Cre recombinase activity in tamoxifen-treated Col2a1-CreER mouse and acceleration of bone formation in the IVD of tamoxifen-treated Col2a1-CreER/β-cateninfl/fl mouse. Col2a1-CreER (A), Col2a1-CreER/Rosa26A (B), β-catenin fl/fl (C, E and G) or Col2a1-CreER/β-cateninfl/fl (D, F and H) mice received three daily injections of tamoxifen (200 µg/20 µl/day) when they were 5-days-old. The vertebrae were dissected at ages of 5-weeks-old (A and B) or 9-weeks-old (C–H). The tissues sections were subjected to β-galactosidase activity staining (A and B) or HE staining. Green bars represent EP and yellow arrows show bone formation. Bar, 300 µm.