Fig. 5. Accelerated chondrocyte maturation in malformed skeletal structures of Pbx1-/- embryos. Histologic analysis shows H and E and von Kossa-stained transverse sections of wild-type and Pbx1-/- embryos. Aggregations of small chondrocytes are present in the ribs of wild-type (A,B) and Pbx1-/- (C,D) embryos at E13.5. In Pbx1-/- embryos, the center of the growing rib cartilage (green arrows) shows subtle morphologic features of more advanced chondrocyte maturation evidenced by the presence of more cells with small nuclei and large lipid droplets (black arrowheads). At E15.5, the Pbx1-/- rib (G,H) is prematurely comprised exclusively of hypertrophic chondrocytes, some clearly undergoing autolysis (red arrowhead, inset in H), and surrounded by extensive perichondral bone formation (blue arrows). In contrast, normal chondrocyte maturation appears to be present in the distal forelimbs of wild-type (I, J) and Pbx1-/- (K, L) embryos. At E 15.5, von Kossa staining shows the presence of extensive calcium deposits in Pbx1-/- rib cartilage (N), that are practically absent from wild-type cartilage (M). Magnifications: A,C,E,G,I,K (20x); B,D,F,H,J,L (40x); M, N and insets in F,H (100x).
