A. Representative images of X-gal staining with no tamoxifen, and 1, 5, and 12 days post tamoxifen (1 mg) injection. X-gal staining (blue) after 1 tamoxifen injection indicates Cre recombinase activity at the crypt base. Days 5 and 12 denote lineage tracing. B. Percentage of crypts expressing Cre recombinase activity 1, 5, and 12 days post tamoxifen injection (means from 3 mice).