Presence of osteonectin/SPARC in mandibular condylar cartilage of the rat.

Osteonectin/SPARC was most abundantly present in adherent osseous tissue of the cartilage explants. In cartilage explants with ossification fronts, it appears to be present in hypertrophic chondroblasts and in the mineralised extracellular cartilage matrix. In a number of cartilage explants it could be demonstrated in the fibroblastic cells of the perichondrium and, intra- and extracellularly, in cartilage located adjacent to the perichondrium. In young mandibular condylar cartilage (20 days post-conception up to 7 days of age) osteonectin/SPARC was characteristically present in the transitional zone, a small area of differentiating skeletoblasts. In cartilage, osteonectin/SPARC might play a role in the process of mineralisation and subsequent replacement by bone. It seems to be an important marker of skeletal differentiation processes.