DISTRIBUTION AND EXPRESSION OF MESSENGER-RNAS FOR THE PROTOONCOGENES C-FOS AND C-JUN IN BONE-CELLS IN-VIVO

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 i nto the role of these proto-oncogenes in bone tissue. Femurs of 4-week -old rats were examined by non-radioactive in situ hybridization, cDNA probes for c-fos- and c-jun-labeled digoxygenin were produced by Poly merase Chain Reaction (PCR). C-fos and c-jun exhibited similar distrib ution in growth plate and bone tissue. Expression of c-fos and c-jun m RNAs in growth plate was observed in the proliferative zone and partly in the upper layer of the hypertrophic zone. In spongy bone, high exp ression of c-fos and c-jun mRNAs was observed in the osteoblast cytopl asm. 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 e xpression was detected in osteocytes that possessed relatively large l acunae in the center of the trabeculae. C-fos and c-jun were also slig htly expressed in osteoclasts. These data strongly suggest that c-fos and c-jun are involved in regulating chondrocyte proliferation as imme diate early genes, and may also be involved in the gene expression of bone matrix proteins as transcription factor (AP-1) in vivo. In additi on, the fact that strong expression was observed in osteoblasts but ha rdly any expression at all in bone lining cells seems to suggest that these genes are also involved in osteoblast activation.