title: Regulatory divergence of homeologous Atlantic salmon elovl5 genes following the salmonid-specific whole-genome duplication.
abstract: Fatty acyl elongase 5 (elovl5) is a critical enzyme in the vertebrate biosynthetic pathway which produces the physiologically essential long-chain polyunsaturated fatty acids (LC-PUFA), docosahexenoic acid (DHA), and eicosapentenoic acid (EPA) from 18 carbon fatty acids precursors. In contrast to most other vertebrates, Atlantic salmon possess two copies of elovl5 (elovl5a and elovl5b) as a result of a whole-genome duplication (WGD) which occurred at the base of the salmonid lineage. WGDs have had a major influence on vertebrate evolution, providing extra genetic material, enabling neofunctionalization to accelerate adaptation and speciation. However, little is known about the mechanisms by which such duplicated homeologous genes diverge. Here we show that homeologous Atlantic salmon elovl5a and elovl5b genes have been asymmetrically colonised by transposon-like elements. Identical locations and identities of insertions are also present in the rainbow trout duplicate elovl5 genes, but not in the nearest extant representative preduplicated teleost, the northern pike. Both elovl5 salmon duplicates possessed conserved regulatory elements that promoted Srebp1- and Srebp2-dependent transcription, and differences in the magnitude of Srebp response between promoters could be attributed to a tandem duplication of SRE and NF-Y cofactor binding sites in elovl5b. Furthermore, an insertion in the promoter region of elovl5a confers responsiveness to Lxr/Rxr transcriptional activation. Our results indicate that most, but not all, transposon mobilisation into elovl5 genes occurred after the split from the common ancestor of pike and salmon, but before more recent salmonid speciations, and that divergence of elovl5 regulatory regions have enabled neofuntionalization by promoting differential expression of these homeologous genes.
authors.affiliation: Institute of Aquaculture, School of Natural Sciences, University of Stirling, Pathfoot Building, Stirling FK9 4LA, Scotland, UK. Electronic address: gec1@stir.ac.uk.
authors.forename: Greta
authors.initials: G
authors.lastname: Carmona-Antoñanzas
authors.affiliation: Institute of Aquaculture, School of Natural Sciences, University of Stirling, Pathfoot Building, Stirling FK9 4LA, Scotland, UK. Electronic address: xzheng@staffmail.ed.ac.uk.
authors.forename: Xiaozhong
authors.initials: X
authors.lastname: Zheng
authors.affiliation: Institute of Aquaculture, School of Natural Sciences, University of Stirling, Pathfoot Building, Stirling FK9 4LA, Scotland, UK. Electronic address: d.r.tocher@stir.ac.uk.
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Tocher
authors.affiliation: Institute of Aquaculture, School of Natural Sciences, University of Stirling, Pathfoot Building, Stirling FK9 4LA, Scotland, UK. Electronic address: m.j.leaver@stir.ac.uk.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Leaver
mesh_terms: D000123:Acetyltransferases / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D004252:DNA Mutational Analysis; D019143:Evolution, Molecular; D020440:Gene Duplication; D005786:Gene Expression Regulation; D016678:Genome; D016296:Mutagenesis / Q000235:genetics; D011401:Promoter Regions, Genetic; D020317:Salmo salar / Q000235:genetics*; D016415:Sequence Alignment; D017384:Sequence Deletion / Q000235:genetics; D013045:Species Specificity; D051780:Sterol Regulatory Element Binding Protein 1 / Q000235:genetics / Q000378:metabolism
chemical_list: D051780:Sterol Regulatory Element Binding Protein 1; D000123:Acetyltransferases
keywords: Atlantic salmon; DNA transposon; Fatty acid biosynthesis; Homeologous genes; Neofunctionalisation; Transposable elements; Whole-genome duplication