title: The capacity for long-chain polyunsaturated fatty acid synthesis in a carnivorous vertebrate: Functional characterisation and nutritional regulation of a Fads2 fatty acyl desaturase with Δ4 activity and an Elovl5 elongase in striped snakehead (Channa striata).
abstract: The endogenous production of long-chain polyunsaturated fatty acids (LC-PUFA) in carnivorous teleost species inhabiting freshwater environments is poorly understood. Although a predatory lifestyle could potentially supply sufficient LC-PUFA to satisfy the requirements of these species, the nutrient-poor characteristics of the freshwater food web could impede this advantage. In this study, we report the cloning and functional characterisation of an elongase enzyme in the LC-PUFA biosynthesis pathway from striped snakehead (Channa striata), which is a strict freshwater piscivore that shows high deposition of LC-PUFA in its flesh. We also functionally characterised a previously isolated fatty acyl desaturase cDNA from this species. Results showed that the striped snakehead desaturase is capable of Δ4 and Δ5 desaturation activities, while the elongase showed the characteristics of Elovl5 elongases. Collectively, these findings reveal that striped snakehead exhibits the genetic resources to synthesise docosahexaenoic acid (DHA; 22:6n-3) from eicosapentaenoic acid (EPA; 20:5n-3). Both genes are expressed at considerable levels in the brain and the liver. In liver, both genes were up-regulated by dietary C18 PUFA, although this increase did not correspond to a significant rise in the deposition of muscle LC-PUFA. Brain tissue of fish fed with plant oil diets showed higher expression of fads2 gene compared to fish fed with fish oil-based diet, which could ensure DHA levels remain constant under limited dietary DHA intake. This suggests the importance of DHA production from EPA via the ∆4 desaturation step in order to maintain an optimal reserve of DHA in the neuronal tissues of carnivores.
authors.affiliation: Assay Development Division, Malaysian Institute of Pharmaceuticals and Nutraceuticals, Ministry of Science, Technology and Innovations, Block 5-A, Halaman Bukit Gambir, Penang 11700, Malaysia.
authors.forename: Meng-Kiat
authors.initials: MK
authors.lastname: Kuah
authors.affiliation: School of Biological Sciences, Universiti Sains Malaysia, Minden, Penang 11800, Malaysia.
authors.forename: Annette
authors.initials: A
authors.lastname: Jaya-Ram
authors.affiliation: School of Biological Sciences, Universiti Sains Malaysia, Minden, Penang 11800, Malaysia; Center for Marine and Coastal Studies, Universiti Sains Malaysia, Minden, Penang 11800, Malaysia. Electronic address: alex@usm.my.
authors.forename: Alexander Chong
authors.initials: AC
authors.lastname: Shu-Chien
mesh_terms: D000123:Acetyltransferases / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism; D060435:Carnivory; D003001:Cloning, Molecular; D004032:Diet; D004281:Docosahexaenoic Acids / Q000096:biosynthesis*; D015118:Eicosapentaenoic Acid / Q000096:biosynthesis*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D044943:Fatty Acid Desaturases / Q000235:genetics / Q000378:metabolism*; D000081031:Fatty Acid Elongases; D005395:Fish Oils / Q000008:administration & dosage; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D008099:Liver / Q000378:metabolism; D008969:Molecular Sequence Data; D009132:Muscles / Q000378:metabolism; D009928:Organ Specificity; D010473:Perciformes / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D010938:Plant Oils / Q000008:administration & dosage; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D005395:Fish Oils; D029941:Fish Proteins; D010938:Plant Oils; D011994:Recombinant Proteins; D004281:Docosahexaenoic Acids; D015118:Eicosapentaenoic Acid; D044943:Fatty Acid Desaturases; D000123:Acetyltransferases; D000081031:Fatty Acid Elongases
keywords: Channa striata; Elongase; Long-chain polyunsaturated fatty acids biosynthesis; Nutritional regulation; Δ4 desaturase