Proteasome components are up-regulated in β-thalassemic erythroblasts. (A) Transcriptome analysis was performed on FACS-purified, developmental stage–matched fetal liver erythroblasts from wild-type, heterozygous (Th3/+), and homozygous (Th3/Th3) thalassemic mouse embryos (supplemental Figure 1). Gene Set Enrichment Analysis (GSEA) reveals the induction of proteasome subunit mRNAs in Th3/+ (left) and Th3/Th3 (right) erythroblasts compared with wild-type controls. (B) Relative expression levels of proteasome subunit mRNAs in β-thalassemic erythroblasts normalized to wild-type controls. (C) Proteasome activities in fetal liver erythroid cultures using the fluorescent proteasome activity indicator MV151. Samples were costained for expression of the erythroid-specific antigen Ter119 and for DNA using Hoescht33342 to distinguish nucleated and enucleated erythroid cells. (D) MV151 mean fluorescence intensity (MFI) for nucleated (top) and enucleated (bottom) erythroid cells (Ter119⁺) in 48-hour erythroid cultures from wild-type and Th3/+ fetal livers; n = 4 embryos/genotype. (E) MV151 MFI for circulating human reticulocytes (Hoescht33342⁻, thiazole orange⁺) from control or β-thalassemia major patients. Values are normalized to controls.