Fig. 1. Tamoxifen (TM)-dependent and osteoblast-specific Cre activity using Cre-ER^TM mice. (A) Cre-ER^TM transgenic mice mated with ROSA26 Cre reporter mice (R26R). TM was injected daily into pregnant females for 3 days from E13.5 to E15.5. Cre-negative and -positive littermates were stained for β-gal at E18.5. (B) Cre activity in long bones. Forelimbs were stained for β-gal at E18.5. C, chondrocytes; black arrow, periosteum; red arrow, osteogenic center. Scale bars: 50 µm. (C) Cre recombination in calvariae at E15.5, E16.5 and E18.5 in whole head (lateral and overhead views) and histology of E18.5 calvariae. Broken line, areas of parietal bones (P). Scale bar: 20 µm. (D) BMPR1A as evaluated by immunohistochemistry using cKO calvariae at E18.5. BMPR1A, green; DAPI (nuclei), blue. Scale bars: 10 µm. (E) Immunoblotting for phosphorylated Smad 1/5/8 using E18.5 calvariae. The membrane was treated with polyclonal rabbit anti-phospho-Smad1/5/8 (1:1000) and monoclonal mouse anti-beta-actin (1:2000), and visualized by ECL.