FIG. 5.

LRCs undergo differentiation in mutant mice. (A to C) Autoradiography of mouse intestine injected with tritiated TdR 20 days after labeling. In wild-type epithelium (A), LRCs (arrow) are found in the crypts above Paneth cells. In 4-day mutant epithelium (B), LRCs (arrow) are found in similar numbers but at aberrant positions. Bar, 25 μm. (C) Scheme of the localization pattern of LRCs in control (left) and mutants for which the frequency of LRCs in a certain position is depicted as black lines of different widths. Initially, LRCs in uninduced β-catenin^−/lox mice (0d) are localized as in the control. Two days after β-catenin deletion, mutant LRCs are dispersed throughout the crypt area (data not shown), followed by an even distribution along the crypt-villus axis at day 4 (4d). We quantified 300 crypt-villus units for two mice per group. In both groups, about 20% of crypts (control) or crypt-villus units (mutant) were found to contain LRCs, which were scored as positive when retaining more than five grains per nucleus. (D and E) Counterstaining for the enterocytic differentiation marker FabpL demonstrates that LRCs (arrows) are differentiated in the mutant 4 days after β-catenin deletion (E), whereas they remain undifferentiated in the control (D). The picture gives a representative example; all LRCs in the mutants express FabpL at this time point. Bar, 25 μm. (F to I) In vivo intestinal epithelial cell migration assay. Proliferating cells were BrdU pulse-labeled immediately prior to tamoxifen injection, and subsequently migrating cells were localized by immunohistochemistry at day 2 (F and G) and day 3 (H to I) after tamoxifen injection in control (F and H) and mutant (G and I) epithelium. Bar, 50 μm. wt, wild type.