Expression of type X collagen mRNA levels in embryonic chick sternum during development.

Embryonic chick sternum cartilage exhibits profound spatial and temporal changes in Type X collagen biosynthesis during development. Production of this collagen is confined to the presumptive calcification region and its expression is not acquired until stage 43. To examine the mechanisms responsible for regulation of developmental changes in biosynthetic expression of Type X collagen, we determined the levels of translatable Type X procollagen mRNA employing a cell-free translation system. We found that mRNA capable of directing Type X collagen synthesis was present exclusively in cartilage destined to undergo calcification and that its levels were nearly equivalent at all stages of development. These findings suggest that expression of Type X collagen in embryonic chick sternum is determined at the translational level.