<i>Mmp13</i> expression during non-stabilized fracture healing.

<p>(Left column) Safranin-O/Fast Green (SO) and Trichrome (TC) stained sagittal sections through the WT callus at 6 (A), 10 (E) and 14 (I) days post-fracture. Cartilage (red) develops during the soft callus phase of healing (A), is resorbed during the hard callus phase (E) and is replaced by bone (blue, I). (Middle/Right column) In situ hybridization analyses of <i>Mmp13</i> expression and osteoblast/chondrocyte differentiation markers. (B–D) At 6 days post-fracture, <i>Mmp13</i> is expressed in the callus and overlaps with <i>Col1</i>-expressing cells (early osteoblasts) but not <i>Mmp9</i>-expressing cells (osteoclasts and inflammatory cells). (F–H) At day 10, <i>Mmp13</i> mRNA is detected in hypertrophic chondrocytes also expressing <i>Col10</i> and <i>Vegf</i>. (J–L) At day 14, <i>Mmp13</i> is expressed in mature osteoblasts co-expressing <i>Col1</i> and/or <i>Oc</i>. Scale bars: A, E, I = 1mm; B-D, F-H, J-L-200 µm.