Fig. 2. Inactivation of Ptch1 during endochondral skeletogenesis resulted in multiple defects. (A-H) Sections of developing long bones. (A,B) Safranin O staining of sections of humerus from 18.5 dpc embryos at low magnification. Proliferative chondrocytes were bright red, whereas hypertrophic chondrocytes were light red. Hypertrophic chondrocytes were not detected in the Ptch1^c/-; Col2a1-Cre mutant. (C,D) Joint regions between radius and carpel bones at 14.5 dpc are shown at higher magnification. Robust upregulation of Pthrp expression in the articular cartilage was observed in the mutant (arrow, D). (E,F) von Kossa staining of the distal humerus at 18.5 dpc. Ectopic ossification was observed in the joint of the mutant (arrow, F). (G,H) Safranin O staining of the radius/ulna/carpel junction at 18.5 dpc. Radius and ulna were fused with carpel bones in the mutant (arrows). (I-N) Skeletal preparations of 18.5 dpc wild-type (I-K) and Ptch1^c/-; Col2a1-Cre (L-N) mouse embryos. (I,L) Whole embryos; (J,M) forelimbs; (K,N) hindlimbs. Inactivation of Ptch1 resulted in extensive ossification. Ectopic ossification at the joint is indicated by arrows (M,N). Skull formation was defective in the mutant (arrowhead, L). S, scapula; H, humerus; R, radius; U, ulna; Fe, femur; Fi, fibula; Ti, tibia.