Signaling aberrations in Ptpn11^D61Y cells. (A,B) Lin⁻ BM cells from control and Ptpn11^D61Y mice were purified by FACS and starved for 1 hour in serum-free medium before they were either left untreated or stimulated with 50 ng/mL SCF for 5 or 10 minutes. Cells were fixed, permeabilized, and stained with anti-cKit and anti-Sca1 and antibodies against pErk (A) and pAkt (B). Levels of phospho-specific antigens in the LSK population were determined by flow cytometry. (C,D) GMPs from control and Ptpn11^D61Y mice were purified and starved before they were either left untreated or stimulated with GM-CSF (5 ng/mL) for 5 or 10 minutes. Cells were fixed, permeabilized, and stained with antibodies against pErk (C) and pStat5 (D), and levels of phospho-specific antigens quantified by flow cytometry (± SEM; *P < .05, by Wilcoxon-Mann-Whitney test).