A Dominant Negative Zebrafish Ahr2 Partially Protects Developing Zebrafish from Dioxin Toxicity

Abstract

The toxicity by 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) is thought to be caused by activation of the aryl hydrocarbon receptor (AHR). However, our understanding of how AHR activation by TCDD leads to toxic effects is poor. Ideally we would like to manipulate AHR activity in specific tissues and at specific times. One route to this is expressing dominant negative AHRs (dnAHRs). This work describes the construction and characterization of dominant negative forms of the zebrafish Ahr2 in which the C-terminal transactivation domain was either removed, or replaced with the inhibitory domain from the Drosophila engrailed repressor protein. One of these dnAhr2s was selected for expression from the ubiquitously active e2fα promoter in transgenic zebrafish. We found that these transgenic zebrafish expressing dnAhr2 had reduced TCDD induction of the Ahr2 target gene cyp1a, as measured by 7-ethoxyresorufin-O-deethylase activity. Furthermore, the cardiotoxicity produced by TCDD, pericardial edema, heart malformation, and reduced blood flow, were all mitigated in the zebrafish expressing the dnAhr2. These results provide in vivo proof-of-principle results demonstrating the effectiveness of dnAHRs in manipulating AHR activity in vivo, and demonstrating that this approach can be a means for blocking TCDD toxicity.

When evolution is the solution to pollution: Key principles, and lessons from rapid repeated adaptation of killifish (Fundulus heteroclitus) populations

“…Fish typically have four AHR genes, products of a tandem gene duplication ( AHR1 and AHR2 ) and paralogs of each of these (designated “a” and “b”), the result of a whole‐genome duplication at the base of the teleost lineage, after its divergence from the lineage leading to tetrapods (Hahn et al., 2006, 2017). The relative roles of each AHR are not yet fully understood, but the AHR2 paralogs appear to mediate many of the toxic and adaptive responses to DLCs and some PAHs (Antkiewicz, Peterson, & Heideman, 2006; Billiard et al., 2006; Clark et al., 2010; Dong, Teraoka, Tsujimoto, Stegeman, & Hiraga, 2004; Goodale et al., 2012; Incardona et al., 2006; Jönsson et al., 2007; Lanham, Prasch, Weina, Peterson, & Heideman, 2011; Prasch et al., 2003; Waits & Nebert, 2011). For some chemicals, however, responses may be mediated by AHR1 (Goodale et al., 2012; Incardona et al., 2006).…”

Macondo crude oil from the Deepwater Horizon oil spill disrupts specific developmental processes during zebrafish embryogenesis

“…The small adult fish size, large embryo clutches, ex utero development, and transparent embryo and larval stages of zebrafish enable cost effective maintenance of many fish, reproducible sample sizes, simple application of toxin treatments, and easy evaluation of end-point toxicity [ 14 - 18 ]. The use of zebrafish to assay drug and pollutant toxicity has already provided insights into the developmental and molecular mechanistic roles of metals [ 19 , 20 ], dioxins [ 21 - 24 ], pesticides [ 25 , 26 ], endocrine disruptors [ 27 , 28 ], alcohols [ 29 - 31 ], chemotherapies [ 32 - 34 ] and specific pharmaceutical compounds many of which were assessed via high-throughput screening [ 35 ].…”

Cardiac Myocyte-Specific AHR Activation Phenocopies TCDD-Induced Toxicity in Zebrafish

“…In zebrafish, AHR2 and Arnt1c mediate the developmental toxicity of TCDD: loss of either protein protects the developing fish from TCDD-induced cardiotoxicity (Antkiewicz et al, 2006;Prasch et al, 2003Prasch et al, , 2006. Loss of the AHR2 transcriptional activation domain (TAD) also prevents toxicity (Goodale et al, 2012;Lanham et al, 2011).…”