Efficient Prx1Cre- and Col2Cre-mediated targeted gene recombination in fracture callus.

A tissue section from long bone of Prx1Cre; RosaR mice show intense LacZ staining in bone and cartilage, but not in bone marrow (A). The boxed region in A, shown at a higher magnification (20×), demonstrates LacZ staining in periosteum (arrows in B). Fracture callus at day 7 from Prx1Cre; RosaR shows intense LacZ staining throughout the callus region at the cortical bone junction (C). Boxed regions in C (from top to bottom), shown at a higher magnification (20×), illustrate effective gene recombination in chondrocytes (D), mesenchyme (E) and osteoblasts (arrows in F). Col2Cre; RosaR fracture callus at day 5 shows effective gene recombination in chondroprogenitors and chondrocytes, but not mesenchymal cells (G). Higher magnification images (20×) in the boxed region (from top to bottom) show positive LacZ staining in chondrocytes (H) but not in mesenchyme cells (I) or osteoblasts (J).