TEMPORAL VARIATION OF C-FOS PROTOONCOGENE EXPRESSION DURING OSTEOBLAST DIFFERENTIATION AND OSTEOGENESIS IN DEVELOPING RAT BONE

To delineate the implication of c-fos protooncogenic in the osteogenie process, we have investigated the temporal pattern of c-fos mRNA expr ession in fetal and neonatal rat bone during intramembranous and endoc hondral bone formation. Northern blot analysis of mRNA extracted from calvaria and femur showed that expression of c-fos, Histone H4, and os teocalcin mRNAs followed a temporal sequence during bone development. The levels of histone H4 mRNA, a marker of cell proliferation, were hi gh at early stages of fetal development of calvaria and femur, and dec reased until birth. In both the postnatal calvaria and femur, c-fos mR NA levels increased transiently at birth and preceded a rise in osteoc alcin transcripts, a marker of the mature osteoblast phenotype. The im munohistochemical analysis showed that c-Fos protein was expressed in osteoprogenitor cells in the perichondrium and periosteum, and not in mature osteoblasts which expressed markers of differentiated osteoblas ts such as type-I collagen, bone sialoprotein, and osteocalcin. Thus, the transient c-fos proto-oncogene expression during the postnatal lif e that precedes the osteocalcin expression may be involved in the tran sition from the precursor state to mature osteoblasts. These results s uggest that c-fos proto-oncogene may play an important role in osteoge nesis during rat postnatal life. (C) 1995 Wiley-Liss, Inc.