Morphology of cells expressing cytoplasmic tyrosine mutants of the FIΔ activated mutant. (A) Cells expressing the indicated cytoplasmic tyrosine substitutions were cultured in the absence of growth factor for 5 days and cytocentrifuged to assess morphology. Original magnification, × 400. (B) Differential counts from cytospins done at day 5. For each sample, 200 cells were scored microscopically for morphology. The combined data from a minimum of 3 independent experiments is shown. The standard error of the mean was less than 10% for all samples except for FIΔ Y577F blasts (SEM = 14.7%), and FIΔ Y577F macrophages (SEM = 18.4%).