Molecular cloning, functional characterization and nutritional regulation of two elovl4b elongases from rainbow trout (Oncorhynchus mykiss)

Elongation of very long-chain fatty acids 4 (Elovl4b) is a critical enzyme in the biosynthesis of long-chain and very long-chain polyunsaturated fatty acids (LC- and VLC-PUFAs) in animals. So far, very little is known about the molecular function of Elovl4 in biosynthetic process, especially in fish. In this study, two elovl4 paralogs (elovl4b1 and elovl4b2) were successfully cloned from rainbow trout (Oncorhynchus mykiss). The full-length cDNAs of elovl4b1 and elovl4b2 were shown to comprise 1896 bp and 2227 bp, respectively, and both contained 921 bp open reading frames (ORFs), encoded 306 amino acids in high homology. Heterologous expression in yeast showed that rainbow trout Elovl4b1 and Elovl4b2 proteins are able to effectively convert C18-22 polyunsaturated fatty acids (PUFAs) to the polyenoic products up to C32 or C36. Especially, compared with Elovl4b2, Elovl4b1 had much higher efficiency for converting 20:5n-3 and 22:5n-3 to 24:5n-3. Tissue distribution analysis revealed that rainbow trout elovl4b were widely transcribed in various tissues with the highest level in eye, brain and gill. Feeding experiment was conducted with three groups of rainbow trout fed diets with either fish oil (FO) or 100% of the FO replaced by soybean oil (SO) and linseeds oil (LO). Compared to fish fed the diet with FO, elovl4b was significantly up-regulated in the liver of fish fed the diet with SO and in the entire intestine of fish fed the diet with LO, which suggested that elovl4b expression is regulated by dietary lipid sources. These results may contribute to better understand the LC-PUFAs and VLC-PUFAs biosynthetic pathway and the regulation mechanism in rainbow trout.