Fig. 7. Osteoblast versus chondrocyte differentiation from the perichondrial progenitors. (A-D) Histology of the femur from an E18.5 DKO embryo. Areas in yellow, green and blue boxes (in A) are shown at a higher magnification in B-D, respectively. H, hypertrophy zone; PC, perichondrium; RC, red blood cells. Red asterisks in A,B indicate mesenchymal cells; green asterisk in C marks the death zone. (B1-B3) In situ hybridization using ³⁵S-labeled riboprobes against Ap (B1), Osx (B2) and Col10a1 (B3), on sections adjacent to that in A. Areas similar to that in B are shown at the same magnification. Hybridization signals are in red. PC, perichondrium. (E,F) Histology of the humerus from an E18.5 Dermo1-Cre; ß-catenin^c/c embryo. Area in purple box (E) is shown at a higher magnification (F). Asterisks in E,F indicate ectopic chondrocytes. (F1,F2) In situ hybridization using ³⁵S-labeled riboprobes against Col2a1 (F1) and Col10a1 (F2), on sections adjacent to that in E. Areas similar to that in F are shown at the same magnification. Hybridization signals are in red. PC, perichondrium. (G-G1) Histology of the humerus from an E18.5 Ihh^-/- embryo. Asterisk in G indicates areas of vascularization. (G1) Area in yellow box (in G) is shown at a higher magnification in G1. Green lines indicate the outer (2) and inner (1) regions of the perichondrium; red and yellow arrows indicate cuboidal and elongated cells, respectively. (H-J1) In situ hybridization using ³⁵S-labeled riboprobes against Runx2 (H,H1), Osx (I,I1) and Ap (J,J1) on sections adjacent to that in G. (H1-J1) Areas similar to that in G1, marked by yellow boxes in H-J, are shown at the same magnification as in G1. Hybridization signals are in red. Green lines demarcate the outer and inner regions of the perichondrium.