Fig. 2. Histological examination of the Mmp13^–/– growth plate defect. (A) Alizarin Red/Alcian Blue staining of whole skeletons from 2-week-old wild-type and Mmp13^–/– mice showing no overt difference in overall skeletal structure between genotypes. (B,C) Von Kossa stained tibia from 15 dpc wild-type and Mmp13^–/– mice shows the presence of mineralized tissue in the diaphyses of both genotypes. No overt difference is evident in proliferating chondrocyte (PC) zones, hypertrophic chondrocyte (HC) zones or primary ossification centers (PO) between genotypes. (D,E) Safranin-O stained metatarsals from 10-day-old wild-type and Mmp13^–/– mice; (F,G) Safranin-O stained tibia from 10-day-old wild-type and Mmp13^–/– mice. Mmp13^–/– mice have an expansion of the hypertrophic chondrocyte (HC) zone of the growth plates of (compare lengths indicated by black bars). (H,I) Safranin-O stained tibia from 12-week-old wild-type and Mmp13^–/– mice. The expansion of the hypertrophic cartilage is ameliorated but Safranin-O staining remains more intense in the mutant growth plate (TB, trabecular bone). Scale bars: 100 µm in B-G; 200 µm in H,I.