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Abnormal liver development and resistance to 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity in mice carrying a mutation in the DNA-binding domain of the aryl hydrocarbon receptor.

Bunger MK, Glover E, Moran SM, Walisser JA, Lahvis GP, Hsu EL, Bradfield CA - Toxicol. Sci. (2008)

Bottom Line: The aryl hydrocarbon receptor (AHR) is known for its role in the adaptive and toxic responses to a large number of environmental contaminants, as well as its role in hepatovascular development.The classical AHR pathway involves ligand binding, nuclear translocation, heterodimerization with the AHR nuclear translocator (ARNT), and binding of the heterodimer to dioxin response elements (DREs), thereby modulating the transcription of an array of genes.These data suggest that DNA binding is necessary for AHR-mediated developmental and toxic signaling.

View Article: PubMed Central - PubMed

Affiliation: McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Wisconsin 53706, USA.

ABSTRACT
The aryl hydrocarbon receptor (AHR) is known for its role in the adaptive and toxic responses to a large number of environmental contaminants, as well as its role in hepatovascular development. The classical AHR pathway involves ligand binding, nuclear translocation, heterodimerization with the AHR nuclear translocator (ARNT), and binding of the heterodimer to dioxin response elements (DREs), thereby modulating the transcription of an array of genes. The AHR has also been implicated in signaling events independent of nuclear localization and DNA binding, and it has been suggested that such pathways may play important roles in the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Here, we report the generation of a mouse model that expresses an AHR protein capable of ligand binding, interactions with chaperone proteins, functional heterodimerization with ARNT, and nuclear translocation, but is unable to bind DREs. Using this model, we provide evidence that DNA binding is required AHR-mediated liver development, as Ahr(dbd/dbd) mice exhibit a patent ductus venosus, similar to what is seen in Ahr(-/-) mice. Furthermore, Ahr(dbd/dbd) mice are resistant to TCDD-induced toxicity for all endpoints tested. These data suggest that DNA binding is necessary for AHR-mediated developmental and toxic signaling.

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Developmental phenotype of Ahrdbd/dbd mice. (A) Relative organ wet weights of Ahrdbd/dbd mice (white bars) and wild-type littermates (black bars) sacrificed at 8 weeks of age (n = 5). *Indicates p < 0.01 by Student's t-test (wild-type versus Ahrdbd/dbd). (B) Representative H&E sections of livers from 7-day-old wild-type (littermate), Ahrdbd/dbd, and Ahr−/− mice (40× magnification). (C) Time-lapse angiography of wild-type (top row) and Ahrdbd/dbd (bottom row) littermates. Arrows identify key features as follows: BV, branching vessel; PV, portal vein; shIVC, suprahepatic inferior vena cava; ihIVC, infrahepatic inferior vena cava. Total time elapsed from the first panel to the last is approximately 10 s. (D) Incidence of patent DV in wild-type and Ahrdbd/dbd male mice as measured by trypan blue perfusion.
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fig6: Developmental phenotype of Ahrdbd/dbd mice. (A) Relative organ wet weights of Ahrdbd/dbd mice (white bars) and wild-type littermates (black bars) sacrificed at 8 weeks of age (n = 5). *Indicates p < 0.01 by Student's t-test (wild-type versus Ahrdbd/dbd). (B) Representative H&E sections of livers from 7-day-old wild-type (littermate), Ahrdbd/dbd, and Ahr−/− mice (40× magnification). (C) Time-lapse angiography of wild-type (top row) and Ahrdbd/dbd (bottom row) littermates. Arrows identify key features as follows: BV, branching vessel; PV, portal vein; shIVC, suprahepatic inferior vena cava; ihIVC, infrahepatic inferior vena cava. Total time elapsed from the first panel to the last is approximately 10 s. (D) Incidence of patent DV in wild-type and Ahrdbd/dbd male mice as measured by trypan blue perfusion.

Mentions: Wild-type and Ahrdbd/dbd mice were examined for the developmental phenotypes found previously in Ahr−/− mice (Fernandez-Salguero et al., 1996, 1997; Gonzalez and Fernandez-Salguero, 1998; McDonnell et al., 1996; Schmidt et al., 1996; Lahvis and Bradfield, 1998; Lahvis et al., 2000; Peters et al., 1999; Zaher et al., 1998). Tissue wet weights were determined for liver, spleen, heart, thymus, and testis of 8-week-old male Ahrdbd/dbd and wild-type littermates. Similar to Ahr- mice, the Ahrdbd/dbd mice were found to exhibit 25% smaller livers than wild-type littermate controls. Conversely, the hearts and spleens were 25 and 58% larger, respectively, in these animals (p < 0.005, Fig. 6A). Histopathological analysis of livers taken from Ahrdbd/dbd mice at postnatal days (PND) 7, 14, and 21 revealed a transient microvesicular steatosis around PND 7, which resolved by PND 14, and appeared identical to livers from age-matched Ahr−/− mice (Fig. 6B and data not shown). Histopathological analyses were also performed on adult spleen, heart, thymus, testis, lung, colon, kidney, eye, and brain, but revealed no significant differences between Ahrdbd/dbd and wild-type mice (data not shown). These findings are consistent with those reported in our previous work characterizing the Ahr−/− mouse (Schmidt et al., 1996).


Abnormal liver development and resistance to 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity in mice carrying a mutation in the DNA-binding domain of the aryl hydrocarbon receptor.

Bunger MK, Glover E, Moran SM, Walisser JA, Lahvis GP, Hsu EL, Bradfield CA - Toxicol. Sci. (2008)

Developmental phenotype of Ahrdbd/dbd mice. (A) Relative organ wet weights of Ahrdbd/dbd mice (white bars) and wild-type littermates (black bars) sacrificed at 8 weeks of age (n = 5). *Indicates p < 0.01 by Student's t-test (wild-type versus Ahrdbd/dbd). (B) Representative H&E sections of livers from 7-day-old wild-type (littermate), Ahrdbd/dbd, and Ahr−/− mice (40× magnification). (C) Time-lapse angiography of wild-type (top row) and Ahrdbd/dbd (bottom row) littermates. Arrows identify key features as follows: BV, branching vessel; PV, portal vein; shIVC, suprahepatic inferior vena cava; ihIVC, infrahepatic inferior vena cava. Total time elapsed from the first panel to the last is approximately 10 s. (D) Incidence of patent DV in wild-type and Ahrdbd/dbd male mice as measured by trypan blue perfusion.
© Copyright Policy - open-access
Related In: Results  -  Collection

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fig6: Developmental phenotype of Ahrdbd/dbd mice. (A) Relative organ wet weights of Ahrdbd/dbd mice (white bars) and wild-type littermates (black bars) sacrificed at 8 weeks of age (n = 5). *Indicates p < 0.01 by Student's t-test (wild-type versus Ahrdbd/dbd). (B) Representative H&E sections of livers from 7-day-old wild-type (littermate), Ahrdbd/dbd, and Ahr−/− mice (40× magnification). (C) Time-lapse angiography of wild-type (top row) and Ahrdbd/dbd (bottom row) littermates. Arrows identify key features as follows: BV, branching vessel; PV, portal vein; shIVC, suprahepatic inferior vena cava; ihIVC, infrahepatic inferior vena cava. Total time elapsed from the first panel to the last is approximately 10 s. (D) Incidence of patent DV in wild-type and Ahrdbd/dbd male mice as measured by trypan blue perfusion.
Mentions: Wild-type and Ahrdbd/dbd mice were examined for the developmental phenotypes found previously in Ahr−/− mice (Fernandez-Salguero et al., 1996, 1997; Gonzalez and Fernandez-Salguero, 1998; McDonnell et al., 1996; Schmidt et al., 1996; Lahvis and Bradfield, 1998; Lahvis et al., 2000; Peters et al., 1999; Zaher et al., 1998). Tissue wet weights were determined for liver, spleen, heart, thymus, and testis of 8-week-old male Ahrdbd/dbd and wild-type littermates. Similar to Ahr- mice, the Ahrdbd/dbd mice were found to exhibit 25% smaller livers than wild-type littermate controls. Conversely, the hearts and spleens were 25 and 58% larger, respectively, in these animals (p < 0.005, Fig. 6A). Histopathological analysis of livers taken from Ahrdbd/dbd mice at postnatal days (PND) 7, 14, and 21 revealed a transient microvesicular steatosis around PND 7, which resolved by PND 14, and appeared identical to livers from age-matched Ahr−/− mice (Fig. 6B and data not shown). Histopathological analyses were also performed on adult spleen, heart, thymus, testis, lung, colon, kidney, eye, and brain, but revealed no significant differences between Ahrdbd/dbd and wild-type mice (data not shown). These findings are consistent with those reported in our previous work characterizing the Ahr−/− mouse (Schmidt et al., 1996).

Bottom Line: The aryl hydrocarbon receptor (AHR) is known for its role in the adaptive and toxic responses to a large number of environmental contaminants, as well as its role in hepatovascular development.The classical AHR pathway involves ligand binding, nuclear translocation, heterodimerization with the AHR nuclear translocator (ARNT), and binding of the heterodimer to dioxin response elements (DREs), thereby modulating the transcription of an array of genes.These data suggest that DNA binding is necessary for AHR-mediated developmental and toxic signaling.

View Article: PubMed Central - PubMed

Affiliation: McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Wisconsin 53706, USA.

ABSTRACT
The aryl hydrocarbon receptor (AHR) is known for its role in the adaptive and toxic responses to a large number of environmental contaminants, as well as its role in hepatovascular development. The classical AHR pathway involves ligand binding, nuclear translocation, heterodimerization with the AHR nuclear translocator (ARNT), and binding of the heterodimer to dioxin response elements (DREs), thereby modulating the transcription of an array of genes. The AHR has also been implicated in signaling events independent of nuclear localization and DNA binding, and it has been suggested that such pathways may play important roles in the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Here, we report the generation of a mouse model that expresses an AHR protein capable of ligand binding, interactions with chaperone proteins, functional heterodimerization with ARNT, and nuclear translocation, but is unable to bind DREs. Using this model, we provide evidence that DNA binding is required AHR-mediated liver development, as Ahr(dbd/dbd) mice exhibit a patent ductus venosus, similar to what is seen in Ahr(-/-) mice. Furthermore, Ahr(dbd/dbd) mice are resistant to TCDD-induced toxicity for all endpoints tested. These data suggest that DNA binding is necessary for AHR-mediated developmental and toxic signaling.

Show MeSH
Related in: MedlinePlus