Transcriptional regulation of type X collagen during chondrocyte maturation.

The 18-day embryonic chick sternum expresses type X collagen only in the cephalic, presumptive mineralization zone which consists primarily of hypertrophic chondrocytes. The smaller chondrocytes of the caudal, permanent cartilaginous zone do not express this protein. Run-off transcriptions of nuclei isolated directly from cephalic and caudal 18-day embryonic sterna demonstrate that type X collagen is specifically transcribed by cells of the cephalic zone. In addition, type X mRNA is localized to the cephalic zone as detected by in situ hybridization. The results suggest that the cell-specific expression of the type X collagen gene is due entirely to transcriptional regulation.