Delayed differentiation of c-Myc mutant glands in a second pregnancy. (a) Immunohistochemistry (IHC) against mouse milk in glands taken from wild type (WT) and mutant mice at second pregnancy day 14.5 and 16.5. Milk proteins are stained in brown, lipid droplets in the magnification are circled in red. Scale bar, 20 μm. (b) IHC against Cre on heterozygous and mutant glands taken at the indicated time points of a second pregnancy and lactation as described in Figure 1(b). Scale bar, 100 μm. (c) Quantification of alveolar area in glands as described in Figure 2(c). Three and two pairs of animals (two sections per animal) were quantified at second pregnancy day 16.5 and lactation day 3.5, respectively. *, P = 0.0082; **, P = 0.013. (d) Whole mounts of WT and mutant mice at second pregnancy day 16.5 and lactation day 3.5. Scale bar, 1 mm.