ZKS cells stimulate differentiation of hematopoietic precursors. (A) Populations containing hematopoietic progenitors differentiate in culture on ZKS cells. Lymphoid fraction from βactin:GFP⁺ WKM, which contains rare HSCs, was sorted, plated, and analyzed after culture for the time period indicated at top (top row). βactin:GFP⁺ WKM precursor fraction, which contains erythroid, myeloid, and lymphoid progenitors was sorted, plated, and analyzed after culture for time period indicated at top (bottom row). Reanalysis of sorted GFP⁺ lymphoid and precursor fractions from βactin:GFP⁺ WKM (day 0) shows 99% purity. Data are representative of 3 independent experiments. Scatter gates drawn as in Figure 2. (B) Total number of GFP⁺ lymphoid (left), precursor (center), and myeloid (right) cells present over time from cultured βactin:GFP⁺ lymphoid (top, circles) and precursor (bottom, diamonds) fractions (n = 3). Each graph depicts the mean and SD for 3 independent replicates.