Quantitative analysis of extracellular matrix proteins in hypertrophic layers of the mandibular condyle and temporal bone during human fetal development

A computer image analysis of immunostained extracellular matrix (ECM) proteins (collagen types I, II, III and V, fibronectin and tenascin) in hypertrophic layers in the mandibular condyle and temporal bone of human fetuses, which ranged in gestational age from 12 to 32 weeks, was performed. The percentage of cells positive for proliferating cell nuclear antigen (PCNA) increased in almost the same manner in each region. The level of PCNA was markedly elevated at 16 weeks. The percentage of PCNA-positive cells was low in temporal bone and in the bone-forming layer of the mandibular condyle at 24 weeks. Specific concentration patterns of proteins in the ECM were found at each stage of development. The extent of accumulation of fibrillar collagen and of fibronectin differed, while those of other proteins in the ECM, such as tenascin, osteocalcin and osteonectin, were similar at the two sites.