AH receptor, ARNT, glucocorticoid receptor, EGF receptor, EGF, TGFα, TGFβ1, TGFβ2, and TGFβ3 expression in human embryonic palate, and effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Protein and mRNA for epidermal growth factor (EGF), transforming growth factor-alpha (TGFα), EGF receptor, transforming growth factor-beta 1 (TGFβ1), TGFβ2, TGFβ3, glucocorticoid receptor (GR), the aryl hydrocarbon receptor (AhR), and the Ah receptor nuclear translocator (ARNT) were localized in gestational days (GD) 49-59 human embryonic secondary palates. The response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was determined for expression of these genes following palatal organ culture. Craniofacial tissues were shipped in medium from the Human Embryology Laboratory, University of Washington, Seattle, WA. Half of each specimen was cultured in control medium and half in medium containing TCDD at either 1 x 10^-8 or 1 x 10^-10 M. After fixation and paraffin-embedding, sections were examined either immunohistochemically or by in situ hybridization. Expression patterns were determined for each gene for the major stages of palatogenesis and in response to TCDD and compared to previously determined patterns of expression in the same developmental stages of palatogenesis for the mouse (GD49-59 in human palatogenesis corresponds to GD12-16 in the mouse). Human and mouse palates were dissimilar in particular spatiotemporal patterns of expression of these genes. Relative to patterns in mouse palatal development, human tissues demonstrated expression of EGF at early palatal stages, expression of EGF receptor and TGfα throughout fusion events, and uniform expression of TGFβ3 in all epithelial regions without specifically higher levels in the medial cells. The responses to TCDD also differed in patterns of gene expression as well as in concentration required to induce hyperplasia of the medial epithelium. In summary, human palates expressed all of these regulatory genes, responses to TCDD were detected, and comparison between mouse and human palates revealed interspecies variation that may be a factor in each species' response to TCDD, as well as other teratogenic exposures.