Evaluation of 4OHT-induced Cre recombination in Tg(BK5-CreERT)I;R26R mice. After 10 days of vehicle control (4OHT (-)) or 4OHT (+) treatment, the presence of β-galactosidase activity in the skin (a & b), the esophagus (c & d), the stomach (e & f), the lower female reproductive tract (g & h) and the thymus (i & j) was examined by X-gal staining. Histological sections of the corresponding X-gal stained organs were counterstained by Nuclear Fast Red and it was then possible to detect positive X-gal stained epithelial cells (arrows). Non-specific β-galactosidase activities were noticed in the hindstomach. FS, forestomach; HS, hindstomach; U, uterus; V, vagina; T, thymus; H, heart; M, thymic medulla; C, thymic cortex.