Effects of HSPC depletion on hematopoietic niche cells. (A) HSC-CreERT⁺R26^EYFP/EYFP animals (n = 7-9 per cell population, black bars indicate means) were TAM-treated (4 × 0.2 mg/g BW plus TAM chow) for 4 weeks and BM niche cell subsets were analyzed for EYFP expression. BM LT-HSCs from the same animals served as a positive control for TAM induction. Identification of CXCL12-abundant reticular (CAR) cells, mesenchymal stem/progenitor cells (MSC), osteoblasts (OB), and ECs is shown in supplemental Figure 1C. (B) HSC-CreERT/R26^DTA/DTA animals (n = 7-12 per group) were TAM-treated (as described in panel A) and selected BM niche cell subsets were quantified by flow cytometry. Absolute cell numbers from 2 femora and 2 tibiae were determined. Mean population size of Cre⁻ controls was set to 1. Means ± SD are shown. (C) HSC-CreERT⁺R26^DTA/DTA (Cre⁺) and Cre⁻ control recipients (Cre⁻) were lethally irradiated and transplanted with 5 × 10⁶ WBMCs from B6.ubiEYFP donors which were wt except for ubiquitous EYFP expression (left). Ten weeks after transfer, chimeras were TAM-induced for 4 weeks (4 × 0.2 mg/g BW plus TAM chow) and absolute numbers of LT-HSCs and ECs per 2 femora and 2 tibiae were determined (right); n = 5 per genotype, black bar mean. (D) HSC-CreERT/R26^DTA/DTA recipients (n = 3 to 5 per genotype) were TAM-induced for 4 weeks (4 × 0.2 mg/g BW and TAM chow; see also supplemental Figure 2A,C) and transplanted with 2.5 × 10⁷ WBMCs from B6.ubiRFP donors which were wt except for ubiquitous RFP expression. PB neutrophil (NEUT, CD11b⁺Gr-1^hi) and lymphoid cell (LYMPH, FSC^loSSC^loCD11b⁻Gr-1⁻) chimerism (middle) were monitored thereafter and BM donor chimerism (right) was analyzed 23 weeks after transfer. Experiment is representative of 2 individual replicates.