EGF regulates early embryonic mouse gut development in chemically defined organ culture

The profound intestinal epithelial defects in the newborn epidermal growth factor receptor (EGFR) knockout mouse suggests that EGFR signaling plays im portant roles in embryonic gut development. Herein, we further elucidated t he function of EGFR signaling on early embryonic gut development by compari ng the effects of 1-10 ng/mL of exogenous epidermal growth factor (EGF) or 10-25 muM of the tyrphostin 3,4,5 trihydroxybenzene malononitrile, a specif ic inhibitor of EGFR tyrosine kinase, on intact E12 Swiss-Webster mouse mid gut grown in chemically defined organ culture using Fitton-Jackson BGJb med ium for 4 or 6 d. Intestinal development during culture was assayed by morp hometry, histology, reverse transcription/competitive PCR for villin and in testinal fatty acid binding protein mRNA, and immunohistochemistry for epit helial proliferative markers. During organ culture, control specimens grew in length, developed smooth muscle, simple columnar epithelial and goblet c ell phenotypes, showed early villus formation in the proximal intestine, an d increased expression of villin and intestinal fatty acid binding protein mRNA. EGF failed to significantly alter small intestinal lengthening, where as EGF 10 ng/mL inhibited colonic length growth. Tyrphostin 25 muM resulted in regional losses of stromal and smooth muscle cells in the small intesti ne and absent colonic goblet cells. In controls, cellular proliferation ini tially occurred throughout the small intestinal epithelium but became incre asingly localized to the intervillus crypt regions. This sequestration of e pithelial proliferation into crypts was much more apparent in EGF-treated v ersus tyrphostin-treated specimens. EGER activation, therefore, appears to accelerate the maturation rate of goblet cells and the differential crypt/v illus proliferation pattern in early embryonic mouse gut.