The major human erythroid DNA-binding protein (GF-1): primary sequence and localization of the gene to the X chromosome

The Mutational Landscape of Myeloid Leukaemia in Down Syndrome

Children with Down syndrome (DS) are particularly prone to haematopoietic disorders. Paediatric myeloid malignancies in DS occur at an unusually high frequency and generally follow a well-defined stepwise clinical evolution. First, the acquisition of mutations in the GATA1 transcription factor gives rise to a transient myeloproliferative disorder (TMD) in DS newborns. While this condition spontaneously resolves in most cases, some clones can acquire additional mutations, which trigger myeloid leukaemia of Down syndrome (ML-DS). These secondary mutations are predominantly found in chromatin and epigenetic regulators-such as cohesin, CTCF or EZH2-and in signalling mediators of the JAK/STAT and RAS pathways. Most of them are also found in non-DS myeloid malignancies, albeit at extremely different frequencies. Intriguingly, mutations in proteins involved in the three-dimensional organization of the genome are found in nearly 50% of cases. How the resulting mutant proteins cooperate with trisomy 21 and mutant GATA1 to promote ML-DS is not fully understood. In this review, we summarize and discuss current knowledge about the sequential acquisition of genomic alterations in ML-DS.

How haematopoiesis research became a fertile ground for regulatory network biology as pioneered by Eric Davidson

PURPOSE OF REVIEW

This historical perspective reviews how work of Eric H. Davidson was a catalyst and exemplar for explaining haematopoietic cell fate determination through gene regulation.

RECENT FINDINGS

Researchers studying blood and immune cells pioneered many of the early mechanistic investigations of mammalian gene regulatory processes. These efforts included the characterization of complex gene regulatory sequences exemplified by the globin and T-cell/B-cell receptor gene loci, as well as the identification of many key regulatory transcription factors through the fine mapping of chromosome translocation breakpoints in leukaemia patients. As the repertoire of known regulators expanded, assembly into gene regulatory network models became increasingly important, not only to account for the truism that regulatory genes do not function in isolation but also to devise new ways of extracting biologically meaningful insights from even more complex information. Here we explore how Eric H. Davidson's pioneering studies of gene regulatory network control in nonvertebrate model organisms have had an important and lasting impact on research into blood and immune cell development.

SUMMARY

The intellectual framework developed by Davidson continues to contribute to haematopoietic research, and his insistence on demonstrating logic and causality still challenges the frontier of research today.

Regulation of GATA1 levels in erythropoiesis

GATA1 is considered as the "master" transcription factor in erythropoiesis. It regulates at the transcriptional level all aspects of erythroid maturation and function, as revealed by gene knockout studies in mice and by genome-wide occupancies in erythroid cells. The GATA1 protein contains two zinc finger domains and an N-terminal transactivation domain. GATA1 translation results in the production of the full-length protein and of a shorter variant (GATA1s) lacking the N-terminal transactivation domain, which is functionally deficient in supporting erythropoiesis. GATA1 protein abundance is highly regulated in erythroid cells at different levels, including transcription, mRNA translation, posttranslational modifications, and protein degradation, in a differentiation-stage-specific manner. Maintaining high GATA1 protein levels is essential in the early stages of erythroid maturation, whereas downregulating GATA1 protein levels is a necessary step in terminal erythroid differentiation. The importance of maintaining proper GATA1 protein homeostasis in erythropoiesis is demonstrated by the fact that both GATA1 loss and its overexpression result in lethal anemia. Importantly, alterations in any of those GATA1 regulatory checkpoints have been recognized as an important cause of hematological disorders such as dyserythropoiesis (with or without thrombocytopenia), β-thalassemia, Diamond-Blackfan anemia, myelodysplasia, or leukemia. In this review, we provide an overview of the multilevel regulation of GATA1 protein homeostasis in erythropoiesis and of its deregulation in hematological disease.

GATA1 mutations in red cell disorders

GATA1 is an essential regulator of erythroid cell gene expression and maturation. In its absence, erythroid progenitors are arrested in differentiation and undergo apoptosis. Much has been learned about GATA1 function through animal models, which include genetic knockouts as well as ones with decreased levels of expression. However, even greater insights have come from the finding that a number of rare red cell disorders, including Diamond-Blackfan anemia, are associated with GATA1 mutations. These mutations affect the amino-terminal zinc finger (N-ZF) and the amino-terminus of the protein, and in both cases can alter the DNA-binding activity, which is primarily conferred by the third functional domain, the carboxyl-terminal zinc finger (C-ZF). Here we discuss the role of GATA1 in erythropoiesis with an emphasis on the mutations found in human patients with red cell disorders.

Advances in understanding the pathogenesis of congenital erythropoietic porphyria

Congenital erythropoietic porphyria (CEP) is a rare genetic disease resulting from the remarkable deficient activity of uroporphyrinogen III synthase, the fourth enzyme of the haem biosynthetic pathway. This enzyme defect results in overproduction of the non-physiological and pathogenic porphyrin isomers, uroporphyrin I and coproporphyrin I. The predominant clinical characteristics of CEP include bullous cutaneous photosensitivity to visible light from early infancy, progressive photomutilation and chronic haemolytic anaemia. The severity of clinical manifestations is markedly heterogeneous among patients; and interdependence between disease severity and porphyrin amount in the tissues has been pointed out. A more pronounced endogenous production of porphyrins concomitant to activation of ALAS2, the first and rate-limiting of the haem synthesis enzymes in erythroid cells, has also been reported. CEP is inherited as autosomal recessive or X-linked trait due to mutations in UROS or GATA1 genes; however an involvement of other causative or modifier genes cannot be ruled out.

Multiple nuclear localization signals mediate nuclear localization of the GATA transcription factor AreA

The Aspergillus nidulans GATA transcription factor AreA activates transcription of nitrogen metabolic genes in response to nitrogen limitation and is known to accumulate in the nucleus during nitrogen starvation. Sequence analysis of AreA revealed multiple nuclear localization signals (NLSs), five putative classical NLSs conserved in fungal AreA orthologs but not in the Saccharomyces cerevisiae functional orthologs Gln3p and Gat1p, and one putative noncanonical RRX33RXR bipartite NLS within the DNA-binding domain. In order to identify the functional NLSs in AreA, we constructed areA mutants with mutations in individual putative NLSs or combinations of putative NLSs and strains expressing green fluorescent protein (GFP)-AreA NLS fusion genes. Deletion of all five classical NLSs individually or collectively did not affect utilization of nitrogen sources or AreA-dependent gene expression and did not prevent AreA nuclear localization. Mutation of the bipartite NLS conferred the inability to utilize alternative nitrogen sources and abolished AreA-dependent gene expression likely due to effects on DNA binding but did not prevent AreA nuclear localization. Mutation of all six NLSs simultaneously prevented AreA nuclear accumulation. The bipartite NLS alone strongly directed GFP to the nucleus, whereas the classical NLSs collaborated to direct GFP to the nucleus. Therefore, AreA contains multiple conserved NLSs, which show redundancy and together function to mediate nuclear import. The noncanonical bipartite NLS is conserved in GATA factors from Aspergillus, yeast, and mammals, indicating an ancient origin.

Transcriptional mechanisms underlying hemoglobin synthesis

The physiological switch in expression of the embryonic, fetal, and adult β-like globin genes has garnered enormous attention from investigators interested in transcriptional mechanisms and the molecular basis of hemoglobinopathies. These efforts have led to the discovery of cell type-specific transcription factors, unprecedented mechanisms of transcriptional coregulator function, genome biology principles, unique contributions of nuclear organization to transcription and cell function, and promising therapeutic targets. Given the vast literature accrued on this topic, this article will focus on the master regulator of erythroid cell development and function GATA-1, its associated proteins, and its frontline role in controlling hemoglobin synthesis. GATA-1 is a crucial regulator of genes encoding hemoglobin subunits and heme biosynthetic enzymes. GATA-1-dependent mechanisms constitute an essential regulatory core that nucleates additional mechanisms to achieve the physiological control of hemoglobin synthesis.

Characterization of the TGF-β1 signaling abnormalities in the Gata1low mouse model of myelofibrosis

Primary myelofibrosis (PMF) is characterized by fibrosis, ineffective hematopoiesis in marrow, and hematopoiesis in extramedullary sites and is associated with abnormal megakaryocyte (MK) development and increased transforming growth factor (TGF)-β1 release. To clarify the role of TGF-β1 in the pathogenesis of this disease, the TGF-β1 signaling pathway of marrow and spleen of the Gata1(low) mouse model of myelofibrosis (MF) was profiled and the consequences of inhibition of TGF-β1 signaling on disease manifestations determined. The expression of 20 genes in marrow and 36 genes in spleen of Gata1(low) mice was altered. David-pathway analyses identified alterations of TGF-β1, Hedgehog, and p53 signaling in marrow and spleen and of mammalian target of rapamycin (mTOR) in spleen only and predicted that these alterations would induce consequences consistent with the Gata1(low) phenotype (increased apoptosis and G1 arrest both in marrow and spleen and increased osteoblast differentiation and reduced ubiquitin-mediated proteolysis in marrow only). Inhibition of TGF-β1 signaling normalized the expression of p53-related genes, restoring hematopoiesis and MK development and reducing fibrosis, neovascularization, and osteogenesis in marrow. It also normalized p53/mTOR/Hedgehog-related genes in spleen, reducing extramedullary hematopoiesis. These data identify altered expression signatures of TGF-β1 signaling that may be responsible for MF in Gata1(low) mice and may represent additional targets for therapeutic intervention in PMF.

CXCR4-independent rescue of the myeloproliferative defect of the Gata1low myelofibrosis mouse model by Aplidin

The discovery of JAK2 mutations in Philadelphia-negative myeloproliferative neoplasms has prompted investigators to evaluate mutation-targeted treatments to restore hematopoietic cell functions in these diseases. However, the results of the first clinical trials with JAK2 inhibitors are not as promising as expected, prompting a search for additional drugable targets to treat these disorders. In this paper, we used the hypomorphic Gata1(low) mouse model of primary myelofibrosis (PMF), the most severe of these neoplasms, to test the hypothesis that defective marrow hemopoiesis and development of extramedullary hematopoiesis in myelofibrosis is due to insufficient p27(Kip1) activity and is treatable by Aplidin, a cyclic depsipeptide that activates p27(Kip1) in several cancer cells. Aplidin restored expression of Gata1 and p27(Kip1) in Gata1(low) hematopoietic cells, proliferation of marrow progenitor cells in vitro and maturation of megakaryocytes in vivo (reducing TGF-beta/VEGF levels released in the microenvironment by immature Gata1(low) megakaryocytes). Microvessel density, fibrosis, bone growth, and marrow cellularity were normal in Aplidin-treated mice and extramedullary hematopoiesis did not develop in liver although CXCR4 expression in Gata1(low) progenitor cells remained low. These results indicate that Aplidin effectively alters the natural history of myelofibrosis in Gata1(low) mice and suggest this drug as candidate for clinical evaluation in PMF.

Evidence for organ-specific stem cell microenvironments

The X-linked Gata1(low) mutation in mice induces strain-restricted myeloproliferative disorders characterized by extramedullary hematopoiesis in spleen (CD1 and DBA/2) and liver (CD1 only). To assess the role of the microenvironment in establishing this myeloproliferative trait, progenitor cell compartments of spleen and marrow from wild-type and Gata1(low) mice were compared. Phenotype and clonal assay of non-fractionated cells indicated that Gata1(low) mice contain progenitor cell numbers 4-fold lower and 10-fold higher than normal in marrow and spleen, respectively. However, progenitor cells prospectively isolated from spleen, but not from marrow, of Gata1(low) mice expressed colony-forming function in vitro. Therefore, calculation of cloning activity of purified cells demonstrated that the total number of Gata1(low) progenitor cells was 10- to 100-fold lower than normal in marrow and >1,000 times higher than normal in spleen. This observation indicates that Gata1(low) hematopoiesis is favored by the spleen and is in agreement with our previous report that removal of this organ induces wild-type hematopoiesis in heterozygous Gata1(low/+) females (Migliaccio et al., 2009, Blood 114:2107). To clarify if rescue of wild-type hematopoiesis by splenectomy prevented extramedullary hematopoiesis in liver, marrow cytokine expression profile and liver histopathology of splenectomized Gata1(low/+) females were investigated. After splenectomy, the marrow expression levels of TGF-beta, VEGF, osteocalcin, PDGF-alpha, and SDF-1 remained abnormally high while Gata1(low) hematopoiesis was detectable in liver of both CD1 and DBA/2 mutants. Therefore, in the absence of the spleen, Gata1(low) hematopoiesis is supported by the liver suggesting that treatment of myelofibrosis in these animals requires the rescue of both stem cell and microenvironmental functions.

Gata1 expression driven by the alternative HS2 enhancer in the spleen rescues the hematopoietic failure induced by the hypomorphic Gata1low mutation

Rigorously defined reconstitution assays developed in recent years have allowed recognition of the delicate relationship that exists between hematopoietic stem cells and their niches. This balance ensures that hematopoiesis occurs in the marrow under steady-state conditions. However, during development, recovery from hematopoietic stress and in myeloproliferative disorders, hematopoiesis occurs in extramedullary sites whose microenvironments are still poorly defined. The hypomorphic Gata1(low) mutation deletes the regulatory sequences of the gene necessary for its expression in hematopoietic cells generated in the marrow. By analyzing the mechanism that rescues hematopoiesis in mice carrying this mutation, we provide evidence that extramedullary microenvironments sustain maturation of stem cells that would be otherwise incapable of maturing in the marrow.

Human phenotypes associated with GATA-1 mutations

GATA-1 is one of the six members of the GATA gene family, a group of related transcription factors discovered in the 1980s. In the past few decades, the crucial role of GATA-1 in normal human hematopoiesis has been delineated. As would be expected, mutations in GATA-1 have subsequently been found to have important clinical significance, and are directly linked to deregulated formation of certain blood cell lineages. This paper reviews the functional consequences of GATA-1 mutations by linking specific errors in the gene, or its downstream protein products, to documented human diseases. These five human diseases are: X-linked thrombocytopenia (XLT), X-linked thrombocytopenia with thalassemia (XLTT), congenital erythropoietic porphyria (CEP), transient myeloproliferative disorder (TMD) and acute megarakaryoblastic leukemia (AMKL) associated with Trisomy 21, and, lastly, a particular subtype of anemia associated with the production of GATA-1s, a shortened, mutant isoform of the wild-type GATA-1. The different phenotypic expressions associated with GATA-1 mutations illustrate the integral function of the transcription factor in overall body homeostasis. Furthermore, these direct genotype-phenotype correlations reinforce the importance of unraveling the human genome, as such connections may lead to important therapeutic or preventive therapies.

Molecular signature of mice T lymphocytes following tolerance induction by allogeneic BMT and CD40-CD40L costimulation blockade

Tolerance induction by mixed chimerism and costimulation blockade is a promising approach to avoid immunosuppression, but the molecular basis of tolerant T lymphocytes remains elusive. We investigated the genome-wide gene expression profile of murine T lymphocytes after tolerance induction by allogeneic bone marrow transplantation (BMT) and costimulatory blockade using the anti-CD40L antibody MR1. Molecular functions, biological processes, cellular locations, and coregulation of identified genes were determined. A total of 113 unique genes exhibited a significant differential expression between the lymphocytes of MR1-treated Tolerance (TOL) and untreated recipients Control (CTRL). The majority of genes upregulated in the TOL group are involved in several signal transduction cascades such as members of the MAPKKK cascade (IL6, Tob2, Stk39, and Dusp24). Other genes involved in lymphocyte differentiation and highly expressed in the TOL group are lymphotactin, the estrogen receptors (ERs) and the suppressor of cytokine signaling 7. Common transcription factors such as ER 1 alpha, GATA-binding protein 1, insulin promoter factor 1, and paired-related homeobox 2 could be identified in the promoter regions of upregulated genes in the TOL group. These data suggest that T lymphoctes of tolerant mice exhibit a distinct molecular expression profile, which needs to be evaluated in other experimental tolerance models to determine whether it is a universal signature of tolerance.

Differential effects of GATA-1 on proliferation and differentiation of erythroid lineage cells

The zinc finger transcription factor GATA-1 is essential for both primitive (embryonic) and definitive (adult) erythropoiesis. To define the roles of GATA-1 in the production and differentiation of primitive and definitive erythrocytes, we established GATA-1-null embryonic stem cell lines in which GATA-1 was able to be conditionally expressed by using the tetracycline conditional gene expression system. The cells were subjected to hematopoietic differentiation by coculturing on OP9 stroma cells. We expressed GATA-1 in the course of primitive and definitive erythropoiesis and analyzed the ability of GATA-1 to rescue the defective erythropoiesis caused by the GATA-1 null mutation. Our results show that GATA-1 functions in the proliferation and maturation of erythrocytes in a distinctive manner. The early-stage expression of GATA-1 during both primitive and definitive erythropoiesis was sufficient to promote the proliferation of red blood cells. In contrast, the late-stage expression of GATA-1 was indispensable to the terminal differentiation of primitive and definitive erythrocytes. Thus, GATA-1 affects the proliferation and differentiation of erythrocytes by different mechanisms.

GATA-1: friends, brothers, and coworkers

GATA-1 is the founding member of the GATA family of transcription factors. GATA-1 and GATA family member GATA-2 are expressed in erythroid and megakaryocytic lineages, in which they play a crucial role in cell maturation and differentiation. GATA-1 regulates the transcription of many specific and nonspecific erythroid genes by binding to DNA at the consensus sequence WGATAR, which is recognized by all of the GATA family of transcription factors. However, it was identified in eosinophilic cells and also in Sertoli cells in testis. Its activity depends on close cooperation with a functional network of cofactors, among them Friend of GATA, PU.1, and CBP/p300. The GATA-1 protein structure has been well described and includes two zinc fingers that are directly involved in the interaction with DNA and other proteins in vivo. GATA-1 mutations in the zinc fingers can cause deregulation of required interactions and lead to severe dysfunction in the hematopoietic system.

Important roles of reversible acetylation in the function of hematopoietic transcription factors

Hematopoiesis is a very complex process whose proper functioning requires the regulated action of a number of transcription factors. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) play significant roles in the regulation of hematopoietic transcription factors activity. Transcription factors such as GATA-1, EKLF, NF-E2, GATA-1, PU.1 recruit HATs and HDACs to chromatin, leading to histone acetylation and deacetylation, that affect chromatin structure and result in gene expression changes. On the other hand, transcription factors themselves can be acetylated and deacetylated by HATs and HDACs, respectively. Consequently, some important functions of these transcription factors are influenced, including DNA binding, transcription activation, repressor activity and proteinprotein interactions. The regulation of hematopoietic transcription factors activity by HATs and HDACs may serve as a good model for studying how tissue-specific and lineage-specific gene expression is controlled through acetylation/ deacetylation of histone/nonhistone proteins.

Gene expression regulation and domain function of hematopoietic GATA factors

The hierarchical gene regulatory network in hematopoiesis is highly complex, making elucidation of the processes of specification and differentiation of hematopoietic cells a challenging task. Recent discoveries have divulged the GATA factors as central to the genetic control of hematopoiesis. In particular, hematopoietic development is subject to extensive and precise regulation of GATA-1 and GATA-2 at the molecular level. We wish to emphasize the regulatory relationships between GATA-1 and GATA-2 implicated in cell development. An advanced experimental genetic approach has provided evidence that abnormalities in this network may result in a variety of blood disorders. The most striking new finding is the novel pathogenesis arising from GATA-1 dysfunction that leads to leukemia.

Homotypic signalling regulates Gata1 activity in the erythroblastic island

Gata1 is a transcription factor essential for erythropoiesis. Erythroid cells lacking Gata1 undergo apoptosis, while overexpression of Gata1 results in a block in erythroid differentiation. However, erythroid cells overexpressing Gata1 differentiate normally in vivo when in the presence of wild-type cells. We have proposed a model, whereby a signal generated by wild-type cells (red cell differentiation signal; REDS) overcomes the intrinsic defect in Gata1-overexpressing erythroid cells. The simplest interpretation of this model is that wild-type erythroid cells generate REDS. To substantiate this notion, we have exploited a tissue specific Cre/loxP system and the process of X-inactivation to generate mice that overexpress Gata1 in half the erythroid cells and are Gata1 null in the other half. The results show that the cells supplying REDS are erythroid cells. This study demonstrates the importance of intercellular signalling in regulating Gata1 activity and that this homotypic signalling between erythroid cells is crucial to normal differentiation.

Flow cytometry of GATA transcription factors

BACKGROUND

Although GATA-1 and GATA-2 have been shown to play an important role in hematopoiesis, the expression levels of these GATA proteins in the targeted cell population of clinical samples have not been studied. We applied flow cytometry (FCM) to examine the expression levels of these GATA proteins in the selected subpopulation in heterogeneous blood cells.

METHODS

Cells were treated with a fixing solution and methanol followed by staining with specific antibodies to GATA proteins in a permeabilizing solution. Immunofluorescence microscopy and Northern blot analysis using GATA-1 and GATA-2 transfected cell lines and various leukemic cell lines were used to confirm the specificity of this method. Subsequently, the method was applied in two-parameter studies combining GATA expression with surface marker expression in clinical samples.

RESULTS

The positive signals were specifically detected in transfected cells and leukemic cell lines by FCM in agreement with the results of Northern blot and immunofluorescence microscopy. The expression of these GATA factors in the targeted cell population was easily detectable by gating with lineage-specific cell surface markers. When the expression of these GATA proteins was examined in glycophorin A-positive cells in clinical samples, the level of GATA-1 was markedly different among the samples.

CONCLUSIONS

This detection system is useful to evaluate the relative expression level of each GATA protein in the targeted cell population among heterogeneous cells, and the results suggest an aberrant expression of GATA factors in hematological diseases.

Transcriptional regulation of erythropoiesis. Fine tuning of combinatorial multi-domain elements

Haematopoiesis, the differentiation of haematopoietic stem cells and progenitors into various lineages, involves complex interactions of transcription factors that modulate the expression of downstream genes and mediate proliferation and differentiation signals. Commitment of pluripotent haematopoietic stem cells to the erythroid lineage induces erythropoiesis, the production of red blood cells. This process involves a concerted progression through an erythroid burst forming unit (BFU-E), an erythroid colony forming unit (CFU-E), proerythroblast and an erythroblast. The terminally differentiated erythrocytes, in mammals, lose their nucleus yet function several more months. A well-coordinated cohort of transcription factors regulates the formation, survival, proliferation and differentiation of multipotent progenitor into the erythroid lineage. Here, we discuss broad-spectrum factors essential for self-renewal and/or differentiation of multipotent cells as well as specific factors required for proper erythroid development. These factors may operate solely or as part of transcriptional complexes, and exert activation or repression. Sequence comparisons reveal evolutionarily conserved modular composition for these factors; X-ray crystallography demonstrates that they include multidomain elements (e.g. HLH or zinc finger motifs), consistent with their complex interactions with other proteins. Finally, transfections and genomic studies show that the timing of each factor's expression during the hematopoietic process, the cell lineages affected and the existing combination of other factors determine the erythroid cell fate.

Platelet characteristics in patients with X-linked macrothrombocytopenia because of a novel GATA1 mutation

A new mutation is described in the X-linked gene GATA1, resulting in macrothrombocytopenia and mild dyserythropoietic features but no marked anemia in a 4-generation family. The molecular basis for the observed phenotype is a substitution of glycine for aspartate in the strictly conserved codon 218 (D218G) of the amino-terminal zinc finger loop of the transcription factor GATA1. Zinc finger interaction studies demonstrated that this mutation results in a weak loss of affinity of GATA1 for its essential cofactor FOG1, whereas direct D218G-GATA1 binding to DNA was normal. The phenotypic effects of this mutation in the patients' platelets have been studied. Semiquantitative RNA analysis, normalized for beta-actin messenger RNA, showed extremely low transcription of the GATA1 target genes GPIbbeta and GPIX but also a significantly lower expression of the nondirectly GATA1-regulated Gsalpha gene, suggestive of incomplete megakaryocyte maturation. In contrast, GPIIIa expression was close to normal in agreement with its early appearance during megakaryocyte differentiation. Flow cytometric analysis of patient platelets confirmed the existence of a platelet population with abnormal size distribution and reduced GPIb complex levels but with normal GPIIIa expression. It also showed the presence of very immature platelets lacking almost all membrane glycoproteins studied (GPIbalpha, GPIbbeta, GPIIIa, GPIX, and GPV). Patients' platelets showed weak ristocetin-induced agglutination, compatible with the disturbed GPIb complex. Accordingly, electron microscopy of the patients' platelets revealed giant platelets with cytoplasmic clusters consisting of smooth endoplasmic reticulum and abnormal membrane complexes. In conclusion, GATA1 mutations can lead to isolated X-linked macrothrombocytopenia without anemia.

Modulation of fetal hemoglobin in sickle cell anemia

A partial understanding of the pathophysiology of sickle cell disease has suggested one means of treatment-increasing the distribution and concentration of fetal hemoglobin in sickle erythrocytes. Although this can be accomplished clinically with drugs like hydroxyurea, a complete understanding of the molecular and cellular basis of fetal hemoglobin regulation may suggest new and better ways of attaining this goal.

Structure and specificity of GATA proteins in Th2 development

Development of Th2 subset of CD4+ T cells involves the interleukin-4 (IL-4)- and Stat6-dependent increase in GATA-3 expression during primary activation. Recently we reported that the phenotypic stability and factor independence of Th2 cells involves acquisition of an intracellular pathway that maintains GATA-3 expression. Evidence from retroviral expression studies implied that this pathway involved an autoactivation of GATA-3 expression, since Stat6-deficient T cells induced endogenous GATA-3 when infected with GATA-3-expressing retroviruses. That study left unresolved the issue of whether GATA-3 autoactivation was direct or indirect. Several other Th2-specific transcription factors have been described, including c-Maf and JunB. We therefore examined the ability of these other transcription factors to induce GATA-3 expression and promote Th2 development. Neither c-Maf nor JunB induced Th2 development in Stat6-deficient CD4+ T cells, in contrast to GATA-3. Consistent with this indication of a possible direct autoactivation pathway, we also observed that heterologous GATA family proteins GATA-1, GATA-2, and GATA-4 were also capable of inducing GATA-3 expression in developing Stat6-deficient T cells and promote Th2 development. Mutational analysis revealed evidence for two distinct mechanisms of GATA-3 action. IL-4 induction by GATA-3 required each of the functional domains to be present, whereas repression of gamma interferon could occur even when mutants of GATA-3 lacking the second transactivation domain, TA2, were expressed. The GATA-dependent induction of the GATA-3 but not the other GATA genes in T cells suggests that T-cell-specific cis elements within the GATA-3 locus likely cooperate with a general GATA recognition motif to allow GATA-3-dependent autoactivation.

Expression of transcription factors during megakaryocytic differentiation of CD34+ cells from human cord blood induced by thrombopoietin

Although normal megakaryocytic development has been shown to require the presence of functional GATA-1 and NF-E2 transcription factors in vivo, the roles of other members of the GATA binding factors and NF-E2 family during megakaryocytic differentiation are unclear. the present study, the expression of GATA family members, GATA-1 and GATA-2, a GATA-binding factor, EVI-1, the large subunit of NF-E2 factor, p45 and the related factors, Nrf1, Nrf2, Nrf3, BACH1, BACH2, and the small subunit of NF-E2, MAFK and MAFG has been examined in human megakaryocytic and erythroid cells by reverse transcriptase-polymerase chain reaction. CD34+ cells isolated from human cord blood were induced to unilineage megakaryocytic or erythroid differentiation in liquid suspension culture in the presense of thrombopoietin or erythropoietin, respectively. Each lineage was identified by monoclonal antibody against GPIIb/IIIa or glycophorin A. In megakaryocytic culture, p45, Nrf1, Nrf2, BACH1, MAFK and MAFG mRNAs were induced similarly to erythroid culture. Nrf3 mRNA was barely detected in both cultures. BACH2 was induced only in megakaryocytic culture, although the level of expression was low. Furthermore, the profiles of transcription factors involved in hematopoiesis, EVI-1 and Ets-1 mRNAs were induced only in megakaryocytic culture. Megakaryocytic and erythroid differentiation pathways are closely related to each other, and these two lineage cells share a number of lineage-specific transcription factors. However, the results showed that the profile of the expression of these transcription factors in megakaryocytic cells is distinct from that of erythroid lineage. The dynamic changes in the levels of different transcription factors that occur during primary megakaryocytic differentiation suggest that the levels of these factors may influence the progression to specific hematopoietic pathways.

GATA factor transgenes under GATA-1 locus control rescue germline GATA-1 mutant deficiencies

GATA-1 germline mutation in mice results in embryonic lethality due to defective erythroid cell maturation, and thus other hematopoietic GATA factors do not compensate for the loss of GATA-1. To determine whether the obligate presence of GATA-1 in erythroid cells is due to its distinct biochemical properties or spatiotemporal patterning, we attempted to rescue GATA-1 mutant mice with hematopoietic GATA factor complementary DNAs (cDNAs) placed under the transcriptional control of the GATA-1gene. We found that transgenic expression of a GATA-1 cDNA fully abrogated the GATA-1–deficient phenotype. Surprisingly, GATA-2 and GATA-3 factors expressed from the same regulatory cassette also rescued the embryonic lethal phenotype of the GATA-1 mutation. However, adult mice rescued with the latter transgenes developed anemia, while GATA-1 transgenic mice did not. These results demonstrate that the transcriptional control dictating proper GATA-1 accumulation is the most critical determinant of GATA-1 activity during erythropoiesis. The results also show that there are biochemical distinctions among the hematopoietic GATA proteins and that during adult hematopoiesis the hematopoietic GATA factors are not functionally equivalent.

GATA factor transgenes under GATA-1 locus control rescue germline GATA-1 mutant deficiencies

GATA-1 germline mutation in mice results in embryonic lethality due to defective erythroid cell maturation, and thus other hematopoietic GATA factors do not compensate for the loss of GATA-1. To determine whether the obligate presence of GATA-1 in erythroid cells is due to its distinct biochemical properties or spatiotemporal patterning, we attempted to rescue GATA-1 mutant mice with hematopoietic GATA factor complementary DNAs (cDNAs) placed under the transcriptional control of the GATA-1gene. We found that transgenic expression of a GATA-1 cDNA fully abrogated the GATA-1–deficient phenotype. Surprisingly, GATA-2 and GATA-3 factors expressed from the same regulatory cassette also rescued the embryonic lethal phenotype of the GATA-1 mutation. However, adult mice rescued with the latter transgenes developed anemia, while GATA-1 transgenic mice did not. These results demonstrate that the transcriptional control dictating proper GATA-1 accumulation is the most critical determinant of GATA-1 activity during erythropoiesis. The results also show that there are biochemical distinctions among the hematopoietic GATA proteins and that during adult hematopoiesis the hematopoietic GATA factors are not functionally equivalent.

Gene expression in proliferating human erythroid cells

A complete understanding of human erythropoiesis will require a robust description of transcriptional activity in hematopoietic cells that proliferate and differentiate in response to erythropoietin (EPO). For this purpose, we cultured peripheral blood mononuclear cells in the presence or in the absence of EPO and examined the transcriptional profile of those cells arising only in response to EPO. A distinct population of CD71( +) cells that demonstrated an average of six additional doublings in suspension culture and erythroid colony formation in methylcellulose was isolated. Suppression subtractive hybridization of mRNA isolated from those cells permitted the identification of transcribed genes. A summary of 719 expressed sequence tags (ESTs) describing 505 independent transcripts is provided here with a full analysis of each EST available at http://hembase.niddk.nih.gov. Several transcripts that matched genes previously reported in the context of erythroid differentiation including 4 cell surface proteins were expressed at this developmental stage. Active chromatin remodeling was suggested by the identification of 4 histone proteins, 4 high-mobility group proteins, 13 transcription factors, and 6 genes involved in DNA recombination and repair. Numerous genes associated with leukemic translocations were also recognized including topoisomerases I and II, nucleophosmin, Translin, EGR1, dek, pim-1, TFG, and MLL. In addition to known transcripts, 44 novel EST were discovered. This transcriptional profile provides the first genomic-scale description of gene activity in erythroid progenitor cells.

GATA-1 Regulates Growth and Differentiation of Definitive Erythroid Lineage Cells During In Vitro ES Cell Differentiation

Although the importance of GATA-1 in both primitive and definitive hematopoietic lineages has been shown in vivo, the precise roles played by GATA-1 during definitive hematopoiesis have not yet been clarified. In vitro differentiation of embryonic stem (ES) cells using OP9 stroma cells can generate primitive and definitive hematopoietic cells separately, and we have introduced a method that separates hematopoietic progenitors and differentiated cells produced in this system. Closer examination showed that the expression of erythroid transcription factors in this system is regulated in a differentiation stage-specific manner. Therefore, we examined differentiation of GATA-1 promoter-disrupted (GATA-1.05) ES cells using this system. Because the GATA-1.05 mice die by 12.5 embryonic days due to the lack of primitive hematopoiesis, the in vitro analysis is an important approach to elucidate the roles of GATA-1 in definitive hematopoiesis. Consistent with the in vivo observation, differentiation of GATA-1.05 mutant ES cells along both primitive and definitive lineages was arrested in this ES cell culture system. Although the maturation-arrested primitive lineage cells did not express detectable amounts of ɛy-globin mRNA, the blastlike cells accumulated in the definitive stage showed β-globin mRNA expression at approximately 70% of the wild type. Importantly, the TER119 antigen was expressed and porphyrin was accumulated in the definitive cells, although the levels of both were reduced to approximately 10%, indicating that maturation of definitive erythroid cells is arrested by the lack of GATA-1 with different timing from that of the primitive erythroid cells. We also found that the hematopoietic progenitor fraction of GATA-1.05 cells contains more colony-forming activity, termed CFU-OP9. These results suggest that theGATA-1.05 mutation resulted in proliferation of proerythroblasts in the definitive lineage.

GATA-1 Regulates Growth and Differentiation of Definitive Erythroid Lineage Cells During In Vitro ES Cell Differentiation

Although the importance of GATA-1 in both primitive and definitive hematopoietic lineages has been shown in vivo, the precise roles played by GATA-1 during definitive hematopoiesis have not yet been clarified. In vitro differentiation of embryonic stem (ES) cells using OP9 stroma cells can generate primitive and definitive hematopoietic cells separately, and we have introduced a method that separates hematopoietic progenitors and differentiated cells produced in this system. Closer examination showed that the expression of erythroid transcription factors in this system is regulated in a differentiation stage-specific manner. Therefore, we examined differentiation of GATA-1 promoter-disrupted (GATA-1.05) ES cells using this system. Because the GATA-1.05 mice die by 12.5 embryonic days due to the lack of primitive hematopoiesis, the in vitro analysis is an important approach to elucidate the roles of GATA-1 in definitive hematopoiesis. Consistent with the in vivo observation, differentiation of GATA-1.05 mutant ES cells along both primitive and definitive lineages was arrested in this ES cell culture system. Although the maturation-arrested primitive lineage cells did not express detectable amounts of ɛy-globin mRNA, the blastlike cells accumulated in the definitive stage showed β-globin mRNA expression at approximately 70% of the wild type. Importantly, the TER119 antigen was expressed and porphyrin was accumulated in the definitive cells, although the levels of both were reduced to approximately 10%, indicating that maturation of definitive erythroid cells is arrested by the lack of GATA-1 with different timing from that of the primitive erythroid cells. We also found that the hematopoietic progenitor fraction of GATA-1.05 cells contains more colony-forming activity, termed CFU-OP9. These results suggest that theGATA-1.05 mutation resulted in proliferation of proerythroblasts in the definitive lineage.

Role of GATA-1 in Proliferation and Differentiation of Definitive Erythroid and Megakaryocytic Cells In Vivo

To elucidate the contributions of GATA-1 to definitive hematopoiesis in vivo, we have examined adult mice that were rendered genetically defective in GATA-1 synthesis (Takahashi et al, J Biol Chem272:12611, 1997). Because the GATA-1 gene is located on the X chromosome, which is randomly inactivated in every cell, heterozygous females can bear either an active wild-type or mutant (referred to asGATA-1.05) GATA-1 allele, consequently leading to variable anemic severity. These heterozygous mutant mice usually developed normally, but they began to die after 5 months. These affected animals displayed marked splenomegaly, anemia, and thrombocytopenia. Proerythroblasts and megakaryocytes massively accumulated in the spleens of the heterozygotes, and we showed that the neomycin resistance gene (which is the positive selection marker in ES cells) was expressed profusely in the abnormally abundant cells generated in the GATA-1.05 mutant females. We also observed hematopoiesis outside of the bone marrow in the affected mutant mice. These data suggest that a small number of GATA-1.05 mutant hematopoietic progenitor cells begin to proliferate vigorously during early adulthood, but because the cells are unable to terminally differentiate, this leads to progenitor proliferation in the spleen and consequently death. Thus, GATA-1 plays important in vivo roles for directing definitive hematopoietic progenitors to differentiate along both the erythroid and megakaryocytic pathways. The GATA-1 heterozygous mutant mouse shows a phenotype that is analogous to human myelodysplastic syndrome and thus may serve as a useful model for this disorder.

Role of GATA-1 in Proliferation and Differentiation of Definitive Erythroid and Megakaryocytic Cells In Vivo

To elucidate the contributions of GATA-1 to definitive hematopoiesis in vivo, we have examined adult mice that were rendered genetically defective in GATA-1 synthesis (Takahashi et al, J Biol Chem272:12611, 1997). Because the GATA-1 gene is located on the X chromosome, which is randomly inactivated in every cell, heterozygous females can bear either an active wild-type or mutant (referred to asGATA-1.05) GATA-1 allele, consequently leading to variable anemic severity. These heterozygous mutant mice usually developed normally, but they began to die after 5 months. These affected animals displayed marked splenomegaly, anemia, and thrombocytopenia. Proerythroblasts and megakaryocytes massively accumulated in the spleens of the heterozygotes, and we showed that the neomycin resistance gene (which is the positive selection marker in ES cells) was expressed profusely in the abnormally abundant cells generated in the GATA-1.05 mutant females. We also observed hematopoiesis outside of the bone marrow in the affected mutant mice. These data suggest that a small number of GATA-1.05 mutant hematopoietic progenitor cells begin to proliferate vigorously during early adulthood, but because the cells are unable to terminally differentiate, this leads to progenitor proliferation in the spleen and consequently death. Thus, GATA-1 plays important in vivo roles for directing definitive hematopoietic progenitors to differentiate along both the erythroid and megakaryocytic pathways. The GATA-1 heterozygous mutant mouse shows a phenotype that is analogous to human myelodysplastic syndrome and thus may serve as a useful model for this disorder.

The making of an erythroid cell. Molecular control of hematopoiesis

The number of circulating red cells is regulated by the daily balance between two processes: the destruction of the old red cells in the liver and the generation of new cells in the bone marrow. The process during which hematopoietic stem cells generate new red cells is called erythropoiesis. This manuscript will describe the molecular mechanisms involved in the process of erythroid differentiation as we understand them today. In particular it will review how erythroid specific growth factor-receptor interactions activate specific transcription factors to turn on the expression of the genes responsible for the establishment of the erythroid phenotype.

Alternative promoters regulate transcription of the mouse GATA-2 gene

Transcription factor GATA-2 has been shown to be a key regulator in hematopoietic progenitor cells. To elucidate how the expression of the GATA-2 gene is controlled, we isolated the mouse GATA-2 (mGATA-2) gene. Transcription of mGATA-2 mRNAs was found to initiate from two distinct first exons, both of which encode entirely untranslated regions, while the remaining five exons are shared by each of the two divergent mRNAs. Reverse transcriptase-polymerase chain reaction analysis revealed that GATA-2 mRNA initiated at the upstream first exon (IS) in Sca-1+/c-kit+ hematopoietic progenitor cells, whereas mRNA that initiates at the downstream first exon (IG) is expressed in all tissues and cell lines that express GATA-2. While the structure of the IG exon/promoter shows high similarity to those of the Xenopus and human GATA-2 genes, the IS exon/promoter has not been described previously. When we examined the regulation contributing to IS transcription using transient transfection assays, we found that sequences lying between -79 and -61 are critical for the cell type-specific activity of the IS promoter. DNase I footprinting experiments and electrophoretic mobility shift assays demonstrated the binding of transcription factors to this region. These data indicate that the proximal 80 base pair region of IS promoter is important for the generation of cell type-specific expression of mGATA-2 from the IS exon.

Cross regulation of four GATA factors that control nitrogen catabolic gene expression in Saccharomyces cerevisiae

Nitrogen catabolic gene expression in Saccharomyces cerevisiae has been reported to be regulated by three GATA family proteins, the positive regulators Gln3p and Gat1p/Nil1p and the negative regulator Dal80p/Uga43p. We show here that a fourth member of the yeast GATA family, the Dal80p homolog Deh1p, also negatively regulates expression of some, but not all, nitrogen catabolic genes, i.e., GAP1, DAL80, and UGA4 expression increases in a deh1 delta mutant. Consistent with Deh1p regulation of these genes is the observation that Deh1p forms specific DNA-protein complexes with GATAA-containing UGA4 and GAP1 promoter fragments in electrophoretic mobility shift assays. Deh1p function is demonstrable, however, only when a repressive nitrogen source such as glutamine is present; deh1 delta mutants exhibit no detectable phenotype with a poor nitrogen source such as proline. Our experiments also demonstrate that GATA factor gene expression is highly regulated by the GATA factors themselves in an interdependent manner. DAL80 expression is Gln3p and Gat1p dependent and Dal80p regulated. Moreover, Gln3p and Dal80p bind to DAL80 promoter fragments. In turn, GAT1 expression is Gln3p dependent and Dal80p regulated but is not autogenously regulated like DAL80. DEH1 expression is largely Gln3p independent, modestly Gat1p dependent, and most highly regulated by Dal80p. Paradoxically, the high-level DEH1 expression observed in a dal80::hisG disruption mutant is highly sensitive to nitrogen catabolite repression.

The second finger of Urbs1 is required for iron-mediated repression of sid1 in Ustilago maydis

The urbs1 gene encodes a transcriptional regulator of siderophore biosynthesis in Ustilago maydis. Biological and DNA-binding activities of the two putative zinc-finger motifs of Urbs1 were studied by analyzing mutants containing altered finger domains. The mutated urbs1 alleles from three previously described N'-methyl-N'-nitro-N-nitrosoguanidine (NTG) mutants were mapped and cloned by a gap-repair procedure. Sequence analyses revealed single amino acid substitutions in two of the NTG mutants. Both mutations (G-507 to D in urbs1-1 and P-491 to L in urbs1-3), which are located in the Urbs1 C-terminal finger domain, reduced DNA-binding activity by 10-fold and were sufficient to confer a urbs1-minus phenotype. The third NTG urbs1 mutant (urbs1-2) also contained a mutation in one of the conserved amino acids (P-518 to S) in the C-terminal finger domain, but this mutation alone was not sufficient to confer a urbs1-minus phenotype. A second frame shift mutation was identified in urbs1-2 and is necessary for the urbs1-minus phenotype. In an analysis of the function of the N-terminal finger of Urbs1, the conserved amino acid Arg-350 was mutated to leucine. A Urbs1 protein with this mutation complemented a urbs1 null mutant strain. By contrast, a similar mutation in the C-terminal domain abolished the ability of Urbs1 to regulate siderophore biosynthesis and greatly reduced its ability to bind target DNA.

Arrest in primitive erythroid cell development caused by promoter-specific disruption of the GATA-1 gene

To elucidate the in vivo function of GATA-1 during hematopoiesis, we specifically disrupted the erythroid promoter of the GATA-1 gene in embryonic stem cells and generated germ line chimeras. Male offspring of chimeras bearing the targeted mutation were found to die by 12.5 days post coitus due to severe anemia while heterozygous females displayed characteristics ranging from severe anemia to normal erythropoiesis. When female heterozygotes were crossed with transgenic males carrying a reporter gene, which specifically marks primitive erythroid progenitors, massive accumulation of undifferentiated erythroid cells were observed in the yolk sacs of the GATA-1-mutant embryos, demonstrating that GATA-1 is required for the terminal differentiation of primitive erythroid cells in vivo.

Adjacent GATA and kappa B-like motifs regulate the expression of a Drosophila immune gene

The GATA motif is a well known positive cis -regulatory element in vertebrates. In this work we report experimental evidence for the direct participation of a GATA motif in the expression of the Drosophila antibacterial peptide gene Cecropin A1 . Previously we have shown that a kappaB-like site is necessary for Cecropin A1 gene expression. Here we present evidence that the Drosophila Rel protein which binds to the kappaB-like site requires an intact GATA site for maximal Dif-mediated transactivation of the Cecropin A1 gene. We show that a Drosophila blood cell line contains factors binding specifically to the GATA motif of the Cecropin A1 gene. The GATA binding activity is likely to include member(s) of the GATA family of transcriptional regulators. We show that the promoters of several inducible insect immune genes possess GATA sites 0-12 base pairs away from kappaB-like sites in functionally important promoter regions. Clusters of GATA and kappaB sites are also observed in the promoters of two important mammalian immune genes, namely IL6 and IL3. The consistent proximity of GATA and kappaB sites appears to be a common theme in the immune gene expression of insects and mammals.

Negative Regulation of the Erythropoietin Gene Expression by the GATA Transcription Factors

We examined regulation of the human erythropoietin (Epo) gene through the GATA sequence in the Epo promoter and showed that Hep3B and HepG2 cells express human GATA-2 (hGATA-2) mRNA and protein. Nuclear extracts of QT6 cells transfected with hGATA-1, 2, or 3 transcription factors showed specific binding to the GATA element in the human Epo gene promoter by gel mobility shift assay. Transient transfection of Hep3B cells with hGATA-1, 2, or 3 showed that each of these transcription factors significantly decreased the level of expression of Epo mRNA as assessed by a competitive polymerase chain reaction. Transient transfection of Hep3B cells with hGATA-1, 2, and 3 and an Epo-reporter gene (growth hormone [GH]) construct showed significant inhibition of the Epo promoter. Antisense oligonucleotide for hGATA-2 transcription factor significantly increased the Epo protein in Hep3B cells under 1% O2 for 24 hours incubation. Furthermore, transient transfection of Hep3B cells with hGATA-1, 2, and 3 and an Epo-reporter gene (luciferase) construct also showed significant inhibition of the Epo promoter. However, transfection of the mutated GATA sequence of the Epo-luciferase gene with hGATA-1, 2, and 3 interfere with the inhibition of the Epo promoter. We conclude that the hGATA-1, 2, and 3 transcription factors specifically bind to the GATA element in the human Epo gene promoter and negatively regulate Epo gene expression.

A molecular aspect of hematopoiesis and endoderm development common to vertebrates and Drosophila

In vertebrates, transcriptional regulators of the GATA family appear to have a conserved function in differentiation and organ development. GATA-1, −2 and −3 are required for different aspects of hematopoiesis, while GATA-4, −5 and −6 are expressed in various organs of endodermal origin, such as intestine and liver, and are implicated in endodermal differentiation. Here we report that the Drosophila gene serpent (srp) encodes the previously described GATA factor ABF. The multiple functions of srp in Drosophila suggest that it is an ortholog of the entire vertebrate Gata family. srp is required for the differentiation and morphogenesis of the endodermal gut. Here we show that it is also essential for Drosophila hematopoiesis and for the formation of the fat body, the insect organ analogous to the liver. These findings imply that some aspects of the molecular mechanisms underlying blood cell development as well as endodermal differentiation are early acquisitions of metazoan evolution and may be common to most higher animals.

Long-range map of a 3.5-Mb region in Xp11.23-22 with a sequence-ready map from a 1.1-Mb gene-rich interval

Most of the yeast artificial chromosomes (YACs) isolated from the Xp11.23-22 region have shown instability and chimerism and are not a reliable resource for determining physical distances. We therefore constructed a long-range pulsed-field gel electrophoresis map that encompasses approximately 3.5 Mb of genomic DNA between the loci TIMP and DXS146 including a CpG-rich region around the WASP and TFE-3 gene loci. A combined YAC-cosmid contig was constructed along the genomic map and was used for fine-mapping of 15 polymorphic microsatellites and 30 expressed sequence tags (ESTs) or sequence transcribed sites (STSs), revealing the following order: tel-(SYN-TIMP)-(DXS426-ELK1)-ZNF(CA) n-L1-DXS1367-ZNF81-ZNF21-DXS6616- (HB3-OATL1pseudogenes-DXS6950)-DXS6949-DXS694 1-DXS7464E(MG61)-GW1E(EBP)- DXS7927E(MG81)-RBM- DXS722-DXS7467E(MG21)-DXS1011E-WASP-DXS6940++ +-DXS7466E(MG44)-GF1- DXS226-DXS1126-DXS1240-HB1- DXS7469E-(DXS6665-DXS1470)-TFE3-DXS7468E-+ ++SYP-DXS1208-HB2E-DXS573-DXS1331- DXS6666-DXS1039-DXS 1426-DXS1416-DXS7647-DXS8222-DXS6850-DXS255++ +-CIC-5-DXS146-cen. A sequence-ready map was constructed for an 1100-kb gene-rich interval flanked by the markers HB3 and DXS1039, from which six novel ESTs/STSs were isolated, thus increasing the number of markers used in this interval to thirty. This precise ordering is a prerequisite for the construction of a transcription map of this region that contains numerous disease loci, including those for several forms of retinal degeneration and mental retardation. In addition, the map provides the base to delineate the corresponding syntenic region in the mouse, where the mutants scurfy and tattered are localized.

Arrested development of embryonic red cell precursors in mouse embryos lacking transcription factor GATA-1

The X chromosome-linked transcription factor GATA-1 is expressed specifically in erythroid, mast, megakaryocyte, and eosinophil lineages, as well as in hematopoietic progenitors. Prior studies revealed that gene-disrupted GATA-1- embryonic stem cells give rise to adult (or definitive) erythroid precursors arrested at the proerythroblast stage in vitro and fail to contribute to adult red blood cells in chimeric mice but did not clarify a role in embryonic (or yolk sac derived) erythroid cells. To examine the consequences of GATA-1 loss on embryonic erythropoiesis in vivo, we inactivated the GATA-1 locus in embryonic stem cells by gene targeting and transmitted the mutated allele through the mouse germ line. Male GATA-1- embryos die between embryonic day 10.5 and 11.5 (E10.5-E11.5) of gestation. At E9.5, GATA-1- embryos exhibit extreme pallor yet contain embryonic erythroid cells arrested at an early proerythroblast-like stage of their development. Embryos stain weakly with benzidine reagent, and yolk sac cells express globin RNAs, indicating globin gene activation in the absence of GATA-1. Female heterozygotes (GATA-1+/-) are born pale due to random inactivation of the X chromosome bearing the normal allele. However, these mice recover during the neonatal period, presumably as a result of in vivo selection for progenitors able to express GATA-1. Our findings conclusively establish the essential role for GATA-1 in erythropoiesis within the context of the intact developing mouse and further demonstrate that the block to cellular maturation is similar in GATA-1- embryonic and definitive erythroid precursors. Moreover, the recovery of GATA-1+/- mice from anemia seen at birth provides evidence indicating a role for GATA-1 at the hematopoietic progenitor cell level.

Nitrogen metabolite signalling involves the C-terminus and the GATA domain of the Aspergillus transcription factor AREA and the 3' untranslated region of its mRNA

AREA is a GATA transcription factor which mediates nitrogen metabolite repression in Aspergillus nidulans in response to intracellular glutamine levels. We have identified and localized three elements important to modulation of AREA function: a region of 13 residues within the DNA-binding GATA domain which forms a putative extended loop structure, the 12 C-terminal residues, and sequences within a 218 nucleotide region of the 3' UTR. The 12 C-terminal residues are also required for transcriptional activation at a subset of loci under areA control. Specific deletions within the 3' UTR and the C-terminus cause similar levels of derepression and the mutations are additive, implicating two principal signal transduction pathways. The contribution of the 3' UTR to AREA modulation is effected at the level of transcript stability such that the areA mRNA is at least five times more stable under nitrogen-derepressing conditions than it is under repressing growth conditions.

Isolation of a gene encoding a functional zinc finger protein homologous to erythroid Krüppel-like factor: identification of a new multigene family

We have identified and characterized the gene for a novel zinc finger transcription factor which we have termed lung Krüppel-like factor (LKLF). LKLF was isolated through the use of the zinc finger domain of erythroid Krüppel-like factor (ELKF) as a hybridization probe and is closely related to this erythroid cell-specific gene. LKLF is expressed in a limited number of tissues, with the predominant expression seen in the lungs and spleen. The gene is developmentally controlled, with expression noted in the 7-day embryo followed by a down-regulation at 11 days and subsequent reactivation. A high degree of similarity is noted in the zinc finger regions of LKLF and EKLF. Beyond this domain, the sequences diverge significantly, although the putative transactivation domains for both LKLF and EKLF are proline-rich regions. In the DNA-binding domain, the three zinc finger motifs are so closely conserved that the predicted DNA contact sites are identical, suggesting that both proteins may bind to the same core sequence. This was further suggested by transactivation assays in which mouse fibroblasts were transiently transfected with a human beta-globin reporter gene in the absence and presence of an LKLF cDNA construct. Expression of the LKLF gene activates this human beta-globin promoter containing the CACCC sequence previously shown to be a binding site for EKLF. Mutation of this potential binding site results in a significant reduction in the reporter gene expression. LKLF and EKLF can thus be grouped as members of a unique family of transcription factors which have discrete patterns of expression in different tissues and which appear to recognize the same DNA-binding site.

Expression of a Drosophila GATA transcription factor in multiple tissues in the developing embryos. Identification of homozygous lethal mutants with P-element insertion at the promoter region

GATA transcription factors are DNA-binding proteins that recognize the core consensus sequence, WGATAR. Previous studies indicated that GATA factors play ann important role in the development of tissue-specific functions in vertebrates. Here we report the identification of a new Drosophila melanogaster GATA factor, dGATAc, which displays a distinct expression pattern in embryos. The local concentration of dGATAc transcripts varies at different stages, being most prominent in the procephalic region at stages 6-10 and in the posterior spiracles, the gut, and the central nervous system at stages 11-13. On the basis of its predicted sequence, DNA-binding assays were performed to confirm that the dGATAc gene encodes a zinc finger protein that can bind the GATA consensus motif with predicted specificity. Two independent mutants carrying a P-element insertion at the dGATAc gene promoter region were identified that are homozygous lethal at the embryonic stage. Using a genetic scheme, it was demonstrated that the lack of dGATAc function can block normal embryonic development. Our results suggest that the dGATAc protein is a tissue-specific transcription factor that is vital to the development of multiple organ systems in D. melanogaster.

Association of erythroid transcription factors: complexes involving the LIM protein RBTN2 and the zinc-finger protein GATA1

The RBTN2 LIM-domain protein, originally identified as an oncogenic protein in human T-cell leukemia, is essential for erythropoiesis. A possible role for RBTN2 in transcription during erythropoiesis has been investigated. Direct interaction of the RBTN2 protein was observed in vivo and in vitro with the GATA1 or -2 zinc-finger transcription factors, as well as with the basic helix-loop-helix protein TAL1. By using mammalian two-hybrid analysis, complexes involving RBTN2, TAL1, and GATA1, together with E47, the basic helix-loop-helix heterodimerization partner of TAL1, could be demonstrated. Thus, a molecular link exists between three proteins crucial for erythropoiesis, and the data suggest that variations in amounts of complexes involving RBTN2, TAL1, and GATA1 could be important for erythroid differentiation.

Of the GATA-binding proteins, only GATA-4 selectively regulates the human interleukin-5 gene promoter in interleukin-5-producing cells which express multiple GATA-binding proteins

Interleukin-5 (IL-5) is produced by T lymphocytes and known to support B-cell growth and eosinophilic differentiation of the progenitor cells. Using ATL-16T cells which express IL-5 mRNA, we have identified a region within the human IL-5 gene promoter that regulates IL-5 gene transcription. This cis-acting sequence contains the core binding motif, (A/T)GATA(A/G), for GATA-binding family proteins and thus suggests the involvement of this family members. In this report, we describe the cloning of human GATA-4 (hGATA-4) and show that hGATA-4 selectively interacts with the -70 GATA site within the IL-5 proximal promoter region. By promoter deletion and mutation analyses, we established this region as a positive regulatory element. Cotransfection experiments revealed that both hGATA-4 and phorbol-12-myristate-13-acetate (PMA)-A23187 stimulation are necessary for IL-5 promoter activation. The requirement for another regulatory element called CLE0, which lies downstream of the -70 GATA site, was also demonstrated. ATL-16T cells express mRNAs of three GATA-binding proteins, hGATA-2, hGATA-3, and hGATA-4, and each of them has a potential to bind to the consensus (A/T)GATA(G/A) motif. However, using ATL-16T nuclear extract, we demonstrated that GATA-4 is the only GATA-binding protein that forms a specific DNA-protein complex with the -70 GATA site. An electrophoretic mobility shift assay with extracts of COS cells expressing GATA-binding proteins showed that GATA-4 has the highest binding affinity for the -70 GATA site among the three GATA-binding proteins. When the transactivation abilities were compared among the three, GATA-4 showed the highest activity. These results demonstrate the selective role of GATA-4 in the transcriptional regulation of the IL-5 gene in a circumstance where multiple members of the GATA-binding proteins are expressed.