Mx1-Cre–mediated inactivation of Rb and E2f8 in HSCs results in enhanced but ineffective erythropoiesis. (A) Representative pictures of whole spleens of mice with the indicated genotypes. (B) Representative pictures of H&E-stained sections of spleens from mice with indicated genotypes. The scale bar indicates 100 μm. (C-D) Spleen weights (C) and spleen cell numbers (D) of mice with the indicated genotypes. (E-J) Flow cytometric analysis for total erythroid cells, late erythroid cells, and early erythroid cells in spleens (E-G) and BM (H-J). (K-L) Cell-cycle distributions based on a BrdU incorporation assay for early erythroid cells (CD71⁺Ter119⁺) in spleens (K) and BM (L) from mice with the indicated genotypes (n = 3 mice/genotypic group). (M-P) Erythroid staging by flow cytometric analysis of Ter119⁺ BM (M-N) and spleen cells (O-P) sorted by CD71 and cell size (forward scatter, FSC). (M,O) Representative flow cytometric profiles. (N,P) Percentages of different erythroid subpopulations were normalized to total Ter119⁺ cells (n = 4 mice/genotypic group). In all figures, asterisks indicate statistical comparisons with control (Rb^LoxP/LoxP) mice and asterisks in parentheses indicate statistical comparisons with Rb-knockout mice as follows: *P < .05; **P < .01; and ***P < .001.