Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2017 Apr 1.
Published in final edited form as: Br J Haematol. 2016 Feb 5;173(2):206–218. doi: 10.1111/bjh.13938

Advances in Understanding Erythropoiesis: Evolving Perspectives

Satish K Nandakumar 1,2,3, Jacob C Ulirsch 1,2,3, Vijay G Sankaran 1,2,*
PMCID: PMC4833665  NIHMSID: NIHMS747594  PMID: 26846448

Abstract

Red blood cells (RBCs) are generated from haematopoietic stem and progenitor cells (HSPCs) through the step-wise process of differentiation known as erythropoiesis. In this review, we discuss our current understanding of erythropoiesis and highlight recent advances in this field. During embryonic development, erythropoiesis occurs in three distinct waves comprising first, the yolk sac-derived primitive RBCs, followed sequentially by the erythro-myeloid progenitor (EMP) and HSPC-derived definitive RBCs. Recent work has highlighted the complexity and variability that may exist in the hierarchical arrangement of progenitors responsible for erythropoiesis. Using recently defined cell surface markers, it is now possible to enrich the erythroid progenitors and precursors to a much greater extent than has been possible before. While a great deal of knowledge has been gained on erythropoiesis from model organisms, our knowledge of this process is being refined through human genetic studies. Genes mutated in erythroid disorders can now be identified more rapidly by the use of next-generation sequencing techniques. Genome-wide association studies on erythroid traits in healthy populations have also revealed new modulators of erythropoiesis. All of these recent developments have significant promise not only for increasing our understanding of erythropoiesis, but also for improving our ability to intervene when RBC production is perturbed in disease.

Keywords: erythropoiesis, haemopoiesis, haemopoietic progenitors, red cell disorders, red cells

Developmental and Hierarchical Origins for Erythropoiesis

Three Developmental Waves of Erythropoiesis

During embryonic development, mammalian haematopoiesis emerges in three distinct waves (Figure 1A). Most of our understanding of this process comes from extensive mouse studies (Palis, 2014a; Yoder, 2014). The first wave of haematopoiesis emerges from the yolk sac at embryonic day 7.5 (E7.5) in mice. This first wave, commonly known as the primitive wave, is characterized by the production of nucleated megaloblastic erythroblasts that are referred to as primitive erythroblasts (PEs), along with diploid platelet progenitor cells and macrophages (Potts et al., 2014). PEs are characterized by the predominant expression of embryonic globin genes. While it was initially assumed that PEs could not enucleate, studies have shown that PEs eventually enucleate in the circulation in both mice and humans (Kingsley et al., 2004; Van Handel et al., 2010). The close proximity of the blood and endothelial cells in the yolk sac led to the hypothesis nearly 100 years ago that haematopoietic cells and blood vessels originate from a common precursor. This precursor, referred to as the haemangioblast, has been suggested to arise from a unique population of primitive streak mesodermal cells (Palis, 2014a).

Figure 1.

Figure 1

Open in a new tab

A) There are three developmental waves of erythropoiesis in mammals. The first wave is marked by the emergence of primitive erythroblasts (PE) that express embryonic globins in yolk sac blood islands. In the second wave, the erythro-myeloid progenitor (EMP) emerges from yolk sac and migrates to the fetal liver, producing definitive erythroblasts expressing predominantly mouse adult globins. In the third wave, the haematopoietic stem cell (HSC) emerges from the haemogenic endothelium in the aorto-gonad mesonephros (AGM) and other sites. The HSC migrates to fetal liver and eventually to the adult bone marrow (BM), producing definitive erythroblasts. B) Classical (in black) and alternate (in red) models of the adult haematopoietic hierarchy. In the classical model, the adult HSCs in the BM gives rise to either a common myeloid progenitor (CMP) or common lymphoid progenitor (CLP). The CMP then differentiates into either a granulocyte monocyte progenitor (GMP) or megakaryocyte erythroid progenitor (MEP). These progenitors differentiate into mature cells of distinct lineages. Several alternate pathways have been discovered by recent studies (in red). HSCs were shown to differentiate directly into CMP, MEP and megakaryocytes. HSC can also differentiate into a lymphoid primed multipotent progenitor (LMPP) lacking any megakaryocyte erythroid potential. NK, Natural killer cell; LT-HSC, long-term HSC; ST-HSC; short-term HSC; MPP, multipotent progenitor; RBC, red blood cell.

The second wave of haematopoiesis is characterized by the emergence of erythro-myeloid progenitors (EMPs) in the yolk sac at approximately E8.25 in mice (Palis, 2014a). Yolk sac EMPs can generate erythroid colonies similar to those derived from adult bone marrow (BM) and these cells have also been shown to have at least the capacity to produce multiple other myeloid lineages (Gomez Perdiguero et al., 2015; McGrath et al., 2015). Some work has suggested that specific lymphocyte populations may also be produced from the EMP or a related lineage transiently produced in the yolk sac (Boiers et al., 2013). The EMPs eventually migrate to the fetal liver and produce definitive erythroblasts, which predominantly express mouse adult globins (McGrath et al., 2011). Recent work has shown that EMP-derived erythroblasts can self-renew, at least in vitro, in the presence of dexamethasone, stem cell factor (SCF, also termed KITLG) and erythropoietin (EPO) (Kim et al., 2015). To what extent this self-renewal occurs in vivo is currently unknown.

The third wave of haematopoiesis is characterized by the emergence of haematopoietic stem cells (HSCs) from a unique population of endothelial cells termed the haemogenic endothelium, which can be found in the dorsal aorta of the aorta-gonad-mesonephros (AGM) region at approximately E10.5 in mice. In parallel, HSCs may also emerge from other haemogenic endothelial cells within the arteries found in the umbilical, vitelline, cranial, yolk sac and placental regions (Yoder, 2014). These HSCs migrate to the fetal liver where they undergo an expansion period before reaching their final destination in the BM, where the HSCs primarily remain in a quiescent state (Kiel et al., 2007). The relative contribution from HSC-derived cells during embryonic development and when the EMP-derived contribution wanes is currently unknown and is confounded by the similarity between EMP- and HSC-derived differentiated definitive haematopoietic cells. In mutant mice lacking HSCs, EMPs are able to maintain embryonic viability until birth, suggesting broad functions for this lineage throughout much of gestation (Chen et al., 2011). In addition, the number of HSCs that seed the BM to give rise to mature adult haematopoiesis remains unknown.

Erythropoiesis in the Haematopoietic Hierarchy

In humans, after birth, HSCs reside in the BM and are thought to give rise to all mature haematopoietic cells, including the erythroid lineage, through a series of intermediate progenitors (Figure 1B). Although there is a classical model of haematopoietic differentiation that involves differentiation into increasingly more lineage-restricted progenitors, recent work suggests that there may be alternate pathways that could be used in specific circumstances or concomitant with differentiation through the classical pathway. Using functional transplantation studies and lineage tracing in mice, it was shown that differentiation into erythroid- and megakaryocyte-committed progenitors occurs early in the haematopoietic hierarchy from HSCs or their immediate downstream progenitors (Sanjuan-Pla et al., 2013; Yamamoto et al., 2013). Single cell gene expression analysis of various mouse stem and progenitor populations has shown that the phenotypically defined megakaryocyte and erythroid progenitors (MEPs) cluster closely with HSCs and segregate distinctly from lymphomyeloid lineages (Guo et al., 2013). Recent studies in human haematopoietic cells have also demonstrated that lineage specification of the erythroid and megakaryocyte lineages appears to occur early in the hierarchy at either the stem or multipotential progenitor stage (Notta et al., 2015). These data suggest a more complex model in which committed erythroid progenitors can directly differentiate from the HSC or immediate downstream multipotential progenitors, although in vivo haematopoiesis may be more complicated.

The committed erythroid progenitors are the burst-forming unit erythroid (BFU-E) and colony-forming unit erythroid (CFU-E) cells, which are named for their ability to form colonies in semisolid media. The BFU-E is the earliest committed erythroid progenitor and can form significantly larger colonies than the CFU-E. BFU-Es can be found in the circulation, whereas CFU-Es cannot except under pathological conditions (Clarke and Housman, 1977). While BFU-Es and CFU-Es can be functionally distinguished and enriched using surface marker expression, their morphology cannot be distinguished from other blast cells of different lineages. BFU-Es and CFU-Es further differentiate into erythroid precursor cells with distinct morphologies. The earliest morphologically identifiable erythroid precursor is the proerythroblast, which differentiates sequentially into the basophilic, polychromatophilic and orthochromatic erythroblast, which can then enucleate to form a reticulocyte. The precursors show a gradual reduction in cell and nuclear size, while a robust increase in the accumulation of haemoglobin occurs.

The prospective enrichment of erythroid progenitor and precursor cells has enabled an improved understanding of the molecular basis of erythroid differentiation and its disorders (Figure 2). Several groups have suggested strategies by which human MEPs can be enriched from the fraction of progenitor cells that express CD34 and CD38 in the absence of lineage markers (Doulatov et al., 2010; Edvardsson et al., 2006; Manz et al., 2002). However, it is clear that these MEP populations are extremely heterogeneous and probably contain committed erythroid progenitors. CD105 (endoglin) expression has been suggested to mark one of the first steps of erythroid commitment and may help to further enrich for BFU-Es found using MEP enrichment approaches (Mori et al., 2015). Independent work has allowed significant enrichment of BFU-Es and CFU-Es based on CD34, CD36, CD71 and CD45RA marker expression from subfractions of cord blood, BM and peripheral blood (Li et al., 2014). More differentiated human erythroid precursors can be isolated by surface expression of the transferrin receptor (CD71) and glycophorin A (CD235a). More recently used markers, including α4-integrin (CD49d) and band 3, have been shown to improve the resolution of the various stages of erythroid precursor differentiation (Hu et al., 2013). Similarly, mouse erythroid progenitors and precursors can be enriched using various combinations of cell surface markers including CD71, glycophorin A (Ter119), CD44 and KIT (Chen et al., 2009; Flygare et al., 2011). As multiple and sometimes conflicting strategies exist to isolate erythroid progenitor and precursor populations, future research comparing the overlap of the proposed markers will allow for isolation and characterization of increasingly pure populations from a variety of sources (Figure 2).

Figure 2.

Figure 2

Open in a new tab

The differentiation steps from the megakaryocyte erythroid progenitor (MEP) to the mature red blood cell (RBC) are shown. An overview of recent strategies to isolate these cell types based on surface markers is given. Note that the current MEP isolation strategies also appear to contain BFU-Es and CFU-Es. MEP, Megakaryocyte erythroid progenitor; BFU-E, blast colony forming unit - erythroid; CFU-E, colony forming unit - erythroid; ProE, proerythroblast; BasoE, basophilic erythroblast; PolyE, polychromatic erythroblast; OrthoE, orthochromatic erythroblast; Retic, reticulocyte.

Developmental Switching of Haemoglobin

Haemoglobin is a tetramer of 2 α-like globin polypeptide chains and 2 β-like globin chains with an iron containing porphyrin ring called haem bound to each subunit that allows for effective oxygen transport. The sequential expression of embryonic, fetal and adult globin genes during development occurs through a series of two haemoglobin switches, mediated primarily through changes in expression of the β-like globin genes expressed, which have been extensively studied and reviewed in detail elsewhere (Sankaran and Orkin, 2013). Here, we provide a brief overview of this process. In humans, there are five functional β-like globin genes: embryonic (HBE1), fetal (HBG1, HBG2), and adult (HBD and HBB). There is initially a switch from predominant expression of the embryonic globin (HBE1) in primitive erythroid cells to the fetal globins (HBG1, HBG2) that coincides with the onset of definitive erythropoiesis. Shortly after birth, fetal globin expression in the definitive erythroid cells is gradually replaced by the adult globins. There are three major functional α-like globin genes: HBZ, HBA1 and HBA2. The embryonic HBZ globin is expressed almost exclusively in primitive erythroid cells, while the adult globins (HBA1, HBA2) are expressed at all stages of erythropoiesis.

Understanding the molecular basis of the fetal-to-adult haemoglobin switch has been of long-standing interest in the field due to its therapeutic relevance. There is substantial clinical evidence that elevated fetal haemoglobin (HbF) production reduces disease severity in β-thalassaemia and sickle cell disease (SCD) (Sankaran and Weiss, 2015). Individuals with hereditary persistence of fetal haemoglobin (HPFH) concomitantly with β-thalassaemia or SCD have reduced disease severity and are often clinically asymptomatic (Galanello et al., 2009). Modest induction of HbF by hydroxycarbamide can alleviate symptoms, organ damage and mortality in SCD and in some patients with β-thalassaemia (Musallam et al., 2013).

The molecular regulation of the haemoglobin switches has been extensively covered in other reviews (Sankaran and Orkin, 2013) and will only be briefly discussed here. By using insight from genome-wide association study (GWAS) examining common variation in HbF levels, the multi-zinc finger containing transcriptional regulator, BCL11A, was identified as a key regulator of the fetal-to-adult haemoglobin switch and HbF silencing (Sankaran et al., 2008). BCL11A binds to the β-globin enhancer and also to an intergenic region between the HBG1 and HBD genes that is often deleted in individuals with HPFH (Sankaran et al., 2011a). The exact mechanisms by which BCL11A acts to silence HbF remain unclear and may either involve direct modification of chromatin and/or alteration of long-range interactions. Erythroid-specific enhancers of BCL11A have also been identified (Bauer et al., 2013). BCL11A appears to be a promising target for therapeutic HbF induction and recent work has shown that humans with haploinsufficiency of this gene have substantial persistence of HbF, although there appear to be adverse neurodevelopmental phenotypes found in such patients, which emphasizes the need to develop targeted approaches to suppress BCL11A (Basak et al., 2015). GWAS studies have also implicated the transcription factor, MYB, as a regulator of HbF levels and reduction of this factor does appear to robustly induce HbF production, although its mechanism of action remains unknown (Sankaran et al., 2013; Stadhouders et al., 2014). Additionally, rare mutations in KLF1 have been associated with increased HbF levels in some patients, but the effects are variable and certain mutations in this factor have been associated with both increased HbF and congenital anaemias (Sankaran and Orkin, 2013). A number of other factors have also been suggested to be involved in this process, but in vivo evidence for most of these other factors is currently limited and further work is necessary (Sankaran and Orkin, 2013; Sankaran and Weiss, 2015).

Model Systems and Organisms Used for Understanding Erythropoiesis

Mouse and Zebrafish Models

Much of our knowledge regarding the process of erythropoiesis comes from studies of valuable model organisms, including mice and zebrafish (Figure 3) (Carroll and North, 2014; Schmitt et al., 2014). Morphologically and at the molecular level, erythropoiesis is largely conserved between mice and humans. Studies of erythropoiesis have been facilitated through the availability of well-established tools, including the ability to readily manipulate the mouse genome with reverse genetic engineering approaches and the extensive availability of antibodies for stage-specific enrichment of haematopoietic progenitors (Orkin and Zon, 2008). Erythroid disorders, including SCD and β-thalassaemia, have been modelled in mice and are actively used in preclinical studies (Nienhuis and Persons, 2012; Xu et al., 2011). Mouse haematopoietic cytokines are readily available, leading to development of in vitro culture and colony assays.

Figure 3.

Figure 3

Open in a new tab

Brief overview of the advantages and disadvantages of model systems commonly used to understand erythropoiesis. PSC, pluripotent stem cell.

Despite their evolutionary distance from humans, many haematopoietic genes are conserved in zebrafish, making it a valuable model system. The ability to economically screen a large number of zebrafish has facilitated extensive forward genetic screens that have identified numerous genes involved in erythropoiesis (Jing and Zon, 2011). Moreover, zebrafish undergo external fertilization, allowing for in vivo imaging of embryonic development. Thousands of mutants have been generated by these forward genetic screens and screened for haematopoietic phenotypes. Analysis of many of these mutant fish has led to advances in our understanding of erythropoiesis, including the identification of key molecules involved in iron metabolism from hypochromic zebrafish mutants, such as the key plasma membrane iron transporter SLC40A1/ferroportin 1 (Donovan et al., 2000).

Cellular Models

One of the unique aspects of erythropoiesis, compared with many other examples of physiological differentiation, has been the long-standing availability of both primary and immortalized in vitro cellular models. Currently, the gold standard is the primary culture of haematopoietic stem and progenitor cells (HSPCs) obtained from the peripheral blood (either mobilized or normal mononuclear cells), BM, cord blood or fetal liver of human donors or mice. In general, the culture of primary cells has involved multiple phases that promote either the expansion of progenitor cells or the differentiation toward precursors that can eventually enucleate. It should be noted that enucleation rates in such systems tend to be modest and can vary considerably (Hu et al., 2013). Thus, primary cell systems may not fully recapitulate the efficient expansion and differentiation observed in vivo. The use of cells differentiated from immortalized pluripotent stem cells also offers the prospect of modelling specific erythroid disorders (Mills et al., 2014), but at the current time, these cells can only be differentiated toward erythroid cells resembling those that arise in the initial haematopoietic waves from the yolk sac (Yoder, 2014).

A number of cell lines have proven incredibly valuable in improving our understanding of erythropoiesis and its molecular regulation. One of the most useful models is the mouse erythroblast cell line G1E and its derivative, G1E-ER4. These cell lines are derived from GATA1-null mouse embryonic stem (ES) cells and are arrested at a stage that resembles the proerythroblast (Welch et al., 2004). These cells can be rescued by the addition of GATA1 to semi-synchronously complete erythroid differentiation, which has provided important insight into erythroid transcriptional regulation. Similar cell lines with both megakaryocyte/erythroid potential have revealed important biology about the megakaryocyte/erythroid lineage decision (Noh et al., 2015). Mouse erythroleukaemia cells have been particularly valuable in broadening our understanding of certain aspects of gene regulation, particularly given their adult globin gene expression pattern (Bauer et al., 2013). Human erythroleukaemia cell lines, including TF-1, which is cytokine responsive, and K562 cells, which are cytokine independent, have also proven to be valuable models (Sankaran et al., 2012a; Stadhouders et al., 2014; Ulirsch et al., 2014). More recently, immortalized human erythroid cell lines have been created through a variety of methods, and some of these lines may be valuable in future studies (Kurita et al., 2013). Some of these newer cell lines have the distinct advantage of showing an adult-type haemoglobin expression pattern as well as allowing for increased terminal differentiation, compared with more traditional erythroid cell lines, such as TF-1 or K562 cells. With the advent of precise and efficient genome editing through the use of CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats-associated protein 9 nuclease) or other related approaches, these cell models have become increasingly utilized.

Xenograft Models

Humanized mouse models allow engraftment of human haematopoietic cells and are thus excellent tools to study human haematopoiesis in conditions that can mimic normal physiology. The NOD/SCID IL2Rγnull (NSG) and BALB/c Rag−/− IL2Rγnull (Brg) immunodeficient mice lacking T cells, B cells and NK cells show robust engraftment of human haematopoietic cells (Ishikawa et al., 2005; Rongvaux et al., 2013). Unfortunately, these mice have poor human erythroid differentiation because human erythroid progenitors make up a low and highly variable fraction of the human haematopoietic cells in the BM and circulating human RBCs have not been found in peripheral blood. Interestingly, inactivation of mouse macrophages resulted in a low transient level of circulating human RBCs (Hu et al., 2011). Recently, both NSG and Brg mice carrying a mutant Kit gene showed increased engraftment of erythroid progenitors (~30%) and show great promise for the study of human erythropoiesis (McIntosh et al., 2015). One distinct advantage of these newer models is that they do not rely upon irradiation to allow human cell engraftment. Humanized mouse models that express human cytokines are being developed and may allow for even greater erythroid engraftment (Rongvaux et al., 2013).

Humans as an Emerging Model System

While model organisms are indispensible for the study of erythropoiesis, there are specific aspects of human erythroid biology that do not replicate well. For example, mutations of the human SEC23B gene result in congenital dyserythropoietic anaemia type II, but a mouse knockout of this gene does not have a haematological phenotype (probably due to compensation from species-specific expression of the paralog, SEC23A) (Khoriaty et al., 2014; Ulirsch et al., 2014). As another example, mutations in GLUT1 alter RBC volume in adult humans, but GLUT1 is not expressed in the erythroid lineage of adult mice (Montel-Hagen et al., 2008). Fortunately, advances in both sequencing technology and functional approaches have allowed for the direct study of human erythropoiesis and disorders due to alterations of this process. GWAS coupled with thorough functional follow-up have identified novel roles for BCL11A as an essential HbF silencing factor (Sankaran et al., 2008), CCND3 and CCNA2 as regulators of RBC size and number (Ludwig et al., 2015; Sankaran et al., 2012a), TRIM58 as a regulator of enucleation (Thom et al., 2014), and SMIM1 as a key RBC surface protein encoding the Vel blood antigen (Cvejic et al., 2013). Studies of rare genetic disorders in humans have revealed novel, and sometimes unexpected, findings, such as an erythroid-specific defect due to ribosomal protein haploinsufficiency in Diamond Blackfan anaemia (Ludwig et al., 2014). Importantly, support from human genetics can identify novel therapeutic targets (e.g. BCL11A in β-thalassaemia and SCD) and has the potential to improve the success of therapeutic drug development (Nelson et al., 2015).

Molecular Regulation of Erythropoiesis

Cellular Signaling Pathways

Several cytokines and growth factors have essential roles in erythropoiesis. One of the most well studied cytokines is erythropoietin (EPO) (Kuhrt and Wojchowski, 2015). EPO primarily acts on erythroid progenitors and early precursors. CFU-Es require EPO for survival during in vitro cell culture, as well as for forming colonies in methylcellulose media. Some BFU-Es or earlier progenitors may require EPO and some evidence exists to suggest that EPO receptor may be expressed on such progenitor cells, at least in mice (Singbrant et al., 2011). Even though EPO is required for in vitro culture systems, BFU-E and CFU-E populations can be found in Epo and Epor knockout mice, although they both die at the fetal liver stage with the onset of definitive erythropoiesis (Wu et al., 1995a). Although this initially suggested that this signalling was dispensable for yolk sac primitive erythropoiesis, recent careful analysis of these mutants suggests a critical role for maturation of primitive erythroid cells as well (Malik et al., 2013).

Another well-studied growth factor, stem cell factor (SCF, KITLG), binds to the KIT receptor that functions as a receptor tyrosine kinase (Lemmon and Schlessinger, 2010). SCF can synergize with EPO to promote erythropoiesis (Wu et al., 1995b). Kitl (Scf) null (steel mutants) and Kit null (W mutants) mice have reduced CFU-E colonies in the fetal liver (Nocka et al., 1989). Moreover, SCF can indirectly phosphorylate EPOR through KIT receptor. Other factors that positively regulate erythropoiesis include insulin, insulin-like growth factor, activin and angiotension II. Transforming growth factor β and a related ligand, growth and differentiation factor 11, inflammatory cytokines, such as γ-interferon, tumour necrosis factor α, and tumour necrosis factor-related apoptosis-inducing ligand all have negative effects on erythropoiesis (Dussiot et al., 2014; Suragani et al., 2014). The precise relevance of these pathways for in vivo erythropoiesis remains to be established in most of these cases.

Transcriptional Regulation and non-Coding RNAs in Erythropoiesis

The commitment of multipotent progenitor cells to the erythroid lineage and their subsequent differentiation into mature RBCs is ultimately controlled by master transcription factors (TFs) that tightly regulate erythroid-specific gene expression networks. The importance of a core erythroid network (CEN) of TFs for proper red cell development is increasingly appreciated (Figure 4). This CEN is comprised of DNA-binding TFs: GATA1, TAL1, and KLF1 (Xu et al., 2012), as well as those that are non-DNA-binding: LDB1 and LMO2. Knockout mice lacking any TF from the CEN exhibit severe impairments in erythropoiesis and generally do not survive past gestation. In humans, mutations in GATA1 and KLF1 result in multiple anaemia phenotypes (Sankaran et al., 2012b). Moreover, these factors have been shown to co-occupy regulatory elements in erythroblasts proximal to key erythroid genes and are more predictive of enhancer activity in comparison with histone modifications (Dogan et al., 2015; Ulirsch et al., 2014; Xu et al., 2012). Impairment of one or more of these TFs often destabilizes the binding of the other factors at co-occupied elements.

Figure 4.

Figure 4

Open in a new tab

A) The core erythroid network (CEN) of transcription factors (TFs) is composed of the DNA-binding TFs, GATA1, TAL1 and KLF1, as well as the non-DNA-binding TFs, LDB1 and LMO2. The CEN loops from enhancers to promoters to activate target gene expression. B) TFs in the CEN often interact with additional TFs at a subset of regulatory elements. For example, GATA1 and TAL1 interact with GFI1B and the nucleosome remodelling deacetylase (NuRD) complex, resulting in target gene repression. C) Long non-coding RNAs (lncRNAs) that are transcribed during erythropoiesis are regulated by the CEN. Future studies will probably refine our understanding of the role of lncRNAs in erythropoiesis.

Outside the CEN, important roles for other TFs, often requiring cooperativity with the core TFs, have been delineated in erythropoiesis. For example, BCL11A interacts with GATA1 and is the key regulator of the fetal-to-adult haemoglobin switch, as discussed above (Sankaran et al., 2008). Other factors with novel and evolving roles include ZFPM1/FOG1, NFE2, GFI1B, ETO2, TAF10, MYB, and ZNF148/ZBP-89. Other studies have proposed a role for the BMP and Wnt-responsive TFs, SMAD1 and TCF7L2, respectively, in erythropoiesis (Trompouki et al., 2011). Occupancy by SMAD1 and TCF7L2 was shown to shift from GATA2-occupied elements proximal to genes important for multipotency in HSPCs to GATA1-occupied enhancers near key erythroid genes in erythroblasts (Figure 4).

Although model organisms, such as mouse and zebrafish, have been instrumental in improving our understanding of the gene expression networks regulated by the CEN, recent studies have surprisingly shown a marked divergence in the global patterns of gene expression between human and mouse erythroblasts (Palis, 2014b). While the overall CEN of TFs governing erythropoiesis is broadly the same for human and mouse, recent studies have shown that occupancy sites for TFs in the CEN are generally poorly conserved at orthologous DNA (Ulirsch et al., 2014), similar to findings in multiple unrelated lineages (Villar et al., 2014). Moreover, species-specific binding by TFs in the CEN has been shown to significantly associate with species-specific expression patterns in erythroblasts (Ulirsch et al., 2014).

The role of non-coding RNAs, including microRNAs and long non-coding RNAs (lncRNAs), in erythropoiesis is increasingly being appreciated. miR-451 (MIR451A) was identified as a microRNA that was dramatically upregulated during erythroid maturation and its role in fine-tuning erythropoiesis has been substantiated by a number of independent studies (Yu et al., 2010). Other microRNAs have also been suggested to have roles in erythropoiesis. For example, miR-24 binds to the 3’ UTR of ALK4 to repress translation, resulting in maturation defects, (Wang et al., 2008), miR-15a (MIR15A) acts through MYB to restrict colony formation and regulate HbF levels (Sankaran et al., 2011b), and miR-221/222 (MIR221/222) regulate KIT translation to potentially alter erythroid differentiation (Gabbianelli et al., 2010). Recently, hundreds of lncRNAs have been shown to have dynamic expression patterns during erythropoiesis, many of which show evidence of regulation by the CEN (Alvarez-Dominguez et al., 2014) (Figure 4). Interestingly, the knockdown of multiple lncRNAs in primary cell culture appeared to inhibit erythroid maturation, suggesting that some lncRNAs may serve as key regulators of erythropoiesis. However, lncRNA expression in humans and mice is substantially divergent, and the study of lncRNA function has been an area of considerable controversy that will probably undergo substantial refinement in the coming years (Bassett et al., 2014).

Translational Regulation

Most research into the regulation of erythropoiesis has focused heavily on transcription, but an increasingly important role for mRNA translation has recently begun to be appreciated. Recent studies have shown an important role for alterations in protein synthesis rates during haematopoiesis (Buszczak et al., 2014). Moreover, Diamond-Blackfan anaemia (DBA), an anaemia characterized by a specific reduction in the earliest erythroid-commited progenitors with defective maturation of erythroid precursors, can be caused by autosomal dominant mutations in one of 17 different ribosomal protein genes (Boria et al., 2010). The involvement of ribosomal proteins in DBA suggested that changes in protein translation might cause this disorder. Indeed, rare mutations in GATA1 have been identified in DBA patients (Sankaran et al., 2012b), which led to the identification of altered translation of GATA1 mRNA due to ribosomal protein haploinsufficiency as a common pathogenic mechanism for DBA (Ludwig et al., 2014). While further work investigating the underlying mechanisms is necessary, translational regulation appears to have a role in the earliest lineage-commitment decisions, allowing for specification of multipotent progenitors into the erythroid lineage.

During the later stages of erythropoiesis, translational regulation also has a key role. Under specific conditions, such as with iron deficiency, iron responsive proteins (IRPs) bind to stem-loop structured iron responsive elements (IREs) in mRNA UTRs. When IRPs bind to IREs in the 5’ UTR of ALAS2, FTH1/ FTL (heavy and light ferritin chains), and SLC40A1 (ferroportin) mRNAs, their translation is repressed, resulting in decreased haem biosynthesis (Hentze and Kuhn, 1996). However, the binding of an IRP to an IRE in the 3’ UTR of TFRC (transferrin receptor) actually increases mRNA stability, resulting in increased cellular iron intake (Hentze and Kuhn, 1996). The identification of other novel canonical and non-canonical IREs, such as those in AHSP (α-haemoglobin stabilizing protein) mRNA, increases our understanding of the process of cellular iron homeostasis and may inform the treatment of iron deficiency anaemia (dos Santos et al., 2008). In the setting of haem deficiency or oxidative stress, the haem-regulated eIF2α kinase (HRI), an eIF2α kinase that is specific to the erythroid lineage, phosphorylates eukaryotic initiation factor 2 alpha (eIF2α/EIF2A), inhibiting translational initiation and decreasing overall protein synthesis (Chen, 2014). This pathway appears to exist to ensure that globin synthesis remains balanced and can be regulated by the availability of iron and haem. Moreover, recent studies have shown that HRI-dependent eIF2α phosphorylation (eIF2αP) preferentially up-regulates translation of ATF4 mRNA, which then transcriptionally activates both stress response and erythroid differentiation pathways (Suragani et al., 2012).

An Overview of Disorders Affecting Erythropoiesis

Most intrinsic erythroid disorders can be broadly classified into two categories: disorders where the most significant defects occur during differentiation, such as is observed in conditions characterized by dyserythropoiesis, and those where differentiation proceeds more or less normally, but mature RBCs have defective function or structure. Some intrinsic disorders involve a combination of these defects. Here, we highlight a few representative disorders in each category, focusing on recent advances in our understanding of their underlying molecular mechanisms. More detailed reviews on such disorders have been published elsewhere (Sankaran and Weiss, 2015), and we therefore only briefly discuss the disorders to highlight aspects relevant to our evolving understanding of erythropoiesis.

Defective Differentiation

There is a spectrum of disorders that affect various aspects of erythropoiesis. At one extreme is DBA, which is characterized by a paucity of the earliest erythroid progenitors and defective maturation of the few remaining progenitors into mature erythroid precursors (Nathan et al., 1978). Other aspects of the maturation process can also go awry in certain disorders. For example, excess free α-globin chains in β-thalassaemia – where there is defective production of β-globin due to a variety of different types of mutations – can cause cytotoxicity in erythroid precursors and therefore impair maturation (Arlet et al., 2014). It is for this reason that increasing other β-like globin chains, as occurs with increased γ-globin (which forms HbF), or reducing α-globin (as occurs with concomitant α-thalassaemia) can ameliorate symptoms in patients with β-thalassaemia (Mettananda et al., 2015). RBCs from patients with β-thalassaemia also have a shortened lifespan, which contributes to the anaemia.

Other rare forms of anaemia can impair maturation of erythroid precursors. A rare set of disorders, known as the congenital dyserythropoietic anaemias, are characterized by such defects and can be due to mutations in the CDAN1, SEC23B, KIF23, C15ORF41, LPIN2, KLF1 or GATA1 genes (Iolascon et al., 2013). In addition, we have identified at least one family with features of dyserythropoietic anaemia due to X-linked dominant mutations in the haem biosynthetic enzyme, ALAS2, which appear to act in a cell non-autonomous manner (Sankaran et al., 2015). In most cases, the underlying basis for the dyserythropoiesis resulting from such mutations is unknown. Interestingly, similar features can also be observed in some acquired conditions, in the setting of infections or treatment with specific medications. Of note, this category of diseases can also be characterized by production of RBCs that exhibit defects during circulation.

Faulty Mature Red Cells

The RBC membrane is a specialized phospholipid bilayer comprised of multiple integral membrane proteins that are stabilized by a skeleton of ankyrin and spectrin. As RBCs must be deformable, the RBC membrane skeleton has undergone specialized adaptation to effectively circulate through the narrow capillaries in the bloodstream. This allows the RBC to survive in the circulation for an average of 120 days. A series of disorders disrupt this membrane skeleton and result in anaemia. These disorders include hereditary spherocytosis (HS), hereditary elliptocytosis (HE) and Southeast Asian Ovalocytosis (SAO) (Da Costa et al., 2013). In nearly all cases, a genetic lesion can be identified in one of multiple causal genes encoding membrane and cytoskeletal proteins (Da Costa et al., 2013). In addition, there are disorders that affect volume and ion homeostasis, which are due to mutations in various channel-encoding genes. These include overhydrated stomatocytosis (OHSt) and dehydrated stomatocytosis or hereditary xerocytosis (HX). Recent studies of OHSt have identified genetic lesions in SLC4A1 (Band 3), RHAG, and the glucose transporter SCL2A1 (previously termed GLUT1). Identification of causal genetic lesions in HX has proven more difficult, but recent studies have used modern sequencing approaches to identify heterozygous mutations in PIEZO1, a gene encoding a mechanosensitive ion channel, and KCNN4, the gene encoding for the potassium selective Gardos channel (Rapetti-Mauss et al., 2015; Zarychanski et al., 2012). For each membranopathy, identification and follow-up of a new causal gene has lead to novel molecular insights that informs both diagnostic and therapeutic approaches, such as the potential use of Gardos channel blockers in HX.

Modifier Alleles in Erythroid Disorders

A major question is whether any two cases of an identical erythroid disorder with identical or similar genetic lesions will share a similar phenotype and disease progression. In many cases the answer is no. Even when the primary genetic lesion is identical between cases, modifier alleles can dramatically alter disease severity. The prototype for this is present in both of the major disorders of β-globin: β-thalassaemia and SCD. There is substantial variation between individuals with similar mutations, but much of this variation can be explained by genetic factors (both common and rare) affecting the expression of HbF (Nuinoon et al., 2010; Sankaran et al., 2011a). Modifier alleles have also been observed in other erythroid disorders, like HS, which exhibits substantial clinical heterogeneity, even within an individual pedigree (Iolascon and Avvisati, 2008). For example, partial pyruvate kinase deficiency due to a PKLR mutation has been observed to aggravate HS disease severity by additively affecting RBC fragility (van Zwieten et al., 2015). However, most modifiers remain to be identified and larger studies are needed to define the extent to which these disorders are simply monogenic, as opposed to being on the spectrum of more complex disorders.

Rare modifier alleles can also inform therapeutic approaches. In congenital erythropoietic porphyria (CEP), an intrinsic erythroid disorder due to mutations in the gene encoding uroporphyrinogen III synthase (UROS) - the fourth enzyme in the haem biosynthesis pathway - gain-of-function mutations in the first and rate-limiting enzyme, 5-aminolevulinate synthase 2 (ALAS2), were associated with increased disease severity (To-Figueras et al., 2011). This suggested that CEP severity could be modulated by altering ALAS2 activity. Indeed, by restricting iron availability with the iron chelator deferasirox, the translation of ALAS2 mRNA could be reduced, resulting in a decrease in the toxic coproporphyrin 1 byproducts and an amelioration of CEP severity in vivo, at least in one case (Egan et al., 2015).

In DBA, specific modifier alleles have not yet been identified, but variable expressivity and penetrance is observed in DBA cases with similar genetic lesions. In some cases, first-degree relatives with identical genetic lesions are almost entirely asymptomatic (Boria et al., 2010). Although preliminary, some studies have identified non-coding regulatory mutations near RP genes that may affect DBA clinical severity (Cretien et al., 2010). Future studies will identify true modifier alleles and may reveal potential therapeutic targets.

Concluding Remarks

As a result of extensive studies, we have a solid understanding of erythropoiesis and this process has thus long served as a paradigm for cellular differentiation more broadly. Nevertheless, with the advent and availability of many new technologies, such as high-throughput sequencing, our understanding of the complexities of haematopoiesis has grown and novel regulators that govern erythroid differentiation have been uncovered at a rapid pace. Moreover, comprehensive human genetic studies have revealed the underlying molecular aetiologies of many erythroid diseases and, furthermore, have accelerated the identification of therapeutic targets for these disorders. Future studies that leverage human genetics in conjunction with the clever use of model systems, such as through the use of improved humanized mice or by applying genome editing to cellular models, will probably reveal important erythroid biology and inform therapeutic strategies for the numerous and varied disorders that occur in this lineage.

Acknowledgements

We apologize to all the authors whose work we were unable to specifically discuss due to space constraints. We thank all the members of the Sankaran laboratory for their valuable input. This work was supported by the National Institutes of Health grants R01 DK103794, R21 HL120791, and U01 HL117720 to V.G. Sankaran.

Footnotes

Author contributions

All authors performed the literature review and wrote the article

References

  1. Alvarez-Dominguez JR, Hu W, Yuan B, Shi J, Park SS, Gromatzky AA, van Oudenaarden A, Lodish HF. Global discovery of erythroid long noncoding RNAs reveals novel regulators of red cell maturation. Blood. 2014;123:570–581. doi: 10.1182/blood-2013-10-530683. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Arlet JB, Ribeil JA, Guillem F, Negre O, Hazoume A, Marcion G, Beuzard Y, Dussiot M, Moura IC, Demarest S, de Beauchene IC, Belaid-Choucair Z, Sevin M, Maciel TT, Auclair C, Leboulch P, Chretien S, Tchertanov L, Baudin-Creuza V, Seigneuric R, Fontenay M, Garrido C, Hermine O, Courtois G. HSP70 sequestration by free alpha-globin promotes ineffective erythropoiesis in beta-thalassaemia. Nature. 2014;514:242–246. doi: 10.1038/nature13614. [DOI] [PubMed] [Google Scholar]
  3. Basak A, Hancarova M, Ulirsch JC, Balci TB, Trkova M, Pelisek M, Vlckova M, Muzikova K, Cermak J, Trka J, Dyment DA, Orkin SH, Daly MJ, Sedlacek Z, Sankaran VG. BCL11A deletions result in fetal hemoglobin persistence and neurodevelopmental alterations. Journal of Clinical Investigation. 2015;125:2363–2368. doi: 10.1172/JCI81163. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Bassett AR, Akhtar A, Barlow DP, Bird AP, Brockdorff N, Duboule D, Ephrussi A, Ferguson-Smith AC, Gingeras TR, Haerty W, Higgs DR, Miska EA, Ponting CP. Considerations when investigating lncRNA function in vivo. Elife. 2014;3:e03058. doi: 10.7554/eLife.03058. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Bauer DE, Kamran SC, Lessard S, Xu J, Fujiwara Y, Lin C, Shao Z, Canver MC, Smith EC, Pinello L, Sabo PJ, Vierstra J, Voit RA, Yuan GC, Porteus MH, Stamatoyannopoulos JA, Lettre G, Orkin SH. An erythroid enhancer of BCL11A subject to genetic variation determines fetal hemoglobin level. Science. 2013;342:253–257. doi: 10.1126/science.1242088. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Boiers C, Carrelha J, Lutteropp M, Luc S, Green JC, Azzoni E, Woll PS, Mead AJ, Hultquist A, Swiers G, Perdiguero EG, Macaulay IC, Melchiori L, Luis TC, Kharazi S, Bouriez-Jones T, Deng Q, Ponten A, Atkinson D, Jensen CT, Sitnicka E, Geissmann F, Godin I, Sandberg R, de Bruijn MF, Jacobsen SE. Lymphomyeloid contribution of an immune-restricted progenitor emerging prior to definitive hematopoietic stem cells. Cell Stem Cell. 2013;13:535–548. doi: 10.1016/j.stem.2013.08.012. [DOI] [PubMed] [Google Scholar]
  7. Boria I, Garelli E, Gazda HT, Aspesi A, Quarello P, Pavesi E, Ferrante D, Meerpohl JJ, Kartal M, Da Costa L, Proust A, Leblanc T, Simansour M, Dahl N, Frojmark AS, Pospisilova D, Cmejla R, Beggs AH, Sheen MR, Landowski M, Buros CM, Clinton CM, Dobson LJ, Vlachos A, Atsidaftos E, Lipton JM, Ellis SR, Ramenghi U, Dianzani I. The ribosomal basis of Diamond-Blackfan Anemia: mutation and database update. Human Mutation. 2010;31:1269–1279. doi: 10.1002/humu.21383. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Buszczak M, Signer RA, Morrison SJ. Cellular differences in protein synthesis regulate tissue homeostasis. Cell. 2014;159:242–251. doi: 10.1016/j.cell.2014.09.016. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Carroll KJ, North TE. Oceans of opportunity: exploring vertebrate hematopoiesis in zebrafish. Experimental Hematology. 2014;42:684–696. doi: 10.1016/j.exphem.2014.05.002. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Chen JJ. Translational control by heme-regulated eIF2alpha kinase during erythropoiesis. Current Opinion in Hematology. 2014;21:172–178. doi: 10.1097/MOH.0000000000000030. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Chen K, Liu J, Heck S, Chasis JA, An X, Mohandas N. Resolving the distinct stages in erythroid differentiation based on dynamic changes in membrane protein expression during erythropoiesis. Proceedings of the National Academy of Sciences of the United States of America. 2009;106:17413–17418. doi: 10.1073/pnas.0909296106. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Chen MJ, Li Y, De Obaldia ME, Yang Q, Yzaguirre AD, Yamada-Inagawa T, Vink CS, Bhandoola A, Dzierzak E, Speck NA. Erythroid/myeloid progenitors and hematopoietic stem cells originate from distinct populations of endothelial cells. Cell Stem Cell. 2011;9:541–552. doi: 10.1016/j.stem.2011.10.003. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Clarke BJ, Housman D. Characterization of an erythroid precursor cell of high proliferative capacity in normal human peripheral blood. Proceedings of the National Academy of Sciences of the United States of America. 1977;74:1105–1109. doi: 10.1073/pnas.74.3.1105. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Cretien A, Proust A, Delaunay J, Rince P, Leblanc T, Ducrocq R, Simansour M, Marie I, Tamary H, Meerpohl J, Niemeyer C, Gazda H, Sieff C, Ball S, Tchernia G, Mohandas N, Da Costa L. Genetic variants in the noncoding region of RPS19 gene in Diamond-Blackfan anemia: potential implications for phenotypic heterogeneity. American Journal of Hematology. 2010;85:111–116. doi: 10.1002/ajh.21601. [DOI] [PubMed] [Google Scholar]
  15. Cvejic A, Haer-Wigman L, Stephens JC, Kostadima M, Smethurst PA, Frontini M, van den Akker E, Bertone P, Bielczyk-Maczynska E, Farrow S, Fehrmann RS, Gray A, de Haas M, Haver VG, Jordan G, Karjalainen J, Kerstens HH, Kiddle G, Lloyd-Jones H, Needs M, Poole J, Soussan AA, Rendon A, Rieneck K, Sambrook JG, Schepers H, Sillje HH, Sipos B, Swinkels D, Tamuri AU, Verweij N, Watkins NA, Westra HJ, Stemple D, Franke L, Soranzo N, Stunnenberg HG, Goldman N, van der Harst P, van der Schoot CE, Ouwehand WH, Albers CA. SMIM1 underlies the Vel blood group and influences red blood cell traits. Nature Genetics. 2013;45:542–545. doi: 10.1038/ng.2603. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Da Costa L, Galimand J, Fenneteau O, Mohandas N. Hereditary spherocytosis, elliptocytosis, and other red cell membrane disorders. Blood Reviews. 2013;27:167–178. doi: 10.1016/j.blre.2013.04.003. [DOI] [PubMed] [Google Scholar]
  17. Dogan N, Wu W, Morrissey CS, Chen KB, Stonestrom A, Long M, Keller CA, Cheng Y, Jain D, Visel A, Pennacchio LA, Weiss MJ, Blobel GA, Hardison RC. Occupancy by key transcription factors is a more accurate predictor of enhancer activity than histone modifications or chromatin accessibility. Epigenetics Chromatin. 2015;8:16. doi: 10.1186/s13072-015-0009-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Donovan A, Brownlie A, Zhou Y, Shepard J, Pratt SJ, Moynihan J, Paw BH, Drejer A, Barut B, Zapata A, Law TC, Brugnara C, Lux SE, Pinkus GS, Pinkus JL, Kingsley PD, Palis J, Fleming MD, Andrews NC, Zon LI. Positional cloning of zebrafish ferroportin1 identifies a conserved vertebrate iron exporter. Nature. 2000;403:776–781. doi: 10.1038/35001596. [DOI] [PubMed] [Google Scholar]
  19. dos Santos CO, Dore LC, Valentine E, Shelat SG, Hardison RC, Ghosh M, Wang W, Eisenstein RS, Costa FF, Weiss MJ. An iron responsive element-like stem-loop regulates alpha-hemoglobin-stabilizing protein mRNA. Journal of Biological Chemistry. 2008;283:26956–26964. doi: 10.1074/jbc.M802421200. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Doulatov S, Notta F, Eppert K, Nguyen LT, Ohashi PS, Dick JE. Revised map of the human progenitor hierarchy shows the origin of macrophages and dendritic cells in early lymphoid development. Nature Immunology. 2010;11:585–593. doi: 10.1038/ni.1889. [DOI] [PubMed] [Google Scholar]
  21. Dussiot M, Maciel TT, Fricot A, Chartier C, Negre O, Veiga J, Grapton D, Paubelle E, Payen E, Beuzard Y, Leboulch P, Ribeil JA, Arlet JB, Cote F, Courtois G, Ginzburg YZ, Daniel TO, Chopra R, Sung V, Hermine O, Moura IC. An activin receptor IIA ligand trap corrects ineffective erythropoiesis in beta-thalassemia. Nature Medicine. 2014;20:398–407. doi: 10.1038/nm.3468. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Edvardsson L, Dykes J, Olofsson T. Isolation and characterization of human myeloid progenitor populations--TpoR as discriminator between common myeloid and megakaryocyte/erythroid progenitors. Experimental Hematology. 2006;34:599–609. doi: 10.1016/j.exphem.2006.01.017. [DOI] [PubMed] [Google Scholar]
  23. Egan DN, Yang Z, Phillips J, Abkowitz JL. Inducing iron deficiency improves erythropoiesis and photosensitivity in congenital erythropoietic porphyria. Blood. 2015;126:257–261. doi: 10.1182/blood-2014-07-584664. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Flygare J, Rayon Estrada V, Shin C, Gupta S, Lodish HF. HIF1alpha synergizes with glucocorticoids to promote BFU-E progenitor self-renewal. Blood. 2011;117:3435–3444. doi: 10.1182/blood-2010-07-295550. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Gabbianelli M, Testa U, Morsilli O, Pelosi E, Saulle E, Petrucci E, Castelli G, Giovinazzi S, Mariani G, Fiori ME, Bonanno G, Massa A, Croce CM, Fontana L, Peschle C. Mechanism of human Hb switching: a possible role of the kit receptor/miR 221-222 complex. Haematologica. 2010;95:1253–1260. doi: 10.3324/haematol.2009.018259. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Galanello R, Sanna S, Perseu L, Sollaino MC, Satta S, Lai ME, Barella S, Uda M, Usala G, Abecasis GR, Cao A. Amelioration of Sardinian beta0 thalassemia by genetic modifiers. Blood. 2009;114:3935–3937. doi: 10.1182/blood-2009-04-217901. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Gomez Perdiguero E, Klapproth K, Schulz C, Busch K, Azzoni E, Crozet L, Garner H, Trouillet C, de Bruijn MF, Geissmann F, Rodewald HR. Tissue-resident macrophages originate from yolk-sac-derived erythro-myeloid progenitors. Nature. 2015;518:547–551. doi: 10.1038/nature13989. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Guo G, Luc S, Marco E, Lin TW, Peng C, Kerenyi MA, Beyaz S, Kim W, Xu J, Das PP, Neff T, Zou K, Yuan GC, Orkin SH. Mapping cellular hierarchy by single-cell analysis of the cell surface repertoire. Cell Stem Cell. 2013;13:492–505. doi: 10.1016/j.stem.2013.07.017. [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Hentze MW, Kuhn LC. Molecular control of vertebrate iron metabolism: mRNA-based regulatory circuits operated by iron, nitric oxide, and oxidative stress. Proceedings of the National Academy of Sciences of the United States of America. 1996;93:8175–8182. doi: 10.1073/pnas.93.16.8175. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Hu J, Liu J, Xue F, Halverson G, Reid M, Guo A, Chen L, Raza A, Galili N, Jaffray J, Lane J, Chasis JA, Taylor N, Mohandas N, An X. Isolation and functional characterization of human erythroblasts at distinct stages: implications for understanding of normal and disordered erythropoiesis in vivo. Blood. 2013;121:3246–3253. doi: 10.1182/blood-2013-01-476390. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Hu Z, Van Rooijen N, Yang YG. Macrophages prevent human red blood cell reconstitution in immunodeficient mice. Blood. 2011;118:5938–5946. doi: 10.1182/blood-2010-11-321414. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Iolascon A, Avvisati RA. Genotype/phenotype correlation in hereditary spherocytosis. Haematologica. 2008;93:1283–1288. doi: 10.3324/haematol.13344. [DOI] [PubMed] [Google Scholar]
  33. Iolascon A, Heimpel H, Wahlin A, Tamary H. Congenital dyserythropoietic anemias: molecular insights and diagnostic approach. Blood. 2013;122:2162–2166. doi: 10.1182/blood-2013-05-468223. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Ishikawa F, Yasukawa M, Lyons B, Yoshida S, Miyamoto T, Yoshimoto G, Watanabe T, Akashi K, Shultz LD, Harada M. Development of functional human blood and immune systems in NOD/SCID/IL2 receptor {gamma} chain(null) mice. Blood. 2005;106:1565–1573. doi: 10.1182/blood-2005-02-0516. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Jing L, Zon LI. Zebrafish as a model for normal and malignant hematopoiesis. Disease Models & Mechanisms. 2011;4:433–438. doi: 10.1242/dmm.006791. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Khoriaty R, Vasievich MP, Jones M, Everett L, Chase J, Tao J, Siemieniak D, Zhang B, Maillard I, Ginsburg D. Absence of a Red Blood Cell Phenotype in Mice with Hematopoietic Deficiency of SEC23B. Molecular and Cellular Biology. 2014;34:3721–3734. doi: 10.1128/MCB.00287-14. [DOI] [PMC free article] [PubMed] [Google Scholar]
  37. Kiel MJ, He S, Ashkenazi R, Gentry SN, Teta M, Kushner JA, Jackson TL, Morrison SJ. Haematopoietic stem cells do not asymmetrically segregate chromosomes or retain BrdU. Nature. 2007;449:238–242. doi: 10.1038/nature06115. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Kim AR, Olsen JL, England SJ, Huang YS, Fegan KH, Delgadillo LF, McGrath KE, Kingsley PD, Waugh RE, Palis J. Bmi-1 Regulates Extensive Erythroid Self-Renewal. Stem Cell Reports. 2015;4:995–1003. doi: 10.1016/j.stemcr.2015.05.003. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Kingsley PD, Malik J, Fantauzzo KA, Palis J. Yolk sac-derived primitive erythroblasts enucleate during mammalian embryogenesis. Blood. 2004;104:19–25. doi: 10.1182/blood-2003-12-4162. [DOI] [PubMed] [Google Scholar]
  40. Kuhrt D, Wojchowski DM. Emerging EPO and EPO receptor regulators and signal transducers. Blood. 2015;125:3536–3541. doi: 10.1182/blood-2014-11-575357. [DOI] [PMC free article] [PubMed] [Google Scholar]
  41. Kurita R, Suda N, Sudo K, Miharada K, Hiroyama T, Miyoshi H, Tani K, Nakamura Y. Establishment of immortalized human erythroid progenitor cell lines able to produce enucleated red blood cells. PloS One. 2013;8:e59890. doi: 10.1371/journal.pone.0059890. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Lemmon MA, Schlessinger J. Cell signaling by receptor tyrosine kinases. Cell. 2010;141:1117–1134. doi: 10.1016/j.cell.2010.06.011. [DOI] [PMC free article] [PubMed] [Google Scholar]
  43. Li J, Hale J, Bhagia P, Xue F, Chen L, Jaffray J, Yan H, Lane J, Gallagher PG, Mohandas N, Liu J, An X. Isolation and transcriptome analyses of human erythroid progenitors: BFU-E and CFU-E. Blood. 2014;124:3636–3645. doi: 10.1182/blood-2014-07-588806. [DOI] [PMC free article] [PubMed] [Google Scholar]
  44. Ludwig LS, Gazda HT, Eng JC, Eichhorn SW, Thiru P, Ghazvinian R, George TI, Gotlib JR, Beggs AH, Sieff CA, Lodish HF, Lander ES, Sankaran VG. Altered translation of GATA1 in Diamond-Blackfan anemia. Nature Medicine. 2014;20:748–753. doi: 10.1038/nm.3557. [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Ludwig LS, Cho H, Wakabayashi A, Eng JC, Ulirsch JC, Fleming MD, Lodish HF, Sankaran VG. Genome-wide association study follow-up identifies cyclin A2 as a regulator of the transition through cytokinesis during terminal erythropoiesis. American Journal of Hematology. 2015;90:386–391. doi: 10.1002/ajh.23952. [DOI] [PMC free article] [PubMed] [Google Scholar]
  46. Malik J, Kim AR, Tyre KA, Cherukuri AR, Palis J. Erythropoietin critically regulates the terminal maturation of murine and human primitive erythroblasts. Haematologica. 2013;98:1778–1787. doi: 10.3324/haematol.2013.087361. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. Manz MG, Miyamoto T, Akashi K, Weissman IL. Prospective isolation of human clonogenic common myeloid progenitors. Proceedings of the National Academy of Sciences of the United States of America. 2002;99:11872–11877. doi: 10.1073/pnas.172384399. [DOI] [PMC free article] [PubMed] [Google Scholar]
  48. McGrath KE, Frame JM, Fromm GJ, Koniski AD, Kingsley PD, Little J, Bulger M, Palis J. A transient definitive erythroid lineage with unique regulation of the beta-globin locus in the mammalian embryo. Blood. 2011;117:4600–4608. doi: 10.1182/blood-2010-12-325357. [DOI] [PMC free article] [PubMed] [Google Scholar]
  49. McGrath KE, Frame JM, Fegan KH, Bowen JR, Conway SJ, Catherman SC, Kingsley PD, Koniski AD, Palis J. Distinct Sources of Hematopoietic Progenitors Emerge before HSCs and Provide Functional Blood Cells in the Mammalian Embryo. Cell Reports. 2015;11:1892–1904. doi: 10.1016/j.celrep.2015.05.036. [DOI] [PMC free article] [PubMed] [Google Scholar]
  50. McIntosh BE, Brown ME, Duffin BM, Maufort JP, Vereide DT, Slukvin II, Thomson JA. Nonirradiated NOD,B6.SCID Il2rgamma−/− Kit(W41/W41) (NBSGW) mice support multilineage engraftment of human hematopoietic cells. Stem Cell Reports. 2015;4:171–180. doi: 10.1016/j.stemcr.2014.12.005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  51. Mettananda S, Gibbons RJ, Higgs DR. alpha-Globin as a molecular target in the treatment of beta-thalassemia. Blood. 2015;125:3694–3701. doi: 10.1182/blood-2015-03-633594. [DOI] [PMC free article] [PubMed] [Google Scholar]
  52. Mills JA, Paluru P, Weiss MJ, Gadue P, French DL. Hematopoietic differentiation of pluripotent stem cells in culture. Methods in Molecular Biology. 2014;1185:181–194. doi: 10.1007/978-1-4939-1133-2_12. [DOI] [PubMed] [Google Scholar]
  53. Montel-Hagen A, Kinet S, Manel N, Mongellaz C, Prohaska R, Battini JL, Delaunay J, Sitbon M, Taylor N. Erythrocyte Glut1 triggers dehydroascorbic acid uptake in mammals unable to synthesize vitamin C. Cell. 2008;132:1039–1048. doi: 10.1016/j.cell.2008.01.042. [DOI] [PubMed] [Google Scholar]
  54. Mori Y, Chen JY, Pluvinage JV, Seita J, Weissman IL. Prospective isolation of human erythroid lineage-committed progenitors. Proceedings of the National Academy of Sciences of the United States of America. 2015;112:9638–9643. doi: 10.1073/pnas.1512076112. [DOI] [PMC free article] [PubMed] [Google Scholar]
  55. Musallam KM, Taher AT, Cappellini MD, Sankaran VG. Clinical experience with fetal hemoglobin induction therapy in patients with beta-thalassemia. Blood. 2013;121:2199–2212. doi: 10.1182/blood-2012-10-408021. quiz 2372. [DOI] [PubMed] [Google Scholar]
  56. Nathan DG, Clarke BJ, Hillman DG, Alter BP, Housman DE. Erythroid precursors in congenital hypoplastic (Diamond-Blackfan) anemia. Journal of Clinical Investigation. 1978;61:489–498. doi: 10.1172/JCI108960. [DOI] [PMC free article] [PubMed] [Google Scholar]
  57. Nelson MR, Tipney H, Painter JL, Shen J, Nicoletti P, Shen Y, Floratos A, Sham PC, Li MJ, Wang J, Cardon LR, Whittaker JC, Sanseau P. The support of human genetic evidence for approved drug indications. Nature Genetics. 2015;47:856–860. doi: 10.1038/ng.3314. [DOI] [PubMed] [Google Scholar]
  58. Nienhuis AW, Persons DA. Development of gene therapy for thalassemia. Cold Spring Harbor Perspectives in Medicine. 2012;2:a011833–a011833. doi: 10.1101/cshperspect.a011833. [DOI] [PMC free article] [PubMed] [Google Scholar]
  59. Nocka K, Majumder S, Chabot B, Ray P, Cervone M, Bernstein A, Besmer P. Expression of c-kit gene products in known cellular targets of W mutations in normal and W mutant mice--evidence for an impaired c-kit kinase in mutant mice. Genes and Development. 1989;3:816–826. doi: 10.1101/gad.3.6.816. [DOI] [PubMed] [Google Scholar]
  60. Noh JY, Gandre-Babbe S, Wang Y, Hayes V, Yao Y, Gadue P, Sullivan SK, Chou ST, Machlus KR, Italiano JE, Jr., Kyba M, Finkelstein D, Ulirsch JC, Sankaran VG, French DL, Poncz M, Weiss MJ. Inducible Gata1 suppression expands megakaryocyte-erythroid progenitors from embryonic stem cells. Journal of Clinical Investigation. 2015;125:2369–2374. doi: 10.1172/JCI77670. [DOI] [PMC free article] [PubMed] [Google Scholar]
  61. Notta F, Zandi S, Takayama N, Dobson S, Gan OI, Wilson G, Kaufmann KB, McLeod J, Laurenti E, Dunant CF, McPherson JD, Stein LD, Dror Y, Dick JE. Distinct routes of lineage development reshape the human blood hierarchy across ontogeny. Science. 2015 doi: 10.1126/science.aab2116. 2015 Nov 5. [Epub ahead of print] DOI:10.1126/science.aab2116. [DOI] [PMC free article] [PubMed] [Google Scholar]
  62. Nuinoon M, Makarasara W, Mushiroda T, Setianingsih I, Wahidiyat PA, Sripichai O, Kumasaka N, Takahashi A, Svasti S, Munkongdee T, Mahasirimongkol S, Peerapittayamongkol C, Viprakasit V, Kamatani N, Winichagoon P, Kubo M, Nakamura Y, Fucharoen S. A genome-wide association identified the common genetic variants influence disease severity in beta0-thalassemia/hemoglobin E. Human Genetics. 2010;127:303–314. doi: 10.1007/s00439-009-0770-2. [DOI] [PubMed] [Google Scholar]
  63. Orkin SH, Zon LI. Hematopoiesis: an evolving paradigm for stem cell biology. Cell. 2008;132:631–644. doi: 10.1016/j.cell.2008.01.025. [DOI] [PMC free article] [PubMed] [Google Scholar]
  64. Palis J. Primitive and definitive erythropoiesis in mammals. Frontiers in Physiology. 2014a;5:3. doi: 10.3389/fphys.2014.00003. [DOI] [PMC free article] [PubMed] [Google Scholar]
  65. Palis J. Of mice and men. Blood. 2014b;123:3367–3368. doi: 10.1182/blood-2014-04-565457. [DOI] [PubMed] [Google Scholar]
  66. Potts KS, Sargeant TJ, Markham JF, Shi W, Biben C, Josefsson EC, Whitehead LW, Rogers KL, Liakhovitskaia A, Smyth GK, Kile BT, Medvinsky A, Alexander WS, Hilton DJ, Taoudi S. A lineage of diploid platelet-forming cells precedes polyploid megakaryocyte formation in the mouse embryo. Blood. 2014;124:2725–2729. doi: 10.1182/blood-2014-02-559468. [DOI] [PubMed] [Google Scholar]
  67. Rapetti-Mauss R, Lacoste C, Picard V, Guitton C, Lombard E, Loosveld M, Nivaggioni V, Dasilva N, Salgado D, Desvignes JP, Beroud C, Viout P, Bernard M, Soriani O, Vinti H, Lacroze V, Feneant-Thibault M, Thuret I, Guizouarn H, Badens C. A mutation in the Gardos channel is associated with hereditary xerocytosis. Blood. 2015;126:1273–1280. doi: 10.1182/blood-2015-04-642496. [DOI] [PubMed] [Google Scholar]
  68. Rongvaux A, Takizawa H, Strowig T, Willinger T, Eynon EE, Flavell RA, Manz MG. Human hemato-lymphoid system mice: current use and future potential for medicine. Annual Review of Immunology. 2013;31:635–674. doi: 10.1146/annurev-immunol-032712-095921. [DOI] [PMC free article] [PubMed] [Google Scholar]
  69. Sanjuan-Pla A, Macaulay IC, Jensen CT, Woll PS, Luis TC, Mead A, Moore S, Carella C, Matsuoka S, Bouriez Jones T, Chowdhury O, Stenson L, Lutteropp M, Green JC, Facchini R, Boukarabila H, Grover A, Gambardella A, Thongjuea S, Carrelha J, Tarrant P, Atkinson D, Clark SA, Nerlov C, Jacobsen SE. Platelet-biased stem cells reside at the apex of the haematopoietic stem-cell hierarchy. Nature. 2013;502:232–236. doi: 10.1038/nature12495. [DOI] [PubMed] [Google Scholar]
  70. Sankaran VG, Orkin SH. The Switch from Fetal to Adult Hemoglobin. Cold Spring Harbor Perspectives in Medicine. 2013;3:a011643. doi: 10.1101/cshperspect.a011643. [DOI] [PMC free article] [PubMed] [Google Scholar]
  71. Sankaran VG, Weiss MJ. Anemia: progress in molecular mechanisms and therapies. Nature Medicine. 2015;21:221–230. doi: 10.1038/nm.3814. [DOI] [PMC free article] [PubMed] [Google Scholar]
  72. Sankaran VG, Menne TF, Xu J, Akie TE, Lettre G, Van Handel B, Mikkola HKA, Hirschhorn JN, Cantor AB, Orkin SH. Human Fetal Hemoglobin Expression Is Regulated by the Developmental Stage-Specific Repressor BCL11A. Science. 2008;322:1839–1842. doi: 10.1126/science.1165409. [DOI] [PubMed] [Google Scholar]
  73. Sankaran VG, Xu J, Byron R, Greisman HA, Fisher C, Weatherall DJ, Sabath DE, Groudine M, Orkin SH, Premawardhena A, Bender MA. A Functional Element Necessary for Fetal Hemoglobin Silencing. New England Journal of Medicine. 2011a;365:807–814. doi: 10.1056/NEJMoa1103070. [DOI] [PMC free article] [PubMed] [Google Scholar]
  74. Sankaran VG, Menne TF, Scepanovic D, Vergilio JA, Ji P, Kim J, Thiru P, Orkin SH, Lander ES, Lodish HF. MicroRNA-15a and -16-1 act via MYB to elevate fetal hemoglobin expression in human trisomy 13. Proceedings of the National Academy of Sciences of the United States of America. 2011b;108:1519–1524. doi: 10.1073/pnas.1018384108. [DOI] [PMC free article] [PubMed] [Google Scholar]
  75. Sankaran VG, Ludwig LS, Sicinska E, Xu J, Bauer DE, Eng JC, Patterson HC, Metcalf RA, Natkunam Y, Orkin SH, Sicinski P, Lander ES, Lodish HF. Cyclin D3 coordinates the cell cycle during differentiation to regulate erythrocyte size and number. Genes and Development. 2012a;26:2075–2087. doi: 10.1101/gad.197020.112. [DOI] [PMC free article] [PubMed] [Google Scholar]
  76. Sankaran VG, Ghazvinian R, Do R, Thiru P, Vergilio JA, Beggs AH, Sieff CA, Orkin SH, Nathan DG, Lander ES, Gazda HT. Exome sequencing identifies GATA1 mutations resulting in Diamond-Blackfan anemia. Journal of Clinical Investigation. 2012b;122:2439–2443. doi: 10.1172/JCI63597. [DOI] [PMC free article] [PubMed] [Google Scholar]
  77. Sankaran VG, Joshi M, Agrawal A, Schmitz-Abe K, Towne MC, Marinakis N, Markianos K, Berry GT, Agrawal PB. Rare complete loss of function provides insight into a pleiotropic genome-wide association study locus. Blood. 2013;122:3845–3847. doi: 10.1182/blood-2013-09-528315. [DOI] [PubMed] [Google Scholar]
  78. Sankaran VG, Ulirsch JC, Tchaikovskii V, Ludwig LS, Wakabayashi A, Kadirvel S, Lindsley RC, Bejar R, Shi JH, Lovitch SB, Bishop DF, Steensma DP. X-linked macrocytic dyserythropoietic anemia in females with an ALAS2 mutation. Journal of Clinical Investigation. 2015;125:1665–1669. doi: 10.1172/JCI78619. [DOI] [PMC free article] [PubMed] [Google Scholar]
  79. Schmitt CE, Lizama CO, Zovein AC. From transplantation to transgenics: mouse models of developmental hematopoiesis. Experimental Hematology. 2014;42:707–716. doi: 10.1016/j.exphem.2014.06.008. [DOI] [PubMed] [Google Scholar]
  80. Singbrant S, Russell MR, Jovic T, Liddicoat B, Izon DJ, Purton LE, Sims NA, Martin TJ, Sankaran VG, Walkley CR. Erythropoietin couples erythropoiesis, B-lymphopoiesis, and bone homeostasis within the bone marrow microenvironment. Blood. 2011;117:5631–5642. doi: 10.1182/blood-2010-11-320564. [DOI] [PubMed] [Google Scholar]
  81. Stadhouders R, Aktuna S, Thongjuea S, Aghajanirefah A, Pourfarzad F, van Ijcken W, Lenhard B, Rooks H, Best S, Menzel S, Grosveld F, Thein SL, Soler E. HBS1L-MYB intergenic variants modulate fetal hemoglobin via long-range MYB enhancers. Journal of Clinical Investigation. 2014;124:1699–1710. doi: 10.1172/JCI71520. [DOI] [PMC free article] [PubMed] [Google Scholar]
  82. Suragani RN, Zachariah RS, Velazquez JG, Liu S, Sun CW, Townes TM, Chen JJ. Heme-regulated eIF2alpha kinase activated Atf4 signaling pathway in oxidative stress and erythropoiesis. Blood. 2012;119:5276–5284. doi: 10.1182/blood-2011-10-388132. [DOI] [PMC free article] [PubMed] [Google Scholar]
  83. Suragani RN, Cadena SM, Cawley SM, Sako D, Mitchell D, Li R, Davies MV, Alexander MJ, Devine M, Loveday KS, Underwood KW, Grinberg AV, Quisel JD, Chopra R, Pearsall RS, Seehra J, Kumar R. Transforming growth factor-beta superfamily ligand trap ACE-536 corrects anemia by promoting late-stage erythropoiesis. Nature Medicine. 2014;20:408–414. doi: 10.1038/nm.3512. [DOI] [PubMed] [Google Scholar]
  84. Thom CS, Traxler EA, Khandros E, Nickas JM, Zhou OY, Lazarus JE, Silva AP, Prabhu D, Yao Y, Aribeana C, Fuchs SY, Mackay JP, Holzbaur EL, Weiss MJ. Trim58 degrades Dynein and regulates terminal erythropoiesis. Developmental Cell. 2014;30:688–700. doi: 10.1016/j.devcel.2014.07.021. [DOI] [PMC free article] [PubMed] [Google Scholar]
  85. To-Figueras J, Ducamp S, Clayton J, Badenas C, Delaby C, Ged C, Lyoumi S, Gouya L, de Verneuil H, Beaumont C, Ferreira GC, Deybach JC, Herrero C, Puy H. ALAS2 acts as a modifier gene in patients with congenital erythropoietic porphyria. Blood. 2011;118:1443–1451. doi: 10.1182/blood-2011-03-342873. [DOI] [PubMed] [Google Scholar]
  86. Trompouki E, Bowman TV, Lawton LN, Fan ZP, Wu DC, DiBiase A, Martin CS, Cech JN, Sessa AK, Leblanc JL, Li P, Durand EM, Mosimann C, Heffner GC, Daley GQ, Paulson RF, Young RA, Zon LI. Lineage regulators direct BMP and Wnt pathways to cell-specific programs during differentiation and regeneration. Cell. 2011;147:577–589. doi: 10.1016/j.cell.2011.09.044. [DOI] [PMC free article] [PubMed] [Google Scholar]
  87. Ulirsch JC, Lacy JN, An XL, Mohandas N, Mikkelsen TS, Sankaran VG. Altered Chromatin Occupancy of Master Regulators Underlies Evolutionary Divergence in the Transcriptional Landscape of Erythroid Differentiation. Plos Genetics. 2014;10:e1004890. doi: 10.1371/journal.pgen.1004890. [DOI] [PMC free article] [PubMed] [Google Scholar]
  88. Van Handel B, Prashad SL, Hassanzadeh-Kiabi N, Huang A, Magnusson M, Atanassova B, Chen A, Hamalainen EI, Mikkola HK. The first trimester human placenta is a site for terminal maturation of primitive erythroid cells. Blood. 2010;116:3321–3330. doi: 10.1182/blood-2010-04-279489. [DOI] [PMC free article] [PubMed] [Google Scholar]
  89. van Zwieten R, van Oirschot BA, Veldthuis M, Dobbe JG, Streekstra GJ, van Solinge WW, Schutgens RE, van Wijk R. Partial pyruvate kinase deficiency aggravates the phenotypic expression of band 3 deficiency in a family with hereditary spherocytosis. American Journal of Hematology. 2015;90:E35–39. doi: 10.1002/ajh.23899. [DOI] [PubMed] [Google Scholar]
  90. Villar D, Flicek P, Odom DT. Evolution of transcription factor binding in metazoans - mechanisms and functional implications. Nature Reviews: Genetics. 2014;15:221–233. doi: 10.1038/nrg3481. [DOI] [PMC free article] [PubMed] [Google Scholar]
  91. Wang Q, Huang Z, Xue H, Jin C, Ju XL, Han JD, Chen YG. MicroRNA miR-24 inhibits erythropoiesis by targeting activin type I receptor ALK4. Blood. 2008;111:588–595. doi: 10.1182/blood-2007-05-092718. [DOI] [PubMed] [Google Scholar]
  92. Welch JJ, Watts JA, Vakoc CR, Yao Y, Wang H, Hardison RC, Blobel GA, Chodosh LA, Weiss MJ. Global regulation of erythroid gene expression by transcription factor GATA-1. Blood. 2004;104:3136–3147. doi: 10.1182/blood-2004-04-1603. [DOI] [PubMed] [Google Scholar]
  93. Wu H, Liu X, Jaenisch R, Lodish HF. Generation of committed erythroid BFU-E and CFU-E progenitors does not require erythropoietin or the erythropoietin receptor. Cell. 1995a;83:59–67. doi: 10.1016/0092-8674(95)90234-1. [DOI] [PubMed] [Google Scholar]
  94. Wu H, Klingmuller U, Besmer P, Lodish HF. Interaction of the erythropoietin and stem-cell-factor receptors. Nature. 1995b;377:242–246. doi: 10.1038/377242a0. [DOI] [PubMed] [Google Scholar]
  95. Xu J, Peng C, Sankaran VG, Shao Z, Esrick EB, Chong BG, Ippolito GC, Fujiwara Y, Ebert BL, Tucker PW, Orkin SH. Correction of Sickle Cell Disease in Adult Mice by Interference with Fetal Hemoglobin Silencing. Science. 2011;334:993–996. doi: 10.1126/science.1211053. [DOI] [PMC free article] [PubMed] [Google Scholar]
  96. Xu J, Shao Z, Glass K, Bauer DE, Pinello L, Van Handel B, Hou S, Stamatoyannopoulos JA, Mikkola HK, Yuan GC, Orkin SH. Combinatorial assembly of developmental stage-specific enhancers controls gene expression programs during human erythropoiesis. Developmental Cell. 2012;23:796–811. doi: 10.1016/j.devcel.2012.09.003. [DOI] [PMC free article] [PubMed] [Google Scholar]
  97. Yamamoto R, Morita Y, Ooehara J, Hamanaka S, Onodera M, Rudolph KL, Ema H, Nakauchi H. Clonal analysis unveils self-renewing lineage-restricted progenitors generated directly from hematopoietic stem cells. Cell. 2013;154:1112–1126. doi: 10.1016/j.cell.2013.08.007. [DOI] [PubMed] [Google Scholar]
  98. Yoder MC. Inducing definitive hematopoiesis in a dish. Nature Biotechnology. 2014;32:539–541. doi: 10.1038/nbt.2929. [DOI] [PubMed] [Google Scholar]
  99. Yu D, dos Santos CO, Zhao G, Jiang J, Amigo JD, Khandros E, Dore LC, Yao Y, D'Souza J, Zhang Z, Ghaffari S, Choi J, Friend S, Tong W, Orange JS, Paw BH, Weiss MJ. miR-451 protects against erythroid oxidant stress by repressing 14-3-3zeta. Genes and Development. 2010;24:1620–1633. doi: 10.1101/gad.1942110. [DOI] [PMC free article] [PubMed] [Google Scholar]
  100. Zarychanski R, Schulz VP, Houston BL, Maksimova Y, Houston DS, Smith B, Rinehart J, Gallagher PG. Mutations in the mechanotransduction protein PIEZO1 are associated with hereditary xerocytosis. Blood. 2012;120:1908–1915. doi: 10.1182/blood-2012-04-422253. [DOI] [PMC free article] [PubMed] [Google Scholar]

RESOURCES