Fig. 1

Blimp1 marks unipotent embryonic luminal stem cells. a Lineage tracing strategy adopted in b-d. Prdm1Cre ^ERT2 mice are crossed to R26R ^mTmG reporter mice. Pregnant females were injected intraperitoneally with tamoxifen (TAM, 0.5 mg/25 g body weight) at embryonic day (E) E12.5, E14.5 or E17.5. Double transgenic littermates Prdm1Cre ^ERT2/+;R26R ^mTmG/+ were analysed 24 h later. b Cryosections (100 μm thick) from E13.5, E15.5 and E18.5 embryonic mammary glands stained for GFP (green), keratin 8 (K8, grey) and keratin 14 (K14, blue). mT is displayed in red (n = 4 embryos). Scale bars, 50 μm. c Representative line scan-analysis (representative fluorescence intensity, minimum 20 cell clusters analysed). d Cryosections (100 μm thick) from E18.5 embryonic mammary glands stained for GFP (green) and Blimp1 (red) and counterstained with DAPI (Nuclei, blue). e Lineage tracing strategy adopted in f–j. Females are injected with TAM at pregnancy day (P) P17.5. Double transgenic littermates Prdm1Cre ^ERT2/+;R26R ^mTmG/+ were analysed 11 weeks (11w) after birth. f 3D imaging of SeeDB-cleared 11-week-old adult virgin mammary tissue. Glands are stained for GFP (green) and K14 (blue). mT is displayed in red (n = 3 mice). Scale bars, 100 μm. g Cryosections (50 μm thick) from 11-week-old adult virgin mammary glands stained for GFP (green), K8 (grey) and K14 (blue) (n = 3 mice). Scale bar, 50 μm. h FACS analysis of MECs from 11-week-old adult virgin mammary glands. CD45⁺ leukocytes and CD31⁺ endothelial cells were removed and total epithelial cells gated on a CD24/CD49f plot. Left: FACS plot showing discrimination of basal (CD24^lowCD49f^high) and luminal (CD24^highCD49f^low) cell populations. Right: FACS plot showing distribution of GFP⁺ cells within stromal, luminal and basal cell populations. (n = 6 mice pooled from two independent experiments). i Percentages of GFP⁺ stromal (0.65% GFP⁺ cells), luminal (1.26% GFP⁺ cells) and basal (0.02% GFP⁺ cells) cell populations. Data are presented as mean ± s.e.m. (n = 6 mice pooled from two independent experiments). j Cryosections (20 μm thick) from E18.5 rudiments and 11-week-old adult virgin mammary glands stained for GFP (green), ERα (red) and counterstained with DAPI (Nuclei, blue). (n = 3 mice). Scale bars, 50 μm