Sox6^–/– erythroid populations show impaired expansion and maturation in vitro. (A) CD71/TER119 and c-kit/CD71 FACS profiles of magnetically sorted TER119^– liver cells from E14.5 control and Sox6^–/– littermates. (B) CFU-E assay using control and Sox6^–/– TER119^– sorted cells. Data are presented as average with standard deviation of quadruplicates in a representative experiment. (C) Mature BFU-E assay in the same experiment as in panel B. (D) CD71/TER119 FACS profiles of control and Sox6^–/– erythroid cells cultured on fibronectin with 2 U/mL Epo for 0, 12, and 48 hours. (E) Forward scatter (FSC)/TO FACS profiles of TER119⁺ cells from similar cultures as in panel D. (F) Graph combining cell counts and data from CD71/TER119 and FSC/TO FACS analysis for similar cultures as in panels E and F, maintained for 0 to 72 hours. Erythroid precursors/nonerythroid cells (Er prec/non-Er) are CD71^–/TER119^–; proerythroblasts (proEB) are CD71⁺/TER119^–; early erythroblasts (EB) are TER119⁺and FSC^high and/or TO^high; late erythroblasts/reticulocytes (retic) are TER119⁺/FSC^low/TO^low.