Expansion of BM stromal cells in Rs1 mice. Nine-week-old (9 wk) and 12-week-old (12 wk) control (Ctrl) and ColI(2.3)⁺/Rs1⁺ (Rs1) mice (n = 4-12 per group) were used for these analyses. (A) Gating strategy used to identify subpopulations of endosteal BM stromal cells (top row) and to monitor ColI(2.3) promoter activity in ColI(2.3)-tTA/TetO-H2B-GFP double-transgenic reporter mice (bottom row). (B) Frequencies of stromal BM cell subpopulations expressing GFP in ColI(2.3)-tTA/TetO-H2B-GFP mice (n = 4). (C) Total cells for the indicated endosteal BM stromal cells. (D) Quantitative RT-PCR analysis of purified OBCs for expression of the indicated osteoblastic lineage genes. Data are expressed as log₂ fold relative to the average of the Ctrl samples (set to 0). Averages are shown as black bars. (E-F) Frequencies of CFU-F, CFU-Alk, and CFU-OB formed by OBCs (E) and MSCs (F) isolated from 12-week-old Ctrl and Rs1 mice. Data are mean ± SD. *P ≤ .05. **P ≤ .01. ***P ≤ .001.