Fig. 9. Altered ECM remodeling in Mmp9^–/–, Mmp13^–/– and Mmp9^–/–;Mmp13^–/– long bones. (A) Immunostaining of 2-week-old tibia of wild-type, Mmp9^–/–, Mmp13^–/– and Mmp9^–/–;Mmp13^–/– mice with an antibody to the DIPEN neoepitope of Mmp-cleaved aggrecan. Cleaved aggrecan (brown staining) is present along the primary front of ossification in wild-type, Mmp9^–/– and Mmp13^–/– bones, no positive staining is apparent in Mmp9^–/–;Mmp13^–/– bones. (B) Immunostaining of 2-week-old tibia of wild-type, Mmp9^–/–, Mmp13^–/– and Mmp9^–/–;Mmp13^–/– mice with an antibody to the 3/4 cleavage fragment of col1 and col2. The primary front of ossification (indicated by a broken line) shows the presence of cleaved collagen (pink staining) in transverse septa surrounding the most terminal hypertrophic chondrocytes (arrows) in wild-type and Mmp9^–/– bones, along the trabeculae of the developing trabecular bone (arrowheads) in wild-type and Mmp13^–/– bones, and at random throughout the hypertrophic chondrocyte zone (arrows) and trabecular bone (arrowheads) in Mmp9^–/–;Mmp13^–/– bones. Scale bars: 200 µm in A; 100 µm in B.