MEKK2 is dispensable for JNK activation and responses to BMPs in osteoblasts. (A) Primary COBs were isolated from Mekk2+/+ and Mekk2−/− pups, cultured under osteoblast differentiation conditions for 7 d, and immunoblotted with the indicated antibodies. (B) Alternatively, expression of Jun and Fra1 was analyzed by RT-PCR analysis. P = N.S., not significant. (C and D) Primary COBs were cultured under osteoblast differentiation conditions in the presence or absence of 100 ng/mL of BMP2/7 for 7 d, and BMP-induced osteoblast differentiation was determined by ALP activity (C) and ALP staining (D). In C, P = N.S. for all comparisons between Mekk2+/+ and corresponding Mekk2−/− samples. P values for two-way t tests of samples ± BMP2/7 are indicated: ***P < 0.001.