Sbds is required for in vitro and in vivo OCG. (A) Photomicrographs of TRACP-stained osteoclasts derived from WT and Sbds-null mice after 6 days in culture with RANKL and M-CSF (both original magnification ×200). Significantly more large multinucleated osteoclasts were observed in WT cultures. (B) The marked difference in OCG between WT and SBDS-null cultures is visible to the eye. Shown are cultures derived from 3 separate WT (left) and Sbds-null (right) mice. (C) The number of osteoclasts and the number of nuclei per osteoclast were quantified. Sbds-null osteoclast cultures exhibited decreased OCG compared with WT cultures, as shown by significantly lower numbers of small (3 or 4 nuclei/osteoclast), medium (5-7 nuclei/osteoclast), and large (≥ 8 nuclei/osteoclast) osteoclasts (n = 8): *P < .01. (D) Western blots showing that Sbds was deleted from Sbds-null monocytes. Levels of RANK and c-Fms between WT and Sbds-null cells were similar after 2 days of culture with RANKL and M-CSF. β-actin was used as a loading control. (E) There was no difference in osteoclast progenitor levels between WT and Sbds-null mice as measured by a colony-forming assay after 10 days in culture with M-CSF and RANKL (n = 3): P > .05. (F) Photomicrographs of TRACP-stained distal femoral bone sections at low magnification (original magnification ×100), and the boxed areas at high magnification (original magnification ×400), representative of more intense staining in WT sections. Osteoclasts were quantified in 3 bone sections per mouse and 3 mice per genotype (right). Significantly more small, medium and large osteoclasts were counted in WT sections (n = 3): *P < .001; **P < .005. (G) DXA analysis of age-matched female animals showed that WT mice had significantly higher BMD (top panel) and BMC (lower panel) in the whole body, lumbar vertebrae, and left femur than Sbds-null mice (n = 6): *P < .01; **P < .005.