Fracture healing induces expression of the proto-oncogene c-fos in vivo Possible involvement of the Fos protein in osteoblastic differentiation

Here we report marked in vivo expression of the c-fos gene in the external soft callus (ESC) and periosteal hard callus (PHC) at the fracture site of adult rat tibia. Northern-blot analysis showed that the ESC expressed a high level of c-fos mRNA from post-fracture day 10 to day 28, the time when endochondral ossification progressed, and that the ossifying PHC also expressed c-fos mRNA. This c-fos expression was followed by sequential expression of the genes for alkaline phosphatase, osteopontin and osteocalcin, which are osteoblastic markers. Immunohistochemical analysis showed that the c-Fos protein was predominantly located in osteoblasts in the ossifying calluses.