TR2 and TR4 (NR2C1 and NR2C2, respectively) are evolutionarily conserved nuclear orphan receptors capable of binding direct repeat sequences in a stage-specific manner. Like other nuclear receptors, TR2 and TR4 possess important roles in transcriptional activation or repression with developmental stage and tissue specificity. TR2 and TR4 bind DNA and possess the ability to complex with available cofactors mediating developmental stage-specific actions in primitive and definitive erythrocytes. In erythropoiesis, TR2 and TR4 are required for erythroid development, maturation, and key erythroid transcription factor regulation. TR2 and TR4 recruit and interact with transcriptional corepressors or coactivators to elicit developmental stage-specific gene regulation during hematopoiesis.

Nuclear receptor TR4 (NR2C2) was previously shown to bind to the –117 position of the γ-globin gene promoters in vitro, which overlaps the more recently described BCL11 transcription factor A (BCL11A) binding site. The role of TR4 in human γ-globin gene repression has not been extensively characterized in vivo, whereas any relationship between TR4 and BCL11A regulation through the γ-globin promoters is unclear at present. We show here that TR4 and BCL11A competitively bind in vitro to distinct, overlapping sequences, including positions overlapping –117 of the γ-globin promoter. We found that TR4 represses γ-globin transcription and fetal hemoglobin accumulation in vivo in a BCL11A-independent manner. Finally, examination of the chromatin occupancy of TR4 within the β-globin locus, compared with BCL11A, shows that both bind avidly to the locus control region and other sites, but only BCL11A binds to the γ-globin promoters at statistically significant frequency. These data resolve an important discrepancy in the literature and, thus, clarify possible approaches to the treatment of sickle cell disease and β-thalassaemia.

Analysis of Diamond Blackfan anemia syndrome (DBAS) cohorts and animal models has not revealed a potential mechanism for the variable anemia phenotype, a key feature of this disease. Here, we used an established Rpl5Skax23-Jus/+ murine DBAS model to study this dynamic erythropoiesis deficiency. These haploinsufficient mice exhibit variably penetrant craniofacial and cardiac defects mimicking the phenotypes of patients with DBAS bearing RPL5 mutations. We additionally discovered that this specific heterozygous splicing mutation is pathogenic and leads to partial intron retention. By examining the transcriptome of fetal liver erythroid progenitors at embryonic day 12.5 (E12.5), we demonstrate downregulation of erythroid differentiation pathways consistent with the DBAS phenotype. We also identified dysregulated transcription of lipid metabolism genes with significant reduction in Scd1 expression in the subset of E12.5 mutant embryos at risk for erythroid failure. Stearoyl–coenzyme A desaturase 1, a key enzyme that converts saturated to monounsaturated fatty acids, has not been previously linked to erythropoiesis or DBAS. When anemia was induced in adult Rpl5Skax23-Jus/+ mice, mutant mice exhibited delayed erythroid recovery, whereas pretreatment with an stearoyl–coenzyme A desaturase 1 inhibitor resulted in improved erythropoiesis in both wild-type and mutant mice. This analysis suggests a potential role of lipid metabolism in the variable anemia penetrance in DBAS and highlights a previously unappreciated pathway that requires further study as a potential target for drug development.