Early and late stages in erythropoiesis are rescued in Gfi-1^−/− mice by reducing Id2 levels. (A) Representative flow cytometric analyses of erythroid development in BMCs using CD71 and Ter119 surface markers. Upper left quadrant of contour plot contains CD71⁺/Ter119^−/lo erythroid-committed progenitors, which further develop into CD71⁺/Ter119⁺ erythroblasts in the upper right quadrant of the contour plot, which differentiate into more mature CD71⁻/Ter119⁺ erythroid contains in the lower right quadrant of the contour plot. (B) Bar graph showing the percentages of erythroid populations identified by CD71 and Ter119 expression on Gfi-1^+/+, Gfi-1^−/−, and Gfi-1^−/−;Id2^+/− BMCs. The percentages can be directly compared between mice, because the total BM cellularity of all mice examined was equivalent. The data are presented as mean ± SD and are representative of 3 independent experiments. *P < .05 for Gfi-1^−/− compared with Gfi-1^−/−;Id2^+/− CD71⁺/Ter119^−/lo and CD71⁻/Ter119⁺ cell populations. (C-D) Bar graphs showing the percentages of erythroid populations identified by CD71 and Ter119 expression on (C) Gfi-1^+/+;Id1^+/−, Gfi-1^−/−;Id1^+/+, and Gfi-1^−/−;Id1^+/− BMCs and (D) Gfi-1^+/+;Id3^+/−, Gfi-1^−/−;Id3^+/+, and Gfi-1^−/−;Id3^+/− BMCs. The data are presented as the mean ± SD. (E) Analysis of CD71 and Ter119 expression in c-Kit⁺ BMCs in Gfi-1^+/+, Gfi-1^−/−, and Gfi-1^−/− ; Id2^+/− mice. These include the percentages of CD71^med/loTer119^−/lo (A), CD71^hiTer119^med (B), and CD71^loTer119^lo (C) c-Kit⁺ BMCs. CD71^hiTer119^med erythroid progenitors in c-Kit⁺ BMCs were restored by reducing Id2 levels in Gfi-1^−/− mice, and the increase in c-Kit⁺ CD71^loTer119^lo cell population in Gfi-1^−/− BMCs was reduced by decreasing Id2 levels in vivo. (F) Total number of c-Kit⁺ CD71^med/loTer119^−/lo, c-Kit⁺ CD71^hiTer119^med, and c-Kit⁺ CD71^loTer119^lo erythroid progenitor cells in BMCs using total BM cellularity, percentage of c-Kit⁺ BMCs, and percentage of erythroid progenitors from 2 femurs and 2 tibias of each mouse. Data are presented as the mean ± SD.