Fig. 3. Increased BrdU incorporation in the mutant mammary glands. Five-week-old (A) and 14-week-old (B) virgin control and mutant mice were pulse-labeled with BrdU. The numbers of BrdU⁺ cells were counted in the TEB region (for 5-week-old samples) or in the ductal areas (for 14-week-old samples). The proliferation index for 5-week-old mice was calculated as follows: [number of BrdU⁺-labeled cells]/[total number of cells]x100; Error bars represent standard errors of the mean, P<0.01, ²-test, n=3. For 14-week-old mice, all of the BrdU-labeled cells from the whole sections were counted; values were expressed as [number of BrdU⁺-labeled cells]/[100 ductal structures]. Bar: 40 µm.