Expression of type X collagen, Indian hedgehog and parathyroid hormone related-protein in normal and tibial dyschondroplastic chick growth plates

Tibial dyschondroplasia (TD) is a form of aberrant endochondral ossification in chickens, in that a plug of avascular cartilage (TD lesion) is formed within the growth plate. Histologically, the lesion is filled with apparently transitional chondrocytes that have been unable to differentiate to hypertrophic chondrocytes. We have examined the spatial expression of mRNAs for type X collagen, Indian hedgehog (Ihh) and Parathyroid Hormone-related protein (PTHrP) in the TD growth plate by in situ hybridization in order to ascertain at which stage chondrocyte differentiation is arrested in TD. In the normal growth plate, type X collagen mRNA was expressed by both prehypertrophic and hypertrophic chondrocytes. Indian Hedgehog mRNA was detected in a band of prehypertrophic chondrocytes and PTHrP expression was localized to a narrow band of prehypertrophic chondrocytes and in osteoblasts within the diaphysis. In TD sections, collagen X expression was seen within differentiating cells, within a small number of lesi...