In vitro experiments. (A) Schematic representation of in vitro experiments performed with young and aged LT-HSCs. (B) Single-cell proliferation assay of young and aged CD61^High and CD61^Low LT-HSCs; size 0: no cells; size 1: 1 to 30 cells; size 2: 31 to 100 cells; size 3: 101 to 1000 cells; size 4: 5000 cells; size 5: 15 000 cells; size 6: 30 000 cells; and size 7: >30 000 cells. (C) Cell cycle analysis using Ki67/4′,6-diamidino-2-phenylindole (DAPI) staining of young CD61^High and CD61^Low LT-HSCs. (D) Cell cycle analysis using Ki67/DAPI staining of aged CD61^High and CD61^Low LT-HSCs. (E) Single-cell division assay of young and aged CD61^High and CD61^Low LT-HSCs. (F) DAPI/γH2AX immunofluorescent staining of aged CD61^High LT-HSCs, CD61^Low LT-HSCs and LT-HSCs. (G) Number of γH2AX foci per cell in CD61^High and CD61^Low aged LT-HSCs.