The environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin disrupts morphogenesis of the rat pre-implantation embryo

© 2008 Hutt et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The definitive version was published in BMC Developmental Biology 8 (2008): 1, doi:10.1186/1471-213X-8-1.Environmental toxicants, whose actions are often mediated through the aryl hydrocarbon receptor (AhR) pathway, pose risks to the health and well-being of exposed species, including humans. Of particular concern are exposures during the earliest stages of development that while failing to abrogate embryogenesis, may have long term effects on newborns or adults. The purpose of this study was to evaluate the effect of maternal exposure to the AhR-specific ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the development of rat pre-implantation embryos with respect to nuclear and cytoskeletal architecture and cell lineage allocation. We performed a systematic 3 dimensional (3D) confocal microscopy analysis of rat pre-implantation embryos following maternal exposure to environmentally relevant doses of TCDD. Both chronic (50 ng/kg/wk for 3 months) and acute (50 ng/kg and 1 μg/kg at proestrus) maternal TCDD exposure disrupted morphogenesis at the compaction stage (8–16 cell), with defects including monopolar spindle formation, f-actin capping and fragmentation due to aberrant cytokinesis. Additionally, the size, shape and position of nuclei were modified in compaction stage pre-implantation embryos collected from treated animals. Notably, maternal TCDD exposure did not compromise survival to blastocyst, which with the exception of nuclear shape, were morphologically similar to control blastocysts. We have identified the compaction stage of pre-implantation embryogenesis as critically sensitive to the effects of TCDD, while survival to the blastocyst stage is not compromised. To the best of our knowledge this is the first in vivo study to demonstrate a critical window of pre-implantation mammalian development that is vulnerable to disruption by an AhR ligand at environmentally relevant doses.This research was supported by NIH/NIEHS-012916 (BKP), ESHE Fund (DFA), Hall Family Foundation (DFA and KJH) and Biomedical Research Training Grant KUMC (KJH)

Bioactivation versus detoxication of the urothelial carcinogen aristolochic acid I by human cytochrome P450 1A1 and 1A2

Exposure to aristolochic acid (AA) is associated with human nephropathy and urothelial cancer. Individual susceptibility to AA-induced disease likely reflects individual differences in enzymes that metabolize AA. Herein, we evaluated AAI metabolism by human cytochrome P450 (CYP) 1A1 and 1A2 in two CYP1A-humanized mouse lines that carry functional human CYP1A1 and CYP1A2 genes in the absence of the mouse Cyp1a1/1a2 orthologs. Human and mouse hepatic microsomes and human CYPs were also studied. Human CYP1A1 and 1A2 were found to be principally responsible for reductive activation of AAI to form AAI-DNA adducts and for oxidative detoxication to 8-hydroxyaristolochic acid (AAIa), both in the intact mouse and in microsomes. Overall, AAI-DNA adduct levels were higher in CYP1A-humanized mice relative to wild-type mice, indicating that expression of human CYP1A1 and 1A2 in mice leads to higher AAI bioactivation than in mice containing the mouse CYP1A1 and 1A2 orthologs. Furthermore, an exclusive role of human CYP1A1 and 1A2 in AAI oxidation to AAIa was observed in human liver microsomes under the aerobic (i.e., oxidative) conditions. Because CYP1A2 levels in human liver are at least 100-fold greater than those of CYP1A1 and there exists a > 60-fold genetic variation in CYP1A2 levels in human populations, the role of CYP1A2 in AAI metabolism is clinically relevant. The results suggest that, in addition to CYP1A1 and 1A2 expression levels, in vivo oxygen concentration in specific tissues might affect the balance between AAI nitroreduction and demethylation, which in turn would influence tissue-specific toxicity or carcinogenicity

The Environmental Toxicant 2,3,7,8-Tetrachlorodibenzo-p-Dioxin Disturbs the Establishment and Maintenance of Cell Polarity in Preimplantation Rat Embryos1

Maternal exposure to the environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces a variety of defects in compaction-stage embryos, including monopolar spindle formation, errors in chromosome segregation, and fragmentation resulting from aberrant cytokinesis. In this study, we investigated the possibility that a failure in centrosome duplication, separation, or positioning within blastomeres might underlie the observed effects of TCDD on early embryos. The subcellular localization of the centrosomal marker TUBG1 was analyzed in preimplantation embryos collected from female rats exposed to either chronic (50 ng kg−1 wk−1 for 3 wk) or acute (50 ng/kg or 1 μg/kg at proestrus) doses of TCDD. In treated embryos, interphase TUBG1 foci were more abundant and cortically displaced when compared to those in controls. At prophase, some blastomeres exhibited a single large perinuclear TUBG1 aggregate, suggesting a failure in centrosome duplication or separation. Furthermore, the presence of monopolar spindles at metaphase was confirmed by the localization of TUBG1 to the single spindle pole. Therefore, the misregulation of centrosome number and localization, as indicated by TUBG1 staining, may contribute to errors in chromosome segregation and cytokinesis in embryos following maternal TCDD exposure

The environmental toxicant 2,3,7,8-tetrachlorodibenzo--dioxin disrupts morphogenesis of the rat pre-implantation embryo-6

<p><b>Copyright information:</b></p><p>Taken from "The environmental toxicant 2,3,7,8-tetrachlorodibenzo--dioxin disrupts morphogenesis of the rat pre-implantation embryo"</p><p>http://www.biomedcentral.com/1471-213X/8/1</p><p>BMC Developmental Biology 2008;8():1-1.</p><p>Published online 2 Jan 2008</p><p>PMCID:PMC2254588.</p><p></p>ssed for visualization of microtubules, f-actin and DNA by confocal microscopy. (A-D) Control 8-cell pre-implantation embryo with blastomeres of similar size and shape, basally positioned interphase nuclei and cytoplasmic microtubule arrays. F-actin is distributed at the cell cortex. (E-H) Control 12-cell pre-implantation embryo with a normal bipolar mitotic spindle (E and H, arrows), metaphase chromosome configuration (F, arrow) and cortical f-actin localization (G, arrow). (I-L) 50 ng/kg/wk TCDD exposed 9-cell pre-implantation embryo with abnormal mitotic spindles (L, arrow) and metaphase chromosome configurations (J, arrow), and enhanced f-actin cortical localization (K, arrow) in multiple blastomeres. (M-P) 50 ng/kg/wk TCDD exposed 8-cell pre-implantation embryo with an anucleate fragment (M, arrow) and abnormal cytokinesis (O, arrows). Monopolar spindle (P, arrow). PB, polar body. Scale bar: 15 μm

The environmental toxicant 2,3,7,8-tetrachlorodibenzo--dioxin disrupts morphogenesis of the rat pre-implantation embryo-7

<p><b>Copyright information:</b></p><p>Taken from "The environmental toxicant 2,3,7,8-tetrachlorodibenzo--dioxin disrupts morphogenesis of the rat pre-implantation embryo"</p><p>http://www.biomedcentral.com/1471-213X/8/1</p><p>BMC Developmental Biology 2008;8():1-1.</p><p>Published online 2 Jan 2008</p><p>PMCID:PMC2254588.</p><p></p>fferent pre-implantation embryo) for each group (Control and 50 ng/kg/wk TCDD) were compared

The environmental toxicant 2,3,7,8-tetrachlorodibenzo--dioxin disrupts morphogenesis of the rat pre-implantation embryo-0

<p><b>Copyright information:</b></p><p>Taken from "The environmental toxicant 2,3,7,8-tetrachlorodibenzo--dioxin disrupts morphogenesis of the rat pre-implantation embryo"</p><p>http://www.biomedcentral.com/1471-213X/8/1</p><p>BMC Developmental Biology 2008;8():1-1.</p><p>Published online 2 Jan 2008</p><p>PMCID:PMC2254588.</p><p></p>ssed for visualization of microtubules, f-actin and DNA by confocal microscopy. (A-D) Control 8-cell pre-implantation embryo with blastomeres of similar size and shape, basally positioned interphase nuclei and cytoplasmic microtubule arrays. F-actin is distributed at the cell cortex. (E-H) Control 12-cell pre-implantation embryo with a normal bipolar mitotic spindle (E and H, arrows), metaphase chromosome configuration (F, arrow) and cortical f-actin localization (G, arrow). (I-L) 50 ng/kg/wk TCDD exposed 9-cell pre-implantation embryo with abnormal mitotic spindles (L, arrow) and metaphase chromosome configurations (J, arrow), and enhanced f-actin cortical localization (K, arrow) in multiple blastomeres. (M-P) 50 ng/kg/wk TCDD exposed 8-cell pre-implantation embryo with an anucleate fragment (M, arrow) and abnormal cytokinesis (O, arrows). Monopolar spindle (P, arrow). PB, polar body. Scale bar: 15 μm