Fig. 2. Cartilage-specific PPR ablation. (A) Tissue-specific activity of Cre recombinase. A Col2-Cre:R26R doubly transgenic, E15.5 embryo was stained with X-gal to visualize Cre activity. As well as chondrocytes, a part of perichondrium, ligaments, tendon and intra-joint tissues are stained blue representing lacZ activity. (B-K) Tibia of E17.5 embryos of homozygous floxed mice with (C,E,G,I,K) or without (B,D,F,H,J) Col2-Cre gene. (B-E) Bright field views of Hematoxylin and Eosin stained sections. (F-K) Dark field views of in situ hybridization with type II collagen (F,G), type X collagen (H,I) and PPR detected by a specific probe for the E1 exon (J,K). (L,M) The sterna of E 16.5 day-old embryos at the third inter-costal space of Ppr^fl/fl (L) and Col2-Cre:Ppr^fl/fl(M). The sternum of the Col2-Cre:Ppr^fl/fl mice is mostly occupied with hypertrophic chondrocytes.