EXPRESSION OF INTERSTITIAL COLLAGENASE DURING SKELETAL DEVELOPMENT OFTHE MOUSE IS RESTRICTED TO OSTEOBLAST-LIKE CELLS AND HYPERTROPHIC CHONDROCYTES

We determined the expression pattern of the matrix metalloproteinase i nterstitial collagenase (MMP-1) during mouse embryo development using in situ hybridization and immunohistochemistry. Localized MMP-1 mRNA w as first detected at 14.5 days postconceptus. The spatial and temporal expression was restricted to areas of endochondral and intramembranou s bone formation, such as in the mandibula, maxilla, clavicle, scapula , in the vertebrae, and in the dorsal, but not the ventral part of the ribs. The highest levels of MMP-1 transcripts and MMP-1 protein were found in the metaphyses and diaphyses of the long bones. MMP-1 was exp ressed by hypertrophic chondrocytes and by osteoblastic cells localize d along the newly formed bone trabeculae. No expression was detected i n osteoclasts. Two other related members of the MMP family, stromelysi n-l (MMP-3) and stromelysin-a (MMP-10), were not expressed during days 7.5 and 16.5 of mouse embryogenesis. The tissue-specific expression o f MMP-1 and the exclusive ability of interstitial collagenase to diges t native collagen of types I, 11, III, and X, the major components of bone, cartilage, and tendon, strongly suggests an important and specif ic function of this enzyme in bone development and remodeling.