HSPCs are transiently driven into cell cycle by Notch signaling. (A) Lethally irradiated mice were reconstituted with 5-FU–treated donor Rag1^−/− BM cells transduced with MigR1 control or activated Notch1. At 2 weeks and 6 weeks after transplantation, the mice were injected with BrdU and then killed 16 hours later. (A) The donor-derived BM HSPC compartment (GFP⁺Lineage⁻Sca-1⁺c-Kit⁺) was stained with 7-AAD and intracellular antibody against BrdU. Cells entering cell cycle are BrDU⁺ with 2N DNA content by 7-AAD stain. Apoptotic cells are BrdU⁻ and found in the sub2N region of the 7-AAD stain. (B) Bar graph analysis of BrdU⁺ MigR1 control and Notch HSPCs entering cell cycle at 2 and 6 weeks after transplantation. Three mice per condition.