Genome-wide identification and functional characterization of fatty acyl desaturase (fads2) gene in Chinese sturgeon (Acipenser sinensis)

Fatty acyl desaturases (Fads) are crucial enzymes that catalyze the rate-limiting step of the desaturation reactions by introducing a double bond into to pre-existing fatty acyl chains. As a group of key enzymes involved in the biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFAs), Fads have been well investigated in teleost fishes but they are still rarely known in chondrichthyans. In this study, we first identified a fatty acyl desaturases gene (fads2) from the Chinese sturgeon (Acipenser sinensis), a critically endangered cartilaginous species in China, by combining with bioinformatic analyses and molecular cloning methods. Then, the spatio-temporal distribution patterns, functional characteristics and transcriptional changes of this gene in response to different nutritional conditions were investigated. The coding sequences of the fads2 gene was 1350 bp in length, encoding a protein of 449 amino acids. Multiple protein sequences alignment, genetic synteny and phylogenetic analyses further suggested that fads2 gene was evolutionary conserved. Functional characterization by heterologous expression in yeast showed that Fads2 exhibited Delta 6 and Delta 8 bifunctional desaturation activities, and possessed capacities to convert 18:2n-6, 18:3n-3, 20:2n-6 and 20:3n-3-18:3n-6, 18:4n-3, 20:3n-6 and 20:4n-3, respectively. In vivo experiment, diets full with C18 PUFA but not LC-PUFA significantly induced the expression levels of fads2 in Chinese sturgeon brain and liver tissues. Our findings suggest that fads2 is an evolutionary and functionally conserved desaturase in Chinese sturgeon, and which plays important roles in regulation of endogenous LCPUFAs biosynthesis. In summary, these findings will provide a new insight into the evolutionary history of key enzymes of LC-PUFA biosynthesis in vertebrates.