Fig. 1. Primary organoids retain myoepithelial cells and basement membrane. (A) Detection of keratinpositive and -smooth muscle actin-positive cells in primary mammary organoids at the time of preparation. Frozen sections of mammary organoids embedded in OCT were immunostained (A) simultaneously with mouse anti--smooth muscle actin to detect myoepithelial cells (red) and rabbit anti-keratin antibodies (green) as described in Materials and Methods. (B) Organoids were stained with rabbit anti-laminin antibodies (green). Scale bars: 50 µm. DAPI nuclear counterstain is in blue.