Function of fos family genes in the differentiation of chicken chondrocytes

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In this study, we have analyzed the expression levels of Fos/Jun family proteins (AP-1) and the biological effects of ectopic expression of each fos/jun family genes in the cultured chondrocytes or in limb buds of early chicken embryo.1.We have established a methodology to introduce and express exogenous genes in the entire limb region of chicken embryo (day 1.5) by microinjecting avian replication-competent retrovirus vectors. The ectopic expression of all the known fos or jun family genes of chicken (c-fos, fra-2, c-jun or junD) in the limb buds caused no changes in the pattern formation of bones or in the morphology. When the v-fos gene of FBJ-MuSV was introduced, however, all the long bones such as tibia, fibula and femur were shortened significantly (40-70% of the uninfected counterpart). Pathological analysis indicated that v-fos virus infected chondrocytes have assumed the morphology of proliferating chondrocytes and the differentiation into mature or hypertropic chondrocytes were drastically inhibited.2.We have analyzed the expression levels of Fos or Jun family proteins in the cultured chondrocytes deribed from both lower and upper region of steruna (LS and US,respectively). The most clear difference observed between the two types of chondrocytes were the expression levels in c-Jun, LS,which is in more immature stage, expresses higher levels of c-Jun. And ectopic expression of c-Jun in US cells caused stimulation of cellular growth and inhibition of differentiation, indicating the importance of c-Jun function in the chondrocyte differentiation.