Objectives: Early stages of salivary gland and tooth development share many features in common. We have shown that interference by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) with cultured mouse embryonic tooth morphogenesis requires expression of epidermal growth factor receptor (EGFR). The majority of TCDD effects are thought to be mediated by the aryl hydrocarbon receptor (AhR). The aim of this study was to see if the defective epithelial branching morphogenesis of cultured mouse embryonic submandibular gland caused by TCDD is associated with altered expression of cytochrome P4501A1 (CYP1A1) and if epidermal growth factor (EGF) is capable of modifying the effect of TCDD.

Methods: E13 mouse (NMRI) submandibular glands were cultured in a Trowell type organ culture for 2 days with TCDD (0.1 or 1.0 micromolar in dimethylsulfoxide), EGF (10 or 20 ng/ml) or TCDD and EGF in combination. The explants were examined under stereomicroscope, fixed with 4% paraformaldehyde, processed to paraffin sections and stained with HE.

Results: TCDD at both concentrations impaired the epithelial branching morphogenesis resulting in fewer cords and buds compared with unexposed or dimethylsulfoxide-treated control glands but had no detectable effect on the mesenchyme. EGF alone caused excessive ramification and budding of the epitelium and proliferation of the mesenchyme. When the gland anlage was cultured in combination with TCDD and EGF, epithelial branching was impaired as when cultured with TCDD alone, whereas the mesenchyme had grown as when cultured solely with EGF. TCDD increased the expression of CYP1A1 in the epithelium as detected immunohistochemically, implying activation of AhR.

Conclusion: The failure of EGF to restore morphology of the epithelium after TCDD exposure suggests that the effect of TCDD on submandibular gland branching morphogenesis does not involve direct EGFR signaling by binding of TCDD to EGFR or by increased expression of its major ligands but could involve modulation of EGFR density.