Reduced SHP-1 phosphatase activity is responsible for MDS/MPN development in lyn^−/−;PLC-β3^−/− mice. (A) CD34⁻KSL cells were cultured in the presence of IL-3 and SCF for 4 weeks and were analyzed for SHP-1 phosphatase activity. Data are mean ± SD, *P < .05 versus vector control. Similar expression levels of SHP-1 among the cells can be seen in Figure 5D. (B) CD34⁻KSL cells from lyn^−/−;PLC-β3^−/− mice were retrovirally transduced with empty vector or various SHP-1 mutants. Sorted GFP⁺ cells were cultured in the presence of IL-3 and SCF for 4 weeks and then measured for SHP-1 phosphatase activity. (C) Stat5 phosphorylation in the cells from panel B was measured by flow cytometry. Expression of SHP-1 (C) and Stat5 (D) was assessed by immunoblotting. (D) CD34⁻KSL cells from lyn^−/−;PLC-β3^−/− mice were transduced with a bicistronic retroviral vector encoding wt SHP-1, DYE SHP-1, or empty vector, together with GFP. Transduced GFP⁺ cells were sorted and cultured in the presence of IL-3 and SCF. (E) Transduced lyn^−/−;PLC-β3^−/−CD34⁻KSL cells were adoptively transferred (without sorting) to lethally irradiated C57BL/6-Ly5.1 mice. Donor-derived (Ly5.2⁺) CD11b⁺ cells in peripheral blood were analyzed by flow cytometry. **P < .01.