Functional properties of the four Atlantic salmon (Salmo salar) aryl hydrocarbon receptor type 2 (AHR2) isoforms

Abstract

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor through which organochlorine contaminants including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and some polycyclic aromatic hydrocarbons induce toxicity and altered gene expression. Atlantic salmon has multiple AHR genes, of which two belong to the AHR1 clade and four belong to the AHR2 clade. The four AHR2 forms (α, β, γ, δ) are more highly expressed than the AHR1 (α, β,) forms and all six AHRs are highly similar in pairs, likely originating from a whole-genome duplication in the salmonid ancestor. It has been speculated that having multiple AHRs contributes to the very high sensitivity of salmonid species to TCDD and related chemicals. To test the hypothesis that all four salmon AHR2 proteins are expressed and functional, we measured mRNA transcription for each AHR2 inside several tissues, cloned the cDNAs and evaluated the functional properties of the expressed proteins. Analysis by real-time PCR revealed that the receptors showed differences in transcript levels among salmon tissues and that in general AHR2α was transcribed at higher levels than the other three AHR2s. Velocity sedimentation analysis showed that all four in vitro-expressed AHR2 proteins exhibit specific, high-affinity binding of [ 3 H]TCDD. When expressed in COS-7 cells, all four AHR2 proteins were able to drive the expression of a reporter gene under control of murine CYP1A1 enhancer elements. From EC 50 values determined in TCDD concentration-response experiments, all four salmon AHR2s show similar sensitivity to TCDD. In summary, all four Atlantic salmon AHR2 appear to function in AHR-mediated signaling, suggesting that all four proteins are involved in TCDD-mediated toxicity.

Retene causes multifunctional transcriptomic changes in the heart of rainbow trout ( Oncorhynchus mykiss ) embryos

“…The result is in line with previous research showing that ahr2 and ahrr are up-regulated in fish early life stages exposed to AhR agonists (Carney et al, 2006,Goodale et al, 2013. Rainbow trout AHR2α and AHR2β and all members of Atlantic salmon AHR2 protein family are capable of binding TCDD, and may be involved in AhR signaling (Pollenz et al, 2002,Hansson andHahn, 2008). AhR repressor (AhRR) lowers the activated AhR signal, and also has a developmental role (Jenny et al, 2009).…”

Genomic organization of Atlantic salmon (Salmo salar) fatty acid binding protein (fabp2) genes reveals independent loss of duplicate loci in teleosts

“…Salmonid duplicated genes have been isolated and characterized. Some examples are: Hox (Moghadam et al, 2005), glutamine synthetases (Gharbi et al, 2007), myostatins (Ostbye et al, 2007), MHC class I (Lukacs et al, 2007), aryl hydrocarbon receptors (Hansson and Hahn, 2008), growth hormones and MyoD (MacQueen and Johnston, 2008). In addition, comparative studies using a large salmonid EST database provide further evidence of a salmonid-specific genome duplication .…”

Characterization of the Atlantic salmon (Salmo salar) brain-type fatty acid binding protein (fabp7) genes reveals the fates of teleost fabp7 genes following whole genome duplications

“…The fate of gene duplicates in a duplicated genome has been a lingering question in biology. Several studies have examined the evolution of duplicated genes in salmonids (e.g., Hansson and Hahn, 2008;Koop et al, 2008;Lai et al, 2009;Leong et al, 2010;Lukacs et al, 2007;McKay et al, 2004;Moghadam et al, 2005;Ostbye et al, 2007;Quinn et al, 2010;Yasuike et al, 2010). We are characterizing the structure, genome organization and expression patterns of members of the ilbp gene family in Atlantic salmon (S. salar) and other teleosts as this system can provide insight into the evolution and fates of genes that have experienced at least two rounds WGD.…”