Fig. 4.

Blimp1 conditional inactivation results in defective mammary gland morphogenesis. (A,B) Whole-mount Carmine-stained and histological sections of mammary glands from 5- and 6-week-old virgin K14:Blimp1^cKO or littermate controls (representative images from n=3 mice of each genotype). Red arrows indicate TEBs. Black arrowheads indicate defective lumen formation within the TEBs. (C,D) Histograms showing the number of TEBs (C), and the percentage of the fat pad filled by the invading mammary epithelial front (D) past the mid-point of the lymph node, assessed by whole-mount staining. Histograms are presented as mean±s.e.m. from n=3 mice of each genotype. *P<0.05; **P<0.01. (E,F) Decreased proliferation and apoptosis. TEBs from 5- and 6-week-old Blimp1-deficient virgins stained for BrdU (green) and Krt8 (K8; red), or cleaved caspase-3 (CC-3) show markedly reduced numbers of BrdU⁺ and CC-3⁺ cells (arrows) (representative images from n=3 mice of each genotype). (G,H) Significantly reduced percentages of BrdU⁺ (G) and CC-3⁺ (H) cells within TEBs from 5- and 6-week-old virgin Blimp1 mutants. Histograms are presented as mean±s.e.m. from n=3 mice of each genotype. (I) Whole-mount Carmine-stained and histological sections of mammary glands from 10-week-old virgin K14:Blimp1^cKO or littermate controls (representative images from n=3 mice of each genotype). Arrow indicates defective lumen formation within ducts. (J) Histograms showing the number of primary, secondary and tertiary branches within 10-week-old mammary glands from K14:Blimp1^cKO and control littermates. *P<0.05; **P<0.01. LN, lymph node. Scale bars: 1 mm (whole mount); 50 μm (sections).