Hematopoietic abnormalities in MxPtch1^Δ/Δ mice are cell-extrinsic. (A) Schematic of transplantation experiment. Donor BM cells from MxPtch1^fl/fl or wild-type mice (+/+) were transplanted into lethally irradiated recipients. At 4 to 8 weeks after reconstitution, recipients were injected with poly(I:C) to generate either Ptch1-null hematopoietic cells or a Ptch1-null nonhematopoietic cells including the cell niche. (B) Numbers of LKS and B220^loCD25⁺ pre-BII BM cells and thymocytes were measured 4 to 6 weeks after poly(I:C). Mean plus SD calculated from 4 recipients of each genotype. *P < .05 by 2-tailed Mann-Whitney test. (C) Mean cortical thickness plus SD through the mid-shaft of femurs from 3 mice of each genotype. *P < .05 by unpaired 2-tailed t test. (D) Numbers of osteoblasts along femoral shaft of MxPtch1 mice. Mean plus SD from 3 mice of each genotype. *P < .05 by unpaired 2-tailed t test. (E) Histologic features of periosteum from trabecular bone of femurs from MxPtch1 mice. OB indicates osteoblast. (F) Quantitative RT-PCR for RANKL mRNA expression in BM from MxPtch1 mice. Mean plus SD from 2 mice of each genotype. (G) PCR for Ptch1^fl deletion in sorted osteoblasts from MxPtch1^+/Δ mice (lane 1). As a control for nondeleted Ptch1^fl allele, BM cells from a Ptch1^+/fl mouse is shown (lane 2). (H) Quantitative RT-PCR for Gli1 mRNA expression in whole bone samples from control (Ptch^fl/fl) and MxPtch1-null (Δ/Δ) mice. Results are mean plus SD of 3 mice of each genotype.