Muc1+ cells give rise to endocrine cells during embryogenesis. (A) A single dose of 5 mg tamoxifen was given to pregnant mice at E11.5, and pancreata of Muc1IC2/IC2; Rosa26EYFP/+ offspring were analyzed at E17.5 by immunofluorescence for EYFP (green), DBA lectin (red) and DAPI (blue). Arrowheads indicate DBA+ cells co-expressing EYFP. (B) Quantification of observed co-labeling at E17.5, following tamoxifen administration at indicated time points. Scatter plot depicts the percentages of DBA+ (orange), amylase+ (green), insulin+ (red) and glucagon+ (blue) cells co-expressing EYFP. Each point represents an independent embryo, and means are indicated by dotted lines. (C-D) Pancreata of Muc1IC2/IC2; Rosa26EYFP/+ embryos, administered TM at E11.5 as in (A), stained at E17.5 for EYFP (green), insulin or glucagon (red) and DAPI (blue). Inserts: confocal z-projection (1.36 μm) of the boxed areas, to confirm localization of EYFP to hormone-producing cells. Scale bars: 25 μm.