Time course of changes in the expression of c-kit and Mac-1 on lineage⁻ Sca-1⁺ cells after treatment with 5-FU. Mice were treated with a single dose of 5-FU and bone marrow was harvested after the number of days indicated. RBCs were lysed and the remaining cells were stained with anti-B220, Sca-1, Mac-1, and c-kit. The profiles shown are of Mac-1 and c-kit expression on B220⁻, Sca-1⁺ gated bone marrow cells at the various time points. In the day 0 time point, box (a) represents where the majority of long-term reconstituting stem cells are found2 (Figs 1 and 2), while box (b) is where a mixture of functionally defined long- and short-term reconstituting stem cells are found2 (Figs 1 and 2). Box (c) in the day 3 time point represents the population defined here that contains the majority of long-term reconstituting stem cells and possibly other progenitors (see Fig 6). Note that on day 3, the populations equivalent to (a) or (b) are undetectable.