Localization of FGFR1/2⁺ cells in embryonic, postnatal, and mature bones. Shown is whole-mount immunofluorescence staining of murine bones analyzed by confocal microscopy with 3D reconstruction. For each sample, images of the epiphysis (A), metaphysis (B), and diaphysis (C) were acquired. For embryonic bones, E15.5 distal femurs are shown. For postnatal bones, perichondrium (PC) covering the anterior iliac ala and fossa and periosteum (PO) covering the iliac body are shown. CD31 was used to identify blood vessels, PN was used to visualized periosteum and preosteoblastic cells, PTHrP was used to identify early mesenchymal progenitors, and DAPI was used to stain cell nuclei. Z-stacks 100-300 μm in depth were acquired at 2-μm intervals for all channels to scan the irregular bone surfaces. Three-dimensional reconstruction was done using Imaris without deconvolution. GP indicates growth plate; PS, primary spongiosa; BC, bone collar; CB, cortical bone; SOC, secondary ossification center; and TB, trabecular bone. Scale bars indicate 50 μm.