The Human GATA1 Gene Retains a 5' Insulator That Maintains Chromosomal Architecture and GATA1 Expression Levels in Splenic Erythroblasts

An erythroid-to-myeloid cell fate conversion is elicited by LSD1 inactivation

Histone H3 lysine 4 methylation (H3K4Me) is most often associated with chromatin activation, and removing H3K4 methyl groups has been shown to be coincident with gene repression. H3K4Me demethylase KDM1a/LSD1 is a therapeutic target for multiple diseases, including for the potential treatment of β-globinopathies (sickle cell disease and β-thalassemia), because it is a component of γ-globin repressor complexes, and LSD1 inactivation leads to robust induction of the fetal globin genes. The effects of LSD1 inhibition in definitive erythropoiesis are not well characterized, so we examined the consequences of conditional inactivation of Lsd1 in adult red blood cells using a new Gata1creERT2 bacterial artificial chromosome transgene. Erythroid-specific loss of Lsd1 activity in mice led to a block in erythroid progenitor differentiation and to the expansion of granulocyte-monocyte progenitor-like cells, converting hematopoietic differentiation potential from an erythroid fate to a myeloid fate. The analogous phenotype was also observed in human hematopoietic stem and progenitor cells, coincident with the induction of myeloid transcription factors (eg, PU.1 and CEBPα). Finally, blocking the activity of the transcription factor PU.1 or RUNX1 at the same time as LSD1 inhibition rescued myeloid lineage conversion to an erythroid phenotype. These data show that LSD1 promotes erythropoiesis by repressing myeloid cell fate in adult erythroid progenitors and that inhibition of the myeloid-differentiation pathway reverses the lineage switch induced by LSD1 inactivation.

A new murine Rpl5 (uL18) mutation provides a unique model of variably penetrant Diamond-Blackfan anemia

Ribosome dysfunction is implicated in multiple abnormal developmental and disease states in humans. Heterozygous germline mutations in genes encoding ribosomal proteins are found in most individuals with Diamond-Blackfan anemia (DBA), whereas somatic mutations have been implicated in a variety of cancers and other disorders. Ribosomal protein-deficient animal models show variable phenotypes and penetrance, similar to human patients with DBA. In this study, we characterized a novel ENU mouse mutant (Skax23m1Jus) with growth and skeletal defects, cardiac malformations, and increased mortality. After genetic mapping and whole-exome sequencing, we identified an intronic Rpl5 mutation, which segregated with all affected mice. This mutation was associated with decreased ribosome generation, consistent with Rpl5 haploinsufficiency. Rpl5Skax23-Jus/+ animals had a profound delay in erythroid maturation and increased mortality at embryonic day (E) 12.5, which improved by E14.5. Surviving mutant animals had macrocytic anemia at birth, as well as evidence of ventricular septal defect (VSD). Surviving adult and aged mice exhibited no hematopoietic defect or VSD. We propose that this novel Rpl5Skax23-Jus/+ mutant mouse will be useful in studying the factors influencing the variable penetrance that is observed in DBA.

Reducing Inflammatory Cytokine Production from Renal Collecting Duct Cells by Inhibiting GATA2 Ameliorates Acute Kidney Injury

Acute kidney injury (AKI) is a leading cause of chronic kidney disease. Proximal tubules are considered to be the primary origin of pathogenic inflammatory cytokines in AKI. However, it remains unclear whether other cell types, including collecting duct (CD) cells, participate in inflammatory processes. The transcription factor GATA2 is specifically expressed in CD cells and maintains their cellular identity. To explore the pathophysiological function of GATA2 in AKI, we generated renal tubular cell-specific Gata2 deletion (G2CKO) mice and examined their susceptibility to ischemia reperfusion injury (IRI). Notably, G2CKO mice exhibited less severe kidney damage, with reduced granulomacrophagic infiltration upon IRI. Transcriptome analysis revealed that a series of inflammatory cytokine genes were downregulated in GATA2-deficient CD cells, suggesting that GATA2 induces inflammatory cytokine expression in diseased kidney CD cells. Through high-throughput chemical library screening, we identified a potent GATA inhibitor. The chemical reduces cytokine production in CD cells and protects the mouse kidney from IRI. These results revealed a novel pathological mechanism of renal IRI, namely, that CD cells produce inflammatory cytokines and promote IRI progression. In injured kidney CD cells, GATA2 exerts a proinflammatory function by upregulating inflammatory cytokine gene expression. GATA2 can therefore be considered a therapeutic target for AKI.

The Sea Urchin sns5 Chromatin Insulator Shapes the Chromatin Architecture of a Lentivirus Vector Integrated in the Mammalian Genome

Lentivirus vectors are presently the favorite vehicles for therapeutic gene transfer in hematopoietic cells. Nonetheless, these vectors integrate randomly throughout the genome, exhibiting variegation of transgene expression due to the spreading of heterochromatin into the vector sequences. Moreover, the cis-regulatory elements harbored by the vector could disturb the proper transcription of resident genes neighboring the integration site. The incorporation of chromatin insulators in flanking position to the transferred unit can alleviate both the above-mentioned dangerous effects, due to the insulator-specific barrier and enhancer-blocking activities. In this study, we report the valuable properties of the sea urchin-derived sns5 insulator in improving the expression efficiency of a lentivirus vector integrated in the mammalian erythroid genome. We show that these results neither reflect an intrinsic sns5 enhancer activity nor rely on the recruitment of the erythroid-specific GATA-1 factor to sns5. Furthermore, by using the Chromosome Conformation Capture technology, we report that a single copy of the sns5-insulated vector is specifically organized into an independent chromatin loop at the provirus locus. Our results not only provide new clues concerning the molecular mechanism of sns5 function in the erythroid genome but also reassure the use of sns5 to improve the performance of gene therapy vectors.

Erythroblast enucleation is a dynein-dependent process

Mammalian erythroblasts undergo enucleation through a process thought to be similar to cytokinesis. Microtubule-organizing centers (MTOCs) mediate organization of the mitotic spindle apparatus that separates the chromosomes during mitosis and are known to be crucial for proper cytokinesis. However, the role of MTOCs in erythroblast enucleation remains unknown. We therefore investigated the effect of various MTOC inhibitors on cytokinesis and enucleation using human colony-forming units-erythroid (CFU-Es) and mature erythroblasts generated from purified CD34(+) cells. We found that erythro-9-[3-(2-hydroxynonyl)]adenine (EHNA), a dynein inhibitor, and monastrol, a kinesin Eg5 inhibitor, as well as various inhibitors of MTOC regulators, including ON-01910 (Plk-1), MLN8237 (aurora A), hesperadin (aurora B), and LY294002 (PI3K), all inhibited CFU-E cytokinesis. Among these inhibitors, however, only EHNA blocked enucleation. Moreover, terminally differentiated erythroblasts expressed only dynein; little or none of the other tested proteins was detected. Over the course of the terminal differentiation of human erythroblasts, the fraction of cells with nuclei at the cell center declined, whereas the fraction of polarized cells, with nuclei shifted to a position near the plasma membrane, increased. Dynein inhibition impaired nuclear polarization, thereby blocking enucleation. These data indicate that dynein plays an essential role not only in cytokinesis but also in enucleation. We therefore conclude that human erythroblast enucleation is a process largely independent of MTOCs, but dependent on dynein.

TAF10 Interacts with the GATA1 Transcription Factor and Controls Mouse Erythropoiesis

The ordered assembly of a functional preinitiation complex (PIC), composed of general transcription factors (GTFs), is a prerequisite for the transcription of protein-coding genes by RNA polymerase II. TFIID, comprised of the TATA binding protein (TBP) and 13 TBP-associated factors (TAFs), is the GTF that is thought to recognize the promoter sequences allowing site-specific PIC assembly. Transcriptional cofactors, such as SAGA, are also necessary for tightly regulated transcription initiation. The contribution of the two TAF10-containing complexes (TFIID, SAGA) to erythropoiesis remains elusive. By ablating TAF10 specifically in erythroid cells in vivo, we observed a differentiation block accompanied by deregulated GATA1 target genes, including Gata1 itself, suggesting functional cross talk between GATA1 and TAF10. Additionally, we analyzed by mass spectrometry the composition of TFIID and SAGA complexes in mouse and human cells and found that their global integrity is maintained, with minor changes, during erythroid cell differentiation and development. In agreement with our functional data, we show that TAF10 interacts directly with GATA1 and that TAF10 is enriched on the GATA1 locus in human fetal erythroid cells. Thus, our findings demonstrate a cross talk between canonical TFIID and SAGA complexes and cell-specific transcription activators during development and differentiation.