Fig. 1. ß-Catenin is required for bone formation. (A-B') In situ hybridization using digoxigenin-labeled riboprobes against Tcf1 (A,A') or Dkk1 (B,B') on sections of E14.5 humeri of wild-type (A,B) or Dermo1Cre; ß-catenin^c/c (CKO) embryos (A',B'). Arrows indicate the perichondrium. (C-E') Von Kossa staining of sections through the humerus (C-D') or the parietal bone (E,E') of E18.5 wild-type (C,C',E) or CKO embryos (D,D',E'). Boxed areas in C,D are shown at higher magnification in C',D', respectively. Arrows indicate bone (stained black, C' and E) or equivalent regions where bone is missing (D',E'). Asterisks indicate mineralization in the cartilage (stained black, C',D'). (F-K') In situ hybridization using digoxigenin-labeled (F-H') or ³⁵S-labeled riboprobes (I-K') against Col1a1 (F,F',I,I'), Bsp (G,G',J,J') or OC (H,H',K,K') on sections of E18.5 humeri (F-H') or heads (I-K') of wild type (F-K) or CKO embryos (F'-K'). Arrows indicate the bone collar (F-H) or the frontal bone (I-K) in the wild-type animal or the equivalent regions in the mutant embryo (F'-K'). Asterisks indicate the primary spongiosa. (LO') Histological analyses of the humerus from wild-type (L-O) versus CKO (L'-O') embryos. The distal end of the humerus is towards the right in each panel. Boxed regions are shown at a higher magnification as insets. H, hypertrophic chondrocytes. Red arrow in M indicates a red blood cell present in a blood vessel invading the cartilage. Magenta arrow in M' indicates a cell undergoing hypertrophy, whereas the orange arrows indicate immature chondrocytes. Green arrows in N and O indicate the primary spongiosa and the bone collar, respectively. Blue arrows in O' point to perichondrial cells. B, brain; M, marrow cavity; P, proliferating chondrocytes; H, hypertrophic chondrocytes.