Aged Runx1^−/− stem/progenitor cells maintain proliferative ability. (A) Graphs showing percentage of GFP⁺ cells in PB and number of GFP⁺c-Kit⁺Lin⁻ cells in BM of recipients of Runx1^+/+ (n = 3) and Runx1^−/− (n = 3) BM cells, 2 years after transplantation. (B) Colony assay of GFP⁺c-Kit⁺Lin⁻ cells from recipients of Runx1^+/+ (n = 3) and Runx1^−/− (n = 3) BM cells, 2 years after transplantation. (C) Colony assay of KSL cells from 40-week-old mice, after 30 days of long-term culture on OP9 stromal cells. Statistical differences using the unpaired Student t test are given at the bottom.