Defective hematopoiesis in Pot1b^Δ/Δ mice. (A) The long-term culture-initiation cell assay was used to enumerate primitive BM progenitor cells in 2-month-old wild-type and Pot1b^Δ/Δ mice (n = 4 mice per genotype, P = 1.0 × 10⁻⁴). (B) Numbers of total BM nucleated cells isolated from 6-month-old Pot1b^Δ/Δ mice compared with age- and sex-matched wild-type controls (n = 7 mice per genotype, P = 2.2 × 10⁻⁴). Error bars represent SEM. (C) Numbers of colonies arising from 10⁴ mono-nucleated wild-type (WT) and Pot1b^Δ/Δ BM cells seeded in methylcellulose. Results are mean from 5 experiments (P = 3.7 × 10⁻³). Error bars represent SEM. Representative images were obtained after 12 days in culture. (D) BM morphology of bone diaphysis of a pair of a 15-month-old wild-type and Pot1b^Δ/Δ mice (magnification ×20). (E) Expression of Sca-1 and c-Kit in multilineage-negative BM cells from wild-type (WT) and Pot1b^Δ/Δ mice. Results were expressed as percentage of total nucleated BM cells for each fraction. The bottom panel shows data from 4 wild-type mice and 9 Pot1b^Δ/Δ mice (P = 1.2 × 10⁻⁷). (F) Annexin V/7-AAD FACS profiles of BM derived from aged wild-type and Pot1b^Δ/Δ mice. Bottom panel shows data from 4 wild-type and 4 Pot1b^Δ/Δ mice (P = 2.9 × 10⁻³).