ADAR1 Is Essential For Erythroid Development

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 9-9
Author(s):  
Brian Liddicoat ◽  
Jochen Hartner ◽  
Alistair Chalk ◽  
Jun Lu ◽  
Stuart H. Orkin ◽  
...  
Keyword(s):  
Cell Fate ◽  
Rna Editing ◽  
Fetal Liver ◽  
Erythroid Differentiation ◽  
Negative Regulator ◽  
Erythroid Cell ◽  
Compensatory Mechanism ◽  
Type I ◽  
Hematopoietic Stem ◽  
Erythroid Development

Abstract Understanding the mechanisms controlling erythroid differentiation may allow therapeutic regulation of erythropoiesis. Focus so far has concentrated on the roles of transcription factors in determining erythroid fate, however one mechanism of gene regulation that has been poorly explored is that of direct modification of RNA. It is now becoming apparent that RNA sequences can be widely modified by RNA editing. Adenosine-to-Inosine (A-to-I) RNA editing is a posttranscriptional process resulting in sequence alterations to RNA transcripts, which is catalyzed by members of the adenosine deaminase acting on RNA (ADAR) family of enzymes. We have previously reported that targeted disruption of ADAR1 in hematopoietic stem cells (HSC) resulted in a global upregulation of type I and II interferon-inducible transcripts and rapid apoptosis (Hartner et al., Nature Immunology 2009). This study identified that ADAR1 is essential for maintenance of both the fetal and adult HSC compartment in a cell-autonomous fashion. Although ADAR1 is dispensable for myeloid development and B-lymphopoiesis, investigation of its role in erythropoiesis is granted owing to the severe loss erythrocytes in ADAR1 null mice. To determine the role of ADAR1 in erythropoiesis, we generated mice with an erythroid-restricted deletion of ADAR1 (EpoR-Cre Adar1fl/-). These animals were found to die in utero at ∼E14.5. The fetal liver (FL) was small and had significantly lower cellularity than in control littermates. Analysis of FL erythropoiesis demonstrated increased apoptosis and a loss of cells after the phenotypic polychromatic erythroblast stage of erythroid differentiation. When transplantation studies were done with EpoR-Cre Adar1fl/- FL and control EpoR-Cre Adar1fl/+ FL, recipients of EpoR-Cre Adar1fl/- FL could not restore erythropoiesis and were anemic in contrast to the controls. They also developed splenomegaly suggestive of extramedullary hemopoiesis occurring as a compensatory mechanism. To understand the mechanism through which ADAR1 regulates erythroid development, gene expression arrays and miRNA profiling were performed. As with HSCs, loss of ADAR1 caused a significant upregulation of IFN signatures in EpoR-Cre Adar1fl/- FL. Interestingly, despite evidence related to regulation of miRNA function by ADARs, there were only subtle changes to the expression pattern and levels of miRNAs in Adar1-deficient erythroid cells. These results demonstrate that ADAR1 is an essential in vivo mediator of erythroid cell fate and a critical negative regulator of the IFN response in cells specifically committed to erythropoiesis. Disclosures: Hartner: TaconicArtemis: Employment.

Sox6 cell-autonomously stimulates erythroid cell survival, proliferation, and terminal maturation and is thereby an important enhancer of definitive erythropoiesis during mouse development

Blood ◽  
2006 ◽  
Vol 108 (4) ◽  
pp. 1198-1207 ◽  
Author(s):  
Bogdan Dumitriu ◽  
Michael R. Patrick ◽  
Jane P. Petschek ◽  
Srujana Cherukuri ◽  
Ursula Klingmuller ◽  
...  
Keyword(s):  
Cell Survival ◽  
Cell Fate ◽  
Fetal Liver ◽  
Cell Development ◽  
Erythroid Cell ◽  
Erythroid Cells ◽  
Mouse Development ◽  
Hematopoietic Stem ◽  
Definitive Erythropoiesis ◽  
Erythrocyte Cytoskeleton

Abstract Erythropoiesis, the essential process of hematopoietic stem cell development into erythrocytes, is controlled by lineage-specific transcription factors that determine cell fate and differentiation and by the hormone erythropoietin that stimulates cell survival and proliferation. Here we identify the Sry-related high-mobility-group (HMG) box transcription factor Sox6 as an important enhancer of definitive erythropoiesis. Sox6 is highly expressed in proerythroblasts and erythroblasts in the fetal liver, neonatal spleen, and bone marrow. Mouse fetuses and pups lacking Sox6 develop erythroid cells slowly and feature misshapen, short-lived erythrocytes. They compensate for anemia by elevating the serum level of erythropoietin and progressively enlarging their erythropoietic tissues. Erythroid-specific inactivation of Sox6 causes the same phenotype, demonstrating cell-autonomous roles for Sox6 in erythroid cells. Sox6 potentiates the ability of erythropoietin signaling to promote proerythroblast survival and has an effect additive to that of erythropoietin in stimulating proerythroblast and erythroblast proliferation. Sox6 also critically facilitates erythroblast and reticulocyte maturation, including hemoglobinization, cell condensation, and enucleation, and ensures erythrocyte cytoskeleton long-term stability. It does not control adult globin and erythrocyte cytoskeleton genes but acts by stabilizing filamentous actin (F-actin) levels. Sox6 thus enhances erythroid cell development at multiple levels and thereby ensures adequate production and quality of red blood cells.

The ribosome-related protein, SBDS, is critical for normal erythropoiesis

Blood ◽  
2011 ◽  
Vol 118 (24) ◽  
pp. 6407-6417 ◽  
Author(s):  
Saswati Sen ◽  
Hanming Wang ◽  
Chi Lan Nghiem ◽  
Kim Zhou ◽  
Janice Yau ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Cell Expansion ◽  
K562 Cells ◽  
Erythroid Differentiation ◽  
Underlying Mechanism ◽  
Erythroid Cell ◽  
Hematopoietic Stem ◽  
Ribosomal Subunits ◽  
Erythroid Development ◽  
Global Translation

AbstractAlthough anemia is common in Shwachman- Diamond syndrome (SDS), the underlying mechanism remains unclear. We asked whether SBDS, which is mutated in most SDS patients, is critical for erythroid development. We found that SBDS expression is high early during erythroid differentiation. Inhibition of SBDS in CD34+ hematopoietic stem cells and early progenitors (HSC/Ps) and K562 cells led to slow cell expansion during erythroid differentiation. Induction of erythroid differentiation resulted in markedly accelerated apoptosis in the knockdown cells; however, proliferation was only mildly reduced. The percentage of cells entering differentiation was not reduced. Differentiation also increased the oxidative stress in SBDS-knockdown K562 cells, and antioxidants enhanced the expansion capability of differentiating SBDS-knockdown K562 cells and colony production of SDS patient HSC/Ps. Erythroid differentiation also resulted in reduction of all ribosomal subunits and global translation. Furthermore, stimulation of global translation with leucine improved the erythroid cell expansion of SBDS-knockdown cells and colony production of SDS patient HSC/Ps. Leucine did not reduce the oxidative stress in SBDS-deficient K562 cells. These results demonstrate that SBDS is critical for normal erythropoiesis. Erythropoietic failure caused by SBDS deficiency is at least in part related to elevated ROS levels and translation insufficiency because antioxidants and leucine improved cell expansion.

scholarly journals Depletion of L3MBTL1 promotes the erythroid differentiation of human hematopoietic progenitor cells: possible role in 20q− polycythemia vera

Blood ◽  
2010 ◽  
Vol 116 (15) ◽  
pp. 2812-2821 ◽  
Author(s):  
Fabiana Perna ◽  
Nadia Gurvich ◽  
Ruben Hoya-Arias ◽  
Omar Abdel-Wahab ◽  
Ross L. Levine ◽  
...  
Keyword(s):  
Polycythemia Vera ◽  
Progenitor Cells ◽  
Cell Fate ◽  
Myeloproliferative Neoplasms ◽  
Erythroid Differentiation ◽  
Polycomb Group ◽  
Human Cord Blood ◽  
Hematopoietic Stem ◽  
Cell Fate Decisions ◽  
Cd34 Cells

Abstract L3MBTL1, the human homolog of the Drosophila L(3)MBT polycomb group tumor suppressor gene, is located on chromosome 20q12, within the common deleted region identified in patients with 20q deletion-associated polycythemia vera, myelodysplastic syndrome, and acute myeloid leukemia. L3MBTL1 is expressed within hematopoietic CD34+ cells; thus, it may contribute to the pathogenesis of these disorders. To define its role in hematopoiesis, we knocked down L3MBTL1 expression in primary hematopoietic stem/progenitor (ie, CD34+) cells isolated from human cord blood (using short hairpin RNAs) and observed an enhanced commitment to and acceleration of erythroid differentiation. Consistent with this effect, overexpression of L3MBTL1 in primary hematopoietic CD34+ cells as well as in 20q− cell lines restricted erythroid differentiation. Furthermore, L3MBTL1 levels decrease during hemin-induced erythroid differentiation or erythropoietin exposure, suggesting a specific role for L3MBTL1 down-regulation in enforcing cell fate decisions toward the erythroid lineage. Indeed, L3MBTL1 knockdown enhanced the sensitivity of hematopoietic stem/progenitor cells to erythropoietin (Epo), with increased Epo-induced phosphorylation of STAT5, AKT, and MAPK as well as detectable phosphorylation in the absence of Epo. Our data suggest that haploinsufficiency of L3MBTL1 contributes to some (20q−) myeloproliferative neoplasms, especially polycythemia vera, by promoting erythroid differentiation.

scholarly journals HIF-1α deletion partially rescues defects of hematopoietic stem cell quiescence caused by Cited2 deficiency

Blood ◽  
2012 ◽  
Vol 119 (12) ◽  
pp. 2789-2798 ◽  
Author(s):  
Jinwei Du ◽  
Yu Chen ◽  
Qiang Li ◽  
Xiangzi Han ◽  
Cindy Cheng ◽  
...  
Keyword(s):  
Stem Cell ◽  
Hematopoietic Stem Cell ◽  
Knockout Mice ◽  
Gene Dosage ◽  
Fetal Liver ◽  
Conditional Knockout ◽  
Negative Regulator ◽  
Transcriptional Level ◽  
Double Knockout ◽  
Hematopoietic Stem

Abstract Cited2 is a transcriptional modulator involved in various biologic processes including fetal liver hematopoiesis. In the present study, the function of Cited2 in adult hematopoiesis was investigated in conditional knockout mice. Deletion of Cited2 using Mx1-Cre resulted in increased hematopoietic stem cell (HSC) apoptosis, loss of quiescence, and increased cycling, leading to a severely impaired reconstitution capacity as assessed by 5-fluorouracil treatment and long-term transplantation. Transcriptional profiling revealed that multiple HSC quiescence- and hypoxia-related genes such as Egr1, p57, and Hes1 were affected in Cited2-deficient HSCs. Because Cited2 is a negative regulator of HIF-1, which is essential for maintaining HSC quiescence, and because we demonstrated previously that decreased HIF-1α gene dosage partially rescues both cardiac and lens defects caused by Cited2 deficiency, we generated Cited2 and HIF-1α double-knockout mice. Additional deletion of HIF-1α in Cited2-knockout BM partially rescued impaired HSC quiescence and reconstitution capacity. At the transcriptional level, deletion of HIF-1α restored expression of p57 and Hes1 but not Egr1 to normal levels. Our results suggest that Cited2 regulates HSC quiescence through both HIF-1–dependent and HIF-1–independent pathways.

The SCL Transcription Factor Supports Erythroid Cell Survival and Differentiation Downstream of the Erythropoietin Receptor.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 818-818
Author(s):  
Rachid Lahlil ◽  
Richard Martin ◽  
Peter D. Aplan ◽  
C. Glenn Begley ◽  
Jacqueline E. Damen ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Cell Survival ◽  
Cell Fate ◽  
Genetic Interaction ◽  
Fetal Liver ◽  
Erythropoietin Receptor ◽  
Erythroid Cell ◽  
Loss Of Function

Abstract Erythroid cell development critically depends on the SCL/Tal1 transcription factor and on erythropoietin signalling. In the present study, we have taken several approaches to show that the two genes operate within the same pathway to consolidate the erythroid lineage. Signaling through the erythropoietin receptor (EpoR) upregulates SCL protein levels in a clonal cell line (TF-1) in vitro, and in murine fetal liver cells in vivo, when Epor−/− cells were compared to those of wild type littermates at E12.5. In addition, we provide functional evidence for a linear pathway from EpoR to SCL that regulates erythropoiesis. Interfering with SCL induction or SCL function prevents the anti-apoptotic effect of Epo in TF-1 cells and conversely, ectopic SCL expression is sufficient to substitute for Epo to transiently maintain cell survival. In vivo, SCL gain of function complements the cellular defects in Epor−/− embryos to support cell survival and maturation during primitive and definitive erythropoiesis, as assessed by cellular and histological analyses of Epor−/− SCLtg embryos. Moreover, several erythroid specific genes that are decreased in Epor−/− embryos are rescued by the SCL transgene including glycophorinA, bH1 and bmaj globin, providing molecular confirmation of the functional and genetic interaction between Epor and SCL. Conversely, erythropoiesis becomes deficient in compound Epor+/−SCL+/− heterozygote mice, indicating that the genetic interaction between EpoR and SCL is synthetic. Finally, using EpoR mutants that harbour well defined signalling deficiencies, combined with gain and loss of function approaches for specific kinases, we identify MAPK as the major signal transduction pathway downstream of EpoR that upregulates SCL function, necessary for erythroid cell survival and differentiation. Taken together, our observations are consistent with the view that cytokines can influence cell fate by altering the dosage of lineage transcriptional regulators.

Constitutive TGF-β1 Deficiency Induces a Defect in Hematopoietic Stem/Progenitor Cell Compartment in Fetus and Neonate.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1397-1397
Author(s):  
Claude Capron ◽  
Catherine Lacout ◽  
Yann Lecluse ◽  
Valérie Jalbert ◽  
Elisabeth Cramer Bordé ◽  
...  
Keyword(s):  
Fetal Liver ◽  
Hematopoietic Cells ◽  
Type I ◽  
Activated T Cells ◽  
Hematopoietic Stem ◽  
Tgf Β1

Abstract TGF-β1 is a cytokine with pleiotropic effects. It has been considered that TGF-β1plays a major role on hematopoietic stem cells (HSC) based on in vitro experiment. Achieving in vivo experiments proved to be difficult because constitutive TGF-β1 knock-out (KO) in mice leads to lethality during the first 4 weeks of life from a wasting syndrome related to tissue infiltration by activated T cells and macrophages. For this reason, hematopoiesis of TGF-β1−/− mice has not been studied in details. In contrast the role of TGF-β1 has been recently extensively studied in conditional TGF-β type I receptor (TβRI) KO mice. No clear effect was observed on HSC functions, suggesting that TGF-β1 was not a key physiological regulator of hematopoiesis in the adult. However, these experiments have some limitations. They do not exclude a putative role for TGF-β1 during fetal hematopoiesis and they do not specifically address the role of TGF-β1 on hematopoiesis because KO of TGF-β receptor leads to signaling arrest for all TGF-βs. In addition, other receptors may be involved in TGF-β1 signaling. For these reasons, we have investigated the hematopoiesis of constitutive TGF-β1 KO mice with a mixed Sv129 × CF-1 genetic background allowing the birth of a high proportion of homozygotes. In 2 week-old neonate mice, we have shown a decrease of bone marrow (BM) and spleen progenitors and a decrease of immature progenitors colony forming unit of the spleen (CFU-s). Moreover this was associated with a loss in reconstitutive activity of TGF-β1−/− HSC from BM. However, although asymptomatic, these mice had an excess of activated lymphocytes and an augmentation of Sca-1 antigen on hematopoietic cells suggesting an excess of γ-interferon release. Thus we studied hematopoiesis of 7 to 10 days-old neonate mice, before phenotypic modification and inflammatory cytokine release. Similar results were observed with a decrease in the number of progenitors and in the proliferation of TGF-β1−/− BM cells along with an increased differentiation but without an augmentation in apoptosis. Moreoever, a loss of long term reconstitutive capacity of BM Lineage negative (Lin−) TGF-β1−/− cells along with a diminution of homing of TGF-β1−/− progenitors was found. These results demonstrate that TGF-β1 may play a major role on the HSC/Progenitor compartment in vivo and that this defect does not seem to be linked to the immune disease. To completely overpass the risk of the inflammatory syndrome, we analyzed hematopoiesis of fetal liver (FL) of TGF-β1−/− mice and still found a decrease in progenitors, a profound defect in the proliferative capacities, in long term reconstitutive activity and homing potential of primitive FL hematopoietic cells. Our results demonstrate that TGF-β1 plays an important role during hematopoietic embryonic development. Altogether these findings suggest that TGF-β1 is a potent positive regulator for the in vivo homeostasis of the HSC compartment.

Klf1 Regulatory Networks in Primary Erythroid Cells.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1462-1462
Author(s):  
Michael Tallack ◽  
Thomas Whitington ◽  
Brooke Gardiner ◽  
Eleanor Wainwright ◽  
Janelle Keys ◽  
...  
Keyword(s):  
Regulatory Networks ◽  
Conflicts Of Interest ◽  
Fetal Liver ◽  
Es Cells ◽  
Erythroid Differentiation ◽  
Erythroid Cell ◽  
Gene Promoters ◽  
Erythroid Cells ◽  
Red Cell Membrane ◽  
Sequencing Platform

Abstract Abstract 1462 Poster Board I-485 Klf1/Eklf regulates a diverse suite of genes to direct erythroid cell differentiation from bi-potent progenitors. To determine the local cis-regulatory contexts and transcription factor networks in which Klf1 works, we performed Klf1 ChIP-seq using the SOLiD deep sequencing platform. We mapped more than 10 million unique 35mer tags and found ∼1500 sites in the genome of primary fetal liver erythroid cells are occupied by endogenous Klf1. Many reside within well characterised erythroid gene promoters (e.g. b-globin) or enhancers (e.g. E2f2 intron 1), but some are >100kb from any known gene. We tested a number of Klf1 bound promoter and intragenic sites for activity in erythroid cell lines and zebrafish. Our data suggests Klf1 directly regulates most aspects of terminal erythroid differentiation including synthesis of the hemoglobin tetramer, construction of a deformable red cell membrane and cytoskeleton, bimodal regulation of proliferation, and co-ordination of anti-apoptosis and enucleation pathways. Additionally, we suggest new mechanisms for Klf1 co-operation with other transcription factors such as those of the gata, ets and myb families based on over-representation and spatial constraints of their binding motifs in the vicinity of Klf1-bound promoters and enhancers. Finally, we have identified a group of ∼100 Klf1-occupied sites in fetal liver which overlap with Klf4-occupied sites in ES cells defined by Klf4 ChIP-seq. These sites are associated with genes controlling the cell cycle and proliferation and are Klf4-dependent in skin, gut and ES cells, suggesting a global paradigm for Klfs as regulators of differentiation in many, if not all, cell types. Disclosures No relevant conflicts of interest to declare.

Primitive Erythroid Progenitors Are Regulated by Hypoxia and Display An Aerobic Glycolytic Metabolic Profile,

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 3159-3159
Author(s):  
Margaret H. Baron ◽  
Joan Isern ◽  
Stuart T. Fraser ◽  
Zhiyong He ◽  
Avi Ma'ayan ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Mammalian Cells ◽  
Enrichment Analysis ◽  
Yolk Sac ◽  
Negative Regulator ◽  
Erythroid Cell ◽  
Cell Type ◽  
Strong Basis ◽  
Stage Of Development ◽  
Erythroid Development

Abstract Abstract 3159 Primitive erythroblasts (EryP) are the first cell type specified from mesodermal progenitors in the mammalian embryo. They are found in the mouse yolk sac from embryonic day (E) ∼E7.5–8.5 and, as circulation initiates, they begin to differentiate to erythroblasts that enter the bloodstream and continue to mature in a stepwise, synchronous fashion until their enucleation several days later. We have purified these first hematopoietic-committed progenitors from staged embryos based on the expression of a nuclear GFP transgene that is expressed specifically within the EryP lineage as early as E7.5. Genome-wide expression profiling allowed us to define the transcriptome from each stage of development and revealed highly dynamic changes during the progression from progenitor to maturing erythroblast. We focused on the emergence of EryP progenitors in the yolk sac and on the transition to circulation stage, when progenitor activity is lost and a peak is observed in the number of genes whose expression changes. TRANSFAC analysis of promoters of differentially expressed genes allowed us to identify candidate transcriptional regulators, some of which have not previously been implicated in erythroid development (e.g. Nkx3.1, known previously as a regulator of prostate stem cells). We designed experiments to test predictions from our microarray analysis and found that EryP progenitor numbers are regulated by TGF-beta1 and hypoxia. In most mammalian cells, the response to hypoxia is mediated by the transcription factor HIF-1. Hif-1 is apparently not expressed in EryP. Howver, Hif3a/Ipas, a Hif-1 target gene that encodes a dominant negative regulator of HIFs and that is thought to function as a feedback regulator in response to hypoxia, is expressed in EryP as early as E7.5 and is upregulated as the cells mature. These findings suggest that the response to hypoxia by EryP may involve a pathway that is distinct from that of most other cells. EryP progenitors express genes associated with aerobic glucose metabolism (the Warburg effect), a phenotype characteristic of cancer and other rapidly proliferating cells. Whether this glycolytic profile reflects the energy needs of these cells or a more unique feature of primitive erythropoiesis is under investigation. Currently we are using computational methods to identify transcription factor (ChEA, ChIP Enrichment Analysis) and kinase (KEA, Kinase Enrichment Analysis) networks that may play a role in the regulation of primitive erythroid development. This study is the first lineage specific transcription profiling of a differentiating cell type in the early mouse embryo and will provide a strong basis for future work on normal erythropoiesis throughout ontogeny. It may also help guide efforts to direct the differentiation of stem/progenitor and cells of other lineages to an erythroid cell fate. Disclosures: No relevant conflicts of interest to declare.

A-To-I RNA Editing By ADAR1 Is Essential For Hematopoiesis

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 1199-1199 ◽  
Author(s):  
Brian Liddicoat ◽  
Robert Piskol ◽  
Alistair Chalk ◽  
Miyoko Higuchi ◽  
Peter Seeburg ◽  
...  
Keyword(s):  
Gene Expression ◽  
Rna Editing ◽  
Fetal Liver ◽  
Expression Profiles ◽  
In Utero ◽  
Tamoxifen Treatment ◽  
Rna Seq ◽  
Data Set ◽  
Hematopoietic Stem

Abstract The role of RNA and its regulation is becoming increasingly appreciated as a vital component of hematopoietic development. RNA editing by members of the Adenosine Deaminase Acting on RNA (ADAR) gene family is a form of post-transcriptional modification which converts genomically encoded adenosine to inosine (A-to-I) in double-stranded RNA. A-to-I editing by ADAR directly converts the sequence of the RNA substrate and can alter the structure, function, processing, and localization of the targeted RNA. ADAR1 is ubiquitously expressed and we have previously described essential roles in the development of hematopoietic and hepatic organs. Germline ablation of murine ADAR1 results in a significant upregulation of interferon (IFN) stimulated genes and embryonic death between E11.5 and E12.5 associated with fetal liver disintegration and failed hemopoiesis. To determine the biological importance of A-to-I editing by ADAR1, we generated an editing dead knock-in allele of ADAR1 (ADAR1E861A). Mice homozygous for the ADAR1E861A allele died in utero at ∼E13.5. The fetal liver (FL) was small and had significantly lower cellularity than in controls. Analysis of hemopoiesis demonstrated increased apoptosis and a loss of hematopoietic stem cells (HSC) and all mature lineages. Most notably erythropoiesis was severely impaired with ∼7-fold reduction across all erythrocyte progenitor populations compared to controls. These data are consistent with our previous findings that ADAR1 is essential for erythropoiesis (unpublished data) and suggest that the ADAR1E861A allele phenocopies the null allele in utero. To assess the requirement of A-to-I editing in adult hematopoiesis, we generated mice where we could somatically delete the wild-type ADAR1 allele and leave only ADAR1E861A expressed in HSCs (hScl-CreERAdar1fl/E861A). In comparison to hScl-CreERAdar1fl/+ controls, hScl-CreERAdar1fl/E861A mice were anemic and had severe leukopenia 20 days post tamoxifen treatment. Investigation of marrow hemopoiesis revealed a significant loss of all cells committed to the erythroid lineage in hScl-CreERAdar1fl/E861A mice, despite having elevated phenotypic HSCs. Upon withdrawal of tamoxifen diet, all blood parameters were restored to control levels within 12 weeks owing to strong selection against cells expressing only the ADAR1E861A allele. To understand the mechanism through which ADAR1 mediated A-to-I editing regulates hematopoiesis, RNA-seq was performed. Gene expression profiles showed that a loss of ADAR1 mediated A-to-I editing resulted in a significant upregulation of IFN signatures, consistent with the gene expression changes in ADAR1 null mice. To define substrates of ADAR1 we assessed A-to-I mismatches in the RNA-seq data sets. 3,560 previously known and 353 novel A-to-I editing sites were identified in our data set. However, no single editing substrate discovered could account for the IFN signature observed or the lethality of ADAR1E861A/E861A mice. These results demonstrate that ADAR1 mediated A-to-I editing is essential for the maintenance of both fetal and adult hemopoiesis in a cell-autonomous manner and a key suppressor of the IFN response in hematopoiesis. Furthermore the ADAR1E861A allele demonstrates the essential role of ADAR1 in vivo is A-to-I editing. Disclosures: Hartner: TaconicArtemis: Employment.

Impaired Erythropoiesis Of Gfi-1 Null Hematopoietic Progenitor Cells Is Rescued By Reducing Id2 Levels

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 737-737
Author(s):  
Wonil Kim ◽  
Kimberly D Klarmann ◽  
Jonathan R Keller
Keyword(s):  
Transcription Factors ◽  
Progenitor Cells ◽  
Molecular Mechanisms ◽  
Early Stage ◽  
Erythroid Cell ◽  
Mouse Bone Marrow ◽  
Short Term ◽  
Erythroid Progenitor ◽  
Hematopoietic Stem ◽  
Erythroid Development

Abstract The survival, self-renewal and differentiation of hematopoietic stem and progenitor cells (HSPC) are tightly regulated by extrinsic signals, and intrinsically by transcription factors and their regulatory networks. The molecular and cellular mechanisms, which regulate the complex process of hematopoiesis, depend upon the correct expression of transcription factors and their regulators. One such family of regulators is the inhibitor of DNA binding/differentiation (Id), which is helix-loop-helix proteins that function by acting as dominant negative regulators of transcription factors such as E proteins, ETS, Pax, and retinoblastoma proteins. Expression of Id2, one of the Id family proteins, is regulated by growth factor independence-1 (Gfi-1) encoding a transcriptional repressor. Gfi-1 is required for the development of multiple cell lineages including HSPC and ultimately differentiated blood cells. Although genes have been identified to mediate hematopoietic defects observed in Gfi-1 knockout (Gfi-1 KO) mice including the maturational and developmental defects in granulocyte (CSF-1, RasGRP1, and PU.1) and B cell (PU.1 or Id2), and myeloid hyperplasia (Id2 or HoxA9), Gfi-1-target genes that mediate the defects in radioprotection, maintenance of HSC, and erythroid hyperplasia in Gfi-1 KO mice are unknown. Since Id2 expression is elevated in HSPC of Gfi-1 KO mice and Id2 promotes cell proliferation, we hypothesized that lowering Id2 expression could rescue the HSPC defects in the Gfi-1 KO mice. By transplanting Gfi-1 KO mouse bone marrow cells (BMC) into lethally-irradiated recipient mice, we observed that short-term reconstituting cell (STRC) activity in Gfi-1 KO BMC is rescued by transplanting Gfi-1 KO; Id2 Het (heterozygosity at the Id2 locus) BMC, while the long-term reconstitution defect of HSC was not. Interestingly, lineage- Sca-1- c-Kithi HPC, which enriched for megakaryocyte-erythroid progenitor (MEP) as one of the STRC, were fully restored in mice transplanted with Gfi-1 KO; Id2 Het BMC, in contrast to lack of the HPC in Gfi-1 KO BM-transplanted mice. The restoration of donor c-Kithi HPC was directly correlated with increased red blood cell (RBC) levels in recipient mice, which was produced after donor BM engraftment. Furthermore, we identified that reduced Id2 levels restore erythroid cell development by rescuing short-term hematopoietic stem cell, common myeloid progenitor and MEP in the Gfi-1 KO mice. In addition, burst forming unit-erythroid (BFU-E) colony assay showed that hemoglobinized BFU-E development was restored in Gfi-1 KO BM and spleen by lowering Id2 levels. Unlike Id2 reduction, reducing other Id family (Id1 or Id3) levels in Gfi-1 KO mice does not rescue the impaired development of erythroid and other hematopoietic lineages including myeloid, T and B cells. Abnormal expansion of CD71+ Ter119-/low erythroid progenitor cells was rescued in Gfi-1 KO; Id2 Het BMC compared to those in Gfi-1 KO mice. Thus, we hypothesized that erythroid development was blocked at the early stage of erythropoiesis due to the ectopic expression of Id2 in Gfi-1 KO mice. Using Id2 promoter-driven YFP reporter mice, we found that Id2 is highly expressed in the CD71+ Ter119-/low erythroid progenitors, and decreases as the cells mature to pro-erythroblasts and erythroblasts, suggesting that repression of Id2 expression is required for proper erythroid differentiation in the later stages. The dramatic changes of Id2 expression during erythroid development support our findings that the overexpression of Id2 in the absence of Gfi-1-mediated transcriptional repression causes impaired erythropoiesis at the early stage. To identify the molecular mechanisms that could account for how reduced Id2 levels rescue erythropoiesis in Gfi-1 KO mice, we compared the expression of genes and proteins in Gfi-1 KO; Id2 Het and Gfi-1 KO BMC. Using microarray, qRT-PCR and western blot, we discovered that reduction of Id2 expression in Gfi-1 KO BMC results in increased expression of Gata1, EKlf, and EpoR genes, which are required for erythropoiesis. However, the expression levels of cell cycle regulators were not altered by lowering Id2 expression in Gfi-1 KO mice. These data suggest a novel molecular mechanism in which Gfi-1 modulates erythropoiesis by repressing the expression of Id2 that reduce the levels of Id2 protein, binding to E2A and inhibiting the formation of E2A/Scl transcription enhancer complex. Disclosures: No relevant conflicts of interest to declare.

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