Fig. 2.

Differential responses of Lgr5⁺ vs. Bmi1⁺ ISCs to acute radiation injury. (A–H) Direct fluorescence detection of Lgr5-eGFP⁺ vs. Bmi1-YFP⁺ ISCs. Phalloidin is depicted in red and DAPI in blue. (A and B) Unirradiated duodenum with Lgr5-eGFP⁺ cells in the crypt bases and rare Bmi1-YFP⁺ ISCs labeled with 1-d tamoxifen exposure in Bmi1-CreER; Rosa-YFP mice. (C–F) Lgr5-eGFP⁺ ISCs are completely lost (C and E), whereas Bmi1-YFP⁺ ISCs (D and F) persist by 2 and 4.5 d after 12 Gy whole-body irradiation. (G and H) Lgr5-eGFP⁺ ISCs return in sporadic (≈1/180) crypt bases (G) and Bmi-YFP⁺ ISCs are quantitatively unchanged by 7 d after 12 Gy whole-body irradiation (H). (I and J) Olfm4 ISH demonstrates loss of Olfm4 expression in crypt bases by 2 d after 12 Gy irradiation confirming loss of Lgr5 expression. (K–N) FACS analysis demonstrates loss of Lgr5-eGFP⁺ epithelial cells by 2 d (K and L), in contrast to expansion of Bmi1-YFP⁺ cells/progeny by 4.5 d after 12 Gy whole-body irradiation (M and N). (O–R) Enhanced proliferation of Bmi1-YFP⁺ ISCs by 2 d after 12 Gy irradiation revealed by EdU incorporation (*P = 0.0006, n = 3 mice, unpaired Student's t test). (Scale bars: 50 μm.)