NOTCH1-transformed mammary tumors consist of mature luminal and luminal progenitor cells. (A) MMVT-tTA/TOP-ICN1 tumors and tumor cell lines are derived from luminal cells. Representative FACS profiles (n = 3) showing the expression of CD29 and CD24 in the CD45-CD31-Ter119- (Lin-) population of the wild-type mammary gland, NOTCH1-transformed mammary tumor, or mammary tumor-derived cell line 8542. (B) Primary tumors consist of mature luminal cells, whereas tumor-derived cell lines consist of luminal progenitors. Representative histogram showing the CD61 expression levels within the Lin-CD29loCD24+ luminal cell populations shown in (A). Dashed line, staining observed with isotype-matched negative control. (C, D) Tumorsphere culture of primary NOTCH1-transformed mammary tumors enriches for CD61+ cells. Tumor-derived cell lines (C) or primary mammary tumor cells (D) or were grown under tumorsphere conditions for 7 days, centrifuged onto slides, and stained with an isotype-matched control or anti-CD61-FITC antibody. Representative fields are shown at 400 × magnification (isotype control is shown in inset). Scale bars, 100 μm.