Fig. 8. Analysis of joint formation in ß-catenin and Ptch1 mutant embryos. (A) Expression of Hip1 in the developing joint (arrows) at 14.5 dpc, as shown by in situ hybridization with ³⁵S-labelled riboprobes. (B) Safranin O staining. Complete fusion of the humerus-ulna joint was observed only in the Ptch1^c/-; Catnb^c/-; Col2a1-Cre mutant (arrow). (C) Consecutive sections of the developing humerus-ulna region at 14.5 dpc were examined by in situ hybridization with the indicated ³⁵S-labelled riboprobes. Upregulation of Bmp2, Bmp4 and Bmp7 (arrows), but not Gdf5, was observed in both Ptch1^c/-; Col2a1-Cre and Ptch1^c/-; Catnb^c/-; Col2a1-Cre mutants. (D) Safranin O staining of sections of the forelimbs that were isolated from 12.5 dpc embryos and cultured in vitro for 4 days. Boxed regions in the humerus-scapula joint are shown at higher magification in the insets. Joint cells are indicated (arrows). The fused joint in the Ptch1^c/-; Col2a1-Cre limb was rescued by noggin treatment. H, humerus; S, scapula. (E) Micromass culture with cells from Catnb^c/c embryonic limb bud mesenchyme at 12.5 dpc. Cartilage nodules were stained blue with Alcian Blue. ß-catenin was deleted by Cre-Adenovirus infection. Bmp2 and noggin were added to the culture on day 2 of the 5-day culture period.