The exosome complex suppresses cell-cycle arrest genes during erythroid maturation. (A) Name and function^{41-43,45,47,52,61}  of genes in “cell cycle arrest” category derived from GO term analysis from GATA-1–activated and Exosc8-repressed genes. (B) ChIP-seq profiles of GATA-1 occupancy at cell-cycle regulatory genes in primary human erythroblasts. All genes were orientated left to right. (C) Real-time RT-PCR analysis of genes in “cell cycle arrest” category upon Exosc8 or Exosc9 knockdown in primary murine erythroid precursor cells under expansion conditions, sorted into distinct, R1, R2, R3, and R4/5 cell populations (mean ± SE; 5 independent experiments). Values were normalized to 18S rRNA and the expression relative to the control R1 population. (D) Flow cytometric cell cycle analysis of primary erythroid precursor cells, within the R3 population, infected with retrovirus expressing control, Exosc8, or Exosc9 shRNA. Representative cell-cycle profile from 2 independent experiments. The percentage of the cell population in each cell cycle stage (mean ± SE; 2 independent experiments). Shaded, S phase; red, G₀/G₁ or G₂/M phase. *P < .05, **P < .01, ***P < .001. (E) Flow cytometric cell cycle analysis of primary erythroid precursor cells treated with 25 μM HU for either 24 or 48 hours. Representative cell-cycle profile. The percentage of the cell population in each cell cycle stage (mean ± SE; 3 independent experiments). Blue, S phase; red, G₀/G₁ or G₂/M phase. (F) Flow cytometric quantitation of erythroid maturation stage by CD71 and Ter119 staining upon 25 μM HU treatment of 24 or 48 hours in primary erythroid precursor cells. Representative flow cytometry data, with the R1-R5 gates denoted (3 independent experiments). (G) Model of GATA-1/Foxo3 function to overcome the exosome complex–dependent erythroid maturation barricade, which involves multiple alterations in erythroid cell function.