Molecular characterization of biosynthesis of polyunsaturated fatty acids during different developmental stages in the copepod Apocyclops royi

Abstract

Copepod Apocyclops royi can biosynthesize long-chain polyunsaturated fatty acids (LC-PUFAs) when fed low-PUFA precursors. Previously, two elongases and two desaturases in the n-3 PUFA biosynthetic pathway were identified from A. royi. However, the complete PUFA biosynthesis pathway in this copepod species is poorly understood. Here, we report 13 genes, of which nine are novel genes, encoding PUFA biosynthesis-related enzymes belonging to the fatty acid desaturases (ArD6D, ArD5D, ArD4D, ArO3D-1, and ArO3D-2) and elongases (Elovl1, 2, 3, 4, 5, 6, 7, and 8) families identified from a Thai culture of A. royi (A. royi-TH). Identification of the fatty acid contents using gas chromatography/mass spectroscopy analysis indicated that the copepodid and adult stages were high in PUFAs, with omega-3 fatty acids, while the nauplius stage had the lowest level of PUFAs. Moreover, all copepod stages of A. royi-TH fed Tetraselmis suecica contained higher levels of LC-PUFAs, including docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), than the microalgae fatty acid content, which was deficient in omega-3 DHA. Changes in transcript expression levels were determined in three developmental stages of A. royi-TH. Interestingly, the increased gene expression of the fatty acid desaturases (ArD6D, ArD5D, ArD4D, ArO3D-1, and ArO3D-2) and elongases (ArElovl3, 4, 5, 6, and 7) in the adult stages was reflected in the increased fatty acid concentration of DHA and EPA in the adult stages compared with the other developmental stages, suggesting the possible function of these genes for LC-PUFA synthesis in the different copepod developmental stages. These results indicate that the nauplius, copepodid, and adult stages are capable of synthesizing DHA from low PUFA through a LC-PUFA biosynthesis pathway.