The Muc1 lineage does not contribute to islets after birth. (A-C) Experiment 1: adult Muc1IC2/+; Rosa26EYFP/+ mice (P60) were treated with a single dose of 10 mg tamoxifen, and analyzed after a 120 d chase period (i.e. to six months of age). Immunofluorescence was performed for EYFP lineage label (green), cytokeratin-19 (A, red), insulin (B-C, red) and glucagon (B, white). Lineage label remains restricted to the exocrine compartment (arrowheads indicate labeled duct cells). (D-F) Experiment 2: Muc1IC2/+; Rosa26LacZ/+ neonates received TM via maternal gavage (sequential 10 mg doses at P0 and P1), and were analyzed after 120 d by immunofluorescence as per A-C (using LacZ, in green, as lineage label). LacZ labeling is confined to duct (white arrowheads) and acinar cells, with no detectable expression in islet cells. Scale bars: A-B and D-E, 100 μm; C and F, 25 μm. Abbreviations: du, duct cells; ac, acini.