Expression of long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis genes during zebrafish Danio rerio early embryogenesis

Abstract

Long-chain polyunsaturated fatty acids (LC-PUFAs) are essential in important physiological processes, many of which are particularly vital during embryonic development. This study investigated the expression of genes encoding enzymes involved in LC-PUFA biosynthesis, namely fatty acyl desaturase (Fad) and Elovl5- and Elovl2-like elongases, during early embryonic development of zebrafish. First, zebrafish elovl2 cDNA was isolated and functionally characterised in yeast, showing high specificity towards C20- and C22-PUFAs, compared to C18 substrates. Second, spatial-temporal expression for elovl2 and the previously cloned fad and elovl5 were studied during zebrafish early embryonic development. Temporal expression shows that all three genes are expressed from the beginning of embryogenesis (zygote), suggesting maternal mRNA transfer to the embryo. However, a complete activation of the biosynthetic pathway seems to be delayed until 12 hpf, when noticeable increases of fad and elovl2 transcripts were observed, in parallel with high docosahexaenoic acid levels in the embryo. Spatial expression was studied by whole-mount in situ hybridisation in 24 hpf embryos, showing that fad and elovl2 are highly expressed in the head area where neuronal tissues are developing. Interestingly, elovl5 shows specific expression in the pronephric ducts, suggesting an as yet unknown role in fatty acid metabolism during zebrafish early embryonic development. The yolk syncytial layer also expressed all three genes, suggesting an important role in remodelling of yolk fatty acids during zebrafish early embryogenesis. Tissue distribution in zebrafish adults demonstrates that the target genes are expressed in all tissues analysed, with liver, intestine and brain showing the highest expression.

Long chain polyunsaturated fatty acid synthesis in a marine vertebrate: Ontogenetic and nutritional regulation of a fatty acyl desaturase with Δ4 activity

“…A previous study demonstrated maternal transfer of elovl5, elovl2 and 5/6fad mRNA in zebrafish zygotes and a coordinated regulation of elovl2 and fad with the start of LC-PUFA biosynthesis in the embryo [51]. However, in the present study the higher levels of elovl5 in the egg may not be related with DHA synthesis to support embryogenesis due to the lack of synchrony in elovl5 and 4fad transcription.…”

“…It was suggested that an Elovl2-like enzyme, with higher substrate specificity towards C22, is required for efficient DHA synthesis from EPA via the Sprecher pathway but a gene coding for this enzyme in fish has, to date, only been shown in Atlantic salmon and zebrafish [50,51].…”

Diversification of substrate specificities in teleostei Fads2: characterization of Δ4 and Δ6Δ5 desaturases of Chirostoma estor

“…Consistently with the mRNA tissue distribution data, previous studies highlighted the unusually high contents of DHA in C. estor liver, brain, and muscle, and also other tissues including gonads and adipose tissues ( 38 ). Similar tissue distribution patterns were observed in freshwater/salmonid species, including Atlantic salmon ( 14,18 ) and zebrafi sh ( 17 ), in which liver and intestine exhibited the highest expression signals of fads2 and elovl2 and elovl5 elongase genes. Marine fi sh species, including Asian sea bass, Atlantic cod, and cobia, had the highest expression levels of LC-PUFA biosynthesis genes in brain ( 15,19,21 ).…”

Biosynthesis of essential fatty acids in Octopus vulgaris (Cuvier, 1797): Molecular cloning, functional characterisation and tissue distribution of a fatty acyl elongase

“…Similarly, fish Elovl5 demonstrated high activity for the elongation of C18 and C20 PUFA substrates, whereas C22 substrates were only elongated to a lesser extend (Agaba et al, 2004;Morais et al, 2009;Mohd-Yusof et al, 2010;Monroig et al, 2012b). Importantly, elongation of C22 PUFA including 22:5n-3 and 22:4n-6 in vertebrates is basically mediated by Elovl2, whose substrate chain-length specificity also includes C20, but not C18, PUFA substrates, the latter being only marginally or not elongated (Tvrdik et al, 2000;Leonard et al, 2002;Monroig et al, 2009;Morais et al, 2009). Overall it can be concluded that the O. vulgaris elongase cloned here is phenotypically an Elovl5-like elongase, but its sequence similarity to vertebrate Elovl2 suggests an interesting evolutionary scenario that is worth exploring in future investigations.…”