Fig. 2. Electron micrographs of filter-cultured pig thyrocytes after TGF-ß1 and EGF stimulations. (A) Portion of an untreated cell monolayer. The cells are polarised with numerous microvilli (arrows) at the apical plasma membrane. (B) Cells exposed to TGF-ß1 (10 ng/ml) for 48 hours. The monolayer organisation is similar to that of control cultures. Apical microvilli are lost and the appearance of submembranous microfilament condensations is evident (arrowheads). (C) Cells treated with EGF (10 ng/ml) for 48 hours. The cells are tall and crowded due to increased proliferation, but the monolayered epithelium is largely maintained. The apical plasma membrane displays microvilli. (D) Cells co-stimulated with TGF-ß1 and EGF (both 10 ng/ml) for 48 hours. The cells are flat and elongated and extend on top of each other in multiple layers. Distinct junctional complexes are not present.