Alternative promoters regulate transcription of the mouse GATA-2 gene

TET2 lesions enhance the aggressiveness of CEBPA-mutant acute myeloid leukemia by rebalancing GATA2 expression

The myeloid transcription factor CEBPA is recurrently biallelically mutated (i.e., double mutated; CEBPADM) in acute myeloid leukemia (AML) with a combination of hypermorphic N-terminal mutations (CEBPANT), promoting expression of the leukemia-associated p30 isoform, and amorphic C-terminal mutations. The most frequently co-mutated genes in CEBPADM AML are GATA2 and TET2, however the molecular mechanisms underlying this co-mutational spectrum are incomplete. By combining transcriptomic and epigenomic analyses of CEBPA-TET2 co-mutated patients with models thereof, we identify GATA2 as a conserved target of the CEBPA-TET2 mutational axis, providing a rationale for the mutational spectra in CEBPADM AML. Elevated CEBPA levels, driven by CEBPANT, mediate recruitment of TET2 to the Gata2 distal hematopoietic enhancer thereby increasing Gata2 expression. Concurrent loss of TET2 in CEBPADM AML induces a competitive advantage by increasing Gata2 promoter methylation, thereby rebalancing GATA2 levels. Of clinical relevance, demethylating treatment of Cebpa-Tet2 co-mutated AML restores Gata2 levels and prolongs disease latency.

Role of the pioneer transcription factor GATA2 in health and disease

The transcription factor GATA2 is involved in human diseases ranging from hematopoietic disorders, to cancer, to infectious diseases. GATA2 is one of six GATA-family transcription factors that act as pioneering transcription factors which facilitate the opening of heterochromatin and the subsequent binding of other transcription factors to induce gene expression from previously inaccessible regions of the genome. Although GATA2 is essential for hematopoiesis and lymphangiogenesis, it is also expressed in other tissues such as the lung, prostate gland, gastrointestinal tract, central nervous system, placenta, fetal liver, and fetal heart. Gene or transcriptional abnormalities of GATA2 causes or predisposes patients to several diseases including the hematological cancers acute myeloid leukemia and acute lymphoblastic leukemia, the primary immunodeficiency MonoMAC syndrome, and to cancers of the lung, prostate, uterus, kidney, breast, gastric tract, and ovaries. Recent data has also linked GATA2 expression and mutations to responses to infectious diseases including SARS-CoV-2 and Pneumocystis carinii pneumonia, and to inflammatory disorders such as atherosclerosis. In this article we review the role of GATA2 in the etiology and progression of these various diseases.

From Basic Biology to Patient Mutational Spectra of GATA2 Haploinsufficiencies: What Are the Mechanisms, Hurdles, and Prospects of Genome Editing for Treatment

Inherited bone marrow failure syndromes (IBMFS) are monogenetic disorders that result in a reduction of mature blood cell formation and predisposition to leukemia. In children with myeloid leukemia the gene most often mutated is Gata binding protein 2 (GATA2) and 80% of patients with GATA2 mutations develop myeloid malignancy before the age of forty. Although GATA2 is established as one of the key regulators of embryonic and adult hematopoiesis, the mechanisms behind the leukemia predisposition in GATA2 haploinsufficiencies is ambiguous. The only curative treatment option currently available is allogeneic hematopoietic stem cell transplantation (allo-SCT). However, allo-SCT can only be applied at a relatively late stage of the disease as its applicability is compromised by treatment related morbidity and mortality (TRM). Alternatively, autologous hematopoietic stem cell transplantation (auto-SCT), which is associated with significantly less TRM, might become a treatment option if repaired hematopoietic stem cells would be available. Here we discuss the recent literature on leukemia predisposition syndromes caused by GATA2 mutations, current knowledge on the function of GATA2 in the hematopoietic system and advantages and pitfalls of potential treatment options provided by genome editing.

Multi-omic profiling of pituitary thyrotropic cells and progenitors

BACKGROUND

The pituitary gland is a neuroendocrine organ containing diverse cell types specialized in secreting hormones that regulate physiology. Pituitary thyrotropes produce thyroid-stimulating hormone (TSH), a critical factor for growth and maintenance of metabolism. The transcription factors POU1F1 and GATA2 have been implicated in thyrotrope fate, but the transcriptomic and epigenomic landscapes of these neuroendocrine cells have not been characterized. The goal of this work was to discover transcriptional regulatory elements that drive thyrotrope fate.

RESULTS

We identified the transcription factors and epigenomic changes in chromatin that are associated with differentiation of POU1F1-expressing progenitors into thyrotropes using cell lines that represent an undifferentiated Pou1f1 lineage progenitor (GHF-T1) and a committed thyrotrope line that produces TSH (TαT1). We compared RNA-seq, ATAC-seq, histone modification (H3K27Ac, H3K4Me1, and H3K27Me3), and POU1F1 binding in these cell lines. POU1F1 binding sites are commonly associated with bZIP transcription factor consensus binding sites in GHF-T1 cells and Helix-Turn-Helix (HTH) or basic Helix-Loop-Helix (bHLH) factors in TαT1 cells, suggesting that these classes of transcription factors may recruit or cooperate with POU1F1 binding at unique sites. We validated enhancer function of novel elements we mapped near Cga, Pitx1, Gata2, and Tshb by transfection in TαT1 cells. Finally, we confirmed that an enhancer element near Tshb can drive expression in thyrotropes of transgenic mice, and we demonstrate that GATA2 enhances Tshb expression through this element.

CONCLUSION

These results extend the ENCODE multi-omic profiling approach to the pituitary gland, which should be valuable for understanding pituitary development and disease pathogenesis.

Identification of Dominant Transcripts in Oxidative Stress Response by a Full-Length Transcriptome Analysis

Our body responds to environmental stress by changing the expression levels of a series of cytoprotective enzymes/proteins through multilayered regulatory mechanisms, including the KEAP1-NRF2 system. While NRF2 upregulates the expression of many cytoprotective genes, there are fundamental limitations in short-read RNA sequencing (RNA-Seq), resulting in confusion regarding interpreting the effectiveness of cytoprotective gene induction at the transcript level. To precisely delineate isoform usage in the stress response, we conducted independent full-length transcriptome profiling (isoform sequencing; Iso-Seq) analyses of lymphoblastoid cells from three volunteers under normal and electrophilic stress-induced conditions. We first determined the first exon usage in KEAP1 and NFE2L2 (encoding NRF2) and found the presence of transcript diversity. We then examined changes in isoform usage of NRF2 target genes under stress conditions and identified a few isoforms dominantly expressed in the majority of NRF2 target genes. The expression levels of isoforms determined by Iso-Seq analyses showed striking differences from those determined by short-read RNA-Seq; the latter could be misleading concerning the abundance of transcripts. These results support that transcript usage is tightly regulated to produce functional proteins under electrophilic stress. Our present study strongly argues that there are important benefits that can be achieved by long-read transcriptome sequencing.

Efferocytic Defects in Early Atherosclerosis Are Driven by GATA2 Overexpression in Macrophages

The loss of efferocytosis-the phagocytic clearance of apoptotic cells-is an initiating event in atherosclerotic plaque formation. While the loss of macrophage efferocytosis is a prerequisite for advanced plaque formation, the transcriptional and cellular events in the pre-lesion site that drive these defects are poorly defined. Transcriptomic analysis of macrophages recovered from early-stage human atherosclerotic lesions identified a 50-fold increase in the expression of GATA2, a transcription factor whose expression is normally restricted to the hematopoietic compartment. GATA2 overexpression in vitro recapitulated many of the functional defects reported in patient macrophages, including deficits at multiple stages in the efferocytic process. These findings included defects in the uptake of apoptotic cells, efferosome maturation, and in phagolysosome function. These efferocytic defects were a product of GATA2-driven alterations in the expression of key regulatory proteins, including Src-family kinases, Rab7 and components of both the vacuolar ATPase and NADPH oxidase complexes. In summary, these data identify a mechanism by which efferocytic capacity is lost in the early stages of plaque formation, thus setting the stage for the accumulation of uncleared apoptotic cells that comprise the bulk of atherosclerotic plaques.

Liganded T3 receptor β2 inhibits the positive feedback autoregulation of the gene for GATA2, a transcription factor critical for thyrotropin production

The serum concentration of thyrotropin (thyroid stimulating hormone, TSH) is drastically reduced by small increase in the levels of thyroid hormones (T3 and its prohormone, T4); however, the mechanism underlying this relationship is unknown. TSH consists of the chorionic gonadotropin α (CGA) and the β chain (TSHβ). The expression of both peptides is induced by the transcription factor GATA2, a determinant of the thyrotroph and gonadotroph differentiation in the pituitary. We previously reported that the liganded T3 receptor (TR) inhibits transactivation activity of GATA2 via a tethering mechanism and proposed that this mechanism, but not binding of TR with a negative T3-responsive element, is the basis for the T3-dependent inhibition of the TSHβ and CGA genes. Multiple GATA-responsive elements (GATA-REs) also exist within the GATA2 gene itself and mediate the positive feedback autoregulation of this gene. To elucidate the effect of T3 on this non-linear regulation, we fused the GATA-REs at -3.9 kb or +9.5 kb of the GATA2 gene with the chloramphenicol acetyltransferase reporter gene harbored in its 1S-promoter. These constructs were co-transfected with the expression plasmids for GATA2 and the pituitary specific TR, TRβ2, into kidney-derived CV1 cells. We found that liganded TRβ2 represses the GATA2-induced transactivation of these reporter genes. Multi-dimensional input function theory revealed that liganded TRβ2 functions as a classical transcriptional repressor. Then, we investigated the effect of T3 on the endogenous expression of GATA2 protein and mRNA in the gonadotroph-derived LβT2 cells. In this cell line, T3 reduced GATA2 protein independently of the ubiquitin proteasome system. GATA2 mRNA was drastically suppressed by T3, the concentration of which corresponds to moderate hypothyroidism and euthyroidism. These results suggest that liganded TRβ2 inhibits the positive feedback autoregulation of the GATA2 gene; moreover this mechanism plays an important role in the potent reduction of TSH production by T3.

Two effects of GATA2 enhancer repositioning by 3q chromosomal rearrangements

Chromosomal inversion and translocation between 3q21 and 3q26 [inv (3)(q21.3q26.2) and t(3;3)(q21.3;q26.2), respectively] give rise to acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS), which have poor prognoses. The chromosomal rearrangements reposition a GATA2 distal hematopoietic enhancer from the original 3q21 locus to the EVI1 (also known as MECOM) locus on 3q26. Therefore, the GATA2 enhancer from one of two GATA2 alleles drives EVI1 gene expression in hematopoietic stem and progenitor cells, which promotes the accumulation of abnormal progenitors and induces leukemogenesis. On the other hand, one allele of the GATA2 gene loses its enhancer, which results in reduced GATA2 expression. The GATA2 gene encodes a transcription factor critical for the generation and maintenance of hematopoietic stem and progenitor cells. GATA2 haploinsufficiency has been known to cause immunodeficiency and myeloid leukemia. Notably, reduced GATA2 expression suppresses the differentiation but promotes the proliferation of EVI1-expressing leukemic cells, which accelerates EVI1-driven leukemogenesis. A series of studies have shown that the GATA2 enhancer repositioning caused by the chromosomal rearrangements between 3q21 and 3q26 provokes misexpression of both the EVI1 and GATA2 genes and that these two effects coordinately elicit high-risk leukemia.

Quantitative and qualitative impairments in GATA2 and myeloid neoplasms

GATA2 is a key transcription factor critical for hematopoietic cell development. During the past decade, it became clear that heterozygous germline mutations in the GATA2 gene cause bone marrow failure and primary immunodeficiency syndrome, conditions that lead to a predisposition toward myeloid neoplasms, such as myelodysplastic syndrome, acute myeloid leukemia, and chronic myelomonocytic leukemia. Somatic mutations of the GATA2 gene are also involved in the pathogenesis of myeloid malignancies. Cases with GATA2 gene mutations are divided into two groups, resulting in either a quantitative deficiency or a qualitative defect in the GATA2 protein depending on the mutation position and type. In the former case, GATA2 mRNA expression from the mutant allele is markedly reduced or completely abrogated, and reduced GATA2 protein expression is involved in the pathogenesis. In the latter case, almost equal amounts of structurally abnormal and wildtype GATA2 proteins are predicted to be present and contribute to the pathogenesis. The development of mouse models of these human GATA2-related diseases has been undertaken, which naturally develop myeloid neoplasms.

The Gata2 repression during 3T3-L1 preadipocyte differentiation is dependent on a rapid decrease in histone acetylation in response to glucocorticoid receptor activation

The transcription factor GATA2 is an anti-adipogenic factor whose expression is downregulated during adipocyte differentiation. The present study attempted to clarify the molecular mechanism underlying the GATA2 repression and found that the repression is dependent on the activation of the glucocorticoid receptor (GR) during 3T3-L1 preadipocyte differentiation. Although several recognition sequences for GR were found in both the proximal and distal regions of the Gata2 locus, the promoter activity was not affected by the GR activation in the reporter assays, and the CRISPR-Cas9-mediated deletion of the two distal regions of the Gata2 locus was not involved in the GR-mediated Gata2 repression. Notably, the level of histone acetylation was markedly reduced at the Gata2 locus during 3T3-L1 differentiation, and the GR-mediated Gata2 repression was significantly relieved by histone deacetylase inhibition. These results suggest that GR regulates the Gata2 gene by reducing histone acetylation in the early phase of adipogenesis.

Genetic redundancy of GATA factors in the extraembryonic trophoblast lineage ensures the progression of preimplantation and postimplantation mammalian development

GATA transcription factors are implicated in establishing cell fate during mammalian development. In early mammalian embryos, GATA3 is selectively expressed in the extraembryonic trophoblast lineage and regulates gene expression to promote trophoblast fate. However, trophoblast-specific GATA3 function is dispensable for early mammalian development. Here, using dual conditional knockout mice, we show that genetic redundancy of Gata3 with paralog Gata2 in trophoblast progenitors ensures the successful progression of both pre- and postimplantation mammalian development. Stage-specific gene deletion in trophoblasts reveals that loss of both GATA genes, but not either alone, leads to embryonic lethality prior to the onset of their expression within the embryo proper. Using ChIP-seq and RNA-seq analyses, we define the global targets of GATA2/GATA3 and show that they directly regulate a large number of common genes to orchestrate stem versus differentiated trophoblast fate. In trophoblast progenitors, GATA factors directly regulate BMP4, Nodal and Wnt signaling components that promote embryonic-extraembryonic signaling cross-talk, which is essential for the development of the embryo proper. Our study provides genetic evidence that impairment of trophoblast-specific GATA2/GATA3 function could lead to early pregnancy failure.

Summary: During trophoblast development in mice, GATA2 and GATA3 act synergistically by directly regulating a large number of common genes, and together are important to ensure trophoblast lineage progression.

The role of GATA2 in lethal prostate cancer aggressiveness

Advanced prostate cancer is a classic example of the intractability and consequent lethality that characterizes metastatic carcinomas. Novel treatments have improved the survival of men with prostate cancer; however, advanced prostate cancer invariably becomes resistant to these therapies and ultimately progresses to a lethal metastatic stage. Consequently, detailed knowledge of the molecular mechanisms that control prostate cancer cell survival and progression towards this lethal stage of disease will benefit the development of new therapeutics. The transcription factor endothelial transcription factor GATA-2 (GATA2) has been reported to have a key role in driving prostate cancer aggressiveness. In addition to being a pioneer transcription factor that increases androgen receptor (AR) binding and activity, GATA2 regulates a core subset of clinically relevant genes in an AR-independent manner. Functionally, GATA2 overexpression in prostate cancer increases cellular motility and invasiveness, proliferation, tumorigenicity, and resistance to standard therapies. Thus, GATA2 has a multifaceted function in prostate cancer aggressiveness and is a highly attractive target in the development of novel treatments against lethal prostate cancer.

Epigenetic regulation of alternative promoters and enhancers in progenitor, immature, and mature gonadotrope cell lines

Gonadotrope cell identity genes emerge in a stepwise process during mouse pituitary development. Cga, encoding for the α-subunit of TSH, LH, and FSH, is initially detected at E11.5 followed by Gnrhr and steroidogenic factor Sf1 at E13.5, specifying cells engaged in a gonadotrope cell fate. Lhb and Fshb appear at E16.5 and 17.5, respectively, typifying differentiated gonadotrope cells. Using the αT1-1, αT3-1 and LβT2 cell lines recapitulating these stages of gonadotrope differentiation, DNA methylation at Gnrhr and Sf1 was investigated. Regulatory regions were found hypermethylated in progenitor αT1-1 cells and hypomethylated in differentiated LβT2 cells. Abundance of RNA polymerase II together with active histone modifications including H3K4me1, H3K4me3, and H3K27ac were strictly correlated with DNA hypomethylation. Analyses of epigenomic modifications and chromatin accessibility were further extended to Isl1, Lhx3, Gata2, and Pitx2, highlighting alternative usages of specific regulatory gene domains in progenitor αT1-1, immature αT3-1, and mature LβT2 gonadotrope cells.

GATA-related hematologic disorders

The transcription factors GATA1 and GATA2 are fundamental regulators of hematopoiesis and have overlapping expression profiles. GATA2 is expressed in hematopoietic stem cells and early erythroid-megakaryocytic progenitors and activates a certain set of early-phase genes, including the GATA2 gene itself. GATA2 also initiates GATA1 gene expression. In contrast, GATA1 is expressed in relatively mature erythroid progenitors and facilitates the expression of genes associated with differentiation, including the GATA1 gene itself; however, GATA1 represses the expression of GATA2. Switching the GATA factors from GATA2 to GATA1 appears to be one of the key regulatory mechanisms underlying erythroid differentiation. Loss-of-function analyses using mice in vivo have indicated that GATA2 and GATA1 are functionally nonredundant and that neither can compensate for the absence of the other. However, transgenic expression of GATA2 under the transcriptional regulation of the Gata1 gene rescues lethal dyserythropoiesis in GATA1-deficient mice, illustrating that the dynamic expression profiles of these GATA factors are critically important for the maintenance of hematopoietic homeostasis. Analysis of naturally occurring leukemias in GATA1-knockdown mice revealed that leukemic stem cells undergo functional alterations in response to exposure to chemotherapeutic agents. This mechanism may also underlie the aggravating features of relapsing leukemias. Recent hematologic analyses have suggested that disturbances in the balance of the GATA factors are associated with specific types of hematopoietic disorders. Here, we describe GATA1- and GATA2-related hematologic diseases, focusing on the regulation of GATA factor gene expression.

Loss of c-Kit and bone marrow failure upon conditional removal of the GATA-2 C-terminal zinc finger domain in adult mice

Heterozygous mutations in the transcriptional regulator GATA-2 associate with multilineage immunodeficiency, myelodysplastic syndrome (MDS), and acute myeloid leukemia (AML). The majority of these mutations localize in the zinc finger (ZnF) domains, which mediate GATA-2 DNA binding. Deregulated hematopoiesis with GATA-2 mutation frequently develops in adulthood, yet GATA-2 function in the bone marrow remains unresolved. To investigate this, we conditionally deleted the GATA-2 C-terminal ZnF (C-ZnF) coding sequences in adult mice. Upon Gata2 C-ZnF deletion, we observed rapid peripheral cytopenia, bone marrow failure, and decreased c-Kit expression on hematopoietic progenitors. Transplant studies indicated GATA-2 has a cell-autonomous role in bone marrow hematopoiesis. Moreover, myeloid lineage populations were particularly sensitive to Gata2 hemizygosity, while molecular assays indicated GATA-2 regulates c-Kit expression in multilineage progenitor cells. Enforced c-Kit expression in Gata2 C-ZnF-deficient hematopoietic progenitors enhanced myeloid colony activity, suggesting GATA-2 sustains myelopoiesis via a cell intrinsic role involving maintenance of c-Kit expression. Our results provide insight into mechanisms regulating hematopoiesis in bone marrow and may contribute to a better understanding of immunodeficiency and bone marrow failure associated with GATA-2 mutation.

High-Throughput siRNA Screening to Reveal GATA-2 Upstream Transcriptional Mechanisms in Hematopoietic Cells

Hematopoietic stem cells can self-renew and differentiate into all blood cell types. The transcription factor GATA-2 is expressed in both hematopoietic stem and progenitor cells and is essential for cell proliferation, survival, and differentiation. Recently, evidence from studies of aplastic anemia, MonoMAC syndrome, and lung cancer has demonstrated a mechanistic link between GATA-2 and human pathophysiology. GATA-2-dependent disease processes have been extensively analyzed; however, the transcriptional mechanisms upstream of GATA-2 remain less understood. Here, we conducted high-throughput small-interfering-RNA (siRNA) library screening and showed that YN-1, a human erythroleukemia cell line, expressed high levels of GATA-2 following the activation of the hematopoietic-specific 1S promoter. As transient luciferase reporter assay in YN-1 cells revealed the highest promoter activity in the 1S promoter fused with GATA-2 intronic enhancer (+9.9 kb/1S); therefore, we established a cell line capable of stably expressing +9.9 kb/1S-Luciferase. Subsequently, we screened 995 transcription factor genes and revealed that CITED2 acts as a GATA-2 activator in human hematopoietic cells. These results provide novel insights into and further identify the regulatory mechanism of GATA-2.

Histone demethylase LSD1-mediated repression of GATA-2 is critical for erythroid differentiation

Background

The transcription factor GATA-2 is predominantly expressed in hematopoietic stem and progenitor cells and counteracts the erythroid-specific transcription factor GATA-1, to modulate the proliferation and differentiation of hematopoietic cells. During hematopoietic cell differentiation, GATA-2 exhibits dynamic expression patterns, which are regulated by multiple transcription factors.

Methods

Stable LSD1-knockdown cell lines were established by growing murine erythroleukemia (MEL) or mouse embryonic stem cells together with virus particles, in the presence of Polybrene^® at 4 μg/mL, for 24–48 hours followed by puromycin selection (1 μg/mL) for 2 weeks. Real-time polymerase chain reaction (PCR)-based quantitative chromatin immunoprecipitation (ChIP) analysis was used to test whether the TAL1 transcription factor is bound to 1S promoter in the GATA-2 locus or whether LSD1 colocalizes with TAL1 at the 1S promoter. The sequential ChIP assay was utilized to confirm the role of LSD1 in the regulation of H3K4me2 at the GATA-2 locus during erythroid differentiation. Western blot analysis was employed to detect the protein expression. The alamarBlue^® assay was used to examine the proliferation of the cells, and the absorbance was monitored at optical density (OD) 570 nm and OD 600 nm.

Results

In this study, we showed that LSD1 regulates the expression of GATA-2 during erythroid differentiation. Knockdown of LSD1 results in increased GATA-2 expression and inhibits the differentiation of MEL and embryonic stem cells. Furthermore, we demonstrated that LSD1 binds to the 1S promoter of the GATA-2 locus and suppresses GATA-2 expression, via histone demethylation.

Conclusion

Our data revealed that LSD1 mediates erythroid differentiation, via epigenetic modification of the GATA-2 locus.

Histone methyltransferase Setd8 represses Gata2 expression and regulates erythroid maturation

Setd8 is the sole histone methyltransferase in mammals capable of monomethylating histone H4 lysine 20 (H4K20me1). Setd8 is expressed at significantly higher levels in erythroid cells than any other cell or tissue type, suggesting that Setd8 has an erythroid-cell-specific function. To test this hypothesis, stable Setd8 knockdown was established in extensively self-renewing erythroblasts (ESREs), a well-characterized, nontransformed model of erythroid maturation. Knockdown of Setd8 resulted in impaired erythroid maturation characterized by a delay in hemoglobin accumulation, larger mean cell area, persistent ckit expression, incomplete nuclear condensation, and lower rates of enucleation. Setd8 knockdown did not alter ESRE proliferation or viability or result in accumulation of DNA damage. Global gene expression analyses following Setd8 knockdown demonstrated that in erythroid cells, Setd8 functions primarily as a repressor. Most notably, Gata2 expression was significantly higher in knockdown cells than in control cells and Gata2 knockdown rescued some of the maturation impairments associated with Setd8 disruption. Setd8 occupies critical regulatory elements in the Gata2 locus, and knockdown of Setd8 resulted in loss of H4K20me1 and gain of H4 acetylation at the Gata2 1S promoter. These results suggest that Setd8 is an important regulator of erythroid maturation that works in part through repression of Gata2 expression.

GATA2 is epigenetically repressed in human and mouse lung tumors and is not requisite for survival of KRAS mutant lung cancer

INTRODUCTION

GATA2 was recently described as a critical survival factor and therapeutic target for KRAS mutant non-small-cell lung cancer (NSCLC). However, whether this role is affected by epigenetic repression of GATA2 in lung cancer is unclear.

METHODS

GATA2 expression and promoter CpG island methylation were evaluated using human and mouse NSCLC cell lines and tumor-normal pairs. In vitro assays were used to study GATA2 repression on cell survival and during tobacco carcinogen-induced transformation.

RESULTS

GATA2 expression in KRAS wild-type (n = 15) and mutant (n = 10) NSCLC cell lines and primary lung tumors (n = 24) was significantly lower, 1.3- to 33.6-fold (p = 2.2 × 10(9)), compared with corresponding normal lung. GATA2 promoter was unmethylated in normal lung (0 of 10) but frequently methylated in lung tumors (96%, 159 of 165) and NSCLC cell lines (97%, 30 of 31). This highly prevalent aberrant methylation was independently validated using The Cancer Genome Atlas data for 369 NSCLC tumor-normal pairs. In vitro studies using an established carcinogen-induced premalignancy model revealed that GATA2 expression was initially repressed by chromatin remodeling followed by cytosine methylation during transformation. Similarly, expression of GATA2 in NNK-induced mouse lung tumors (n = 6) and cell lines (n = 5) was fivefold and 100-fold lower, respectively, than normal mouse lung. Finally, siRNA-mediated knockdown of GATA2 in KRAS mutant (human [n = 4] and murine [n = 5]) and wild-type (human [n = 4]) NSCLC cell lines showed that further reduction of expression (up to 95%) does not induce cell death.

CONCLUSION

GATA2 is epigenetically repressed in human and mouse lung tumors and its further inhibition is not a valid therapeutic strategy for KRAS mutant lung cancer.

Overexpression of human GATA-1 and GATA-2 interferes with spine formation and produces depressive behavior in rats

Functional consequences to which vertebrate GATA transcription factors contribute in the adult brain remain largely an open question. The present study examines how human GATA-1 and GATA-2 (hGATA-1 and hGATA-2) are linked to neuronal differentiation and depressive behaviors in rats. We investigated the effects of adeno-associated viral expression of hGATA-1 and hGATA-2 (AAV-hGATA1 and AAV-hGATA2) in the dentate gyrus (DG) of the dorsal hippocampus on dendrite branching and spine number. We also examined the influence of AAV-hGATA1 and AAV-hGATA2 infusions into the dorsal hippocampus on rodent behavior in models of depression. Viral expression of hGATA-1 and hGATA-2 cDNA in rat hippocampal neurons impaired dendritic outgrowth and spine formation. Moreover, viral-mediated expression of hGATA-1 and hGATA-2 in the dorsal hippocampus caused depressive-like deficits in the forced swim test and learned helplessness models of depression, and decreased the expression of several synapse-related genes as well as spine number in hippocampal neurons. Conversely, shRNA knockdown of GATA-2 increased synapse-related gene expression, spine number, and dendrite branching. The results demonstrate that hGATA-1 and hGATA-2 expression in hippocampus is sufficient to cause depressive like behaviors that are associated with reduction in spine synapse density and expression of synapse-related genes.

Expression of ABCG2 (BCRP) in mouse models with enhanced erythropoiesis

Haem is a structural component of numerous cellular proteins which contributes significantly to iron metabolic processes in mammals but its toxicity demands that cellular levels must be tightly regulated. Breast Cancer Resistance Protein (BCRP/ABCG2), an ATP Binding Cassette G-member protein has been shown to possess porphyrin/haem efflux function. The current study evaluated the expression and regulation of Abcg2 mRNA and protein levels in mouse tissues involved in erythropoiesis. Abcg2 mRNA expression was enhanced in bone marrow hemopoietic progenitor cells from mice that were treated with phenylhydrazine (PHZ). Abcg2 mRNA expression was increased particularly in the extramedullary haematopoietic tissues from all the mice models with enhanced erythropoiesis. Haem oxygenase (ho1) levels tended to increase in the liver of mice with enhanced erythropoiesis and gene expression patterns differed from those observed in the spleen. Efflux of haem biosynthetic metabolites might be dependent on the relative abundance of Abcg2 or ho1 during erythropoiesis. Abcg2 appears to act principally as a safety valve regulating porphyrin levels during the early stages of erythropoiesis and its role in systemic haem metabolism and erythrophagocytosis, in particular, awaits further clarification.

A regulatory network governing Gata1 and Gata2 gene transcription orchestrates erythroid lineage differentiation

GATA transcription factor family members GATA1 and GATA2 play crucial roles in the regulation of lineage-restricted genes during erythroid differentiation. GATA1 is indispensable for survival and terminal differentiation of erythroid, megakaryocytic and eosinophilic progenitors, whereas GATA2 regulates proliferation and maintenance of hematopoietic stem and progenitor cells. Expression levels of GATA1 and GATA2 are primarily regulated at the transcriptional level through auto- and reciprocal regulatory networks formed by these GATA factors. The dynamic and strictly controlled change of expression from GATA2 to GATA1 during erythropoiesis has been referred to as GATA factor switching, which plays a crucial role in erythropoiesis. The regulatory network comprising GATA1 and GATA2 gives rise to the stage-specific changes in Gata1 and Gata2 gene expression during erythroid differentiation, which ensures specific expression of early and late erythroid genes at each stage. Recent studies have also shed light on the genome-wide binding profiles of GATA1 and GATA2, and the significance of epigenetic modification of Gata1 gene during erythroid differentiation. This review summarizes the current understanding of network regulation underlying stage-dependent Gata1 and Gata2 gene expressions and the functional contribution of these GATA factors in erythroid differentiation.

GATA4 autoregulates its own expression in mouse gonadal cells via its distal 1b promoter

Transcription factor GATA4 is required for the development and function of the mammalian gonads. We first reported that the GATA4 gene in both human and rodents is expressed as two major alternative transcripts that differ solely in their first untranslated exon (exon 1a vs. exon 1b). We had also showed by quantitative PCR that in mouse tissues, both Gata4 exon 1a- and 1b-containing transcripts are present in all sites that are normally positive for GATA4 protein. In adult tissues, exon 1a-containing transcripts generally predominate. A notable exception, however, is the testis where the Gata4 exon 1a and 1b transcripts exhibit a similar level of expression. We now confirm by in situ hybridization analysis that each transcript is also strongly expressed during gonad differentiation in both sexes in the rat. To gain further insights into how Gata4 gene expression is controlled, we characterized the mouse Gata4 promoter sequence located upstream of exon 1b. In vitro studies revealed that the Gata4 1b promoter is less active than the 1a promoter in several gonadal cell lines tested. Whereas we have previously shown that endogenous Gata4 transcription driven by the 1a promoter is dependent on a proximally located Ebox motif, we now show using complementary in vitro and in vivo approaches that Gata4 promoter 1b-directed expression is regulated by GATA4 itself. Thus, Gata4 transcription in the gonads and other tissues is ensured by distinct promoters that are regulated differentially and independently.

Expression of different functional isoforms in haematopoiesis

Haematopoiesis is a complex process regulated at various levels facilitating rapid responses to external factors including stress, modulation of lineage commitment and terminal differentiation of progenitors. Although the transcription program determines the RNA pool of a cell, various mRNA strands can be obtained from the same template, giving rise to multiple protein isoforms. The majority of variants and isoforms co-occur in normal haematopoietic cells or are differentially expressed at various maturity stages of progenitor maturation and cellular differentiation within the same lineage or across lineages. Genetic aberrations or specific cellular states result in the predominant expression of abnormal isoforms leading to deregulation and disease. The presence of upstream open reading frames (uORF) in 5' untranslated regions (UTRs) of a transcript, couples the utilization of start codons with the cellular status and availability of translation initiation factors (eIFs). In addition, tissue-specific and cell lineage-specific alternative promoter use, regulates several transcription factors producing transcript variants with variable 5' exons. In this review, we propose to give a detailed account of the differential isoform formation, causing haematological malignancies.

Hes repressors are essential regulators of hematopoietic stem cell development downstream of Notch signaling

Previous studies have identified Notch as a key regulator of hematopoietic stem cell (HSC) development, but the underlying downstream mechanisms remain unknown. The Notch target Hes1 is widely expressed in the aortic endothelium and hematopoietic clusters, though Hes1-deficient mice show no overt hematopoietic abnormalities. We now demonstrate that Hes is required for the development of HSC in the mouse embryo, a function previously undetected as the result of functional compensation by de novo expression of Hes5 in the aorta/gonad/mesonephros (AGM) region of Hes1 mutants. Analysis of embryos deficient for Hes1 and Hes5 reveals an intact arterial program with overproduction of nonfunctional hematopoietic precursors and total absence of HSC activity. These alterations were associated with increased expression of the hematopoietic regulators Runx1, c-myb, and the previously identified Notch target Gata2. By analyzing the Gata2 locus, we have identified functional RBPJ-binding sites, which mutation results in loss of Gata2 reporter expression in transgenic embryos, and functional Hes-binding sites, which mutation leads to specific Gata2 up-regulation in the hematopoietic precursors. Together, our findings show that Notch activation in the AGM triggers Gata2 and Hes1 transcription, and next HES-1 protein represses Gata2, creating an incoherent feed-forward loop required to restrict Gata2 expression in the emerging HSCs.

Regulation of GATA factor expression is distinct between erythroid and mast cell lineages

The zinc finger transcription factors GATA1 and GATA2 participate in mast cell development. Although the expression of these factors is regulated in a cell lineage-specific and differentiation stage-specific manner, their regulation during mast cell development has not been clarified. Here, we show that the GATA2 mRNA level was significantly increased while GATA1 was maintained at low levels during the differentiation of mast cells derived from mouse bone marrow (BMMCs). Unlike in erythroid cells, forced expression or small interfering RNA (siRNA)-mediated knockdown of GATA1 rarely affected GATA2 expression, and vice versa, in mast cells, indicating the absence of cross-regulation between Gata1 and Gata2 genes. Chromatin immunoprecipitation assays revealed that both GATA factors bound to most of the conserved GATA sites of Gata1 and Gata2 loci in BMMCs. However, the GATA1 hematopoietic enhancer (G1HE) of the Gata1 gene, which is essential for GATA1 expression in erythroid and megakaryocytic lineages, was bound only weakly by both GATA factors in BMMCs. Furthermore, transgenic-mouse reporter assays revealed that the G1HE is not essential for reporter expression in BMMCs and peritoneal mast cells. Collectively, these results demonstrate that the expression of GATA factors in mast cells is regulated in a manner quite distinct from that in erythroid cells.

GATA-2 mediated regulation of normal hematopoietic stem/progenitor cell function, myelodysplasia and myeloid leukemia

Unremitting blood cell production throughout the lifetime of an organism is reliant on hematopoietic stem cells (HSCs). A rare and relatively quiescent cell type, HSCs are, on entry into cell cycle fated to self-renew, undergo apoptosis or differentiate to progenitors (HPCs) that eventually yield specific classes of blood cells. Disruption of these HSC fate decisions is considered to be fundamental to the development of leukemia. Much effort has therefore been placed on understanding the molecular pathways that regulate HSC fate decisions and how these processes are undermined in leukemia. Transcription factors have emerged as critical regulators in this respect. Here we review the participation of zinc finger transcription factor GATA-2 in regulating normal hematopoietic stem and progenitor cell functionality, myelodysplasia and myeloid leukemia.

The role of the GATA2 transcription factor in normal and malignant hematopoiesis

Hematopoiesis involves an elaborate regulatory network of transcription factors that coordinates the expression of multiple downstream genes, and maintains homeostasis within the hematopoietic system through the accurate orchestration of cellular proliferation, differentiation and survival. As a result, defects in the expression levels or the activity of these transcription factors are intimately linked to hematopoietic disorders, including leukemia. The GATA family of nuclear regulatory proteins serves as a prototype for the action of lineage-restricted transcription factors. GATA1 and GATA2 are expressed principally in hematopoietic lineages, and have essential roles in the development of multiple hematopoietic cells, including erythrocytes and megakaryocytes. Moreover, GATA2 is crucial for the proliferation and maintenance of hematopoietic stem cells and multipotential progenitors. In this review, we summarize the current knowledge regarding the biological properties and functions of the GATA2 transcription factor in normal and malignant hematopoiesis.

Effect of long-term culture of mouse embryonic stem cells under low oxygen concentration as well as on glycosaminoglycan hyaluronan on cell proliferation and differentiation

OBJECTIVES

Maintaining undifferentiated stem cells in defined conditions is of critical importance to improve their in vitro culture. We have evaluated the effects of culturing mouse stem (mES) cells under physiological oxygen concentration as well as by replacing fibroblast feeder layer (mEF) with gelatin or glycosaminoglycan hyaluronan (HA), on cell proliferation and differentiation.

MATERIALS AND METHODS

After 3 days culture or after long-term cell culture under different conditions, levels of apoptotic cell death were determined by cell cycle and TUNEL (TdT-mediated dUTP nick end labelling) assays and levels of cell proliferation by CFSE (5-(and-6)-carboxyfluorescein diacetate succinimidyl ester) labelling. We assessed spontaneous differentiation into cardiomyocytes and mRNA expression of pluripotency and differentiation biomarkers.

RESULTS

After 3 days culture under hypoxic conditions, levels of proliferation and apoptosis of mES cells were higher, in correlation with increase in intracellular reactive oxygen species. However, when cells were continuously grown for 1 month under those conditions, the level of apoptosis was, in all cases, under 4%. Hypoxia reduced spontaneous differentiation of mES into cardiomyocytes. Long-term culture on HA was more effective in maintaining the pluripotent state of the mES cells when compared to that on gelatin. Level of terminal differentiation was highest on mEF, intermediate on HA and lowest on gelatin.

CONCLUSIONS

Our data suggest that hypoxia is not necessary for maintaining pluripotency of mES cells and appeared to be detrimental during ES differentiation. Moreover, HA may offer a valuable alternative for long-term culture of mES cells in vitro.

A single cis element maintains repression of the key developmental regulator Gata2

In development, lineage-restricted transcription factors simultaneously promote differentiation while repressing alternative fates. Molecular dissection of this process has been challenging as transcription factor loci are regulated by many trans-acting factors functioning through dispersed cis elements. It is not understood whether these elements function collectively to confer transcriptional regulation, or individually to control specific aspects of activation or repression, such as initiation versus maintenance. Here, we have analyzed cis element regulation of the critical hematopoietic factor Gata2, which is expressed in early precursors and repressed as GATA-1 levels rise during terminal differentiation. We engineered mice lacking a single cis element −1.8 kb upstream of the Gata2 transcriptional start site. Although Gata2 is normally repressed in late-stage erythroblasts, the −1.8 kb mutation unexpectedly resulted in reactivated Gata2 transcription, blocked differentiation, and an aberrant lineage-specific gene expression pattern. Our findings demonstrate that the −1.8 kb site selectively maintains repression, confers a specific histone modification pattern and expels RNA Polymerase II from the locus. These studies reveal how an individual cis element establishes a normal developmental program via regulating specific steps in the mechanism by which a critical transcription factor is repressed.

Different cell types are formed and maintained by proteins called transcription factors that directly bind to specific DNA sequences to activate or repress gene expression. While numerous DNA sequences bound by transcription factors are established, many questions remain unanswered regarding how they function at specific sites located at distinct chromosomal regions. As a model to study this process, we examined the regulation of a gene controlling red blood cell development, Gata2, by the transcription factor GATA1. In the DNA sequence upstream of Gata2, there are several sites that GATA1 is known to bind to; however, it is unclear whether these binding sites work together or independently to control expression of Gata2. To study this, we engineered mice to specifically remove one of these GATA1-binding sites. We found that removal of this single site reactivated expression of Gata2 in a specific stage of red blood cell development where Gata2 is normally not expressed, caused a block in differentiation of these cells, and changed the histone modification pattern specifically in the region upstream of Gata2. This work supports a model in which individual transcription factor binding sites within regions of multiple binding sites can independently and distinctly regulate gene expression during development.

Fractionation of mature eosinophils in GATA-reporter transgenic mice

Eosinophils contribute to the pathophysiology of allergic and infectious diseases, albeit their molecular functions remain unknown. Mature eosinophils are identified by their unique morphology and staining characteristics. However, it is difficult to fractionate living eosinophils by flow cytometry because these granulocytes express multiple cell surface markers that are shared by other cells of hematopoietic or non-hematopoietic origin. In this study, we describe a flow cytometry-based method to enumerate and fractionate eosinophils by developmental stages. To fractionate these cell types, we used transgenic mouse lines that express fluorescent proteins under control of the Gata1 gene hematopoietic regulatory region (Gata1-HRD), which is exclusively active in Gata1-expressing hematopoietic cells, including eosinophils. As expected, mature eosinophils were highly enriched in the fluorescent reporter-expressing subfraction of bone marrow myeloid cells that were negatively selected by using multiple antibodies against B220, CD4, CD8, Ter119, c-Kit and CD71. Cytochemical analyses of flow-sorted cells identified the cells in this fraction as eosinophils harboring eosinophilic granules. Additionally, expression of eosinophil-specific genes, for instance eosinophil enzymes and the IL-5 receptor alpha gene, were specifically detected in this fraction. The expression of these eosinophil-specific genes increased as the cells differentiated. This method for enrichment of bone marrow eosinophils is applicable to fractionation of eosinophils and bronchoalveolar lavage fluid from transgenic mice with atopic asthma. Thus, both pathological and developmental stages of eosinophils are efficiently fractionated by this flow cytometry-based method using Gata1-HRD transgenic reporter mice. This study, therefore, proposes a useful means to study the experimental allergic and inflammatory systems.

Acetylation of lysine 564 adjacent to the C-terminal binding protein-binding motif in EVI1 is crucial for transcriptional activation of GATA2

Ecotropic viral integration site 1 (EVI1) is an important transcription factor for leukemogenesis. EVI1 is a member of a group of transcription factors with C-terminal binding protein (CtBP)-binding motifs that act as transcriptional co-repressors; however, we recently found that EVI1 directly activates GATA2 transcription, which is an important gene for the maintenance of hematopoietic stem cells. We show here that EVI1-activated GATA2 transcripts derive from exon 1S of GATA2, which is specifically activated in neural and hematopoietic cells. EVI1 was acetylated by the histone acetyltransferase p300/CBP association factor (P/CAF) in myeloid leukemia cells and hematopoietic progenitor cells. Acetylation at Lys(564), which is adjacent to the CtBP-binding consensus sequence of EVI1, was found to be important for transcriptional activation of GATA2. Mutation of Lys(564) to alanine (K564A) markedly reduced the ability of EVI1 to bind DNA and activate transcription of GATA2. Furthermore, we confirmed that Lys(564) in EVI1 was specifically acetylated in leukemia and primary hematopoietic cells by using an antibody directed against an acetylated Lys(564) EVI1 peptide. Moreover, co-transfection of P/CAF with EVI1 overcame the suppressive effect of the CtBP co-repressor and resulted in GATA2 transcriptional activation; nonetheless, CtBP2 was still included in the protein complex with EVI1 and P/CAF on the EVI1-binding site in the GATA2 promoter region. Thus, acetylation of EVI1 at Lys(564) by P/CAF enhances the DNA binding capacity of EVI1 and thereby contributes to the activation of GATA2.

DNase I hypersensitivity and epsilon-globin transcriptional enhancement are separable in locus control region (LCR) HS1 mutant human beta-globin YAC transgenic mice

Expression of the five beta-like globin genes (epsilon, Ggamma, Agamma, delta, beta) in the human beta-globin locus depends on enhancement by the locus control region, which consists of five DNase I hypersensitive sites (5'HS1 through 5'HS5). We report here a novel enhancer activity in 5'HS1 that appears to be potent in transfected K562 cells. Deletion analyses identified a core activating element that bound to GATA-1, and a two-nucleotide mutation that disrupted GATA-1 binding in vitro abrogated 5'HS1 enhancer activity in transfection experiments. To determine the in vivo role of this GATA site, we generated multiple lines of human beta-globin YAC transgenic mice bearing the same two-nucleotide mutation. In the mutant mice, epsilon-, but not gamma-globin, gene expression in primitive erythroid cells was severely attenuated, while adult beta-globin gene expression in definitive erythroid cells was unaffected. Interestingly, DNaseI hypersensitivity near the 5'HS1 mutant sequence was eliminated in definitive erythroid cells, whereas it was only mildly affected in primitive erythroid cells. We therefore conclude that, although the GATA site in 5'HS1 is critical for efficient epsilon-globin gene expression, hypersensitive site formation per se is independent of 5'HS1 function, if any, in definitive erythroid cells.

Conserved usage of alternative 5' untranslated exons of the GATA4 gene

BACKGROUND

GATA4 is an essential transcription factor required for the development and function of multiple organs. Despite this important role, our knowledge of how the GATA4 gene is regulated remains limited. To better understand this regulation, we characterized the 5' region of the mouse, rat, and human GATA4 genes.

METHODOLOGY/PRINCIPAL FINDINGS

Using 5' RACE, we identified novel transcription start sites in all three species. GATA4 is expressed as multiple transcripts with varying 5' ends encoded by alternative untranslated first exons. Two of these non-coding first exons are conserved between species: exon 1a located 3.5 kb upstream of the GATA4 ATG site in exon 2, and a second first exon (exon 1b) located 28 kb further upstream. Expression of both mRNA variants was found in all GATA4-expressing organs but with a preference for the exon 1a-containing transcript. The exception was the testis where exon 1a- and 1b-containing transcripts were similarly expressed. In some tissues such as the intestine, alternative transcript expression appears to be regionally regulated. Polysome analysis suggests that both mRNA variants contribute to GATA4 protein synthesis.

CONCLUSIONS/SIGNIFICANCE

Taken together, our results indicate that the GATA4 gene closely resembles the other GATA family members in terms of gene structure where alternative first exon usage appears to be an important mechanism for regulating its tissue- and cell-specific expression.

Alternative promoter and GATA5 transcripts in mouse

GATA5 is a member of the GATA zinc finger transcription factor family involved in tissue-specific transcriptional regulation during cell differentiation and embryogenesis. Previous reports indicate that null mutation of the zebrafish GATA5 gene results in embryonic lethality, whereas deletion of exon 1 from the mouse GATA5 gene causes only derangement of female urogenital development. Here, we have identified an alternate promoter within intron 1 of the mouse GATA5 gene that transcribes a 2.5-kb mRNA that lacks exon 1 entirely but includes 82 bp from intron 1 and all of exons 2-6. The alternative promoter was active during transient transfection in cultured airway myocytes and bronchial epithelial cells, and it drove reporter gene expression in gastric epithelial cells in transgenic mice. The 2.5-kb alternative transcript encodes an NH(2)-terminally truncated "short GATA5" comprising aa 226-404 with a single zinc finger, which retains ability to transactivate the atrial natriuretic factor promoter (albeit less efficiently than full-length GATA5). Another new GATA5 transcript contains all of exons 1-5 and the 5' portion of exon 6 but lacks the terminal 1143 bp of the 3'-untranslated region from exon 6. These findings extend current understanding of the tissue distribution of GATA5 expression and suggests that GATA5 expression and function are more complex than previously appreciated.

Gata4 and Gata5 cooperatively regulate cardiac myocyte proliferation in mice

GATA5 is a member of the zinc finger transcription factor GATA family (GATA1-6) that plays a wide variety of roles in embryonic and adult development. Experiments in multiple model systems have emphasized the importance of the GATA family members 4-6 in the development of the endoderm and mesoderm. Yet despite overlapping expression patterns, there is little evidence of an important role for GATA5 in mammalian cardiac development. We have generated a new Gata5 mutant allele lacking exons 2 and 3 that encodes both zinc finger domains (Gata5(tm)(2)(Eem)), and we show that although Gata5(-/-) mice are viable, Gata4(+/-)5(-/-) mutants die at mid-gestation and exhibit profound cardiovascular defects, including abnormalities of cardiomyocyte proliferation and cardiac chamber maturation. These results demonstrate functional redundancy between Gata4 and Gata5 during cardiac development and implicate Gata5 as a candidate modifier gene for congenital heart disease.

Loss of the Gata1 gene IE exon leads to variant transcript expression and the production of a GATA1 protein lacking the N-terminal domain

GATA1 is essential for the differentiation of erythroid cells and megakaryocytes. The Gata1 gene is composed of multiple untranslated first exons and five common coding exons. The erythroid first exon (IE exon) is important for Gata1 gene expression in hematopoietic lineages. Because previous IE exon knockdown analyses resulted in embryonic lethality, less is understood about the contribution of the IE exon to adult hematopoiesis. Here, we achieved specific deletion of the floxed IE exon in adulthood using an inducible Cre expression system. In this conditional knock-out mouse line, the Gata1 mRNA level was significantly down-regulated in the megakaryocyte lineage, resulting in thrombocytopenia with a marked proliferation of megakaryocytes. By contrast, in the erythroid lineage, Gata1 mRNA was expressed abundantly utilizing alternative first exons. Especially, the IEb/c and newly identified IEd exons were transcribed at a level comparable with that of the IE exon in control mice. Surprisingly, in the IE-null mouse, these transcripts failed to produce full-length GATA1 protein, but instead yielded GATA1 lacking the N-terminal domain inefficiently. With low level expression of the short form of GATA1, IE-null mice showed severe anemia with skewed erythroid maturation. Notably, the hematological phenotypes of adult IE-null mice substantially differ from those observed in mice harboring conditional ablation of the entire Gata1 gene. The present study demonstrates that the IE exon is instrumental to adult erythropoiesis by regulating the proper level of transcription and selecting the correct transcription start site of the Gata1 gene.

GATA2-dependent and region-specific regulation of Gata2 transcription in the mouse midbrain

Transcription factor GATA2 is expressed in numerous mammalian tissues, including neural, hematopoietic, cardiovascular and urogenital systems, and yet it plays important roles in the regulation of tissue-restricted gene expression. The Gata2 gene itself is also under stringent tissue-specific control and multiple cis-regulatory domains have been identified in the Gata2 locus. In this study we sought out and then examined in detail the domains that regulate Gata2 in the midbrain. We identified two discrete domains in the Gata2 promoter that direct midbrain expression; these distal 5H and proximal 2H regulatory domains are located 3.0 and 1.9 kbp, respectively, upstream of the transcriptional initiation site. Importantly, both domains contain GATA factor binding sites. Our analyses further revealed that GATA2 is essential for Gata2 gene expression in the midbrain, whereas GATA3 is not. Both the 2H and 5H domains have the independent ability to activate Gata2 gene expression in the midbrain superior colliculus, whereas the distal-5H domain is additionally capable of activating Gata2 transcription in the inferior colliculus. These results demonstrate that two distinct regulatory domains contribute to the Gata2 gene expression in the mouse midbrain and that Gata2 midbrain transcription is under positive autoregulation.

Transcription and splicing regulation in human umbilical vein endothelial cells under hypoxic stress conditions by exon array

Background

The balance between endothelial cell survival and apoptosis during stress is an important cellular process for vessel integrity and vascular homeostasis, and it is also pivotal in angiogenesis during the development of many vascular diseases. However, the underlying molecular mechanisms remain largely unknown. Although both transcription and alternative splicing are important in regulating gene expression in endothelial cells under stress, the regulatory mechanisms underlying this state and their interactions have not yet been studied on a genome-wide basis.

Results

Human umbilical vein endothelial cells (HUVECs) were treated with cobalt chloride (CoCl₂) both to mimic hypoxia and to induce cell apoptosis and alternative splicing responses. Cell apoptosis rate analysis indicated that HUVECs exposed to 300 μM CoCl₂ for 24 hrs were initially counterbalancing apoptosis with cell survival. We therefore used the Affymetrix exon array system to determine genome-wide transcript- and exon-level differential expression. Other than 1583 differentially expressed transcripts, 342 alternatively spliced exons were detected and classified by different splicing types. Sixteen alternatively spliced exons were validated by RT-PCR. Furthermore, direct evidence for the ongoing balance between HUVEC survival and apoptosis was provided by Gene Ontology (GO) and protein function, as well as protein domain and pathway enrichment analyses of the differentially expressed transcripts. Importantly, a novel molecular module, in which the heat shock protein (HSP) families play a significant role, was found to be activated under mimicked hypoxia conditions. In addition, 46% of the transcripts containing stress-modulated exons were differentially expressed, indicating the possibility of combinatorial regulation of transcription and splicing.

Conclusion

The exon array system effectively profiles gene expression and splicing on the genome-wide scale. Based on this approach, our data suggest that transcription and splicing not only regulate gene expression, but also carry out combinational regulation of the balance between survival and apoptosis of HUVECs under mimicked hypoxia conditions. Since cell survival following the apoptotic challenge is pivotal in angiogenesis during the development of many vascular diseases, our results may advance the knowledge of multilevel gene regulation in endothelial cells under physiological and pathological conditions.

Ikaros and GATA-1 combinatorial effect is required for silencing of human gamma-globin genes

During development and erythropoiesis, globin gene expression is finely modulated through an important network of transcription factors and chromatin modifying activities. In this report we provide in vivo evidence that endogenous Ikaros is recruited to the human beta-globin locus and targets the histone deacetylase HDAC1 and the chromatin remodeling protein Mi-2 to the human gamma-gene promoters, thereby contributing to gamma-globin gene silencing at the time of the gamma- to beta-globin gene transcriptional switch. We show for the first time that Ikaros interacts with GATA-1 and enhances the binding of the latter to different regulatory regions across the locus. Consistent with these results, we show that the combinatorial effect of Ikaros and GATA-1 impairs close proximity between the locus control region and the human gamma-globin genes. Since the absence of Ikaros also affects GATA-1 recruitment to GATA-2 promoter, we propose that the combinatorial effect of Ikaros and GATA-1 is not restricted to globin gene regulation.

Context-dependent function of regulatory elements and a switch in chromatin occupancy between GATA3 and GATA2 regulate Gata2 transcription during trophoblast differentiation

GATA transcription factors are important regulators of tissue-specific gene expression during development. GATA2 and GATA3 have been implicated in the regulation of trophoblast-specific genes. However, the regulatory mechanisms of GATA2 expression in trophoblast cells are poorly understood. In this study, we demonstrate that Gata2 is transcriptionally induced during trophoblast giant cell-specific differentiation. Transcriptional induction is associated with displacement of GATA3-dependent nucleoprotein complexes by GATA2-dependent nucleoprotein complexes at two regulatory regions, the -3.9- and +9.5-kb regions, of the mouse Gata2 locus. Analyses with reporter genes showed that, in trophoblast cells, -3.9- and +9.5-kb regions function as transcriptional enhancers in GATA motif independent and dependent fashions, respectively. We also found that knockdown of GATA3 by RNA interference induces GATA2 in undifferentiated trophoblast cells. Interestingly, three other known GATA motif-dependent Gata2 regulatory elements, the -1.8-, -2.8-, and -77-kb regions, which are important to regulate Gata2 in hematopoietic cells are not occupied by GATA factors in trophoblast cells. These elements do not show any enhancer activity and also possess inaccessible chromatin structure in trophoblast cells indicating a context-dependent function. Our results indicate that GATA3 directly represses Gata2 in undifferentiated trophoblast cells, and a switch in chromatin occupancy between GATA3 and GATA2 (GATA3/GATA2 switch) induces transcription during trophoblast differentiation. We predict that this GATA3/GATA2 switch is an important mechanism for the transcriptional regulation of other trophoblast-specific genes.

CREB-binding proteins (CBP) as a transcriptional coactivator of GATA-2

The GATA family consists of six members, GATA 1-6. In this study, we focused on GATA-2, which is expressed predominantly in hematopoietic progenitor cells and plays the key role in keeping these cells in the undifferentiated status. CREB-binding proteins (CBP) are essential transcriptional coactivators for a large number of regulated DNA-binding transcription factors, including GATA-1. But there have been no reports on whether CBP is still a co-activator of GATA-2. Here, we used the immunoprecipitation and pull-down experiments to show that the GATA-2 and CBP were physically binding together, and clarified the binding sites CH1, CH3, CH452 and CT1430 in CBP and N-finger, C-finger and N-C-finger in GATA-2. Luciferase assay results in our experiment indicated that CBP could increase GATA-2 transcriptional activity in the dose-dependent manner. GATA-1 is mainly expressed in differentiated hematopoietic cells, but still has overlap expression with GATA-2. CBP is a coactivator of GATA-2 and GATA-1. The investigation on the mechanism that could decide whether CBP binds to GATA-2 to keep hematopoietic cells in the progenitor status or to GATA-1 to start differentiation will be a very interesting and very meaningful project in the near future.

Mast cell transcriptional networks

Unregulated activation of mast cells can contribute to the pathogenesis of inflammatory and allergic diseases, including asthma, rheumatoid arthritis, inflammatory bowel disease, and multiple sclerosis. Absence of mast cells in animal models can lead to impairment in the innate immune response to parasites and bacterial infections. Aberrant clonal accumulation and proliferation of mast cells can result in a variety of diseases ranging from benign cutaneous mastocytosis to systemic mastocytosis or mast cell leukemia. Understanding mast cell differentiation provides important insights into mechanisms of lineage selection during hematopoiesis and can provide targets for new drug development to treat mast cell disorders. In this review, we discuss controversies related to development, sites of origin, and the transcriptional program of mast cells.

Reduced BMP4 abundance in Gata2 hypomorphic mutant mice result in uropathies resembling human CAKUT

Constitutive loss of transcription factor GATA-2 leads to embryonic lethality from primitive erythropoietic failure. We serendipitously discovered an essential contribution of GATA-2 to urogenital development when the hematopoietic deficiency of Gata2 null mutant animals was complemented by a Gata2 yeast artificial chromosome (YAC) transgene; these mice died from a perinatal lethal urogenital abnormality. Here, we report the generation and analysis of Gata2 hypomorphic mutant (Gata2(fGN)/(/fGN)) mice, which suffered from hydronephrosis and megaureter, as do the YAC-rescued Gata2 null mutants. Gata2(fGN)/(/fGN) mutants exhibit anteriorly displaced ureteric budding from the Wolffian duct as well as reduced BMP4 expression in the intermediate mesoderm derivatives in a manner that is temporally coincident with ureteric bud emergence. In Bmp4 mutant heterozygotes, rostral displacement of the initial bud site on the Wolffian duct results in abnormal urogenital development. We show here that Bmp4 mRNA is reduced approximately twofold in Gata2(fGN)/(/fGN) mice (as in Bmp4 null heterozygotes), and that GATA-2 trans-activates a Bmp4 first intron element-directed reporter plasmid in co-transfection assays. These experiments taken together implicate GATA-2 as a direct regulator of Bmp4 transcription. The pathophysiology described in Gata2 hypomorphic mutant animals resembles human congenital anomalies of the kidney and urinary tract.

Defining the functional boundaries of the Gata2 locus by rescue with a linked bacterial artificial chromosome transgene

Transcription factor GATA-2 is vital for both hematopoietic progenitor cell function and urogenital patterning. Transgenic mapping studies have shown that the hematopoietic and urogenital enhancers are located hundreds of kbp 5' and 3' to the Gata2 structural gene, and both are vital for embryonic development. Because the size of mammalian genes, including all of their associated regulatory elements, can exceed a megabase, transgenic complementation in mice has, in specific instances, proven to be a formidable hurdle. After incorporating the Gata2 structural gene as well as the distant hematopoietic and urogenital enhancers into a single, contiguous piece of DNA by fusing two bacterial artificial chromosomes (BACs) into one, we formally tested the hypothesis that the functional boundaries of this locus are contained within this contiguous genomic span. We show that two independent lines of transgenic mice bearing a multicopy 413-kbp-linked Gata2 BAC transgene (bearing sequences from -187 to +226 kbp of the locus) are able to fully rescue Gata2 null mutant embryonic lethality and that the rescued animals behave and reproduce normally. Surprisingly, the linked BAC confers expression in the ureteric epithelium, whereas sequences within any of the overlapping parental BACs and a yeast artificial chromosome that were originally tested do not, and thus these experiments also define a novel synthetic enhancer activity that has not been previously described. These genetic complementation studies define the required outer limits of the Gata2 locus and formally demonstrate that enhancers lying beyond those boundaries are not necessary for Gata2-regulated viability or fecundity.

Regulation of adipocyte differentiation of bone marrow stromal cells by transcription factor GATA-2

GATA-2 is a transcription factor expressed in stem and progenitor cells of various cell lineages. In this study, we examined the role of GATA-2 in the differentiation of adipocytes, which are the main components of the microenvironment for hematopoiesis. Suppression of GATA-2 in TBR343, a preadipocytic stromal cell line, resulted in the acceleration of adipocyte differentiation. Conversely, overexpression of GATA-2 induced the resistance of adipocyte differentiation. In addition, regulatory elements of the GATA-2 gene in TBR343 are the same as those in hematopoietic cells. These results suggest that GATA-2 maintains a hematopoietic microenvironment by regulating the differentiation of adipocytes.

A global role for zebrafish klf4 in embryonic erythropoiesis

There are two waves of erythropoiesis, known as primitive and definitive waves in mammals and lower vertebrates including zebrafish. The founding member of the Kruppel-like factor (KLF) family of CACCC-box binding proteins, EKLF/Klf1, is essential for definitive erythropoiesis in mammals but only plays a minor role in primitive erythropoiesis. Morpholino knockdown experiments have shown a role for zebrafish klf4 in primitive erythropoiesis and hatching gland formation. In order to generate a global understanding of how klf4 might influence gene expression and differentiation, we have performed expression profiling of klf4 morphants, and then performed validation of many putative target genes by qRT-PCR and whole mount in situ hybridization. We found a critical role for klf4 in embryonic globin, heme synthesis and hatching gland gene expression. In contrast, there was an increase in expression of definitive hematopoietic specific genes such as larval globin genes, runx1 and c-myb from 24 hpf, suggesting a selective role for klf4 in primitive rather than definitive erythropoiesis. In addition, we show klf4 preferentially binds CACCC box elements in the primitive zebrafish beta-like globin gene promoters. These results have global implications for primitive erythroid gene regulation by KLF-CACCC box interactions.

A highly conserved regulatory element controls hematopoietic expression of GATA-2 in zebrafish

Background

GATA-2 is a transcription factor required for hematopoietic stem cell survival as well as for neuronal development in vertebrates. It has been shown that specific expression of GATA-2 in blood progenitor cells requires distal cis-acting regulatory elements. Identification and characterization of these elements should help elucidating transcription regulatory mechanisms of GATA-2 expression in hematopoietic lineage.

Results

By pair-wise alignments of the zebrafish genomic sequences flanking GATA-2 to orthologous regions of fugu, mouse, rat and human genomes, we identified three highly conserved non-coding sequences in the genomic region flanking GATA-2, two upstream of GATA-2 and another downstream. Using both transposon and bacterial artificial chromosome mediated germline transgenic zebrafish analyses, one of the sequences was established as necessary and sufficient to direct hematopoietic GFP expression in a manner that recapitulates that of GATA-2. In addition, we demonstrated that this element has enhancer activity in mammalian myeloid leukemia cell lines, thus validating its functional conservation among vertebrate species. Further analysis of potential transcription factor binding sites suggested that integrity of the putative HOXA3 and LMO2 sites is required for regulating GATA-2/GFP hematopoietic expression.

Conclusion

Regulation of GATA-2 expression in hematopoietic cells is likely conserved among vertebrate animals. The integrated approach described here, drawing on embryological, transgenesis and computational methods, should be generally applicable to analyze tissue-specific gene regulation involving distal DNA cis-acting elements.