(a) Validation of the Slug-YFP knock-in reporter. Mammary tumour section from SlugYFP/+;MMTV-PyMT female mice were stained for YFP (green), Slug (red), cytokeratin (grey), and DAPI (blue). (b) Validation of the Snail-YFP knock-in reporter. Mammary tumour section from SnailYFP/+;MMTV-PyMT female mice were stained for YFP (green), Snail (red), cytokeratin (grey), and DAPI (blue). (c) Lin− cells of normal mammary glands were separated into luminal MECs, basal MECs and stromal fibroblasts using CD24 and CD49f cell-surface markers.(d, e) Representative FACS histogram showing relative expression levels of Slug-YFP and Snail-YFP reporters in the indicated cell populations in mammary glands during puberty (d) and during pregnancy (e). Note that luminal MECs from pregnant females exhibit higher levels of autofluorescence signals (grey dashed line in panel e). (f) Normal human mammary tissue sections were stained for Slug or Zeb1 (green), CK14 (red), CK8 (grey), and DAPI (blue). Arrowheads indicate Slug+CK14+ cells. (g) Representative FACS histogram showing expression level of the epithelial cell-surface marker EpCAM in the indicated populations of the normal mammary gland. (d, e, g) are representative of three independent experiments. All scale bars 10 μm.