Average percentages of apoptotic c-kit⁺/lin⁻ cells in BM. c-kit⁺lin⁻ cells were gated separately from the remainder of the BM population and analyzed for MC540 fluorescence intensity (MC540 bright cells represent the apoptotic fraction of the gated population). The same mice used to obtain results in Fig 1 were assessed independently in two separate experiments. The bars represent the mean ± 1 SEM.