Effects on mammary progenitor cells. (a) Number of alveoli (including mean ± standard deviation) measured in three pairs of animals at second lactation day 3.5, which were used for area measurement in Figure 6(c). Numbers were calculated per analyzed area, and values from wild type (WT) glands were set as 1. *, P = 0.018. (b) Summary of two transplantation experiments with a total of 10 NOD/SCID mice grafted contralaterally with WT and mutant epithelium. Positive outgrowths were classified as '+' (filling <25% of cleared gland), '+ +' (filling 25% to 50%) or '+ + +' (filling about 75%). (c) Wild type: whole mount of virgin recipient gland containing a '+ +' outgrowth from transplanted WT epithelium, 8 weeks after transplantation. Mutants: whole mounts of a negative and a positive ('+ +') outgrowth obtained from mutant epithelium (left and right panel, respectively). Scale bar, 1 mm. (d) Polymerase chain reaction for the recombined allele as described in Figures 1(c) and 5(a), performed on DNA isolated from two recipient mice bearing WT (W) and positive ('+ +') mutant (M) outgrowths. Control: lactating mutant control; R-1, R-2: NOD/SCID recipient 1 and 2.