Overexpression of MafB in BMMs inhibits osteoclastogenesis. (A-B) BMMs were transduced with pMX-IRES-EGFP (control) or MafB retrovirus and cultured for 3 days with M-CSF alone or M-CSF and various concentrations of RANKL as indicated. (A) Cultured cells were fixed and stained for TRAP. (B) Numbers of TRAP⁺ multinucleated cells were counted (#P < .001 versus control vector; *P < .005 versus control vector). (C-D) BMMs were transduced with pMX-IRES-EGFP (control) or MafB retrovirus and cocultured for 6 days with osteoblasts in the presence of 1,25(OH)₂D₃ and PGE₂. (C) Cultured cells were fixed and stained for TRAP. (D) Numbers of TRAP⁺ multinucleated cells were counted (#P < .001 versus control vector). Results are representative of at least 3 independent sets of similar experiments (A-D). (B,D) Data represent mean ± SD of triplicate experiments.