Molecular characterization of the aryl hydrocarbon receptor 2 gene in black rockfish, Sebastes schlegelii, and its expression patterns upon exposure to benzo[a]pyrene, 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin, and β‐naphthoflavone

Abstract

The aryl hydrocarbon receptor (AhR) is a ligand‐activated transcription factor that mediates the toxicity of halogenated and polycyclic aromatic hydrocarbons in vertebrates. Thus, increased knowledge of AhR‐mediated responses to xenobiotics is imperative. Sebastes schlegelii is increasingly being used as a model for studying environmental toxicology; hence, in this study, the presence of AhR2 was evaluated in S. schlegelii. The results showed that the predicted AhR2 amino acid sequence contained regions characteristic of other vertebrate AhRs, including the basic helix–loop–helix and PER–ARNT–SIM domains in the N‐terminal half, but it had minor similarity with other vertebrate AhRs across the C‐terminal half; it did not contain the distinct glutamine‐rich domains found in mammalian AhR2. Phylogenetic analysis demonstrated that S. schlegelii AhR2 was clustered within the teleost AhR2 branch. Additionally, AhR2 mRNA was detectable in all 11 tissues tested, with the highest mRNA levels in the heart, pyloric ceca, and liver. Furthermore, exposure to the AhR agonists showed that 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD, 1 μg/g body weight) induced a significantly higher increases in AhR2 expression in the gills, liver, kidneys, and spleen in 48 h than benzo[a]pyrene (2 μg/g body weight), and β‐naphthoflavone (50‐μg/g body weight); AhR2 mRNA levels upon TCDD exposure were up‐regulated by 16‐ and 10‐fold in the gills and liver, respectively. These findings indicated that AhR was a highly sensitive receptor against TCDD. Thus, investigating AhR2 expression in the presence of other xenobiotics might offer further information for the elucidation of its crucial role in mediating toxicant metabolism in S. schlegelii.

Histopathological and Immunohistochemical Features and Expression Patterns of Cytochrome p450 1 Family Genes in Black Rockfish (Sebastes schlegelii): Exposure to 2,3,7,8-Tetrachlorodibenzo-p-dioxin and β-Naphthoflavone

“…Total RNA was converted to cDNA using SuperScript III reverse transcriptase (Invitrogen, Carlsbad, CA, USA) following the manufacturer's instructions. The real-time polymerase chain reaction was performed using a LightCycler 480 II (Roche Diagnostics, Basel, Switzerland) to assess the expression levels of CYP1A, CYP1B, CYP1C1, and CYP1C2 using gene-specific primers as described previously (Table 2) [41]. The amplification parameters include the following: an initial denaturation step of 95 • C for 5 min; 45 serial cycles of a denaturation step of 95 • C for 10 s, annealing at 58 • C for 10 s, and extension at 72 • C for 10 s; and a final extension step of 72 • C for 5 min.…”