Cloning, tissue specificity and regulation of expression of genes of four key enzymes related to long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis by ambient salinity during embryogenesis in the marine teleost Siganus guttatus.

The rabbitfish Siganus canaliculatus was the first marine teleost reported to possess long-chain polyunsaturated fatty acid (LC-PUFA) biosynthetic ability, and the related molecular mechanisms have been well clarified. Here, we investigated the LC-PUFA biosynthesis capability of the congeneric rabbitfish S. guttatus. First, cDNAs of genes for four key enzymes related to LC-PUFA biosynthesis, namely Δ6Δ5 fatty acyl desaturase (fads 2) (1335 bp; 445 aa), Δ4 fads 2 (1335 bp; 445 aa), and elongation of very long chain fatty acid proteins (elovl 5) (873 bp; 291 aa) and elovl 4 (906 bp; 302 aa) were cloned from the liver of S. guttatus. The Δ6Δ5 fads 2, Δ4 fads 2 and elovl 5 genes showed high expression in brain, liver, spleen, gallbladder, and intestine but relatively low expression in eye, whereas the elovl 4 gene showed specific and high expression in eye. During embryogenesis, mRNA expression of Δ4 fads 2 and elovl 4 was detected from 8 h post-fertilization (hpf) and then maintained a high level to 24 hpf, while mRNA expression of Δ6Δ5 fads 2 and elovl 5 reached a peak at 14 hpf but then declined. In addition, ambient salinity (32 ppt and 20 ppt) exerted some regulatory influence on the expression of the four genes during embryogenesis. The levels of C18 PUFA precursors and, especially, PUFA and DHA of the embryos, decreased from 17 hpf to 24 hpf. These results suggested that S. guttatus , similar to the congeneric S. canaliculatus , would have capability for LC-PUFA biosynthesis, which is still not activated at the fertilized egg stage. [Display omitted] • The mRNA sequences of four key enzymatic genes (Δ6Δ5 fads 2, Δ4 fads 2, elovl 5 and elovl 4) were cloned and characterized in herbivorous marine teleost Siganus guttatus. • The rabbitfish S. guttatus may biosynthesize LC-PUFA from C 18 PUFA precursors, similar to its congeneric S. canaliculatus. • The capacity of LC-PUFA biosynthesis in S. guttatus is still not activated at the fertilized egg stage. • Ambient salinity exerts some regulatory influence on the mRNA expression of the key enzymatic genes involved in LC-PUFA biosynthesis at the fertilized eggs stages in S. guttatus. [ABSTRACT FROM AUTHOR]