripts, including the identification of 267,785 contigs and 203,790 genes. From this total, 91 transcripts were differentially expressed, being 63 and 28 of them positively regulated for females and males, respectively. The functional annotation resulted in a library of 40 candidate genes for females and 20 for males. The functional enrichment classes comprised reproductive processes (GO:0,048,609; GO:0,003,006; GO:0,044,703; GO:0,032,504; GO:0,019,953) being related to sex differentiation (e.g., SAFB) and immune response (e.g., SLC2A6, AHNAK, NLRC3, NLRP3 and IgC MHC I alpha3), thus indicating that the genes in the neurotranscriptome of Tambaqui participate in sex differentiation and homeostasis of captive specimens. These data are useful to design the selection of genes related to sex determination and animal welfare in raising systems of Tambaqui.

Genome-wide identification and expression profile of Elovl genes in threadfin fish Eleutheronema

Long-chain polyunsaturated fatty acids (LC-PUFA), including eicosapentaenoic acid and docosahexaenoic acid, are the essential fatty acids for organs to maintain various biological functions and processes. The threadfin fish Eleutheronema, with its rich nutritional value especially the high fatty acid contents, has become one of the promising aquaculture species in China and the potential food source of fatty acids for human consumption. However, the molecular basis underlying the biosynthesis of fatty acids in Eleutheronema species is still unknown. The elongation of the very long-chain fatty acids (Elovl) gene family in fish plays several critical roles in LC-PUFA synthesis. Therefore, in the present study, we performed genome-wide identification of the Elovl gene family to study their evolutionary relationships and expression profiles in two threadfin fish species Eleutheronema tetradactylum and Eleutheronema rhadinum, the first representatives from the family Eleutheronema. Phylogenetic analysis revealed that the Elovl genes in Eleutheronema were classified into six subfamilies (elovl1a/1b, elovl4a/4b, elovl5, elovl6/6 l, elovl7a, elovl8b). Phylogenetic, gene structure, motif, and conserved domain analysis indicated that the Elovl genes were highly conserved within the same subfamily in Eleutheronema. In addition, the Elovl genes were distributed in 7/26 chromosomes, while the duplicated gene pair, elovl4a and elovl4b, showed collinear relationships. The predicted secondary structure patterns and the 3D models revealed the highly similar functions and evolutionary conserved structure of Elovl proteins in Eleutheronema. The selection pressure analysis revealed that Elovl genes underwent strong purifying selection during evolution, suggesting that their functions might be evolutionarily conserved in Eleutheronema. Additionally, the expression patterns of Elovl genes in different tissues and species were distinct, indicating the possible functional divergence during evolution in the Eleutheronema genus. Collectively, we provided the first comprehensive genomic information on Elovl genes in threadfin fish Eleutheronema. This study enhanced the understanding of the underlying mechanisms of fatty acids biosynthesis in Eleutheronema, and provided new insights on breeding new varieties of fatty acids-enriched fish with potential benefits to farmers and the health of consumers.

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.