Effects of epidermal growth factor (EGF), transforming growth factor-alpha (TGFalpha), and 2,3,7,8-tetrachlorodibenzo-p-dioxin on fusion of embryonic palates in serum-free organ culture using wild-type, EGF knockout, and TGFalpha knockout mouse strains.

Background: 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is teratogenic in mice, producing cleft palate (CP). TCDD exposure disrupts expression of epidermal growth factor (EGF) receptor, EGF, and transforming growth factor-alpha (TGFalpha) in the palate and affects proliferation and differentiation of medial epithelial cells. EGF knockout embryos are less susceptible to the induction of CP by TCDD. This study used palate organ culture to examine the hypothesis that EGF enables a response to TCDD.

Methods: The midfacial tissues from wild-type (WT), EGF knockout, C57BL/6J, and TGFalpha knockout embryos were placed in organ culture on gestational day (GD) 12. Palatal explants were cultured for 4 days in serum-free Bigger's (BGJ) medium with 0.1% dimethyl sulfoxide (DMSO) or 1 x 10(-8) M TCDD with or without 2 ng of EGF/ml, 1 or 2 ng of TGFalpha/ml. Effects on palatal fusion were evaluated on day 4 of culture. EGF levels in explants and medium were determined using Luminex technology.

Results: In serum-free, control medium, palates from all of the strains fused. EGF knockout palates cultured with TCDD (no EGF) fused, but those cultured with TCDD + 2 ng of EGF/ml failed to fuse (p < 0.05 vs. control or TCDD without EGF). TGFalpha knockout palates failed to fuse when cultured with TCDD + 2 ng of TGFalpha/ml. EGF levels increased in tissue and accumulated in the medium after 24 hr of culture.

Conclusions: This study demonstrated that providing EGF to the palates of EGF knockout mice restored the response to TCDD. These studies support the hypothesis that the mechanism for induction of CP by TCDD is mediated via the EGFR pathway.