Short-term linage tracing shows that Sox9 is exclusively expressed in luminal cells. (A). Sox9-CreERT2; CAG-EGFP mice were injected with tamoxifen. 72 hr after injection, the mice were sacrificed for mammary gland staining and FACS analysis. Sections of the mouse mammary gland were stained with GFP (green) and myoepithelial cell marker (α-SMA) (red) antibodies and DAPI (staining nuclei, blue). (B) Flow cytometry analysis of CD24 expression of GFP-positive and -negative cells isolated from above tamoxifen treated mouse mammary glands. (C). Flow cytometry analysis of all CD24+ luminal cells (both GFP+ and GFP-) isolated from the above tamoxifen treated mouse mammary glands using CD61 and CD49f expression. This demonstrates that luminal cells of the mammary gland are comprised of CD61+ luminal progenitors and CD61- differentiated luminal cells. (D). CD61, CD49f flow cytometry analysis of only GFP+ cells isolated from above tamoxifen treated mouse mammary glands shows that GFP+ cells are mostly CD61+ luminal progenitors. (E) CD24, CD29 flow cytometry analysis of GFP positive cells isolated from above tamoxifen treated mouse mammary glands.