Figure 1.

A Triple Transgenic Mouse to Study the Dynamics of Osteolineage Subpopulations

(A) Osterix-Cre (OsxCre) mice were crossed with the Rosa26-loxP-stop-loxP-mCherry reporter mice (Rosa-mCh), which express mCherry fluorescent protein upon Cre-mediated excision of a stop sequence. OsxCre⁺;Rosa-mCh⁺ mice were then crossed with the osteocalcin-Topaz (Ocn:Topaz) mice. Upon tamoxifen injection into the OsxCre⁺;Rosa-mCh⁺;Ocn:Topaz⁺ mice, the Osx⁺ cells and their progeny are labeled red, whereas the Ocn⁺ cells are labeled green. Cells that express osterix following tamoxifen injection and produce osteocalcin are yellow.

(B) Osx⁺, Ocn⁺, and ++ cells were enumerated in femur sections of OsxCre⁺;Rosa-mCh⁺;Ocn:Topaz mice at the indicated time points following tamoxifen injection.

(C) Representative sections of an OsxCre⁺;Rosa-mCh⁺;Ocn:Topaz⁺ mouse 4–6 weeks after tamoxifen injection showing the location of the different osteolineage subsets. Blue indicates DAPI, red mCherry (Osx⁺ cells), and green Topaz (Ocn⁺ cells). Yellow arrow indicates ++ cells and red arrow points to Osx⁺ cells. BT, bone, trabecular; BM, bone marrow cavity. Note the punctated appearance of the mCherry fluorescence. Scale bar, 75 μm.

Experiment repeated once, n = 4/group/experiment (B and C).