VDR is necessary for G-CSF–induced suppression of mature osteoblasts. (A) Immunofluorescence staining of osteocalcin. Green: osteocalcin; blue: DAPI. Representative pictures from 2 different sets of experiments are shown. (B) Plasma osteocalcin levels in WT and Vdr^−/− were determined by ELISA. n = 5-6. Open bar: PBS/BSA–treated; closed bar: G-CSF–treated. (C) Villanueva stain of trabecular bone of 7-week-old WT and Vdr^−/− treated with PBS/BSA or G-CSF. Inset in top right quadrant: typical type II (classical cuboidal or columnar with adjacent nuclear clear zone) osteoblast; bottom left quadrant: typical type IV (lining transitional cytoplasm—extremely thin, undulating line) osteoblast. Red arrowhead: type II osteoblasts; blue arrowhead: type III + IV osteoblasts. (D-G) Histomorphometric indices (n = 4). Osteoblast surface per bone surface (OB.S/BS; D), osteoclast surface per bone surface (OC.S/BS; E), number of type II osteoblasts per mm bone surface (F), and number of type III + IV osteoblast per mm bone surface (G). Open bar: PBS/BSA–treated; closed bar: G-CSF–treated. *P < .05; **P < .01; ***P < .001.