THE PROTOONCOGENE C-RAF-1 IS HIGHLY EXPRESSED ONLY IN THE HYPERTROPHIC ZONE OF THE GROWTH-PLATE

Proto-oncogene c-raf-1, the cellular homologue of the acutely transfor ming oncogene v-raf, has a central role in the signal transduction pat hways. The growth plate, due to its non-overlapping zones of chondrocy te maturation, provides a physiological in situ model for investigatin g the role of c-raf-1 in proliferation and differentiation of chondroc ytes. In this study, Northern blotting was first performed to examine the expression of mRNA for c-raf-1 in the embryonic chick tibial growt h plate. It revealed that the normal levels of c-raf-1 mRNA were assoc iated with the whole growth plate. We then investigated the localizati on of c-raf-1 mRNA and c-raf-1 protein in the growth plate by in situ hybridization and immunohistochemistry in order to determine whether c -raf-1 is involved in chondrocyte maturation. Our results showed that c-raf-1 mRNA and c-raf-1 protein were detected only in the hypertrophi c zone. The data suggest involvement of this proto-oncogene in chondro cyte differentiation and/or hypertrophy rather than in proliferation.