Conclusions
Osteoblastic activities at the sites of modeling-based bone formation may be maintained in the absence of osteoclasts.
Methods
We performed histochemical analyses on the bone of eight-week-old male wild-type and c-fos-/- mice. Histochemical analyses were conducted on primary trabeculae near the chondro-osseous junction (COJ), sites of modeling-based bone formation, and secondary trabeculae, sites of remodeling-based bone formation, in the femora and tibiae of mice.
Results
Alkaline phosphatase (ALP) immunoreactivity, a marker of osteoblastic lineages, was observed in the metaphyseal trabeculae of wild-type mice, while ALP was scattered throughout the femora of c-fos-/- mice. PHOSPHO1, an enzyme involved in matrix vesicle-mediated mineralization, was predominantly detected in primary trabeculae and also within short lines of osteoblasts in secondary trabeculae of wild-type mice. In contrast, femora of c-fos-/- mice showed several patches of PHOSPHO1 positivity in the primary trabeculae, but there were hardly any patches of PHOSPHO1 in secondary trabeculae. Calcein labeling was consistently observed in primary trabeculae close to the COJ in both wild-type and c-fos-/- mice; however, calcein labeling in the secondary trabeculae was only detected in wild-type mice. Transmission electron microscopic examination demonstrated abundant rough endoplasmic reticulum in the osteoblasts in secondary trabeculae of wild-type mice, but not in those of c-fos-/- mice. Conclusions: Osteoblastic activities at the sites of modeling-based bone formation may be maintained in the absence of osteoclasts.