Distribution and expression of mRNAs for the proto-oncogenes c-fos and c-jun in bone cells in vivo

Abstract

In this study we assessed the expression and localization of the proto-oncogenes c-fos and c-jun in normal bone so as to gain more insight into the role of these proto-oncogenes in bone tissue. Femurs of 4-weekold rats were examined by non-radioactive in situ hybridization. cDNA probes for c-fos- and c-jun-labeled digoxygenin were produced by Polymerase Chain Reaction (PCR). C-fos and c-jun exhibited similar distribution in growth plate and bone tissue. Expression of c-fos and cjun mRNAs in growth plate was observed in the proliferative zone and partly in the upper layer of the hypertrophic zone. In spongy bone, high expression of cfos and c-jun mRNAs was observed in the osteoblast cytoplasm. However, there was little expression in bone lining cells. In the bony trabeculae, slight expression of c-fos and c-jun was observed in the premature osteocytes situated close to the bone surface, but no expression was detected in osteocytes that possessed relatively large lacunae in the center of the trabeculae.

C-fos and c-jun were also slightly expressed in osteoclasts. These data strongly suggest that c-fos and c-jun are involved in regulating chondrocyte proliferation as immediate early genes, and may also be involved in the gene expression of bone matrix proteins as transcription factor (M-1) in vivo. In addition, the fact that strong expression was observed in osteoblasts but hardly any expression at all in bone lining cells seems to suggest that these genes are also involved in osteoblast activation.