Fig. 4. BMP4 rescues outgrowth of PTHrP^-/- mammary buds in organ culture. (A-D) Representative examples of bud outgrowths after 7 days in organ culture. (A) Wild-type mammary bud. (B) PTHrP^-/- bud. (C) PTHrP^-/- bud treated with 10^-7 M PTHrP. (D) PTHrP^-/- bud treated with 10 ng/ml BMP4. (E) Quantification of the frequency of bud outgrowth under different conditions as noted on the x-axis. Each experiment was performed on 15 buds over three separate experiments, except for the wild-type buds, which represent a total of 40 buds over eight separate experiments. ^*, P<0.05 for WT versus WT+noggin; #, P<0.05 for WT versus KO; triangle, P<0.05 for KO versus KO+PTHrP and KO versus KO+BMP4.