Figure 4: Immunohistochemistry of Runx2 and Osterix in mandibular osteoblasts of mice at newborn stage. Runx2 protein which was expressed in secondary hypertrophic chondrocytes was not localized in the cells gathering in the erosive front of mandibular secondary cartilages (a), but in some osteoblasts surrounding the trabecular bone and some osteocytes buried in the trabecular bone in the mandible (b). The expression of Runx2 protein in condylar hypertrophic chondrocytes was significantly stronger than that in osteoblasts (e). Meanwhile, Osterix was localized in some osteoblasts and bone marrow cells in subchondral bone area (c), while more positive osteoblasts and osteocytes were visualized in the trabecular bone area (d). The immunohistochemistry of Osterix in hypertrophic chondrocytes of the center of the uncalcified Meckel’s cartilage is still significantly more intense than that in the osteoblasts (f). (** ) CD: condylar cartilage; PM: the posterior portion of intramandibular Meckel’s cartilage; and OB: osteoblasts. Scale bar: 25 μm for (a, b, c, and d).