Figure 3.

mpMSC expansion and differentiation in postnatal bone in vivo

(A) Scheme showing CreERT2-mediated recombination of R26-mT/mG Cre reporter for lineage tracing. Tamoxifen was administered at P1–P3 for analysis at P4 and P21 or at P22–P24 for analysis at P27 and 8 weeks, respectively.

(B and C) Tile scan confocal image of Pdgfrb-CreERT2 R26-mT/mG femurs. Mice received tamoxifen at P1–P3 or P22–P24 for analysis at P4 and P21 (B) or at P27 and 8 weeks (C), respectively. Yellow arrowheads mark GFP⁺ chondrocytes in growth plate, white arrowheads GFP⁺ cells in metaphysis, and bone marrow.

(D) Representative confocal images of 3-week-old Pdgfrb-CreERT2 R26-mT/mG femur showing differentiation of GFP⁺ (green) cells into OSX⁺ osteoprogenitors (top), ACAN⁺ chondrocytes (center), and PLIN⁺ adipocytes (bottom).

(E–G) Tile scan confocal image of tamoxifen-treated Lepr-CreERT2 R26-mT/mG mice analyzed at P4 and P21 (E). Higher magnification shows that GFP⁺ cells co-express the BMSC marker PDGFRβ (red, white arrowheads) and osterix (OSX, small arrows). Yellow arrowheads mark GFP⁺ cells in BM, which represent reticular cells; see bottom in (F) for higher magnification. Analysis of Lepr-CreERT2 R26-mT/mG lineage tracing at P27 and 8 weeks uncovers expansion of GFP⁺ cells from the metaphysis (white arrowheads) into BM (yellow arrowheads) (G).

(H and I) Representative confocal image of young (3 weeks) and adult (12 weeks) wild-type femur and graphs showing reduction of OSX⁺ osteoprogenitors (H) and increase of PLIN⁺ adipocytes (arrowheads) (I) with increased age (n = 6; data are presented as mean ± SEM, p values, two-tailed unpaired t test).

(J) Tile-scan confocal images showing strong increase of PLIN⁺ (red) adipocytes after irradiation.

See also Figures S3 and S4