Analysis of bone marrow cells. Bone marrow cells were isolated from wild-type (n = 4) and C/EBPβ-deficient (n = 4) adult mice. (A) Bone marrow cells (2 × 10⁴) were cultured in 1% methylcellulose supplemented with IL-3 (10 ng/mL), IL-6 (10 ng/mL), SCF (20 ng/mL), and EPO (3 U/mL);or GM-CSF (20 ng/mL); or G-CSF (60 ng/mL) and SCF (20 ng/mL); or G-CSF (60 ng/mL) alone. Colonies were scored if they contained more than 50 cells at day 7. Results in panels A and B represent the mean plus or minus SD of 4 mice in each cohort (*P < .001; **P < .005). (B) Bone marrow cells (2 × 10⁵) were cultured in either 1% methylcellulose or MegaCult-C media (CFU-Meg), supplemented with either EPO (3 U/mL); or EPO (3 U/mL) and SCF (20 ng/mL); or TPO (50 ng/mL), IL-3 (10 ng/mL), IL-6 (20 ng/mL), and IL-11 (10 ng/mL). BFU-E (EPO and SCF) and CFU-Meg (TPO, IL-3, IL-6, and IL-11) were counted on day 7 of culture; CFU-E (EPO alone) was enumerated on day 2. Black and white bars show wild-type and C/EBPβ-deficient mice, respectively. (C) Detection of phospho-STAT3 in bone marrow cells. Bone marrow cells were isolated from C/EBPβ heterozygous mutant and C/EBPβ-deficient adult mice, and the cells were stimulated either with or without G-CSF (100 ng/mL) for 30 minutes. Signals of phospho-STAT3 (pSTAT3) and STAT3 were detected by Western blot analysis.