An Essential Role for the RNA Editor-Exonuclease Axis in Terminal Erythroid Differentiation

Erythropoiesis is an intricate process by which lineage-committed erythroid progenitors become mature red blood cells. Reticulocytes are terminal-staged, immature red blood cells with residual RNA after enucleation. In the absence of pathology, reticulocytes are efficiently processed into mature red blood cells and typically represent a small percentage of cells in human peripheral blood. In contrast, when differentiated in vitro from pluripotent stem cells or CD34+ progenitor cells, red cells tend to arrest at the reticulocyte stage. Recent studies have highlighted that uridylation by Terminal Uridylyl Transferases (TUTases) occurs on a broad spectrum of RNA classes in mammalian cells. Oligo-uridylated RNA is recognized by exoribonucleases and targeted for decay. We posited that the machinery behind RNA degradation that accompanies terminal erythropoiesis might involve RNA tail editors coupled to exonuclease activity. Utilizing constitutional murine knockout models, we observed that blood from the TUTase Zcchc6 RNA editor knockout embryos exhibited reticulocytosis and a terminal maturation defect, as documented by FACS, histology, and hematological profiling. Murine strains deficient in the downstream exonuclease Dis3l2 phenocopied the RNA decay defect of the Zcchc6 KO. Conditional knockout murine models of the TUTase-Dis3l2 axis driven by the red cell specific Erythropoietin Receptor-Cre exhibited comparable phenotypes, suggesting a cell intrinsic and niche-independent role for the TUTase-Dis3l2 axis in promoting red blood cell maturation. We are modulating the expression of this axis by various methods to optimize modeling of hemoglobinopathies such as sickle cell anemia.