Selective inhibition of ErbB2 decreases the incidence of S-phase entry induced by rhGGF2. A, C, Pieces of utricular sensory epithelium fixed after 72 hr in culture in the standard medium with 50 ng/ml rhGGF2. A, Nuclei of cells that entered S-phase and incorporated BrdU were stained black after immunocytochemistry and were visualized by differential interference contrast microscopy. C, Fluorescent DAPI staining revealed the nuclei that did not enter S-phase in the same piece of epithelium. B, D, A piece of epithelium that was preincubated with the ErbB2 inhibitor AG825 at 4 μmfor 60 min and then cultured for 72 hr in the standard medium containing rhGGF2 and 4 μm AG825. All other inhibitors were tested in the same manner unless otherwise noted. The incidence of cells that entered S-phase was qualitatively different in epithelia cultured in the presence of AG825 as shown by the smaller number of darkly stained nuclei in B. E, The fraction of cells that had entered S-phase in the standard control medium (C), in that medium supplemented with 50 ng/ml rhGGF2 (GGF2), and in medium containing both rhGGF2 and 4 μm AG825 (4μ m AG + GGF2). Each bar represents data from 26 to 37 pieces of epithelium. Anasterisk denotes significance compared with cultures treated with rhGGF2 alone unless otherwise noted (p < 0.05). Scale bars, 100 μm.