Fig. 9. Examination of the Ext2^+/– long bone growth plate. Growth plates from ulnae of E18.5 wild type and Ext2^+/– were analyzed for proliferation and differentiation defects. (A,B) Safranin O staining shows a similar overall structure of the growth plates of a wild-type and Ext2^+/– mice. (C,D) Magnification of the rectangular areas in A and B, respectively. Close examination of the chondrocytes in the proliferative zone shows a loss of the characteristic columnar organization normally seen in wild-type growth plates (arrow indicates typical columnar organization). (E,F) Von Kossa stained sections shows the presence of mineralized tissue in the growth plates of both genotypes. (G,H) BrdU labeling shows a similar number of labeled cells in the proliferating zone of the growth plates of wild-type and Ext2^+/– mice. (I-P) In situ hybridization with markers for chondrocyte differentiation show Ext2^+/– mice expressed Ptch1, Ihh, Pthr1 (PPR) and ColX in appropriate places but there is a small decrease in the expression domain of Pthr1 and Ihh (compare arrow in K with arrow in L, and arrow in M with arrow in N). P, Proliferating chondrocytes; Ph, Pre-hypertrophic chondrocytes; H, Hypertrophic chondrocytes. Scale bars: 100 µm in A,B,E-P; 50 µm in C,D.