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The aryl-hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates the toxicity of certain halogenated aromatic hydrocarbons including 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD). These compounds are potent developmental toxicants that can alter gene expression and disrupt processes of proliferation and differentiation. It has not yet been determined which tissues during development are most sensitive to these compounds, nor which genes are directly associated with the toxicities. We developed a transgenic (TG) mouse model to delineate the temporal and spatial context of transcriptionally active AhR by utilizing a dioxin responsive element–linked LacZ reporter system. The present study focuses on the pattern of TCDD-induced transgene expression localized to the footpad and digits of the paws between gestational days (GD) 13 and 18. Paw morphology was evaluated at several developmental stages following TCDD exposure. Gene expression profiles acquired by microarray technology were evaluated in the paws of fetuses exposed at GD 14.5. The results showed that TCDD exposure in utero induced LacZ expression in the developing paws. This expression appeared to be localized to the mesenchymal cell layer. Gross morphological changes were not observed in the paws prior to or after birth following TCDD exposure in utero. However, significant alterations in gene expression profiles in the developing paws were observed at 24 h following TCDD exposure in utero. These results indicate that the developing paw is a target tissue of TCDD in terms of altered gene expression, further validating the use of this AhR responsive reporter gene TG mouse model in studying AhR ligand-mediated responsiveness. However, the linkage of these changes to detectable biological outcomes in the paw remains unclear. [ABSTRACT FROM AUTHOR]

Ovarian granulosa cells play a central role in steroidogenesis, which is critical for female reproduction. Follicle-stimulating hormone (FSH) promotes cyclic adenosine monophosphate (cAMP)-mediated signaling to regulate granulosa cell steroidogenesis. We have shown previously that 2,2-bis-(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE) inhibits FSH- and dibutyryl cAMP-stimulated steroidogenesis and affects the messenger RNA levels of steroidogenic pathway enzymes in rat granulosa cells. However, HPTE showed a differential effect in FSH- and cAMP-stimulated cells in that HPTE more completely blocked FSH- when compared to cAMP-driven steroidogenesis. The objective of this study was to analyze the effects of HPTE on global gene expression profiles in untreated granulosa cells and those challenged with FSH or cAMP. Granulosa cells from immature rats were cultured with 0, 1, 5, or 10μM HPTE in the presence or absence of either 3 ng FSH/ml or 1mM cAMP for 48 h. Total RNA was isolated for real-time quantitative PCR and microarray analysis using the GeneChip Rat Genome 230 2.0 and ArrayAssist Microarray Suite. An investigation of changes in gene expression across all HPTE treatments showed that HPTE altered more genes in FSH- (∼670 genes) than in cAMP-stimulated cells (∼366 genes). Analysis confirmed that HPTE more effectively inhibited FSH- than cAMP-induced steroid pathway gene expression and steroidogenesis. Furthermore, expression patterns of novel genes regulating signal transduction, transport, cell cycle, adhesion, differentiation, motility and growth, apoptosis, development, and metabolism were all altered by HPTE. This study further established that HPTE exerts differential effects within the granulosa cell steroidogenic pathway and revealed that these effects include broader changes in gene expression. [ABSTRACT FROM AUTHOR]