Increased apoptosis in pre–pro-B cells induced by Cbfβ-SMMHC. Flow cytometric analysis for annexin V staining analysis in live (PI⁻) BM CLPs, pre–pro-B, pro-B, and pre-B populations from control (Cbfb^+/56M), control-i (pIpC injected Cbfb^+/56M), and restored (pIpC injected Cbfb^+/56M/Mx1Cre) mice. Shown are representative data from 3 independent experiments. Numbers on plots are percentages of displayed cells.