Differential erythroid effects of monoferric Tfs are associated with increased phosphorylation of the erythropoietin target AKT in early erythroid precursors. Flow cytometry analyses demonstrated no significant differences between strains in the relative proportion of erythroid precursor populations (A), no differences between strains in the percentages of apoptotic erythroid precursor cells (B), no significant differences in the percentages of erythroid lineage cells expressing cell-surface TfR1 (C), no significant differences in the median fluorescence intensity (MFI) of TfR1 in erythroid precursor populations (D), decreased percentages of cells positive for pAKT in early bone marrow (BM) erythroid precursor populations (proerythroblasts [Pro], basophilic [Baso] and polychromatic [Poly] erythroblasts) in the Tf^N-bl/N-bl strain compared with WT (E), no significant differences in MFI of pAKT in early erythroid precursors between strains (F), and significantly decreased MFI of pAKT in Tf^N-bl/N-bl mice compared with Tf^C-bl/C-bl mice upon normalization to serum Epo concentrations (G). Data are presented as bar graphs depicting the mean ± standard error of the mean or Tukey box and whisker plots, with statistical significance analyzed by 1-way ANOVA (n = 4-5 mice per sex for WT and n = 5-7 mice per sex for Tf-mutant mice). *P ≤ .05, **P ≤ .01. Ortho, orthochromatic erythroblast.