A factor binding GATAAG confers tissue specificity on the promoter of the human zeta-globin gene

Distinct negative regulation of the human embryonic globin genes zeta and epsilon

The human embryonic globin genes zeta and epsilon are expressed when erythropoiesis is initiated at about the third week of development but are subsequently repressed as expression of the fetal globins, alpha and gamma, begins. We have examined the promoter region of the human zeta-globin and epsilon-globin genes in order to identify regulatory sequences that may be involved in this process. Stable transfection of the human erythroid cell line K562 with either a truncated form of the zeta-globin gene, containing 112 base pairs (bp) of 5'-flanking sequences, or a larger zeta-globin construct, containing several hundred bp of 5'-flanking sequence, revealed that the zeta-globin gene is subject to negative regulation by its 5'-flanking region. We have defined the sequences responsible for this negative regulation to a 22 bp region immediately upstream of the proximal promoter sequence of the zeta-globin gene. A 22 bp oligonucleotide including this negative element was found to inhibit both the zeta-globin and HSV TK promoters. We have also analyzed the promoter of the human epsilon-globin gene, since it is coordinately expressed with zeta-globin. We show that it is likewise subject to negative regulation, though in this case from a distal silencer element. Gel retardation and methylation interference assays have provided evidence of a factor which binds specifically to the epsilon-globin silencer. However, no obvious sequence homology exists between the zeta and epsilon negative elements, and at least some of the factors that recognize these elements are distinct. We postulate that the negative transcriptional control elements in the human embryonic globin gene promoters contribute to the observed reduction in zeta- and epsilon-globin gene expression that occurs during development.

Reduced expression of PHD2 prolyl hydroxylase gene in primary advanced uterine cervical carcinoma

Decreased PHD2 expression in human carcinomas has been considered a critical factor in supporting tumor angiogenesis and growth. We studied the levels of PHD2 transcript and protein in advanced cervical cancer specimens (n=27) and normal uterine cervical tissue samples (n=27). Real-time quantitative PCR and Western blotting analysis showed significantly lower levels of PHD2 transcript (P=0.0088) and protein (P=0.0095) in cancerous tissues as compared to corresponding normal tissue. Using DNA sequencing analysis, we also found an accumulation of mutations in promoter regions of PHD2 in advanced cervical cancer specimens. Moreover, computer analysis of these mutations showed a loss of binding sites for many transcription factors. Our results suggest PHD2 as a possible target in anti-angiogenic therapies in advanced uterine cervical carcinoma.

Both 5' and 3' flanks regulate Zebrafish brain-derived neurotrophic factor gene expression

BACKGROUND

Precise control of developmental and cell-specific expression of the brain-derived neurotrophic factor (BDNF) gene is essential for normal neuronal development and the diverse functions of BDNF in the adult organism. We previously showed that the zebrafish BDNF gene has multiple promoters. The complexity of the promoter structure and the mechanisms that mediate developmental and cell-specific expression are still incompletely understood.

RESULTS

Comparison of pufferfish and zebrafish BDNF gene sequences as well as 5' RACE revealed three additional 5' exons and associated promoters. RT-PCR with exon-specific primers showed differential developmental and organ-specific expression. Two exons were detected in the embryo before transcription starts. Of the adult organs examined, the heart expressed a single 5' exon whereas the brain, liver and eyes expressed four of the seven 5' exons. Three of the seven 5' exons were not detectable by RT-PCR. Injection of promoter/GFP constructs into embryos revealed distinct expression patterns. The 3' flank profoundly affected expression in a position-dependent manner and a highly conserved sequence (HCS1) present in 5' exon 1c in a dehancer-like manner.

CONCLUSIONS

The zebrafish BDNF gene is as complex in its promoter structure and patterns of differential promoter expression as is its murine counterpart. The expression of two of the promoters appears to be regulated in a temporally and/or spatially highly circumscribed fashion. The 3' flank has a position-dependent effect on expression, either by affecting transcription termination or post-transcriptional steps. HCS1, a highly conserved sequence in 5' exon 1c, restricts expression to primary sensory neurons. The tools are now available for detailed genetic and molecular analyses of zebrafish BDNF gene expression.

Role of GATA motifs in tissue factor pathway inhibitor gene expression in malignant cells

Tissue factor pathway inhibitor (TFPI) is the primary physiologic inhibitor of tissue factor-induced clotting. The TFPI gene contains three GATA motifs in the region flanking its transcription initiation sites. GATA motifs present in promoters of other genes bind GATA-2 transcription factor and thereby regulate their transcriptional expression. Both TFPI and GATA-2 transcription factor are synthesized by a variety of normal as well as malignant cells including hepatocellular carcinoma HepG2 and bladder carcinoma ECV304. Here, we studied whether the three GATA motifs flanking the transcription initiation sites regulate TFPI gene expression in HepG2 and ECV304 cells by binding to the GATA-2 transcription factor. Synthetic oligonucleotides containing GATA sequences from the TFPI regulatory region formed DNA-protein complexes with HepG2 and ECV304 nuclear extracts in an electrophoretic mobility shift assay. Using a 740-bp fragment (-496/+244) from TFPI regulatory region, the effect of base substitutions at each of the three GATA motifs was studied in a luciferase reporter gene system. TFPI promoter activity in HepG2 cells was increased 3-fold with mutation in one of the three GATA motifs and in ECV304 cells was essentially unchanged with mutations in all three GATA motifs. Thus, GATA motifs appear to serve a tissue-specific regulatory role in TFPI gene expression in malignant cells.

In vivo footprinting analysis of the hepatic control region of the human apolipoprotein E/C-I/C-IV/C-II gene locus

Expression of both the apolipoprotein (apo)E and apoC-I genes in the liver is specified by a 319-nucleotide hepatic control region (HCR-1) that is located 15 kilobase pairs downstream of the apoE gene and 5 kilobase pairs downstream of the apoC-I gene. In vivo footprint analysis of HCR-1 in intact nuclei revealed several liver-specific protein-binding sites that were not detectable by in vitro methods. In addition to three previously identified in vitro footprints, four in vivo footprints were identified in a region of HCR-1 that is required for directing gene expression to hepatocytes. Prominent liver-specific DNase I-hypersensitive sites were associated with these footprints. Liver-specific nuclear protein binding to these sites was confirmed by oligonucleotide gel-retention assays. The in vivo analysis also identified a cluster of nuclear protein-binding sites in the Alu family repeat segment adjacent to the domain required for liver expression. Micrococcal nuclease digestion indicated the presence of a nucleosome in the central domain of HCR-1 in liver chromatin that was in phase with the nucleosome location in tissues that did not express the transgene. These results suggest that HCR-1 functions in a highly structured chromatin environment requiring a complex interaction of liver-enriched transcription factors.

Proximal promoter elements of the human zeta-globin gene confer embryonic-specific expression on a linked reporter gene in transgenic mice

We have investigated the transcriptional regulation of the human embryonic zeta-globin gene promoter. First, we examined the effect that deletion of sequences 5' to zeta-globin's CCAAT box have on zeta-promoter activity in erythroid cell lines. Deletions of sequences between -116 and -556 (cap = 0) had little effect while further deletion to -84 reduced zeta-promoter activity by only 2-3-fold in both transiently and stably transfected erythroid cells. Constructs containing 67, 84 and 556 bp of zeta-globin 5' flanking region linked to a beta-galactosidase reporter gene (lacZ) and hypersensitive site -40 (HS-40) of the human alpha-globin gene cluster were then employed for the generation of transgenic mice. LacZ expression from all constructs, including a 67 bp zeta-globin promoter, was erythroid-specific and most active between 8.5 and 10.5 days post-fertilisation. By 16.5 days gestation, lacZ expression dropped 40-100-fold. These results suggest that embryonic-specific activation of the human zeta-globin promoter is conferred by a 67 bp zeta-promoter fragment containing only a CCAAT and TATA box.

A palindromic regulatory site within vertebrate GATA-1 promoters requires both zinc fingers of the GATA-1 DNA-binding domain for high-affinity interaction

GATA-1, a transcription factor essential for the development of the erythroid lineage, contains two adjacent highly conserved zinc finger motifs. The carboxy-terminal finger is necessary and sufficient for specific binding to the consensus GATA recognition sequence: mutant proteins containing only the amino-terminal finger do not bind. Here we identify a DNA sequence (GATApal) for which the GATA-1 amino-terminal finger makes a critical contribution to the strength of binding. The site occurs in the GATA-1 gene promoters of chickens, mice, and humans but occurs very infrequently in other vertebrate genes known to be regulated by GATA proteins. GATApal is a palindromic site composed of one complete [(A/T)GATA(A/G)] and one partial (GAT) canonical motif. Deletion of the partial motif changes the site to a normal GATA site and also reduces by as much as eightfold the activity of the GATA-1 promoter in an erythroid precursor cell. We propose that GATApal is important for positive regulation of GATA-1 expression in erythroid cells.

Zinc fingers 1-7 of EVI1 fail to bind to the GATA motif by itself but require the core site GACAAGATA for binding

EVI1 is a zinc finger oncoprotein that binds via fingers 1-7 to the sequence GACAAGATAA. The target genes on which EVI1 acts are unknown. This binding motif overlaps with that for the GATA transcription factors, (T/A)GATA(A/G), and GATA-1 can bind to and activate transcription via a GACAAGATAA motif. The possibility has been raised that, when overexpressed in leukemogenesis, EVI1 may function by interfering with the differentiation-promoting action of GATA factors. To explore this, we have assessed the affinity of EVI1 for the GATA binding sites derived from erythroid-specific GATA-1 target genes, and found only low affinity interactions. We examined the contacts between EVI1 and DNA by methylation interference studies, which revealed extensive contacts between EVI1 and its binding site. The importance of the contacts for high affinity binding was shown by in vitro quantitative gel shift studies and in vivo cotransfection studies. To examine what types of sequences from mouse genomic DNA bind to EVI1, we isolated and sequenced five EVI1-binding fragments, and each showed the GACAAGATA site. The data presented contribute to our knowledge of the binding specificity of EVI1, and yield a clearer picture of what sequences can, and cannot, act as targets for EVI1 action.

Structure of the hepatic control region of the human apolipoprotein E/C-I gene locus

The specificity of expression in the liver of the human apolipoprotein (apo) E/C-I gene locus is determined by a hepatic control region (HCR) that is located 15 kilobases downstream of the apoE gene. DNase I footprint studies of this sequence using nuclear extracts identified a region of the HCR that is enriched in nuclear protein-binding sites. Nuclease analysis of chromatin revealed liver-specific DNase I-hypersensitive sites that were associated with this region, and additional liver-specific nuclease-sensitive sites associated with the apoE gene were identified. The HCR domain has a limited binding affinity for the nuclear scaffold. The specific domain required for liver expression was tested by ligating subfragments of the HCR to the apoE gene and examining their activity in transgenic mice. A segment of 319 nucleotides that contained several potential regulatory sequences was required for full activity of liver-specific transcription with shorter segments yielding much lower levels of expression in the liver. All constructs that contained a fully active HCR were expressed in approximately a copy-dependent manner, suggesting that transgene expression was independent of integration position. Taken together, the properties of the HCR are consistent with its function as a locus control region for the liver-specific expression of the apoE gene.

A new approach to isolate genomic control regions. Application to the GATA transcription factor family

We have designed a new strategy to isolate unknown DNA regions interacting with one or several related regulatory proteins. It involves trapping such DNAs by their cognate binding proteins followed by PCR amplification, as described previously [Kinzler, K. & Vogelstein, B. (1989) Nucleic Acids Res. 17, 3645-3653]. To overcome the inability of such a procedure to discriminate between functional and non-functional binding sites as well as to specifically trap short DNA motifs from the whole higher eukaryotic genome, we have used as starting material DNA isolated from transcriptionally competent chromatin fractions, instead of total genomic DNA. To test our strategy, we selected human DNA sequences that bind members of the GATA family, known to recognize similar WGATAR motifs. These proteins are expressed in different cell types in which they regulate the transcription of different sets of genes; thus, transcriptionally active chromatin containing GATA motifs should differ according to the cell type. We have trapped and analyzed DNA fragments isolated from an active chromatin fraction, from erythroid cells and lymphoid cells, using GATA-1 and GATA-3 proteins, respectively. We show that regulatory GATA sequences known to be in open chromatin in erythroid cells (typified by the HSIII fragment of the beta-globin locus control region) or in lymphoid cells (typified by a fragment of the CD2 locus control region) are dramatically enriched in a cell-specific manner, demonstrating the potency of the method. The sequences of the erythroid or lymphoid DNA fragments isolated through the procedure described here were determined and display subset-site preference for GATA-1 and GATA-3.

Promoter control of translation in Xenopus oocytes

The HIV-1 promoter directs the high level production of transcripts in Xenopus oocytes. However, despite being exported to the cytoplasm, the transcripts are not translated [M. Braddock, A. M. Thorburn, A. Chambers, G. D. Elliott, G. J. Anderson, A. J. Kingsman and S. M. Kingsman (1990) Cell, 62, 1123-1133]. We have shown previously that this is a function of promoter sequences and is independent of the TAR RNA element that is normally located at the 5' end of all HIV mRNAs. We now show that a three nucleotide substitution at position -340, upstream of the RNA start site, reverses the translation inhibition. This site coincides with a sequence that can bind the haematopoietic transcription factor GATA. The inhibition of translation can also be reversed by treatment with inhibitors of casein kinase II or by injection into the nucleus of antibodies specific for the FRGY2 family of RNP proteins. We suggest that the -340 site influences the quality of the transcription complex such that transcripts are diverted to a nucleus-dependent translation inhibition pathway.

Novel insights into erythroid development revealed through in vitro differentiation of GATA-1 embryonic stem cells

Mouse embryonic stem (ES) cells lacking the transcription factor GATA-1 do not produce mature red blood cells either in vivo or in vitro. To define the consequences of GATA-1 loss more precisely, we used an in vitro ES cell differentiation assay that permits enumeration of primitive (EryP) and definitive (EryD) erythroid precursors and recovery of pure erythroid colonies. In contrast to normal ES cells, GATA-1- ES cells fail to generate EryP precursors. EryD precursors, however, are normal in number but undergo developmental arrest and death at the proerythroblast stage. Contrary to initial expectations, arrested GATA-1(-)-definitive proerythroblasts express GATA target genes at normal levels. Transcripts of the related factor GATA-2 are remarkably elevated in GATA-1- proerythroblasts. These findings imply substantial interchangeability of GATA factors in vivo and suggest that GATA-1 normally serves to repress GATA-2 during erythropoiesis. The approach used here is a paradigm for the phenotypic analysis of targeted mutations affecting hematopoietic development.

A novel, erythroid cell-specific murine transcription factor that binds to the CACCC element and is related to the Krüppel family of nuclear proteins

We describe a novel erythroid cell-specific cDNA (EKLF [erythroid Krüppel-like factor]) isolated by enriching for genes expressed in a mouse erythroleukemia cell line but not expressed in a mouse monocyte-macrophage cell line. The complete cDNA sequence is predicted to encode a protein of approximately 38,000 Da that contains a proline-rich amino domain and three TFIIIA-like zinc fingers within the carboxy domain. Additional sequence analyses reveal that the EKLF zinc fingers are most homologous to the Krüppel family of transcription factors and also allow us to predict potential DNA-binding target sites for the EKLF protein. On the basis of this prediction, we show that EKLF is able to bind the sequence CCA CAC CCT, an essential element of the beta-globin promoter. Its tissue distribution establishes that the EKLF transcript is expressed only in bone marrow and spleen, the two hematopoietic organs of the mouse, and analysis of murine cell lines indicates that EKLF expression is limited to erythroid and mast cell lines. Cotransfection assays establish that EKLF transcriptionally activates a target promoter that contains its DNA-binding site. The tissue expression pattern of EKLF, in conjunction with its function as a transcriptional activator, strongly suggests that the EKLF protein may be intimately involved in establishment and/or maintenance of the erythroid cell phenotype.

A novel, erythroid cell-specific murine transcription factor that binds to the CACCC element and is related to the Krüppel family of nuclear proteins

We describe a novel erythroid cell-specific cDNA (EKLF [erythroid Krüppel-like factor]) isolated by enriching for genes expressed in a mouse erythroleukemia cell line but not expressed in a mouse monocyte-macrophage cell line. The complete cDNA sequence is predicted to encode a protein of approximately 38,000 Da that contains a proline-rich amino domain and three TFIIIA-like zinc fingers within the carboxy domain. Additional sequence analyses reveal that the EKLF zinc fingers are most homologous to the Krüppel family of transcription factors and also allow us to predict potential DNA-binding target sites for the EKLF protein. On the basis of this prediction, we show that EKLF is able to bind the sequence CCA CAC CCT, an essential element of the beta-globin promoter. Its tissue distribution establishes that the EKLF transcript is expressed only in bone marrow and spleen, the two hematopoietic organs of the mouse, and analysis of murine cell lines indicates that EKLF expression is limited to erythroid and mast cell lines. Cotransfection assays establish that EKLF transcriptionally activates a target promoter that contains its DNA-binding site. The tissue expression pattern of EKLF, in conjunction with its function as a transcriptional activator, strongly suggests that the EKLF protein may be intimately involved in establishment and/or maintenance of the erythroid cell phenotype.

The regulation of human globin gene expression

The haemopoietic system provides a well-characterized and accessible system for studying the mechanisms of developmental regulation and differentiation in higher eukaryotes. Our current understanding of the steps involved in the early stages of differentiation are poorly understood but a great deal is now known about the mechanisms by which globin expression is regulated in cells committed to the erythroid lineage. Many of the critical cis-acting sequences and some of the important trans-acting factors involved have been identified and current work is focusing on how these interact to produce high levels of tissue-specific and developmentally regulated expression of the human globin genes.

Enhancer-dependent transcription of the epsilon-globin promoter requires promoter-bound GATA-1 and enhancer-bound AP-1/NF-E2

We analyzed epsilon-globin transcription in erythroid cells and in erythroid extracts to determine the requirements for enhancer-dependent expression of this gene. Mutations that abolished GATA-1 binding at a single position in the promoter prevented interaction with enhancers, whereas elimination of a second more distal promoter GATA-1 site had no effect. Deletion or mutation of the GATA-1 sites in either the human beta-globin locus control region DNase-hypersensitive site II enhancer or the chicken beta A/epsilon-globin enhancer did not diminish the ability of the enhancers to interact with the promoter. In contrast, mutation of the AP-1/NF-E2 sites in these enhancers resulted in elimination of enhancement. In vitro transcription of these constructs was promoter dependent and was not sensitive to abolition of GATA-1 binding in the promoter, consistent with the role of GATA-1 solely as a mediator of the enhancer effect. Thus, GATA-1 regulates the response of the epsilon-globin gene to enhancers through a specific site in the promoter and requires enhancer AP-1/NF-E2 binding to transduce the enhancer effect on transcription.

Enhancer-dependent transcription of the epsilon-globin promoter requires promoter-bound GATA-1 and enhancer-bound AP-1/NF-E2

We analyzed epsilon-globin transcription in erythroid cells and in erythroid extracts to determine the requirements for enhancer-dependent expression of this gene. Mutations that abolished GATA-1 binding at a single position in the promoter prevented interaction with enhancers, whereas elimination of a second more distal promoter GATA-1 site had no effect. Deletion or mutation of the GATA-1 sites in either the human beta-globin locus control region DNase-hypersensitive site II enhancer or the chicken beta A/epsilon-globin enhancer did not diminish the ability of the enhancers to interact with the promoter. In contrast, mutation of the AP-1/NF-E2 sites in these enhancers resulted in elimination of enhancement. In vitro transcription of these constructs was promoter dependent and was not sensitive to abolition of GATA-1 binding in the promoter, consistent with the role of GATA-1 solely as a mediator of the enhancer effect. Thus, GATA-1 regulates the response of the epsilon-globin gene to enhancers through a specific site in the promoter and requires enhancer AP-1/NF-E2 binding to transduce the enhancer effect on transcription.

Murine erythroleukemia cells contain two distinct GATA-binding proteins that have different patterns of expression during cellular differentiation

GATA-1 is a major transcription factor of the erythroid lineage that has been implicated in the induced expression of a variety of red cell-specific genes during terminal differentiation of murine erythroleukemia cells. Although the GATA-1 protein is present at nearly equal levels before and after differentiation of murine erythroleukemia cells, in this study it was found that in the early commitment stages of the differentiation program there is a transient decrease in the GATA-1 mRNA and DNA binding activity levels due to a temporary block in transcription of the gene. Moreover, using a whole cell extraction procedure it was discovered that murine erythroleukemia cells contain a second GATA binding activity (denoted GATA-rel) which appears to be distinct from the GATA-1 factor based on its non-reactivity to two GATA-1 antisera. This protein has a limited tissue specificity, as it could not be detected in extracts from CHO, NIH 3T3, or COS cells. Similarly to the GATA-1 DNA-binding activity, the GATA-rel activity decreased during the early stages of differentiation. However, unlike GATA-1, GATA-rel activity did not return to pre-induced levels at later times. These results suggest that changes in gene expression during erythroid terminal differentiation may involve an interplay on levels of different GATA-binding factors.

The developmental regulation of the human zeta-globin gene in transgenic mice employing beta-galactosidase as a reporter gene

We have investigated the developmental and tissue specific expression of the human embryonic zeta-globin gene in transgenic mice. A construct containing 550 bp of zeta-globin 5' flanking region, fused to a beta-galactosidase (lacZ) reporter gene and linked to the locus control region (LCR)-like alpha positive regulatory element (alpha PRE) was employed for the production of transgenic mice. Firstly, we compared the number of live born transgenic mice containing this construct to the number of live born transgenic mice containing the entire zeta-globin gene linked to the alpha PRE or the beta LCR. Data showed that 12% of mice generated from eggs injected with zeta-promoter/lacZ/alpha PRE DNA were transgenic compared to only 2% of mice generated from eggs injected with the entire zeta-globin gene linked to the alpha PRE or the beta LCR. The reduced number of live born transgenic mice containing the latter constructs suggests that death of transgenic embryos, possibly due to thalassaemia, may be occurring. X-gal staining of whole embryos containing the lacZ gene revealed that zeta-globin promoter activity was most pronounced at 8.5-9.5 days of development and was restricted to erythroid cells. By 15 days of development, no zeta-globin promoter activity was detected. These results suggest that the alpha PRE can direct high level expression from the zeta-globin promoter and that sequences required for the correct tissue and developmental specific expression of the human zeta-globin gene are present within 550 bp's of 5' flanking region. Sequences within the body of the zeta-globin gene or 3' of the cap site do not appear to be necessary for correct zeta-globin developmental regulation.

Differential factor binding at the promoter of early baculovirus gene PE38 during viral infection: GATA motif is recognized by an insect protein

Regulatory elements interacting with DNA-binding proteins have been investigated in the promoter sequence of the early PE38 gene in the Autographa californica nuclear polyhedrosis virus (AcNPV). A GATA motif located 50 nucleotides upstream of the PE38 transcriptional start site is recognized differentially in the course of infection. As demonstrated by footprint and gel mobility shift assays, the GATA sequences TTATCT are protected by nuclear extracts from uninfected Spodoptera frugiperda cells and from S. frugiperda cells early postinfection (p.i.) but not by S. frugiperda cell extracts isolated 40 h p.i. We have compared the binding capacity of the insect GATA-like protein with that of the vertebrate GATA-1 factor identified as erythroid-specific factor. Our results indicate that a factor present in mouse erythroleukemia cells, presumably GATA-1, can bind to the insect GATA motif and vice versa. Evidence from transient expression studies suggests that the mutated GATA sequences do not influence PE38 promoter activity in cell culture.

Rescue of erythroid development in gene targeted GATA-1- mouse embryonic stem cells

Development of definitive (fetal liver-derived) red cells is blocked by a targeted mutation in the gene encoding the transcription factor GATA-1. We used in vitro differentiation of GATA-1- mouse embryonic stem (ES) cells to reveal a requirement for GATA-1 during primitive (yolk sac-derived) erythropoiesis and to establish a rescue assay. We show that the block to development includes primitive, as well as definitive, erythroid cells and is complete at the level of globin RNA expression; that the introduction of a normal GATA-1 gene restores developmental potential both in vivo and in vitro; and that efficient rescue is dependent on a putative autoregulatory GATA-motif in the distal promoter. Use of in vitro differentiated ES cells bridges a gap between conventional approaches to gene function in cell lines and analysis of loss of function mutations in the whole animal.

Isolation and characterization of the gene encoding EF-1 alpha O, an elongation factor 1-alpha expressed during early development of Xenopus laevis

In Xenopus laevis, the gene encoding the elongation factor 1-alpha variant EF-1 alpha O, where O stands for oocyte, is expressed in oocytes and early embryos. A genomic library from X. laevis was screened with a cDNA probe coding for EF-1 alpha O. Two recombinant phages were isolated, one of which carries an entire EF-1 alpha O gene. This clone was characterized by restriction enzyme mapping and sequencing. Comparison of cDNA and genomic sequences revealed that EF-1 alpha O consists of seven exons spanning about 6.5 kb. The structure of the gene is very homologous to the human EF-1 alpha gene, as all locations of the splice junctions are conserved between the two genes. The sequence immediately upstream from the transcription start point (tsp) contains a CCAAT box, but does not contain either a TATA box or a Sp1-binding site. Interestingly, this sequence has a sequence homologous to the negative regulatory element from the TFIIIA promoter. A region located about 400 bp upstream from the tsp contains an additional number of possible regulatory sequence elements. The first intron contains G + C-rich elements which exist both isolated and as part of longer inverted repeats. Furthermore, one octamer and four Sp1-binding sites are found in this intron.

elt-1, an embryonically expressed Caenorhabditis elegans gene homologous to the GATA transcription factor family

The short, asymmetrical DNA sequence to which the vertebrate GATA family of transcription factors binds is present in some Caenorhabditis elegans gene regulatory regions: it is required for activation of the vitellogenin genes and is also found just 5' of the TATA boxes of tra-2 and the msp genes. In vertebrates GATA-1 is specific to erythroid lineages, whereas GATA-2 and GATA-3 are present in multiple tissues. In an effort to identify the trans-acting factors that may recognize this sequence element in C. elegans, we used a degenerate oligonucleotide to clone a C. elegans homolog to this gene. We call this gene elt-1 (erythrocytelike transcription factor). It is single copy and specifies a 1.75-kb mRNA that is present predominantly, if not exclusively, in embryos. The region of elt-1 encoding two zinc fingers is remarkably similar to the DNA-binding domain of the vertebrate GATA-binding proteins. However, outside of the DNA-binding domains the amino acid sequences are quite divergent. Nevertheless, introns are located at identical or nearly identical positions in elt-1 and the mouse GATA-1 gene. In addition, elt-1 mRNA is trans-spliced to the 22-base untranslated leader, SL1. The DNA upstream of the elt-1 TATA box contains eight copies of the GATA recognition sequence within the first 300 bp, suggesting that elt-1 may be autogenously regulated. Our results suggest that the specialized role of GATA-1 in erythroid gene expression was derived after separation of the nematodes and the line that led to the vertebrates, since C. elegans lacks an erythroid lineage.

elt-1, an embryonically expressed Caenorhabditis elegans gene homologous to the GATA transcription factor family

The short, asymmetrical DNA sequence to which the vertebrate GATA family of transcription factors binds is present in some Caenorhabditis elegans gene regulatory regions: it is required for activation of the vitellogenin genes and is also found just 5' of the TATA boxes of tra-2 and the msp genes. In vertebrates GATA-1 is specific to erythroid lineages, whereas GATA-2 and GATA-3 are present in multiple tissues. In an effort to identify the trans-acting factors that may recognize this sequence element in C. elegans, we used a degenerate oligonucleotide to clone a C. elegans homolog to this gene. We call this gene elt-1 (erythrocytelike transcription factor). It is single copy and specifies a 1.75-kb mRNA that is present predominantly, if not exclusively, in embryos. The region of elt-1 encoding two zinc fingers is remarkably similar to the DNA-binding domain of the vertebrate GATA-binding proteins. However, outside of the DNA-binding domains the amino acid sequences are quite divergent. Nevertheless, introns are located at identical or nearly identical positions in elt-1 and the mouse GATA-1 gene. In addition, elt-1 mRNA is trans-spliced to the 22-base untranslated leader, SL1. The DNA upstream of the elt-1 TATA box contains eight copies of the GATA recognition sequence within the first 300 bp, suggesting that elt-1 may be autogenously regulated. Our results suggest that the specialized role of GATA-1 in erythroid gene expression was derived after separation of the nematodes and the line that led to the vertebrates, since C. elegans lacks an erythroid lineage.

Functional analysis and in vivo footprinting implicate the erythroid transcription factor GATA-1 as a positive regulator of its own promoter

Transcription of erythroid-expressed genes and normal erythroid development in vivo are dependent on a regulatory protein (GATA-1) that recognizes a consensus GATA motif. GATA-1 expression is itself restricted to erythroid progenitors and to two related hematopoietic lineages, megakaryocytes and mast cells. During cellular maturation the levels of GATA-1 RNA and protein increase progressively. In an effort to delineate mechanisms by which this pivotal transcription factor is itself regulated we have characterized the mouse GATA-1 gene and cis-elements within its promoter. We find that the isolated promoter retains cell specificity exhibited by the intact gene. Full promoter activity requires the presence of proximal CACCC box sequences and an upstream, double GATA motif that binds a single GATA-1 molecule in an asymmetric fashion. Using in vivo footprinting of mouse erythroleukemic cells we detect protein binding in vivo to both cis-elements. On the basis of these findings we propose that a positive feedback loop mediated through GATA-1 serves two complementary functions: maintenance of the differentiated state by locking the promoter into an "on" state, and programming the progressive increase in protein content throughout cellular maturation.

Transcriptional role of a conserved GATA-1 site in the human epsilon-globin gene promoter

The epsilon-globin gene is the first of the human beta-like globin genes to be expressed during development. We have analyzed protein-DNA interactions in the epsilon-globin promoter region by DNase I footprinting and electrophoretic mobility shift experiments using nuclear extracts from K562 human erythroid cells and from nonerythroid HeLa cells. A restricted set of ubiquitous proteins, including Sp1, bound to regions of the promoter including the CACCC and CCAAT sites. Three interactions, at positions -213, -165, and +3 relative to the transcription start site, were erythroid specific and corresponded to binding of GATA-1, a transcription factor highly restricted to the erythroid lineage. Interestingly, the GATA-1 site at -165 has been conserved in the promoters of 10 mammalian embryonic globin genes. Point mutations demonstrate that GATA-1 binding to this site is necessary for interaction with an erythroid-specific enhancer but that in the absence of an enhancer, GATA-1 does not increase transcription.

Transcriptional role of a conserved GATA-1 site in the human epsilon-globin gene promoter

The epsilon-globin gene is the first of the human beta-like globin genes to be expressed during development. We have analyzed protein-DNA interactions in the epsilon-globin promoter region by DNase I footprinting and electrophoretic mobility shift experiments using nuclear extracts from K562 human erythroid cells and from nonerythroid HeLa cells. A restricted set of ubiquitous proteins, including Sp1, bound to regions of the promoter including the CACCC and CCAAT sites. Three interactions, at positions -213, -165, and +3 relative to the transcription start site, were erythroid specific and corresponded to binding of GATA-1, a transcription factor highly restricted to the erythroid lineage. Interestingly, the GATA-1 site at -165 has been conserved in the promoters of 10 mammalian embryonic globin genes. Point mutations demonstrate that GATA-1 binding to this site is necessary for interaction with an erythroid-specific enhancer but that in the absence of an enhancer, GATA-1 does not increase transcription.

Identification of transcriptional regulatory activity within the 5' A-type monomer sequence of the mouse LINE-1 retroposon

LINE-1 (L1) is a retroposon found in all mammals. In the mouse, approximately 10% of L1 elements are full-length and can be grouped into two classes, A or F, based upon the type of monomer sequence repeated at the 5' end. In order to test for promoter activity in the 5' end of the A-type mouse L1 element, we cloned several different A-monomers into a promoterless chloramphenicol acetyltransferase (CAT) vector. The A-monomer constructs varied in their ability to regulate transcription of the CAT gene, exhibiting CAT activity 16-37% of that detected with the Rous sarcoma virus promoter and enhancer. A series of A-monomer deletions were tested for their ability to regulate CAT expression and gel retardation experiments were performed to identify regions of the A-monomer that may be involved in L1 transcriptional regulation. A-monomer sequences are usually found repeated 2-5 times at the 5' end of a full-length mouse L1. In the absence of long terminal repeats or an internal promoter, the tandem array of A-monomers may provide a mechanism for A-type L1 elements to generate transcripts containing transcriptional regulatory sequences.

Regulated expression of globin chains and the erythroid transcription factor GATA-1 during erythropoiesis in the developing mouse

Erythropoiesis in vertebrates is characterized by sequential changes in erythropoietic site, erythroblast morphology, and hemoglobin synthesis. We have examined the expression of globin chains and the major erythroid transcription factor GATA-1 (previously known as GF-1/NF-E1/Eryf 1) from days 7.5 to 17.5 of mouse development. mRNAs for embryonic (epsilon y2, beta H1, and zeta) and adult (alpha and beta) globin chains were quantitated by RNase protection assays. Switching of globins within the alpha-globin cluster (alpha and zeta) was not strictly coordinated with that within the beta-globin cluster (epsilon y2, beta H1, and beta). Regulation of globin switches during development was primarily transcriptional. Of particular note, we found two developmental switches (beta H1 to epsilon y2 and epsilon y2 to beta) in the mouse, more analogous than previously thought to shifts found in human development. The erythroid transcription factor GATA-1, believed to be a principal regulator of genes expressed in erythroid cells, first appeared in the embryo in yolk sac at the time of blood island formation and remained at a low level during embryonic erythropoiesis (8 to 11 days) relative to that found later in fetal liver (12 to 15 days). The rise in GATA-1 mRNA in fetal liver paralleled and preceded the rapid accumulation of adult beta-globin RNA. RNase protection assays and a GATA-1-specific peptide antiserum were used to establish that a single GATA-1 polypeptide is expressed throughout mouse development. Overall, these findings suggest that the levels of this erythroid transcription factor during development may contribute to the differential gene activation characteristic of definitive versus primitive erythropoiesis.

Regulated expression of globin chains and the erythroid transcription factor GATA-1 during erythropoiesis in the developing mouse

Erythropoiesis in vertebrates is characterized by sequential changes in erythropoietic site, erythroblast morphology, and hemoglobin synthesis. We have examined the expression of globin chains and the major erythroid transcription factor GATA-1 (previously known as GF-1/NF-E1/Eryf 1) from days 7.5 to 17.5 of mouse development. mRNAs for embryonic (epsilon y2, beta H1, and zeta) and adult (alpha and beta) globin chains were quantitated by RNase protection assays. Switching of globins within the alpha-globin cluster (alpha and zeta) was not strictly coordinated with that within the beta-globin cluster (epsilon y2, beta H1, and beta). Regulation of globin switches during development was primarily transcriptional. Of particular note, we found two developmental switches (beta H1 to epsilon y2 and epsilon y2 to beta) in the mouse, more analogous than previously thought to shifts found in human development. The erythroid transcription factor GATA-1, believed to be a principal regulator of genes expressed in erythroid cells, first appeared in the embryo in yolk sac at the time of blood island formation and remained at a low level during embryonic erythropoiesis (8 to 11 days) relative to that found later in fetal liver (12 to 15 days). The rise in GATA-1 mRNA in fetal liver paralleled and preceded the rapid accumulation of adult beta-globin RNA. RNase protection assays and a GATA-1-specific peptide antiserum were used to establish that a single GATA-1 polypeptide is expressed throughout mouse development. Overall, these findings suggest that the levels of this erythroid transcription factor during development may contribute to the differential gene activation characteristic of definitive versus primitive erythropoiesis.

Transcriptional activation and DNA binding by the erythroid factor GF-1/NF-E1/Eryf 1

The murine, erythroid DNA-binding protein GF-1 (also known as NF-E1, Eryf 1), a 413-amino acid polypeptide with two novel finger domains of the Cx-Cx variety, recognizes a consensus GATA motif present in cis elements of the majority of erythroid-expressed genes. We have performed a structure-function analysis of this protein to evaluate its potential as a transcriptional activator and to examine the role of the finger domains in DNA binding. Using a cotransfection assay, we find that GF-1 is a potent transcriptional activator with several activation domains but that this is revealed only in heterologous cells and with reporters containing minimal promoters onto which either a single or multiple GATA-binding sites are placed. The two fingers of GF-1 are functionally distinct and cooperate to achieve specific, stable DNA binding. The amino finger is necessary only for full specificity and stability of binding, whereas the carboxyl finger is required for binding. The role of each finger is more pronounced with some GATA-binding sites than with others, suggesting a diversity of interactions between GF-1 and different target sites. The complex activation and DNA-binding properties of GF-1 are likely to contribute to the ability of this single protein to participate widely in gene expression throughout erythroid development.