GENE-EXPRESSION DURING CARTILAGE DIFFERENTIATION IN TURKEY TIBIAL DYSCHONDROPLASIA, EVALUATED BY IN-SITU HYBRIDIZATION

Gene expression and alkaline phosphatase (AP) activity, associated wit h chondrocyte differentiation, were evaluated in the epiphyses of norm al and tibial dyschondroplasia (TD)-afflicted turkeys. In the normal t urkey growth plate (GP), osteopontin (OPN) and type X collagen genes w ere expressed by the hypertrophic cells in both GP and secondary ossif ication center, parallel to manifestation of AP activity. Collagen typ e II gene expression was restricted to the nonhypertrophic chondrocyte s at the upper part of tile GE OPN or collagen type X genes were not e xpressed within the TD lesion. However, these genes were expressed in areas proximal and distal to the lesion, suggesting that after reachin g Partial differentiation, chondrocytes within the developing TD lesio n de-differentiate into cells that resemble chondrocytes in che prehyp ertrophic zone. This suggestion is supported by the observation that t he cells in the lesion expressed the collagen typo TI gene. In some ca ses, the TD lesion was invaded by fibroblastlike cells that did not ex hibit any AP activity or express the OPN gene. No lesions were observe d in the secondary ossification centers.