Fig. 3.

Response to progesterone in RANKL^−/− MECs. (A–F) Mice engrafted with RANKL^−/− or WT MECs stimulated with progesterone for 24 h (A, B, and C) or 48 h (D, E, and F). The percentage of BrdU-incorporating cells ± SEM in contralateral mammary epithelia of three mice after 24 h (A) and 48 h (D) of stimulation. Open bars, RANKL^−/−; black bars, WT MECS; total of 1,000 cells counted in three different sections from each mouse. (B, C, E, and F) Double-immunofluorescence at 24 h (B and C) and 48 h (E and F) of stimulation. Green, PR; red, BrdU; blue, DAPI. (Scale bar: 40 μm.) Note: at 24 h, RANKL^−/− (B) and WT (C) MECs incorporate BrdU similarly and are PR(+). At 48 h, fewer mutant MECs incorporate BrdU (E) vs. WT (F), and most BrdU-incorporating cells are hormone receptor negative.