* Department of Toxicology, School of Veterinary Medicine, Rakuno Gakuen University, Ebetsu, Japan; and
Department of Biology, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
Received August 13, 2003; accepted October 20, 2003
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ABSTRACT |
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Key Words: apoptosis; aryl hydrocarbon receptor; CYP1A; TCDD; dioxin; oxidative stress.
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INTRODUCTION |
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Based on experiments with Ahr-/- mice, it is evident that the toxicity of TCDD is dependent on the AHR (Fernandez-Salguero et al., 1996; Mimura et al., 1997
; Tanguay et al., 2003
). Several studies in fish embryos point to a possible role for CYP1A and oxidative stress in TCDD developmental toxicity. In the medaka embryo, TCDD causes CYP1A induction and apoptosis in the vitelline vasculature, and both effects are blocked by N-acetylcystein (Cantrell et al., 1996
, 1998
). In the zebrafish and killifish embryo brain, blood flow in the mesencephalic vein, the only vessel perfusing the dorsal midbrain early in development, is transiently reduced 50% by TCDD, and this is associated with increased apoptosis in the dorsal midbrain (Dong et al., 2001
, 2002
; Toomey et al., 2001
). This effect of TCDD in zebrafish is also decreased by CYP1A antagonists and by antioxidants (Dong et al., 2002
).
It is well known that exposure to halogenated aromatic hydrocarbons (HAH) may be associated with long-lasting neurodevelopmental defects in children, as suggested by the poisoning in Yu-Sho and Yu-Cheng (Chen et al., 1992), and cognitive deficits in children born in the vicinity of the Great Lakes (Jacobson and Jacobson, 1996
). Neurological disorders such as sleep disturbances or headache have been observed among some workers who were exposed to TCDD in accidents (Van den Berg et al., 1998
). In monkeys and rats, profound effects of TCDD and other AHR agonistic PCBs on learning and other ability have been reported by Schantz group (Schantz and Bowman 1989
; Widholm et al., 2003
). Many efforts have been made to demonstrate that HAHs reduce long-term potentiation (LTP) in the hippocampus of rats, a possible mechanism effect on memory, especially for ortho-substituted polychrolinated biphenyls (PCBs). On the other hand, expression of AHR, ARNTs, and induction of CYP1A by HAHs have been reported in brain of rats (Huang et al., 2000
), mice (Shimada et al., 2003
), and fish (Andreasen et al., 2002b
; Dong et al., 2002
; Petersen et al., 2000
; Powell et al., 2000
). In relation to this, long-lasting TCDD exposure could induce oxidative stress in rat brain (Hassoun et al., 1998
). However, the significance of the AHR in the neurotoxic effects by HAH remains unclear.
The present study is focused on the early endpoints of TCDD developmental toxicity expressed in the dorsal midbrain of the zebrafish embryo. It seeks to determine if these endpoints are zfAHR2-dependent. To this end a selective gene knock-down technique using morpholino antisense oligonucleotide (Nasevicius and Ekker, 2000) against zfAHR2 (AHR2-MO) was used to decrease the translation of each protein in early stage embryos exposed to vehicle or TCDD. We show that AHR2-MO protected embryos against TCDD-induced increases in vascular permeability, transient decreases in blood flow, and increases in apoptosis in the zebrafish dorsal midbrain. This molecular evidence, together with our separate set of study (Teraoka et al., 2003b
), establishes that AHR2 is required for these early endpoints of TCDD developmental toxicity to be expressed in zebrafish.
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MATERIALS AND METHODS |
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Zebrafish embryos and TCDD exposure.
Fertilized eggs were obtained from natural mating of adult zebrafish (AB line) according to the Zebrafish Book (Westerfield, 1995). Adult fish and embryos were maintained at 28.5°C with a lighting schedule of 14 h light and 10 h dark. Embryos were collected within 1 h of spawning, rinsed, and placed into a clean Petri dish. Within 24 h post fertilization (hpf) of spawning, the embryos were exposed to either the TCDD vehicle (0.1% DMSO) or to graded, apparent concentrations of waterborne TCDD of 0.3, 0.5, or 1.0 parts per billion (ppb) dissolved in 0.1% DMSO. The DMSO or appropriate concentration of TCDD dissolved in DMSO was present in 3 ml of Zebrafish Ringer solution (38.7 mM NaCl, 1.0 mM KCl, 1.7 mM HEPES-NaOH, pH 7.2, 2.4 mM CaCl2) in 3-cm Petri dishes for the duration of the experiment (n = 10 embryos/dish). Some embryos were exposed with N-acetylcysteine with or without 0.3 ppb TCDD from 24 hpf until 50 hpf.
Gene knock-down with morpholino antisense oligonucleotides.
Based on the cDNA sequence published at Genbank for zfAHR2 (AF063446) (Tanguay et al., 1999), a morpholino antisense oligo against zfAHR2 (AHR2-MO) along with a 4 base mismatch negative control morpholino (4mis-AHR2-MO), were synthesized by Gene Tools (Philomath, OR), as described previously (Teraoka et al., 2003b
). Basic procedures are followed according to Nasevicius and Ekker (2000)
. Sequences were 5'-TGTACCGATACCCGCCGACATGGTT-3' (AHR2-MO) and 5'-TGaACCcATACCCGCCGtCATcGTT-3' (4mis-AHR2-MO) with four modified bases indicated by lower case letters. Each morpholino was injected into the yolk of embryos at the one- or two-cell stage with a fine glass needle connected to an automatic injector (IM-300, Narishige, Japan). The volume of the 100 µM morpholino solution injected into each embryos was 100 pl. Occasionally, injected embryos died before 10 hpf, depending on the state of the tip of the glass needle and embryos. Thus 5 or 10 surviving embryos were used for each experiment.
Blood flow in the dorsal midbrain.
Blood flow in the mesencephalic vein was evaluated by time-lapse recording using a digital-video camera (Teraoka et al., 2002). Embryos (50 hpf) were suspended in 200 µl of 3% carboxymethyl cellulose/Zebrafish Ringer solution in a plastic bath mounted on the stage of an inverted microscope (IMT-2, Olympus, Japan). Temperature of the suspension solution was maintained at 28.5°C with a PDMI-2 Micro-Incubator with Bipolar Temperature Controller (TC-202, Medical Systems, Greenvale, NY).
Conventional histology.
At 60 h post fertilization (hpf), embryos were fixed in 10% neutralized formalin for 24 h, followed by the conventional procedure for TUNEL staining (Dong et al., 2001, 2002
). Positive TUNEL signals were detected with ABC KIT (Elite, Vector), and brain sections were counterstained with methyl green. TUNEL-positive cells in both forebrain and midbrain were counted in all serial sections of these brain regions in each embryo, because there was no clear morphological border between the dorsal midbrain and forebrain (Dong et al., 2001
). Immunohistochemistry was performed using a monoclonal antibody specific for fish CYP1A (Mab 1-12-3) (Dong et al., 2002
). Signals were detected with ABC Kit (Vector), with brown color distinct from black pigment in the skin, the eye, and the midline. Methyl green was used for counterstaining.
Vascular permeability.
To assess vascular permeability in the embryonic midbrain in vivo, immunohistochemistry using anti-bovine serum albumin (BSA) was performed. At 50 hpf embryos were injected with 10% BSA into the sinus venosus and fixed with 4% paraformaldehyde after 10 min of BSA injection. The same protocol described above for antibody staining was used, except that the primary antibody was an anti-BSA rabbit antibody (Sigma, St Louis, MO) (153 ng/ml), and the secondary antibody was an anti-rabbit IgG goat antibody (Sigma, St Louis, MO) (7.5 µg/ml). For quantification of vascular permeability, area analysis of BSA immunoreactivity was performed using conventional image software (Photoshop 7.0; Adobe). After several images of the sagital section of dorsal midbrain with vasculature were obtained with digital camera (Penguin 150CL, Pixera) under light microscope (BX50, Olympus), the anti-BSA-immonoreactive area was circled on the Photoshop image at the same magnification, and the area was obtained in pixels.
Statistics.
Results are presented as mean ± SE. Significant differences between means were determined by one-way ANOVA followed by Scheffes test (p < 0.05).
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RESULTS |
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DISCUSSION |
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Since zfAHR1 and zfAHR2 have little sequence similarity near their ATG start sites, it was expected that AHR2-MO would decrease zfAHR2 protein levels selectively without altering levels of zfAHR1. Consistent with this expectation, addition of AHR2-MO to an in vitro transcription and translation reaction containing zfAhr1 and zfAhr2 cDNAs blocked translation of zfAHR2 with no effect on zfAHR1 (Prasch et al., 2003). Furthermore, TCDD induction of zfCYP1A, an AHR-dependent gene, was reduced by pretreatment with AHR2-MO, demonstrating that this effect of TCDD in the zebrafish embryo is mediated by zfAHR2.
The increased bovine serum albumin (BSA) immunostaining in the dorsal midbrain area of TCDD-exposed embryos provided direct evidence of a TCDD-induced increase in vascular permeability. Since the increased BSA immunostaining of the midbrain parenchyma was reduced in zfAHR2 exposed to TCDD, it suggests that zfAHR2 is involved in mediating this response to TCDD. In addition, pretreatment with an antioxidant also blocked the increase in vascular permeability caused by TCDD in the dorsal midbrain, which is entirely consistent with our earlier finding that TCDD-induced circulation failure and apoptosis in the zebrafish dorsal midbrain is markedly reduced by antioxidant treatment (Dong et al., 2002). In medaka embryos treated with TCDD, general circulation failure and mortality also were blocked by antioxidant (Cantrell et al., 1996
). Although we reported a close relationship between circulation failure in the mesencephalic vein, the only vessel in dorsal midbrain at this stage, and apoptosis in the dorsal midbrain in the previous report (Dong et al., 2002
), it is still not certain whether apoptosis could be caused by reduction in blood flow by about half. On the other hand, it is also possible that unidentified substance inducing apoptosis could be released from endothelium or leaked out from blood constituents (Teraoka et al., 2003a
).
It appears that the vascular endothelium of the zebrafish embryo brain, where zfCYP1A is strongly expressed, is the site of toxic action involving CYP1A (Dong et al., 2002). Endothelium has been suggested as a possible site of AHR agonist toxicity ever since high levels of CYP1A were identified in endothelium (Stegeman et al., 1989
). In porcine aortic endothelial cell culture, the AHR agonist PCB 77 increases both lipid peroxidation and albumin permeability, and the latter is reduced by antioxidant (Slim et al., 2000
; Toborek et al., 1995
). Furthermore, the increase in albumin permeability is specific for AHR agonists and is usually accompanied by CYP1A induction in the endothelial cells (Toborek et al., 1995
). The results here support the idea that CYP1A in the vasculature may be involved in a variety of toxic effects of TCDD and other planar halogenated aromatic hydrocarbons. Both AHR2-MO and an antioxidant prevented TCDD-induced mesencephalic circulation failure and apoptosis in the dorsal midbrain of the zebrafish embryo. It is possible in TCDD-exposed zebrafish embryos that oxidative stress is caused by TCDD uncoupling of CYP1A resulting in the production of activated oxygen, as shown with a planar polychlorinated biphenyl AHR agonist (Schlezinger et al., 1999
). Recent studies have shown that TCDD also stimulates ROS release from induced scup liver microsomes (Goldstone and Stegeman, unpublished), consistent with this suggestion. However, induced levels of CYP1A could lead to radical formation originating from increased rates of some endogenous compound metabolism, and this also could be involved in eliciting oxidative stress. While the mechanism by which CYP1A may be involved in causing apoptosis in the zebrafish embryo midbrain is not known, the ability of an antioxidant to block the effect suggests that oxidative stress in the vascular endothelium of this brain region may be involved.
Unlike Ahr -/- null mice that exhibit cardiac hypertrophy, alterations in vascular maturation, and disrupted immune and female reproductive function including impaired ovarian follicle growth (Abbott et al., 1999; Benedict et al., 2000
; Fernandez-Salguero et al., 1996
; Lahvis et al., 2000
), no effects of the AHR2-MO were detected on gross morphology or vascular development of zebrafish embryos at or before 60 hpf. Therefore, even though zfAHR2 and zfARNT2 were expressed by 12 hpf (Andreasen et al., 2002b
), the physiological function of zfAHR2 in early stage embryos is yet to be determined. In contrast, injection of zebrafish embryos with a negative splice variant form of zfARNT2, zfARNT2X, caused severe defects in brain, eye, pectoral fin, heart, and gut development (Hsu et al., 2001
).
In contrast to the observations at the lower concentration of TCDD, AHR2-MO was without effects on mesencephalic circulation failure and apoptosis at higher concentration of TCDD (0.5 and 1 ppb). Similarly, AHR2-MO did not affect CYP1A induction caused by higher concentration of TCDD in mesencephalic vascular endothelium. Reminiscent of these observations, -naphthoflavone and antioxidants blocked mesencephalic circulation failure and apoptosis by 0.3 ppb TCDD but not by 0.5 and 1 ppb TCDD (Dong et al., 2001
, 2002
). Thus, these facts raise the possibility that different mechanisms do exist in TCDD-induced toxicity dependent on the concentration of TCDD. However, we do not know whether our AHR2-MO treatment blocked AHR2 translation completely, since specific antibody to AHR2 is not available at present. As our experiments were performed with 48, 50, or 60 hpf embryos, the effectiveness of the molpholino was expected to decrease. AHR2-MO completely lost its preventive activity against TCDD by 96 hpf, when pericardial edema, general circulation failure, and death occurred (Teraoka et al., 2003b
). Thus, we cannot exclude the possibility that the residual AHR2 could mediate toxicity by higher concentrations of TCDD. Although higher concentrations of TCDD could cause some effects via pathways other than those engaged at lower concentrations of TCDD, 0.3 ppb TCDD caused almost maximal effects in mesencephalic circulation failure and apoptosis (Dong et al., 2001
, 2002
). Interestingly, the magnitude of AHR2-MO effect on CYP1A induction caused by TCDD was different in different regions. Thus, AHR2-MO effectively inhibited CYP1A induction even by 0.5 and 1 ppb TCDD in the skin or pharyngeal arches; the effect of morpholino was slight for CYP1A induction in cranial vascular endothelium at those doses of TCDD. Although CYP1A expressed in the skin might be involved in TCDD-induced toxicity as a barrier to ambient water (Andreasen et al., 2002b
), present endpoints were not correlated to CYP1A induction in the skin, as revealed by different effects of AHR2-MO. Further investigations are required to clarify these issues.
In conclusion, AHR2-MO prevented TCDD-induced mesencephalic circulation failure and apoptosis in the dorsal midbrain of the zebrafish embryo. This suggests the conserved role of AHR in TCDD-induced toxicity for all vertebrates. Mesencephalic vein seems a target of TCDD for the production of these effects (Dong et al., 2002). The mechanism by which TCDD causes apoptosis in the zebrafish embryo midbrain is still not known, but the ability of an antioxidant to block the effect suggests that oxidative stress in the vascular endothelium of this brain region may be involved.
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ACKNOWLEDGMENTS |
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NOTES |
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REFERENCES |
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Andreasen, E. A., Hahn, M. E., Heideman, W., Peterson, R. E., and Tanguay, R. L. (2002a). The zebrafish (Danio rerio) aryl hydrocarbon receptor type 1 (zfAHR1) is a novel vertebrate receptor. Mol. Pharmacol. 62, 234249.
Andreasen, E. A., Spitsbergen, J. M., Tanguay, R. L., Stegeman, J. J., Heideman, W., and Peterson, R. E. (2002b). Tissue-specific expression of AHR2, ARNT2, and CYP1A in zebrafish embryos and larvae: Effects of developmental stage and 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure. Toxicol. Sci. 68, 403419.
Benedict, J. C., Lin, T. M., Loeffler, I. K., Peterson, R. E., and Flaws, J. A. (2000). Physiological role of the aryl hydrocarbon receptor in mouse ovary development. Toxicol. Sci. 56, 382388.
Cantrell, S. M., Joy-Schlezinger, J., Stegeman, J. J., Tillitt, D. E., and Hannink, M. (1998). Correlation of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced apoptotic cell death in the embryonic vasculature with embryotoxicity. Toxicol. Appl. Pharmacol. 148, 2434.[CrossRef][ISI][Medline]
Cantrell, S. M., Lutz, L. H., Tillitt, D. E., and Hannink, M. (1996). Embryotoxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD): The embryonic vasculature is a physiological target for TCDD-induced DNA damage and apoptotic cell death in Medaka (Orizias latipes). Toxicol. Appl. Pharmacol. 141, 2334.[CrossRef][ISI][Medline]
Chen, Y. C., Guo, Y. L., Hsu, C. C., and Rogan, W. J. (1992). Cognitive development of Yu-Cheng ("oil disease") children prenatally exposed to heat-degraded PCBs. JAMA 268, 32133218.[Abstract]
Dong, W., Teraoka, H., Kondo, S., and Hiraga, T. (2001). 2,3,7,8-Tetrachlorodibenzo-p-dioxin induces apoptosis in the dorsal midbrain of zebrafish embryos by activation of aryl hydrocarbon receptor. Neurosci. Lett. 303, 169172.[CrossRef][ISI][Medline]
Dong, W., Teraoka, H., Yamazaki, K., Tsukiyama, S., Imani, S., Imagawa, T., Stegeman, J. J., Peterson, R. E., and Hiraga, T. (2002). 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity in the zebrafish embryo: Local circulation failure in the dorsal midbrain is associated with increased apoptosis. Toxicol. Sci. 69, 191201.
Fernandez-Salguero, P. M., Hilbert, D. M., Rudikoff, S., Ward, J. M., and Gonzalez, F. J. (1996). Aryl hydrocarbon receptor-deficient mice are resistant to 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced toxicity. Toxicol. Appl. Pharmacol. 140, 173179.[CrossRef][ISI][Medline]
Hahn, M. E, Karchner, S. I., Shapiro, M. A., and Perera, S. A. (1997). Molecular evolution of two vertebrate aryl hydrocarbon (dioxin) receptors (AHR1 and AHR2) and the PAS family. Proc. Natl. Acad. Sci. USA 94, 1374313748.
Henry, T. R., Spitsbergen, J. M., Hornung, M. W., Abnet, C. C., and Peterson, R. E. (1997). Early life stage toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin in zebrafish (Danio rerio). Toxicol. Appl. Pharmacol. 142, 5668.[CrossRef][ISI][Medline]
Hassoun, E. A., Wilt, S. C., Devito, M. J., Van Birgelen, A., Alsharif, N. Z., Birnbaum, L. S., and Stohs, S. J. (1998). Induction of oxidative stress in brain tissues of mice after subchronic exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin. Toxicol. Sci. 42, 2327.[Abstract]
Hsu, H. J., Wang, W. D., and Hu, C. H. (2001). Ectopic expression of negative ARNT2 factor disrupts fish development. Biochem. Biophys. Res. Commun. 282, 487492.[CrossRef][ISI][Medline]
Huang, P., Rannug, A., Ahlbom, E., Hakansson, H., and Ceccatelli, S. (2000). Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the expression of cytochrome P450 1A1, the aryl hydrocarbon receptor, and the aryl hydrocarbon receptor nuclear translocator in rat brain and pituitary. Toxicol. Appl. Pharmacol. 169, 159167.[CrossRef][ISI][Medline]
Jacobson, J. L., and Jacobson, S. W. (1996). Intellectual impairment in children exposed to polychlorinated biphenyls in utero. N. Engl. J. Med. 335, 783789.
Lahvis, G. P., Lindell, S. L., Thomas, R. S., McCuskey, R. S., Murphy, C., Glover, E., Bentz, M., Southard, J., and Bradfield, C. A. (2000). Portosystemic shunting and persistent fetal vascular structures in aryl hydrocarbon receptor-deficient mice. Proc. Natl. Acad. Sci. U.S.A. 97, 1044210447.
Mimura, J., Yamashita, K., Nakamura, K., Morita, M., Takagi, T. N., Nakao, K., Ema, M., Sogawa, K., Yasuda, M., Katsuki, M., et al. (1997). Loss of teratogenic response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in mice lacking the Ah (dioxin) receptor. Genes Cells 1, 645654.[ISI]
Nasevicius, A., and Ekker, S. C. (2000). Effective targeted gene knockdown in zebrafish. Nat. Genet. 26, 216220.[CrossRef][ISI][Medline]
Petersen, S. L., Curran, M. A., Marconi, S. A., Carpenter, C. D., Lubbers, L. S., and McAbee, M. D. (2000). Distribution of mRNAs encoding the aryl hydrocarbon receptor, aryl hydrocarbon receptor nuclear translocator, and aryl hydrocarbon receptor nuclear translocator-2 in the rat brain and brainstem. J. Comp. Neurol. 427, 428439.[CrossRef][ISI][Medline]
Powell, W. H., Bright, R., Bello, S. M., and Hahn, M. E. (2000). Developmental and tissue-specific expression of AHR1, AHR2, and ARNT2 in dioxin-sensitive and -resistant populations of the marine fish Fundulus heteroclitus. Toxicol. Sci. 57, 229239.
Prasch, A. L, Teraoka, H., Carney, S. A., Dong, W., Hiraga, T., Stegeman, J. J., Heideman, W., and Peterson, R. E. (2003). Aryl hydrocarbon receptor 2 mediated 2,3,7,8-tetrachlorodibenzo-p-dioxin developmental toxicity in zebrafish. Toxicol. Sci. 76, 138150.
Schantz, S. L., and Bowman, R. E. (1989). Learning in monkeys exposed perinatally to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Neurotoxicol. Teratol. 11, 1319.[CrossRef][ISI][Medline]
Schlezinger, J. J., White, R. D., and Stegeman, J. J. (1999). Oxidative inactivation of cytochrome P-450 1A (CYP1A) stimulated by 3,3',4,4'-tetrachlorobiphenyl: Production of reactive oxygen by vertebrate CYP1As. Mol. Pharmacol. 56, 588597.
Shimada, T., Sugie, A., Shindo, M., Nakajima, T., Azuma, E., Hashimoto, M., and Inoue, K. (2003). Tissue-specific induction of cytochromes P450 1A1 and 1B1 by polycyclic aromatic hydrocarbons and polychlorinated biphenyls in engineered C57BL/6J mice of aryl hydrocarbon receptor gene. Toxicol. Appl. Pharmacol. 187, 110.[CrossRef][ISI][Medline]
Slim, R., Toborek, M., Robertson, L. W., Lehmler, H. J., and Hennig, B. (2000). Cellular glutathione status modulates polychlorinated biphenyl-induced stress response and apoptosis in vascular endothelial cells. Toxicol. Appl. Pharmacol. 166, 3642.[CrossRef][ISI][Medline]
Spitsbergen, J. M., Walker, M. K., Olson, J. R., and Peterson, R. E. (1991). Pathologic alterations in early life stages of lake trout, Salvelinus namaycush, exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin as fertilized eggs. Aquat. Toxicol. 19, 4172.[CrossRef][ISI]
Stegeman, J. J., Miller, M. R., and Hinton, D. E. (1989). Cytochrome P450IA1 induction and localization in endothelium of vertebrate (teleost) heart. Mol. Pharmacol. 36, 723729.[Abstract]
Tanguay, R. L., Abnet, C. C., Heideman, W., and Peterson, R. E. (1999). Cloning and characterization of the zebrafish (Danio rerio) aryl hydrocarbon receptor. Biochim. Biophys. Acta. 1444, 3548.[ISI][Medline]
Tanguay, R. L., Andreasen, E., Heideman, W., and Peterson, R. E. (2000). Identification and expression of alternatively spliced aryl hydrocarbon nuclear translocator 2 (ARNT2) cDNAs from zebrafish with distinct functions. Biochim. Biophys. Acta. 1494, 117128.[ISI][Medline]
Tanguay, R. L., Andreasen, E. A., Walker, M. K., and Peterson, R. E. (2003). Dioxin toxicity and aryl hydrocarbon receptor signaling in fish. In Dioxins and Health, (A. Schecter and T. A. Gasiewicz, Eds.) 2nd ed., pp. 603628. John Wiley & Sons, New York.
Teraoka, T., Dong, W., Ogawa, S., Tsukiyama, S., Okuhara, Y., Niiyama, M., Ueno, N., Peterson, R. E., and Hiraga, T. (2002). 2,3,7,8-Tetrachlorodibenzo-p-dioxin toxicity in the zebrafish embryo: Altered regional blood flow and impaired lower jaw development. Toxicol. Sci. 65, 192199.
Teraoka, H., Dong, W., and Hiraga, T. (2003a). Zebrafish as a novel experimental model for developmental toxicology. Congenit. Anom. 43, 123132.
Teraoka, H., Dong, W., Iwasa, H., Endoh, D., Ueno, N., Stegeman, J. J., Peterson, R. E., and Hiraga, T. (2003b). Induction of cytochrome P4501a is required for malformations by 2,3,7,8-tetrachlorodibenzo-p-dioxin in zebrafish. Biochem. Biophys. Res. Commun. 304, 223228.[CrossRef][ISI][Medline]
Toborek, M., Barger, S. W., Mattson, M. P., Espandiari, P., Robertson, L. W., and Hennig, B. (1995). Exposure to polychlorinated biphenyls causes endothelial cell dysfunction. J. Biochem. Toxicol. 10, 219226.[Medline]
Toomey, B. H., Bello, S., Hahn, M. E., Cantrell, S., Wright, P., Tillitt, D. E., and Di Giulio, R. T. (2001). 2,3,7,8-Tetrachlorodibenzo-p-dioxin induces apoptotic cell death and cytochrome P4501A expression in developing Fundulus heteroclitus embryos. Aquat. Toxicol. 53, 127138.[CrossRef][ISI][Medline]
Van den Berg, M., Birnbaum, L., Bosveld, A. T., Brunstrom, B., Cook, P., Feeley, M., Giesy, J. P., Hanberg, A., Hasegawa, R., Kennedy, S. W., et al. (1998). Toxic equivalency factors (TEFs) for PCBs, PCDDs, PCDFs for humans and wildlife. Environ. Health Perspect. 106, 775792.[ISI][Medline]
Walker, M. K., and Peterson, R. E. (1994). Aquatic toxicity of dioxins and related chemicals. In Dioxins and Health (A. Schecter, Ed.), pp. 347387, Plenum Press, New York.
Westerfield, M. (1995). The Zebrafish Book, University of Oregon Press, Eugene, OR.
Widholm, J. J., Seo, B. W., Strupp, B. J., Seegal, R. F., and Schantz, S. L. (2003). Effects of perinatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin on spatial and visual reversal learning in rats. Neurotoxicol. Teratol. 25, 459471.[CrossRef][ISI][Medline]