Ptch1 may regulate estrogen/progesterone production, but not myeloid cell function, to promote mammary ductal elongation. (A) Whole-mount vehicle- or E+P-treated control or Fsp-Cre;Ptch1fl/fl glands. E+P increases branching (compare top and bottom panels). (B) Quantification showing E+P-mediated rescue of stunted ducts of Fsp-Cre;Ptch1fl/fl mutants (‘Mutant’). (C) BrdU labeling quantification in vehicle- or E+P-treated control and Fsp-Cre;Ptch1fl/fl ducts. E+P induced proliferation, albeit attenuated, in Fsp-Cre;Ptch1fl/fl mutants. (D) Whole-mount glands of control to control (upper left), control to Fsp-Cre;Ptch1fl/fl (upper right) or Fsp-Cre;Ptch1fl/fl to control (lower left) bone marrow-transplanted animals. Inset: inguinal mammary lymph node of Cre- recipient showing colonization by Cre+, mTmG+ cells. Lower right: quantification showing that donor bone marrow does not change mammary ductal outgrowth. Graphs show data as mean±s.e.m. Scale bars: 0.5 mm in A,D; 50 µm in D, inset. **P<0.01, ****P<0.0001 by ANOVA/Tukey's test.