The miR-33 gene is identified in a marine teleost: a potential role in regulation of LC-PUFA biosynthesis in Siganus canaliculatus

As the first marine teleost demonstrated to have the ability to biosynthesize long-chain polyunsaturated fatty acids (LC-PUFA) from C18 PUFA precursors, rabbitfish Siganus canaliculatus provides a good model for studying the regulatory mechanisms of LC-PUFA biosynthesis in teleosts. Here the potential roles of miR-33 in such regulation were investigated. The miR-33 gene was identified within intron 16 of the gene encoding sterol regulatory element-binding protein 1 (Srebp1), an activator of LC-PUFA biosynthesis. Expression of miR-33 in rabbitfish tissues correlated with that of srebp1, while its expression in liver was highly responsive to ambient salinities and PUFA components, factors affecting LC-PUFA biosynthesis. Srebp1 activation promoted the expression of Δ4 and Δ6 Δ5 fatty acyl desaturases (Fad), key enzymes for LC-PUFA biosynthesis, accompanied by elevated miR-33 abundance in rabbitfish hepatocytes. miR-33 overexpression induced the expression of the two fad, but suppressed that of insulin-induced gene 1 (insig1), which encodes a repressor blocking Srebp proteolytic activation and has targeting sites of miR-33. These results indicated that miR-33, cooperating with Srebp1, may be involved in regulation of LC-PUFA biosynthesis by facilitating fad expression, probably through targeting insig1. To our knowledge, this is the first report of the participation of miR-33 in LC-PUFA biosynthesis in vertebrates.