EZH2 overexpression disrupts TEB architecture and branching in 5-week-old nulliparous mice. A: Whole mounts of inguinal mammary glands stained with alum carmine from 5-week-old virgin mice showing aberrant budding and hypercellular TEBs of MMTV-EZH2 mice compared with wild-type (wt) mice (a–d). Higher magnification (×400) showing that whereas wild-type TEBs are small and rounded and undergo dichotomous branching, MMTV-EZH2 TEBs are enlarged and hypercellular and fail to dichotomously branch (c and d). H&E-stained sections show that MMTV-EZH2 TEBs are larger than wild-type TEBs (e and f). B: Bar graph of branch point analysis reveals that MMTV-EZH2 mice have increased secondary branches compared with wild-type virgin mice at 5 weeks of age (n = 5 in each group, Student’s t-test, *P < 0.002, error bars = SD). C: Bar graph showing increased number of TEBs at the leading edge in MMTV-EZH2 mice compared with wild-type mice (each group n = 5, Student’s t-test, * P < 0.05, error bars = SD).