Fig. 1. Tubule formation in response to EGF. Purified rabbit kidney proximal tubules were plated into matrigel in serum free medium supplemented with 5 µg/ml insulin, 5 µg/ml transferrin, 5x10^–8 M hydrocortisone and 10 ng/ml EGF. Subsequently, the cultures were photographed under an inverted microscope. (a) Unbranched tubule, 1 week; (b) branched tubules, 1 week. Bars, 50 µm.