Molecular cloning, characterization, and steady-state levels of retinol-binding protein (rbp) genes in response to dietary soybean oil in brown trout (Salmo trutta)

The cDNA of rbp1a, rbp2a, rbp2b, rbp5, and rbp7b genes was cloned and characterized in brown trout, and their mRNA expressions in response to different levels of dietary soybean oil (SBO) were determined along with their growth parameters, muscle fatty acid (FA) profile, and hepatic retinol level. Dietary SBO did not affect the growth parameters, survival, and hepatosomatic index. The FA composition and retinol content of fish reflected those of experimental diets. The retinol-binding proteins (Rbps; except Rbp5) contained lipocalin domains. The phylogenetic analysis showed that brown trout rbps are orthologs of the rbp/RBPs from other vertebrates; this was also supported by identity/similarity analysis. The rbp genes were exhibited to have conserved synteny with zebrafish and human rbps/RBPs. The tissue-specific transcription of duplicated rbp2a and rbp2b genes varied among all the tested tissues. Moreover, the diet including 100% SBO affected the rbp2a and rbp2b mRNA transcriptions differently, and this was explained by the divergence of the transcriptional regulation site of these genes due to the teleost-specific whole genome duplication. rbp1b and rbp7a were lost in the brown trout genome most likely because of nonfunctionalization. The mRNA expression of all the rbp genes studied was affected by dietary SBO. Therefore, their mRNA expressions could be modulated by dietary FAs and retinol content.