Fig. 2. Skeletal defects heal through recruitment of progenitor cells of their own origin. (A) Pentachrome staining of the mandibular injury site shows bone matrix deposition (blue-green) at post-surgical day 7. (B) GFP-staining reveals that the majority of the cells in the injury site are immunopositive, indicating their neural crest origin. (C) X-Gal staining (a label for mesoderm) is detectable in the surrounding muscle, but is absent in the defect. (D) After 7 days, the tibial defect exhibits a similar amount of osteoid as the mandible. (E) The bony defect is void of GFP-positive neural crest-derived cells. (F) Instead, the defect is occupied by β-galactosidase-positive cells. cb, cortical bone (outlined); is, injury site. Scale bar: 200 µm.