Molecular cloning and characterization of estrogen receptors in Atlantic salmon (Salmo salar)
ABSTRACT
We have isolated a novel Atlantic salmon (Salmo salar) estrogen receptor (esr) cDNA, determined by similarity to be an esr2a isoform. The 2685-bp cDNA isolated from pituitary and testis encoded a 594 amino acid (aa) protein. Esr2 showed 91 - and 60 percent aa sequence identity to Atlantic salmon Esr1 (1) in the DNA binding domain and ligand binding domain, respectively. The esr2 mRNA expression levels, determined by quantitative polymerase chain reaction (qPCR), were moderate in the heart, spleen, kidney and brain, whereas the gene expression was relatively higher in liver and gonads. Reverse transcription polymerase chain reaction (RT-PCR) analysis showed that the overall tissue distribution of esr1 transcript was similar to esr2, and the expression level of the esr1 gene was notably higher in brain and liver than in other tissues examined. Expression of esr1 in the liver of juvenile Atlantic salmon, treated by estradiol-17β (E2) and 4-nonylphenol (NP) was clearly induced (3 fold). In contrast, the esr2 mRNA levels were not influenced by these chemicals in gonads, but significantly reduced in the liver. Altogether, our results indicate that the esr2 gene is constitutively expressed and not inducible. Recently, we isolated a cDNA fragment, which possibly could be the other Esr2 protein in Atlantic salmon. Furthermore, phylogenetic analysis of 67 sequences from 40 species showed that the estrogen receptor proteins from ray-finned fish grouped in three clades; Esr1, Esr2a and/or Esr2b. The presence of up to three isoforms of estrogen receptor in fish and a possibility of even more isoforms of estrogen receptor in Atlantic salmon calls for a nomenclature to prevent confusion in the scientific literature. We suggest here that the zebrafish naming convention for genes is adapted, naming the estrogen receptor gene α; esr1 (Esr1 for protein) and esr2a and esr2b (Esr2a and Esr2b for protein) for the two estrogen receptor β genes.
We have isolated a novel Atlantic salmon (Salmo salar) estrogen receptor (esr) cDNA, determined by similarity to be an esr2a isoform. The 2685-bp cDNA isolated from pituitary and testis encoded a 594 amino acid (aa) protein. Esr2 showed 91 - and 60 percent aa sequence identity to Atlantic salmon Esr1 (1) in the DNA binding domain and ligand binding domain, respectively. The esr2 mRNA expression levels, determined by quantitative polymerase chain reaction (qPCR), were moderate in the heart, spleen, kidney and brain, whereas the gene expression was relatively higher in liver and gonads. Reverse transcription polymerase chain reaction (RT-PCR) analysis showed that the overall tissue distribution of esr1 transcript was similar to esr2, and the expression level of the esr1 gene was notably higher in brain and liver than in other tissues examined. Expression of esr1 in the liver of juvenile Atlantic salmon, treated by estradiol-17β (E2) and 4-nonylphenol (NP) was clearly induced (3 fold). In contrast, the esr2 mRNA levels were not influenced by these chemicals in gonads, but significantly reduced in the liver. Altogether, our results indicate that the esr2 gene is constitutively expressed and not inducible. Recently, we isolated a cDNA fragment, which possibly could be the other Esr2 protein in Atlantic salmon. Furthermore, phylogenetic analysis of 67 sequences from 40 species showed that the estrogen receptor proteins from ray-finned fish grouped in three clades; Esr1, Esr2a and/or Esr2b. The presence of up to three isoforms of estrogen receptor in fish and a possibility of even more isoforms of estrogen receptor in Atlantic salmon calls for a nomenclature to prevent confusion in the scientific literature. We suggest here that the zebrafish naming convention for genes is adapted, naming the estrogen receptor gene α; esr1 (Esr1 for protein) and esr2a and esr2b (Esr2a and Esr2b for protein) for the two estrogen receptor β genes.
Publisert i The Endocrine Society`s 87th Annual Meeting (ENDO 2005), 2005
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