Consequences of Ribosomal Protein Haploinsufficiency in Human Hematopoiesis

Ribosomal protein haploinsufficiency (RPH) underlies diverse human diseases with distinct and specific phenotypes, including Diamond-Blackfan anemia (DBA). Although multiple mechanisms have been proposed for the erythroid-specific hematopoietic defects observed in DBA, only recently has the role of selectively impaired translation been highlighted in these phenotypes. Exactly how and to what extent this impairment of translation occurs is currently unknown. Here, by identifying a novel DBA gene affecting ribosome biogenesis, we show that both RPH and impaired ribosome biogenesis (IRB) limit the availability of actively translating ribosomes, resulting in the hematopoietic and translational defects observed in DBA. Our results show that the selective impairment of translation is due to a quantitative defect, where ribosomes of invariant protein composition have a reduced abundance, rather than a qualitative defect, where a subset of ribosomes lack specific ribosomal proteins (RPs) and thus may have altered translational capacity. In RPH, we find that cellular RP homeostasis is largely maintained through translational co-regulation, and we identify a selective subset of transcripts that have impaired association with the ribosome. Surprisingly, these transcripts have short and unstructured 5’ UTRs and are highly abundant and efficiently translated in healthy human erythroid progenitors, suggesting that the impaired translation of a number of key transcripts, including GATA1, may underlie DBA. Overall, our study identifies mechanisms by which RPH and IRB affect mRNA translation, illuminating how these alterations can result in cell-type specific defects and cause human disease. (mRNA-seq) RNA-seq for control (shLuc), RPL5 knockdown (shRPL5), RPS19 knockdown (shRPS19), and TSR2 knockdown (shTSR2) was performed for two biological replicates of primary human erythroid cells at Day 7 of in vitro culture. (RPF-seq) Ribosome profiling was similarly performed for shLuc, shRPL5, and shRPS19 in the matching biological replicates.