GATA-1 genome-wide occupancy associates with distinct epigenetic profiles in mouse fetal liver erythropoiesis

High altitude polycythemia and its maladaptive mechanisms: an updated review

High altitude polycythemia is a maladaptation of highlanders exposed to hypoxic environment, leading to high blood viscosity and severe cardiorespiratory dysfunction. Prolonged hypoxia causes respiratory depression and severe hypoxemia, and further mediates changes in genetic and molecular mechanisms that regulate erythropoiesis and apoptosis, ultimately resulting in excessive erythrocytosis (EE). This updated review investigated the maladaptive mechanisms of EE, including respiratory chemoreceptor passivation, sleep-related breathing disorders, sex hormones, iron metabolism, and hypoxia-related factors and pathways.

Single-cell and spatial multiomic inference of gene regulatory networks using SCRIPro

MOTIVATION

The burgeoning generation of single-cell or spatial multiomic data allows for the characterization of gene regulation networks (GRNs) at an unprecedented resolution. However, the accurate reconstruction of GRNs from sparse and noisy single-cell or spatial multiomic data remains challenging.

RESULTS

Here, we present SCRIPro, a comprehensive computational framework that robustly infers GRNs for both single-cell and spatial multi-omics data. SCRIPro first improves sample coverage through a density clustering approach based on multiomic and spatial similarities. Additionally, SCRIPro scans transcriptional regulator (TR) importance by performing chromatin reconstruction and in silico deletion analyses using a comprehensive reference covering 1,292 human and 994 mouse TRs. Finally, SCRIPro combines TR-target importance scores derived from multiomic data with TR-target expression levels to ensure precise GRN reconstruction. We benchmarked SCRIPro on various datasets, including single-cell multiomic data from human B-cell lymphoma, mouse hair follicle development, Stereo-seq of mouse embryos, and Spatial-ATAC-RNA from mouse brain. SCRIPro outperforms existing motif-based methods and accurately reconstructs cell type-specific, stage-specific, and region-specific GRNs. Overall, SCRIPro emerges as a streamlined and fast method capable of reconstructing TR activities and GRNs for both single-cell and spatial multi-omic data.

AVAILABILITY

SCRIPro is available at https://github.com/wanglabtongji/SCRIPro.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Broad H3K4me3 Domain Is Associated with Spatial Coherence during Mammalian Embryonic Development

It is well known that the chromatin states play a major role in cell-fate decision and cell-identity maintenance; however, the spatial variation of chromatin states in situ remains poorly characterized. Here, by leveraging recently available spatial-CUT&Tag data, we systematically characterized the global spatial organization of the H3K4me3 profiles in a mouse embryo. Our analysis identified a subset of genes with spatially coherent H3K4me3 patterns, which together delineate the tissue boundaries. The spatially coherent genes are strongly enriched with tissue-specific transcriptional regulators. Remarkably, their corresponding genomic loci are marked by broad H3K4me3 domains, which is distinct from the typical H3K4me3 signature. Spatial transition across tissue boundaries is associated with continuous shortening of the broad H3K4me3 domains as well as expansion of H3K27me3 domains. Our analysis reveals a strong connection between the genomic and spatial variation of chromatin states, which may play an important role in embryonic development.

Long noncoding RNA HIKER regulates erythropoiesis in Monge's disease via CSNK2B

Excessive erythrocytosis (EE) is a major hallmark of patients suffering from chronic mountain sickness (CMS, also known as Monge's disease) and is responsible for major morbidity and even mortality in early adulthood. We took advantage of unique populations, one living at high altitude (Peru) showing EE, with another population, at the same altitude and region, showing no evidence of EE (non-CMS). Through RNA-Seq, we identified and validated the function of a group of long noncoding RNAs (lncRNAs) that regulate erythropoiesis in Monge's disease, but not in the non-CMS population. Among these lncRNAs is hypoxia induced kinase-mediated erythropoietic regulator (HIKER)/LINC02228, which we showed plays a critical role in erythropoiesis in CMS cells. Under hypoxia, HIKER modulated CSNK2B (the regulatory subunit of casein kinase 2). A downregulation of HIKER downregulated CSNK2B, remarkably reducing erythropoiesis; furthermore, an upregulation of CSNK2B on the background of HIKER downregulation rescued erythropoiesis defects. Pharmacologic inhibition of CSNK2B drastically reduced erythroid colonies, and knockdown of CSNK2B in zebrafish led to a defect in hemoglobinization. We conclude that HIKER regulates erythropoiesis in Monge's disease and acts through at least one specific target, CSNK2B, a casein kinase.

EKLF/Klf1 regulates erythroid transcription by its pioneering activity and selective control of RNA Pol II pause-release

EKLF/Klf1 is a zinc-finger transcription activator essential for erythroid lineage commitment and terminal differentiation. Using ChIP-seq, we investigate EKLF DNA binding and transcription activation mechanisms during mouse embryonic erythropoiesis. We utilize the Nan/+ mouse that expresses the EKLF-E339D (Nan) variant mutated in its conserved zinc-finger region and address the mechanism of hypomorphic and neomorphic changes in downstream gene expression. First, we show that Nan-EKLF limits normal EKLF binding to a subset of its sites. Second, we find that ectopic binding of Nan-EKLF occurs largely at enhancers and activates transcription through pioneering activity. Third, we find that for a subset of ectopic targets, gene activation is achieved in Nan/+ only by Nan-EKLF binding to distal enhancers, leading to RNA polymerase II pause-release. These results have general applicability to understanding how a DNA binding variant factor confers dominant disruptive effects on downstream gene expression even in the presence of its normal counterpart.

Erythroid Cell Research: 3D Chromatin, Transcription Factors and Beyond

Studies of the regulatory networks and signals controlling erythropoiesis have brought important insights in several research fields of biology and have been a rich source of discoveries with far-reaching implications beyond erythroid cells biology. The aim of this review is to highlight key recent discoveries and show how studies of erythroid cells bring forward novel concepts and refine current models related to genome and 3D chromatin organization, signaling and disease, with broad interest in life sciences.

Chromatin occupancy and epigenetic analysis reveal new insights into the function of the GATA1 N terminus in erythropoiesis

Mutations in GATA1, which lead to expression of the GATA1s isoform that lacks the GATA1 N terminus, are seen in patients with Diamond-Blackfan anemia (DBA). In our efforts to better understand the connection between GATA1s and DBA, we comprehensively studied erythropoiesis in Gata1s mice. Defects in yolks sac and fetal liver hematopoiesis included impaired terminal maturation and reduced numbers of erythroid progenitors. RNA-sequencing revealed that both erythroid and megakaryocytic gene expression patterns were altered by the loss of the N terminus, including aberrant upregulation of Gata2 and Runx1. Dysregulation of global H3K27 methylation was found in the erythroid progenitors upon loss of N terminus of GATA1. Chromatin-binding assays revealed that, despite similar occupancy of GATA1 and GATA1s, there was a striking reduction of H3K27me3 at regulatory elements of the Gata2 and Runx1 genes. Consistent with the observation that overexpression of GATA2 has been reported to impair erythropoiesis, we found that haploinsufficiency of Gata2 rescued the erythroid defects of Gata1s fetuses. Together, our integrated genomic analysis of transcriptomic and epigenetic signatures reveals that, Gata1 mice provide novel insights into the role of the N terminus of GATA1 in transcriptional regulation and red blood cell maturation which may potentially be useful for DBA patients.

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.

GATA factor transcriptional activity: Insights from genome-wide binding profiles

The members of the GATA family of transcription factors have homologous zinc fingers and bind to similar sequence motifs. Recent advances in genome-wide technologies and the integration of bioinformatics data have led to a better understanding of how GATA factors regulate gene expression; GATA-factor-induced transcriptional and epigenetic changes have now been analyzed at unprecedented levels of detail. Here, we review the results of genome-wide studies of GATA factor occupancy in human and murine cell lines and primary cells (as determined by chromatin immunoprecipitation sequencing), and then discuss the molecular mechanisms underlying the mediation of transcriptional and epigenetic regulation by GATA factors.

Mouse Tryptase Gene Expression is Coordinately Regulated by GATA1 and GATA2 in Bone Marrow-Derived Mast Cells

Mast cell tryptases have crucial roles in allergic and inflammatory diseases. The mouse tryptase genes represent a cluster of loci on chromosome 16p3.3. While their functional studies have been extensively performed, transcriptional regulation of tryptase genes is poorly understood. In this study, we examined the molecular basis of the tryptase gene expression in bone marrow-derived mast cells (BMMCs) of C57BL/6 mice and in MEDMC-BRC6 mast cells. The expression of the Tpsb2 and Tpsg1 genes, which reside at the 3′-end of the tryptase locus, is significantly decreased by the reduction of the GATA transcription factors GATA1 or GATA2. Chromatin immunoprecipitation assays have shown that the GATA factors bind at multiple regions within the locus, including 1.0 and 72.8 kb upstream of the Tpsb2 gene, and that GATA1 and GATA2 facilitate each other’s DNA binding activity to these regions. Deletion of the −72.8 kb region by genome editing significantly reduced the Tpsb2 and Tpsg1 mRNA levels in MEDMC-BRC6 cells. Furthermore, binding of CTCF and the cohesin subunit Rad21 was found upstream of the −72.8 kb region and was significantly reduced in the absence of GATA1. These results suggest that mouse tryptase gene expression is coordinately regulated by GATA1 and GATA2 in BMMCs.

In utero gene expression in the Slc39a8(neo/neo) knockdown mouse

Slc39a8 encodes ZIP8, a divalent cation/bicarbonate symporter expressed in pluripotent mouse embryonic stem cells, and therefore ubiquitous in adult tissues; ZIP8 influxes Zn²⁺, Mn²⁺ and Fe²⁺. Slc39a8(neo/neo) knockdown mice exhibit 10-15% of wild-type ZIP8 mRNA and protein levels, and show pleiotropic phenotype of stunted growth, neonatal lethality, multi-organ dysmorphogenesis, and dysregulated hematopoiesis manifested as severe anemia. Herein we performed RNA-seq analysis of gestational day (GD)13.5 yolk sac and placenta, and GD16.5 liver, kidney, lung, heart and cerebellum, comparing Slc39a8(neo/neo) with Slc39a8(+/+) wild-type. Meta-data analysis of differentially-expressed genes revealed 29 unique genes from all tissues - having enriched GO categories associated with hematopoiesis and hypoxia and KEGG categories of complement, response to infection, and coagulation cascade - consistent with dysregulated hematopoietic stem cell fate. Based on transcription factor (TF) profiles in the JASPAR database, and searching for TF-binding sites enriched by Pscan, we identified numerous genes encoding zinc-finger and other TFs associated with hematopoietic stem cell functions. We conclude that, in this mouse model, deficient ZIP8-mediated divalent cation transport affects zinc-finger (e.g. GATA proteins) and other TFs interacting with GATA proteins (e.g. TAL1), predominantly in yolk sac. These data strongly support the phenotype of dysmorphogenesis and anemia seen in Slc39a8(neo/neo) mice in utero.

Meeting report - INDEPTH kick-off meeting

The precise location of chromatin domains within the cell nucleus has seen growing recognition in the past decade as an additional mechanism of controlling gene expression in both plants and animals (Dekker et al., 2017). Consequently, international efforts are devoted to understanding the organising principle of this organelle in plants, and notably the nature and the role of functional compartments on gene expression (Graumann et al., 2013; Sotelo-Silveira et al., 2018). The European cooperation 'Impact of Nuclear Domains on Gene Expression and Plant Traits' (INDEPTH) brings together molecular cell biologists, plant physiologists, bioinformaticians, image analysts and computer scientists. They aim to address the question of how nuclear architecture, chromatin organisation and gene expression are connected in plants, particularly in relation to traits of interest such as biomass, reproduction and resistance to pathogens (https://www.brookes.ac.uk/indepth/). The kick-off meeting of the INDEPTH consortium took place in Clermont-Ferrand, France, on 12-14th March 2018, where more than 80 researchers set the agenda for the coming four years of research and collaboration.

GATA1 insufficiencies in primary myelofibrosis and other hematopoietic disorders: consequences for therapy

INTRODUCTION

GATA1, the founding member of a family of transcription factors, plays important roles in the development of hematopoietic cells of several lineages. Although loss of GATA1 has been known to impair hematopoiesis in animal models for nearly 25 years, the link between GATA1 defects and human blood diseases has only recently been realized. Areas covered: Here the current understanding of the functions of GATA1 in normal hematopoiesis and how it is altered in disease is reviewed. GATA1 is indispensable mainly for erythroid and megakaryocyte differentiation. In erythroid cells, GATA1 regulates early stages of differentiation, and its deficiency results in apoptosis. In megakaryocytes, GATA1 controls terminal maturation and its deficiency induces proliferation. GATA1 alterations are often found in diseases involving these two lineages, such as congenital erythroid and/or megakaryocyte deficiencies, including Diamond Blackfan Anemia (DBA), and acquired neoplasms, such as acute megakaryocytic leukemia (AMKL) and the myeloproliferative neoplasms (MPNs). Expert commentary: Since the first discovery of GATA1 mutations in AMKL, the number of diseases that are associated with impaired GATA1 function has increased to include DBA and MPNs. With respect to the latter, we are only just now appreciating the link between enhanced JAK/STAT signaling, GATA1 deficiency and disease pathogenesis.

Distinct and overlapping DNMT1 interactions with multiple transcription factors in erythroid cells: Evidence for co-repressor functions

DNMT1 is the maintenance DNA methyltransferase shown to be essential for embryonic development and cellular growth and differentiation in many somatic tissues in mammals. Increasing evidence has also suggested a role for DNMT1 in repressing gene expression through interactions with specific transcription factors. Previously, we identified DNMT1 as an interacting partner of the TR2/TR4 nuclear receptor heterodimer in erythroid cells, implicated in the developmental silencing of fetal β-type globin genes in the adult stage of human erythropoiesis. Here, we extended this work by using a biotinylation tagging approach to characterize DNMT1 protein complexes in mouse erythroleukemic cells. We identified novel DNMT1 interactions with several hematopoietic transcription factors with essential roles in erythroid differentiation, including GATA1, GFI-1b and FOG-1. We provide evidence for DNMT1 forming distinct protein subcomplexes with specific transcription factors and propose the existence of a "core" DNMT1 complex with the transcription factors ZBP-89 and ZNF143, which is also present in non-hematopoietic cells. Furthermore, we identified the short (17a.a.) PCNA Binding Domain (PBD) located near the N-terminus of DNMT1 as being necessary for mediating interactions with the transcription factors described herein. Lastly, we provide evidence for DNMT1 serving as a co-repressor of ZBP-89 and GATA1 acting through upstream regulatory elements of the PU.1 and GATA1 gene loci.

Repression by RB1 characterizes genes involved in the penultimate stage of erythroid development

Retinoblastoma-1 (RB1), and the RB1-related proteins p107 and p130, are key regulators of the cell cycle. Although RB1 is required for normal erythroid development in vitro, it is largely dispensable for erythropoiesis in vivo. The modest phenotype caused by RB1 deficiency in mice raises questions about redundancy within the RB1 family, and the role of RB1 in erythroid differentiation. Here we show that RB1 is the major pocket protein that regulates terminal erythroid differentiation. Erythroid cells lacking all pocket proteins exhibit the same cell cycle defects as those deficient for RB1 alone. RB1 has broad repressive effects on gene transcription in erythroid cells. As a group, RB1-repressed genes are generally well expressed but downregulated at the final stage of erythroid development. Repression correlates with E2F binding, implicating E2Fs in the recruitment of RB1 to repressed genes. Merging differential and time-dependent changes in expression, we define a group of approximately 800 RB1-repressed genes. Bioinformatics analysis shows that this list is enriched for terms related to the cell cycle, but also for terms related to terminal differentiation. Some of these have not been previously linked to RB1. These results expand the range of processes potentially regulated by RB1, and suggest that a principal role of RB1 in development is coordinating the events required for terminal differentiation.

GATA-1 Inhibits PU.1 Gene via DNA and Histone H3K9 Methylation of Its Distal Enhancer in Erythroleukemia

GATA-1 and PU.1 are two important hematopoietic transcription factors that mutually inhibit each other in progenitor cells to guide entrance into the erythroid or myeloid lineage, respectively. PU.1 controls its own expression during myelopoiesis by binding to the distal URE enhancer, whose deletion leads to acute myeloid leukemia (AML). We herein present evidence that GATA-1 binds to the PU.1 gene and inhibits its expression in human AML-erythroleukemias (EL). Furthermore, GATA-1 together with DNA methyl Transferase I (DNMT1) mediate repression of the PU.1 gene through the URE. Repression of the PU.1 gene involves both DNA methylation at the URE and its histone H3 lysine-K9 methylation and deacetylation as well as the H3K27 methylation at additional DNA elements and the promoter. The GATA-1-mediated inhibition of PU.1 gene transcription in human AML-EL mediated through the URE represents important mechanism that contributes to PU.1 downregulation and leukemogenesis that is sensitive to DNA demethylation therapy.

Peak shape clustering reveals biological insights

Background

ChIP-seq experiments are widely used to detect and study DNA-protein interactions, such as transcription factor binding and chromatin modifications. However, downstream analysis of ChIP-seq data is currently restricted to the evaluation of signal intensity and the detection of enriched regions (peaks) in the genome. Other features of peak shape are almost always neglected, despite the remarkable differences shown by ChIP-seq for different proteins, as well as by distinct regions in a single experiment.

Results

We hypothesize that statistically significant differences in peak shape might have a functional role and a biological meaning. Thus, we design five indices able to summarize peak shapes and we employ multivariate clustering techniques to divide peaks into groups according to both their complexity and the intensity of their coverage function. In addition, our novel analysis pipeline employs a range of statistical and bioinformatics techniques to relate the obtained peak shapes to several independent genomic datasets, including other genome-wide protein-DNA maps and gene expression experiments. To clarify the meaning of peak shape, we apply our methodology to the study of the erythroid transcription factor GATA-1 in K562 cell line and in megakaryocytes.

Conclusions

Our study demonstrates that ChIP-seq profiles include information regarding the binding of other proteins beside the one used for precipitation. In particular, peak shape provides new insights into cooperative transcriptional regulation and is correlated to gene expression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-015-0787-6) contains supplementary material, which is available to authorized users.

GATA1 and PU.1 Bind to Ribosomal Protein Genes in Erythroid Cells: Implications for Ribosomopathies

The clear connection between ribosome biogenesis dysfunction and specific hematopoiesis-related disorders prompted us to examine the role of critical lineage-specific transcription factors in the transcriptional regulation of ribosomal protein (RP) genes during terminal erythroid differentiation. By applying EMSA and ChIP methodologies in mouse erythroleukemia cells we show that GATA1 and PU.1 bind in vitro and in vivo the proximal promoter region of the RPS19 gene which is frequently mutated in Diamond-Blackfan Anemia. Moreover, ChIPseq data analysis also demonstrates that several RP genes are enriched as potential GATA1 and PU.1 gene targets in mouse and human erythroid cells, with GATA1 binding showing an association with higher ribosomal protein gene expression levels during terminal erythroid differentiation in human and mouse. Our results suggest that RP gene expression and hence balanced ribosome biosynthesis may be specifically and selectively regulated by lineage specific transcription factors during hematopoiesis, a finding which may be clinically relevant to ribosomopathies.

TAF10 Interacts with the GATA1 Transcription Factor and Controls Mouse Erythropoiesis

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

GATA4 represses an ileal program of gene expression in the proximal small intestine by inhibiting the acetylation of histone H3, lysine 27

GATA4 is expressed in the proximal 85% of small intestine where it promotes a proximal intestinal ('jejunal') identity while repressing a distal intestinal ('ileal') identity, but its molecular mechanisms are unclear. Here, we tested the hypothesis that GATA4 promotes a jejunal versus ileal identity in mouse intestine by directly activating and repressing specific subsets of absorptive enterocyte genes by modulating the acetylation of histone H3, lysine 27 (H3K27), a mark of active chromatin, at sites of GATA4 occupancy. Global analysis of mouse jejunal epithelium showed a statistically significant association of GATA4 occupancy with GATA4-regulated genes. Occupancy was equally distributed between down- and up-regulated targets, and occupancy sites showed a dichotomy of unique motif over-representation at down- versus up-regulated genes. H3K27ac enrichment at GATA4-binding loci that mapped to down-regulated genes (activation targets) was elevated, changed little upon conditional Gata4 deletion, and was similar to control ileum, whereas H3K27ac enrichment at GATA4-binding loci that mapped to up-regulated genes (repression targets) was depleted, increased upon conditional Gata4 deletion, and approached H3K27ac enrichment in wild-type control ileum. These data support the hypothesis that GATA4 both activates and represses intestinal genes, and show that GATA4 represses an ileal program of gene expression in the proximal small intestine by inhibiting the acetylation of H3K27.

Analysis of hundreds of cis-regulatory landscapes at high resolution in a single, high-throughput experiment

Gene expression during development and differentiation is regulated in a cell- and stage-specific manner by complex networks of intergenic and intragenic cis-regulatory elements whose numbers and representation in the genome far exceed those of structural genes. Using chromosome conformation capture, it is now possible to analyze in detail the interaction between enhancers, silencers, boundary elements and promoters at individual loci, but these techniques are not readily scalable. Here we present a high-throughput approach (Capture-C) to analyze cis interactions, interrogating hundreds of specific interactions at high resolution in a single experiment. We show how this approach will facilitate detailed, genome-wide analysis to elucidate the general principles by which cis-acting sequences control gene expression. In addition, we show how Capture-C will expedite identification of the target genes and functional effects of SNPs that are associated with complex diseases, which most frequently lie in intergenic cis-acting regulatory elements.

Ldb1 complexes: the new master regulators of erythroid gene transcription

Elucidation of the genetic pathways that control red blood cell development has been a central goal of erythropoiesis research over the past decade. Notably, data from several recent studies have provided new insights into the regulation of erythroid gene transcription. Transcription profiling demonstrates that erythropoiesis is mainly controlled by a small group of lineage-restricted transcription factors [Gata binding protein 1 (Gata1), T cell acute lymphocytic leukemia 1 protein (Tal1), and Erythroid Kruppel-like factor (EKLF; henceforth referred to as Klf1)]. Binding-site mapping using ChIP-Seq indicates that most DNA-bound Gata1 and Tal1 proteins are contained within higher order complexes (Ldb1 complexes) that include the nuclear adapters Ldb1 and Lmo2. Ldb1 complexes regulate Klf1, and Ldb1 complex-binding sites frequently colocalize with Klf1 at erythroid genes and cis-regulatory elements, indicating strong functional synergy between Gata1, Tal1, and Klf1. Together with new data demonstrating that Ldb1 can mediate long-range promoter-enhancer interactions, these findings provide a foundation for the first comprehensive models of the global regulation of erythroid gene transcription.