Proliferation was monitored in Klf5ERΔ and control Klf5fl/fl colon by staining sections for Ki-67. Images are stained with DAPI (blue), Ki-67 (red) and merged (DAPI + Ki-67). Panels A, B and C show colonic tissues from day 5 tamoxifen-treated control Klf5fl/fl and Panels D through O, those from Klf5ERΔ mice. Panels D-F, G-I, J-L and M-O are representative of 3, 5, 7, and 11 day post-tamoxifen treatment respectively. In the control Klf5fl/fl mice, a strong Ki-67 staining pattern was located at the bottom of the colonic crypts (Panel B). Panels E and H show a decrease in Ki-67 staining at days 3 and 5 after the start of tamoxifen treatment, respectively. Ki-67 expression gradually returns to baseline by days 7 and 11 (Panels K and N, respectively).