Fig. 3. Hypertrophic callus remodeling and bone formation are delayed in Mmp9^-/- mice. Transcripts for collagen type X (ColX, yellow) and osteocalcin (Oc, black) are superimposed onto adjacent sections stained with SO-FG to illustrate the location of hypertrophic cartilage and new bone (same sections showing only SOFG staining are also shown in Fig. 2B). By 14 days, ColX (yellow) is downregulated in the wild-type callus but remains strongly expressed throughout the Mmp9^-/- callus. Conversely, Oc is strongly expressed in the wild-type callus by 14 days but is expressed at much lower levels in the Mmp9^-/- callus. Blue dotted lines represent the boundary of the callus. Scale bar: 1 mm.