a, Noggin (green) in the wild-type tibial metaphysis was detected in Emcn+ (red) endothelial cells as well as surrounding mesenchymal cells. In contrast, the diaphysis contained Noggin+ haematopoietic cells, whereas only weak staining was seen in sinusoidal blood vessels. b, Panels show higher magnifications of insets in a. Nuclei, DAPI (blue). c, Confocal tile scans of osteopontin-immunostained tibia sections showing partial restoration of trabecular bone formation in 4-week-old RbpjiΔEC mice after administration of recombinant Noggin. Left panels show saline-treated RbpjiΔEC mutants and littermate controls. Nuclei, DAPI (blue). d, e, Noggin treatment restored the bone formation rate (BFR, d) and mineral apposition rate (MAR, e) in RbpjiΔEC long bone to control level (n = 6 mice from 4 independent litters). Data represent mean ± s.e.m. One-way ANOVA was performed along with Bonferroni’s multiple comparison post-hoc test. f, Systemic administration of recombinant Noggin protein reduced the number of Osx+ cells (green) and increased Runx2+ early osteoprogenitors in the RbpjiΔEC metaphysis in comparison to vehicle-treated (saline) mutants. g, Maximum intensity projection of Emcn-immunostained control and RbpjiΔEC tibia sections after treatment with saline or recombinant Noggin, as indicated. Emcn staining intensity was increased in Noggin-treated RbpjiΔEC samples, and the organization of endothelial column and arch structures was partially restored. Dashed lines indicate position of boundaries between endothelial arches (A) and columns (C) as seen in littermate control samples. h, i, Confocal images of VEGF-A (green) immunostained tibia sections showing growth plate chondrocytes in RbpjiΔEC mice after Noggin treatment. Note partial restoration (arrows) of VEGF-A expression in Noggin- but not vehicle control-treated (Saline) RbpjiΔEC mutants (h). Nuclei, DAPI (blue). Quantification data showing fluorescence intensity (in arbitrary units) of VEGF-A expression recovered in the tibial sections of these animals (i) (n = 6 mice from 4 independent litters). Data represent mean ± s.e.m. One-way ANOVA was performed along with Bonferroni’s multiple comparison post-hoc test.