(A) Following a single dose of 5-FU at 300 mg/kg, KitY567F/Y567F mice exhibited sustained low-level hematocrits, and compromised survival (mean ± standard error; n = 5). (B) Failed splenic erythropoiesis in KitY567F/Y567F mice following 5-FU dosing—As analyzed at day 15 post 5-FU, splenic hypertrophy faltered in KitY567F/Y567F mice, and Ter119pos erythroblasts were underrepresented. (C) Cytospin analyses of wild-type Kit+/+ (wt) and KitY567F/Y567F bone marrow preparations (day 15 post 5-FU injection, upper panels). As assessed by flow cytometry, Ter119pos cells also were notably underrepresented in bone marrow among KitY567F/Y567F mice. Data shown are representative of two independent analyses.