Fig. 5. Overexpression of Wnt5a in chondrocytes delays chondrocyte differentiation. (A) Morphological analysis of Col2a1-Wnt5a embryos. H, humerus; R, radius; U, ulna. Upper panel: skeletal preparations of mouse embryos at 18.5 dpc. The Col2a1-Wnt5a mouse (right) had shorter snout, smaller rib cage, shorter limb long bones and reduced ossification (arrow) than did the wild type (left). Lower panel: sections of the forelimb at 15.5 dpc. Chondrocyte hypertrophy (arrow) is only detected in a small area in the humerus in the Col2a1-Wnt5a embryo. (B) Expression of markers for prehypertrophic chondrocytes (Ihh and Pthrpr) and hypertrophic chondrocytes (Col10a1) in 14.5 dpc embryos. Wnt5a is expressed at a higher level in Col2a1-Wnt5a number 25 than in Col2a1-Wnt5a number 17. In Col2a1-Wnt5a number 17, there is only one Ihh and Pthrpr expression domain and the Col10a1 domain is much smaller. The undifferentiated chondrocyte region in the wild-type embryo (black line) is shorter than that in Col2a1-Wnt5a number 17 (yellow line), but the entire skeletal element is longer in the wild-type embryo. In Col2a1-Wnt5a number 25, the expression of Ihh, Pthrpr and Col10a1 is not detected. (C) BrdU-labeled cells on sections of the distal radius of 14.5 dpc embryos are shown. Fewer chondrocytes were labeled by BrdU in the Col2a1-Wnt5a embryos, as Wnt5a was expressed at a higher level. The columnar chondrocyte structure was disrupted in the Col2a1-Wnt5a embryo.