C/EBPβ is upregulated in HSPCs under stress conditions. (A) Frequencies of KL (c-kit⁺Sca-1⁻lineage⁻) cells, KSL (c-kit⁺Sca-1⁺lineage⁻) cells, and LT-HSCs (CD135⁻CD150⁺CD48⁻ KSL cells) among BM cells from WT and Cebpb^−/− mice (n = 5 per genotype). (B) Frequencies of LT-HSCs (CD135⁻CD150⁺CD48⁻ KSL cells), ST-HSCs, MPP2s, MPP3s, and MPP4s among KSLs from WT and Cebpb^−/− mice (n = 5 per genotype). (C) Cebpb and Cebpa mRNA expression in LT-HSCs (CD150⁺CD48⁻ KSL cells) and KSL cells before and after 5-FU administration. mRNA levels were normalized against that of Gapdh, and the mean value on day 0 was set to 1 (n = 4 biological replicates of 1000-2000 pooled cells in 3 independent experiments per time point). (D) C/EBPβ protein expression in LT-HSCs (CD150⁺CD48⁻ KSL cells) and KSL cells before and after 5-FU administration. Histograms for the nonspecific isotype control are shown in gray (i-ii). Changes in the relative MFI for C/EBPβ in LT-HSCs (iii) and KSL cells (iv) are plotted (n = 4 per time point in 2 independent experiments). Data are presented as means ± standard deviation (SD). *P < .05; **P < .01; and ***P < .001.