Fig. 5. Gli3 regulates distal chondrocyte differentiation. Two sets of serial sections, A,B,D,E and G,H,J,K, of E16.5 wild-type (A,D,G,J) and Gli3^–/– (B,E,H,K) limbs were hybridized with riboprobes as indicated. Red dashed lines indicate the distal border of the Ihh expression domain. (C,F,I,L) Models of gene expression domains. (A-C) Gli3^–/– mice display a reduced zone of proliferating chondrocytes compared to wild-type mice (red arrow). (D-F) PTHrP is expressed at similar levels in Gli3^–/– and wild-type limbs, however its domain of expression is shifted towards the distal end of the cartilage anlagen in Gli3^–/– limbs. (G-L) In Gli3^–/– limbs the Fgfr1 expression domain (G-I) is reduced (green arrow) and the Fgfr3 expression domain (J-L) is shifted towards the end of the skeletal elements (blue arrow), indicating an accelerated differentiation of distal chondrocytes. (M) The zone of proliferating chondrocytes (red arrow in A-C) is shortened in Gli3^–/– limbs (^***P=0.00003, n=6). The PTHrP-expressing zone of distal chondrocytes (yellow arrow in D-F) is reduced in Gli3^–/– limbs (^*P=0.00008, n=6). The distance between the Ihh expression domain and the central end of the PTHrP expression domain (gray arrow in D-F) is of similar size in both, Gli3^–/– and wild-type limbs (^**P=0.304, n=6). (N) The zone of Fgfr1-expressing distal chondrocytes (green arrow in G-I) is reduced in Gli3^–/– mice (^*P=0.0002, n=5), whereas the zone of Fgfr3 expression (blue arrow in J-L) is of similar size (^**P=0.19, n=5).