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

Hansson, Maria LU ; Wittzell, Håkan LU ; Persson, Kerstin LU and von Schantz, Torbjörn LU (2004) In Aquatic Toxicology 68(3). p.219-232
Abstract
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 (alpha and beta) genes and two additional AhR2 (alpha and beta) 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 AhR2gamma 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) AhR2alpha and beta... (More)
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 (alpha and beta) genes and two additional AhR2 (alpha and beta) 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 AhR2gamma 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) AhR2alpha and beta 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 AhR2alpha and beta orthologs. The salmon AhR2alpha and beta 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 AhR2gamma 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 AhR1alpha and AhR1beta 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 salmortids, like rapid divergences in specialized functions, are discussed. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Aquatic Toxicology
volume
68
issue
3
pages
219 - 232
publisher
Elsevier
external identifiers
  • wos:000222066000002
  • pmid:15159049
  • scopus:2542469651
ISSN
1879-1514
DOI
10.1016/j.aquatox.2004.02.006
language
English
LU publication?
yes
id
3df2c0b1-4bcd-47f8-a97e-0abae4ed08cc (old id 136976)
date added to LUP
2007-06-25 13:26:23
date last changed
2017-07-23 03:45:06
@article{3df2c0b1-4bcd-47f8-a97e-0abae4ed08cc,
  abstract     = {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 (alpha and beta) genes and two additional AhR2 (alpha and beta) 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 AhR2gamma 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) AhR2alpha and beta 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 AhR2alpha and beta orthologs. The salmon AhR2alpha and beta 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 AhR2gamma 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 AhR1alpha and AhR1beta 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 salmortids, like rapid divergences in specialized functions, are discussed.},
  author       = {Hansson, Maria and Wittzell, Håkan and Persson, Kerstin and von Schantz, Torbjörn},
  issn         = {1879-1514},
  language     = {eng},
  number       = {3},
  pages        = {219--232},
  publisher    = {Elsevier},
  series       = {Aquatic Toxicology},
  title        = {Unprecedented genomic diversity of AhR1 and AhR2 genes in Atlantic salmon (Salmo salar L.)},
  url          = {http://dx.doi.org/10.1016/j.aquatox.2004.02.006},
  volume       = {68},
  year         = {2004},
}