Genome-wide identification of a novel elovl4 gene and its transcription in response to nutritional and osmotic regulations in rabbitfish (Siganus canaliculatus)

Elongation of very long-chain fatty acids 4 (Elovl4) proteins, belong to the fatty acyl elongase families that are involved in long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis in animals. Thus far, very little is known about the roles of Elovl4 in fish. Previously, we reported an elovl4 gene named as elovl4b in rabbitfish (Siganus canaliculatus). In this study, a novel elovl4-like gene with a 957-bp open reading frame encoding a 318 amino-acid protein, which shared 67.3% similarity with rabbitfish Elovl4b and more than 80% similarity with Elovl4a from other teleost, was identified in S. canaliculatus, and thus was termed as elovl4a. Multiple protein sequences alignment, gene synteny and phylogenetic analysis indicated that two obviously different elovl4 genes are widespread in various teleost. Different with elovl4b (mainly expressed in eye and slightly expressed in brain), rabbitfish elovl4a was primarily distributed in brain, slightly examined in eye and gonad tissues while hardly detectable in other tissues. The transcription of cerebral elovl4a was significantly higher in fishes cultured in seawater (32 parts per thousand) than that of those maintained at a brackish water environment (15 parts per thousand), when fishes were fed with a vegetable oil (VO) enriched diet. However, the transcriptional pattern was totally inverse when fishes were fed with a fish oil (FO) enriched diet. In the brackish water, diet types had no effect on the transcription of cerebral elovl4a. Whereas in seawater, the transcription of cerebral elovl4a was significantly higher in fishes fed with the VO diet in comparison with those fed with the FO diet. Our findings suggest that elovl4a can be regulated by both nutritional and osmotic factors, and it may play an important role in endogenous biosynthesis of LC-PUFA in the neural system of rabbitfish. This study may help us to understand the effects of nutritional and osmotic factors on the LC-PUFA biosynthesis, as well as contribute to the optimization or enhancement of LC-PUFA biosynthesis in teleost.