Figure 3.

Msx1 marks ectopic crypts formed on the small intestinal villi upon Apc loss. Fluorescent microscopy images of Msx1 (green fluorescent signal) and PCNA (red florescent signal) protein localization in Apc^cKO/cKO Villin-CreERT2 small intestine 2, 3, and 4 days after tamoxifen administration. Rare Msx1-positive cells (white arrow) in PCNA-negative areas are observed at day 2. At day 3, groups of cells expressing Msx1 are detected on the villi (see insets Nos 1 and 2). At day 4, ectopic crypts containing Msx1- and PCNA-positive cells are formed on the villi (white arrowheads in inset No. 3). Some of these cells co-express Msx1 and PCNA (yellow fluorescence). Occasionally, villus cells produce PCNA, but they are Msx1-negative (red arrow in inset No. 4). Specimens were counterstained with 4′,6-diamidine-2′-phenylindole dihydrochloride (DAPI; nuclear blue florescent signal). Notice that the purple color results from the coalescence of the blue and red fluorescent signal. Boxed areas are magnified in the insets. Scale bar: 0.15 mm.