Unprecedented genomic diversity of AhR1 and AhR2 genes in Atlantic salmon ( Salmo salar L.)

• Published in: Aquatic toxicology Vol. 68; no. 3; pp. 219 - 232
• Main Authors: Hansson, Maria C, Wittzell, Håkan, Persson, Kerstin, von Schantz, Torbjörn
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 24.06.2004; Elsevier Science
• Subjects: Agnatha. Pisces; Amino Acid Sequence; Animal, plant and microbial ecology; Animals; Applied ecology; Aryl hydrocarbon receptor; Atlantic salmon; Base Sequence; Biologi; Biological and medical sciences; Biological Sciences; Cluster Analysis; Cosmids - genetics; DNA Primers; DNA, Complementary - genetics; Ecology; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on vertebrates; Ekologi; Evolution; Fundamental and applied biological sciences. Psychology; Gene characterization; Gene Components; Gene Library; Genetic Variation; Marine; Molecular Sequence Data; Natural Sciences; Naturvetenskap; Oncorhynchus mykiss; Phylogeny; Receptors, Aryl Hydrocarbon - genetics; Reverse Transcriptase Polymerase Chain Reaction; Salmo salar; Salmo salar - genetics; Salmon; Sequence Alignment; Sequence Analysis, DNA; Aryl hydrocarbon receptor; Evolution; Atlantic salmon; Gene characterization; Salmon; Salmonidae; Aquatic environment; Ah receptor; Vertebrata; Ecotoxicology; Toxicity; Pisces; Salmo salar; Genetic diversity; Biological effect; Pollutant effect; Biodiversity
• ISSN: 0166-445X; 1879-1514; 1879-1514
• DOI: 10.1016/j.aquatox.2004.02.006

Aryl hydrocarbon receptor (AhR) genes encode proteins involved in mediating the toxic responses induced by several environmental pollutants. Here, we describe the identification of the first two AhR1 ( α and β) genes and two additional AhR2 ( α and β) genes in the tetraploid species Atlantic salmon ( Salmo salar L.) from a cosmid library screening. Cosmid clones containing genomic salmon AhR sequences were isolated using a cDNA clone containing the coding region of the Atlantic salmon AhR2 γ as a probe. Screening revealed 14 positive clones, from which four were chosen for further analyses. One of the cosmids contained genomic AhR sequences that were highly similar to the rainbow trout ( Oncorhynchus mykiss) AhR2 α and β genes. SMART RACE amplified two complete, highly similar but not identical AhR type 2 sequences from salmon cDNA, which from phylogenetic analyses were determined as the rainbow trout AhR2 α and β orthologs. The salmon AhR2 α and β encode proteins of 1071 and 1058 residues, respectively, and encompass characteristic AhR sequence elements like a basic-helix-loop-helix (bHLH) and two PER-ARNT-SIM (PAS) domains. Both genes are transcribed in liver, spleen and muscle tissues of adult salmon. A second cosmid contained partial sequences, which were identical to the previously characterized AhR2 γ gene. The last two cosmids contained partial genomic AhR sequences, which were more similar to other AhR type 1 fish genes than the four characterized salmon AhR2 genes. However, attempts to amplify the corresponding complete cDNA sequences of the inserts proved very difficult, suggesting that these genes are non-functional or very weakly transcribed in the examined tissues. Phylogenetic analyses of the conserved regions did, however, clearly indicate that these two AhRs belong to the AhR type 1 clade and have been assigned as the Atlantic salmon AhR1 α and AhR1 β genes. Taken together, these findings demonstrate that multiple AhR genes are present in Atlantic salmon genome, which likely is a consequence of previous genome duplications in the evolutionary past of salmonids. Plausible explanations for the high incidence of AhR genes in fish and more specifically in salmonids, like rapid divergences in specialized functions, are discussed.