Summary of the effects of the expression of full-length and mutant G-CSFRs on the capacity to differentiate in response to G-CSF in WEHI-3B D⁺ or LGM-1 (indicated by brackets) cells. The critical regions of the G-CSFR cytoplasmic domain that are involved in the induction of three functional markers of mature neutrophils after G-CSF treatment are illustrated. The mutant G-CSFRs with deletions of 27, 59, 87, 117, 147, and 177 amino acids from the C-terminus of the cytoplasmic domain are designated by the letters of the alphabet A, B, C, D, E, and F, respectively. The cytokine receptor superfamily homology regions (Box 1, Box 2, and Box 3) are represented by boxes, and the four tyrosine residues (Tyr⁷⁰³, Tyr⁷²⁸, Tyr⁷⁴³, and Tyr⁷⁶³) in the murine G-CSFR cytoplasmic domain are indicated by “Y.”