Long chain polyunsaturated fatty acid synthesis in a marine vertebrate: Ontogenetic and nutritional regulation of a fatty acyl desaturase with Δ4 activity

• Published in: Biochimica et biophysica acta 2012-04, Vol.1821 (4), p.660-671
• Main Authors: Morais, Sofia, Castanheira, Filipa, Martinez-Rubio, Laura, Conceição, Luis E.C., Tocher, Douglas R.
• Format: Article
• Language: English
• Subjects: Acetyltransferases - genetics; Acetyltransferases - metabolism; Amino Acid Sequence; Animal Nutritional Physiological Phenomena; Animals; aquaculture; biosynthesis; Cloning, Molecular; complementary DNA; diet; DNA, Complementary - chemistry; DNA, Complementary - genetics; docosahexaenoic acid; early development; eggs; eicosapentaenoic acid; embryogenesis; fatty acid composition; Fatty Acid Desaturases - classification; Fatty Acid Desaturases - genetics; Fatty Acid Desaturases - metabolism; Fatty Acids - analysis; Fatty Acids, Unsaturated - analysis; Fatty Acids, Unsaturated - biosynthesis; fish feeds; fish products; Fish Proteins - classification; Fish Proteins - genetics; Fish Proteins - metabolism; Flatfishes - genetics; Flatfishes - growth & development; Flatfishes - metabolism; Gene Expression Regulation, Developmental; hatching; humans; ingredients; Larva - genetics; Larva - growth & development; Larva - metabolism; larvae; larval development; Lipids - chemistry; long chain polyunsaturated fatty acids; Marine teleost; Molecular Sequence Data; Ontogenesis; ontogeny; Phylogeny; Polyunsaturated fatty acid synthesis; postlarvae; Reverse Transcriptase Polymerase Chain Reaction; Sequence Analysis, DNA; Sequence Homology, Amino Acid; sole; Solea senegalensis; synthesis; Time Factors; transcription (genetics); Transcriptional regulation; Δ4 desaturase
• ISSN: 1388-1981; 0006-3002; 1879-2618
• DOI: 10.1016/j.bbalip.2011.12.011

Solea senegalensis is an unusual marine teleost as it has very low dietary requirement for long-chain polyunsaturated fatty acids (LC-PUFA) during early development. Aquaculture is rapidly becoming the main source of health-beneficial fish products for human consumption. This, associated with limited supply of LC-PUFA-rich ingredients for fish feeds, render S. senegalensis a highly interesting species in which to study the LC-PUFA biosynthesis pathway. We have cloned and functionally characterized fatty acyl desaturase and elongase cDNAs corresponding to Δ4fad (with some Δ5 activity for the n−3 series) and elovl5 with the potential to catalyze docosahexaenoic acid (DHA) biosynthesis from eicosapentaenoic acid (EPA). Changes in expression of both transcripts were determined during embryonic and early larval development, and transcriptional regulation in response to higher or lower dietary n−3 LC-PUFA was assessed during larval and post-larval stages. There was a marked pattern of regulation during early ontogenesis, with both transcripts showing peak expression coinciding with the start of exogenous feeding. Although elovl5 transcripts were present in fertilized eggs, Δ4fad only appeared at hatching. However, eggs have high proportions of DHA (~20%) and high DHA/EPA ratio (~11) to meet the high demands for early embryonic development. The fatty acid profile of larvae after the start of exogenous feeding closely reflected dietary composition. Nonetheless, Δ4fad was significantly up-regulated in response to LC-PUFA-poor diets, which may suggest biological relevance of this pathway in reducing LC-PUFA dietary requirements in this species, compared to other marine teleosts. These results indicate that sole is capable of synthesizing DHA from EPA through a Sprecher-independent pathway. ► We functionally characterized a fatty acyl desaturase and elongase in sole. ► Fad has Δ4-activity and Elovl has substrate specificity typical of fish Elovl5. ► Sole appears able to synthesize DHA from EPA via a Sprecher-independent pathway. ► Δ4fad and elovl5 showed a marked pattern of regulation during early ontogenesis. ► Δ4fad shows nutritional regulation, up-regulated in response to LC-PUFA-poor diets.