Key residues characteristic of GATA N-fingers are recognized by FOG

The regulatory function of GATA3 on immune response in Japanese flounder (Paralichthys olivaceus)

GATA3 belongs to the GATA family, and it could interact with the target gene promoter. It has been reported to play a central role in regulating lymphocyte differentiation. In this study, the GATA3 cDNA sequence was identified by a homologous clone and the RACE technology from Japanese flounder (Paralichthys olivaceus). The full-length of the GATA3 cDNA sequence was 2904 bp, including 1332 bp open reading frame (ORF), 265 bp 5 '-untranslated region (5' UTR), and 1308 bp 3 '-UTR, encoding 443 amino acids. GATA3 protein sequence was conserved in vertebrates and invertebrates, including two zinc finger domains. qRT-PCR showed that the expression of GATA3 was high in the gill, kidney, and spleen. Expression of GATA3 slowly increased at the earlier stages and culminated at the late gastrula and somatic stages. Immunohistochemistry (IHC) results showed that the GATA3 protein was expressed in lymphocyte cells, undifferentiated basal and pillar cells of the gills, as well as lymphocyte cells and melanin macrophages of the kidney. The expression of GATA3 was significantly regulated in tissues and different types of lymphocytes after stimulation with Edwardsiella tarda. Dual-luciferase reporter assay indicated that the GATA3 protein could directly interact with promoters of target genes involved in the immune response. These findings suggested that GATA3 plays a major role in regulating the immune response. This study provided a theoretical basis for the immune response mechanism of teleost and a useful reference for later research on fish immunology.

GATA-3 in Atlantic salmon (Salmo salar): Tissue distribution and its regulation of IL-4/13a promoter

GATA3 is a transcription factor that plays an important role in T cell lineage differentiation and T-helper 2 (Th2) type immune responses. In this study, we developed two rat antibodies against Atlantic salmon GATA-3 (anti-rSsGATA-3a and anti-rSsGATA-3b, respectively). The western blotting and immunofluorescence results showed that anti-rSsGATA-3b antibodies recognized endogenous SsGATA-3 proteins, while the anti-rSsGATA-3a antibodies did not bind SsGATA-3. Immunohistochemical analysis revealed that SsGATA-3 positive cells were detected in all tissues tested, with relatively high number of immune reactive cells in the gills and spleen. Furthermore, the immunohistochemical study revealed that SsGATA-3 was expressed in pillar cells, epithelial cells, chondrocytes, perichondrium cells, and some undifferentiated basal cells. In addition, we determined 577 bp of the upstream promoter sequence of SsIL-4/13a and found four motifs that matched SsGATA-3 binding sites. The promoter regions of SsIL-4/13a were assessed by transfecting four deletion reporter constructs and SsGATA-3 overexpression plasmids. The result showed that SsGATA-3 enhanced the activity of SsIL-4/13a promoters within the region ranging from -317 to -302 bp upstream of the transcriptional start site. Antibodies against Th2 markers such as GATA-3 are valuable in addressing the diversity of T cell responses in fish.

Genome-Wide Identification and Functional Characterization of GATA Transcription Factor Gene Family in Alternaria alternata

In the present study, we identified six GATA transcription factors (AaAreA, AaAreB, AaLreA, AaLreB, AaNsdD, and AaSreA) and characterized their functions in response to environmental stress and virulence in the tangerine pathotype of Alternaria alternata. The targeted gene knockout of each of the GATA-coding genes decreased the growth to varying degrees. The mutation of AaAreA, AaAreB, AaLreB, or AaNsdD decreased the conidiation. All the GATA transcription factors were found to be required for tolerance to cumyl hydroperoxide and tert-butyl-hydroperoxide (oxidants) and Congo red (a cell-wall-destructing agent). Pathogenicity assays assessed on detached citrus leaves revealed that mutations of AaAreA, AaLreA, AaLreB, or AaNsdD significantly decreased the fungal virulence. A comparative transcriptome analysis between the ∆AreA mutant and the wild-type strain revealed that the inactivation of AaAreA led to alterations in the expression of genes involved in a number of biological processes, including oxidoreductase activity, amino acid metabolism, and secondary metabolite biogenesis. Taken together, our findings revealed that GATA-coding genes play diverse roles in response to environmental stress and are important regulators involved in fungal development, conidiation, ROS detoxification, as well as pathogenesis. This study, for the first time, systemically underlines the critical role of GATA transcription factors in response to environmental stress and virulence in A. alternata.

GATA1 mutations in red cell disorders

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

GATA4 is a transcriptional regulator of R-spondin1 in Japanese flounder (Paralichthys olivaceus)

GATA4 is a well-known transcription factor of the GATA family implicated in regulation of sex determination and gonadal development in mammals. In this study, we cloned the full-length cDNA of Paralichthys olivaceus gata4 (Po-gata4). Phylogenetic, gene structure, and synteny analysis showed that Po-GATA4 is homologous to GATA4 of teleost and tetrapod. Po-gata4 transcripts were detected in Sertoli cells, spermatogonia, oogonia and oocytes, with higher transcript levels overall in the testis than the ovary. The promoter region of P. olivaceus R-spondin1was found to contain a GATA4-binding motif. Results of CBA (cleaved amplified polymorphic sequence-based binding assay) indicated that GATA4 could indeed bind to the promoter sequence of R-spondin1. Moreover, human GATA4 recombinant protein could upregulate R-spondin1 in P. olivaceus ovary cells and FBCs (flounder brain cell line). In FBCs, overexpression of Po-gata4 resulted in elevated transcript levels of R-spondin1. Taken together, our results indicate that Po-GATA4 is involved in gonadal development by regulating R-spondin1 expression.

Mechanistic insights into the protective impact of zinc on sepsis

Sepsis, a systemic inflammation as a response to a bacterial infection, is a huge unmet medical need. Data accumulated over the last decade suggest that the nutritional status of patients as well as composition of their gut microbiome, are strongly linked with the risk to develop sepsis, the severity of the disease and prognosis. In particular, the essential micronutrient zinc is essential in the resistance against sepsis and has shown to be protective in animal models as well as in human patients. The potential mechanisms by which zinc protects in sepsis are discussed in this review paper: we will focus on the inflammatory response, chemotaxis, phagocytosis, immune response, oxidative stress and modulation of the microbiome. A full understanding of the mechanism of action of zinc may open new preventive and therapeutic interventions in sepsis.

The Role of GATA in Mammalian Reproduction

GATA transcription factors are emerging as critical players in mammalian reproductive development and function. GATA-4 contributes to fetal male gonadal development by regulating genes mediating Müllerian duct regression and the onset of testosterone production. GATA-2 expression appears to be sexually dimorphic being transiently expressed in the germ cell lineage of the fetal ovary but not the fetal testis. In the reproductive system, GATA-1 is exclusively expressed in Sertoli cells at specific seminiferous tubule stages. In addition, GATA-4 and GATA-6 are localized primary to ovarian and testicular somatic cells. The majority of cell transfection studies demonstrate that GATA-1 and GATA-4 can stimulate inhibin subunit gene promoter constructs. Other studies provide strong evidence that GATA-4 and GATA-6 can activate genes mediating gonadal cell steroidogenesis. GATA-2 and GATA-3 are found in pituitary and placental cells and can regulate alpha-glycoprotein subunit gene expression. Gonadal expression and activation of GATAs appear to be regulated in part by gonadotropin signaling via the cyclic AMP-protein kinase A pathway. This review will cover the current knowledge regarding GATA expression and function at all levels of the reproductive axis.

Interaction between ANXA1 and GATA-3 in Immunosuppression of CD4+ T Cells

Decreased Th1/Th2 ratio is one of the major characteristics of immunosuppression in sepsis. Both membrane adhesive protein Annexin-A1 (ANXA1) and transcription factor GATA-3 have been reported to play important roles in T cell differentiation. However, the relationship between ANXA1 and GATA-3 in Th1/Th2 shift is unknown. Our study investigated the interaction effects of ANXA1 and GATA-3 to influence T cell differentiation in CD4+ T cells. We found that GATA-3 and ANXA1 were coexpressed on Th0/Th1/Th2 cytoplasm and nuclear. Overexpressed ANXA1 significantly increased the expression of IFNγ and reduced IL-4 expression in T cells, while ANXA1-silenced T cells exhibited decreased production of IFNγ and increased production of IL-4. Knockdown of ANXA1 promoted higher expression level of GATA-3 and low level of T-box transcription factor (T-bet/Tbx21). Further study demonstrated that ANXA1 regulated GATA-3 expression through the formyl peptide receptor like-1 (FPRL-1) downstream signaling pathways ERK and PKB/Akt. These results suggested that ANXA1 modulates GATA-3/T-bet expression induced Th0/Th1 differentiation. Moreover, we found that GATA-3 inhibited ANXA1 expression by binding to its promoter for the first time. It is proposed that the interactions between ANXA1 and GATA-3 may provide clues to understand the immunosuppression and have potential as new therapeutic targets in immunotherapy after sepsis.

GATA1 directly mediates interactions with closely spaced pseudopalindromic but not distantly spaced double GATA sites on DNA

The transcription factor GATA1 helps regulate the expression of thousands of genes involved in blood development, by binding to single or double GATA sites on DNA. An important part of gene activation is chromatin looping, the bringing together of DNA elements that lie up to many thousands of basepairs apart in the genome. It was recently suggested, based on studies of the closely related protein GATA3, that GATA-mediated looping may involve interactions of each of two zinc fingers (ZF) with distantly spaced DNA elements. Here we present a structure of the GATA1 ZF region bound to pseudopalindromic double GATA site DNA, which is structurally equivalent to a recently-solved GATA3-DNA complex. However, extensive analysis of GATA1-DNA binding indicates that although the N-terminal ZF (NF) can modulate GATA1-DNA binding, under physiological conditions the NF binds DNA so poorly that it cannot play a direct role in DNA-looping. Rather, the ability of the NF to stabilize transcriptional complexes through protein-protein interactions, and thereby recruit looping factors such as Ldb1, provides a more compelling model for GATA-mediated looping.

B-GATA transcription factors - insights into their structure, regulation, and role in plant development

GATA transcription factors are evolutionarily conserved transcriptional regulators that recognize promoter elements with a G-A-T-A core sequence. In comparison to animal genomes, the GATA transcription factor family in plants is comparatively large with approximately 30 members. Here, we review the current knowledge on B-GATAs, one of four GATA factor subfamilies from Arabidopsis thaliana. We show that B-GATAs can be subdivided based on structural features and their biological function into family members with a C-terminal LLM- (leucine-leucine-methionine) domain or an N-terminal HAN- (HANABA TARANU) domain. The paralogous GNC (GATA, NITRATE-INDUCIBLE, CARBON-METABOLISM INVOLVED) and CGA1/GNL (CYTOKININ-INDUCED GATA1/GNC-LIKE) are introduced as LLM-domain containing B-GATAs from Arabidopsis that control germination, greening, senescence, and flowering time downstream from several growth regulatory signals. Arabidopsis HAN and its monocot-specific paralogs from rice (NECK LEAF1), maize (TASSEL SHEATH1), and barley (THIRD OUTER GLUME) are HAN-domain-containing B-GATAs with a predominant role in embryo development and floral development. We also review GATA23, a regulator of lateral root initiation from Arabidopsis that is closely related to GNC and GNL but has a degenerate LLM-domain that is seemingly specific for the Brassicaceae family. The Brassicaceae-specific GATA23 and the monocot-specific HAN-domain GATAs provide evidence that neofunctionalization of B-GATAs was used during plant evolution to expand the functional repertoire of these transcription factors.

GATA-3 function in innate and adaptive immunity

The zinc-finger transcription factor GATA-3 has received much attention as a master regulator of T helper 2 (Th2) cell differentiation, during which it controls interleukin-4 (IL-4), IL-5, and IL-13 expression. More recently, GATA-3 was shown to contribute to type 2 immunity through regulation of group 2 innate lymphoid cell (ILC2) development and function. Furthermore, during thymopoiesis, GATA-3 represses B cell potential in early T cell precursors, activates TCR signaling in pre-T cells, and promotes the CD4(+) T cell lineage after positive selection. GATA-3 also functions outside the thymus in hematopoietic stem cells, regulatory T cells, CD8(+) T cells, thymic natural killer cells, and ILC precursors. Here we discuss the varied functions of GATA-3 in innate and adaptive immune cells, with emphasis on its activity in T cells and ILCs, and examine the mechanistic basis for the dose-dependent, developmental-stage- and cell-lineage-specific activity of this transcription factor.

A conserved zinc finger transcription factor GATA involving in the hemocyte production of scallop Chlamys farreri

GATA are a family of transcription factors characterized by their ability to bind to the DNA sequence "GATA", and involved in a myriad of cellular processes. GATA1/2/3 factors are known as the hematopoietic GATA factors, which play dominated roles in regulating hematopoiesis. In the present study, a gene encoding GATA transcription factor (designed as CfGATA) was cloned and characterized from the scallop Chlamys farreri. The full-length cDNA of CfGATA is of 2058 bp encoding a predicted polypeptide of 457 amino acids with two conserved zinc finger domains, which shared high similarity with other reported GATA1/2/3 proteins. The mRNA transcripts of CfGATA showed higher expression in gills, hepatopancreas, hemocytes and heart, and the CfGATA protein expressed in HEK293 cells was found to be localized specifically in the nuclei. The recombinant CfGATA protein (rCfGATA) exhibited strong ability to bind specific WGATAR DNA sequence by electrophoretic mobility shift assay in vitro. After CfGATA gene was silenced by RNA interference, the hemocyte renewal rate and circulating total hemocyte count (THC) decreased significantly, which was 7.85-fold and 19.46-fold lower than that of PBS control, respectively (P < 0.05). After LPS stimulation, the expression level of CfGATA mRNA decreased significantly in the hemocytes of PBS or EGFP dsRNA treated scallops, which was accompanied by the increase of hemocyte renewal rate and the reduced circulating THC at 24 h. In contrast, the hemocyte renewal rate and circulating THC did not change significantly in CfGATA gene interfered scallops after LPS stimulation. These results suggested that CfGATA, as a conserved GATA1/2/3 transcription factor, plays essential roles in regulating hemocyte production of scallop.

A study of the role of GATA4 polymorphism in cardiovascular metabolic disorders

BACKGROUND

The study was designed to evaluate the association of GATA4 gene polymorphism with coronary artery disease (CAD) and its metabolic risk factors, including dyslipidaemic disorders, obesity, type 2 diabetes and hypertension, following a preliminary study linking early onset of CAD in heterozygous familial hypercholesterolaemia to chromosome 8, which harbours the GATA4 gene.

RESULTS

We first sequenced the whole GATA4 gene in 250 individuals to identify variants of interest and then investigated the association of 12 single-nucleotide polymorphisms (SNPs) with the disease traits using Taqman chemistry in 4,278 angiographed Saudi individuals. Of the studied SNPs, rs804280 (1.14 (1.03 to 1.27); p = 0.009) was associated with CAD (2,274 cases vs 2,004 controls), hypercholesterolaemia (1,590 vs 2,487) (1.61 (1.03-2.52); p = 0.037) and elevated low-density lipoprotein-cholesterol (hLDLC) (575 vs 3,404) (1.87 (1.10-3.15); p = 0.020). Additionally, rs3729855_T (1.52 (1.09-2.11; p = 0.013)) and rs17153743 (AG + GG) (2.30 (1.30-4.26); p = 0.005) were implicated in hypertension (3,312 vs 966), following adjustments for confounders. Furthermore, haplotypes CCCGTGCC (χ2 = 4.71; p = 0.041) and GACCCGTG (χ2 = 3.84; p = 0.050) constructed from the SNPs were associated with CAD and ACCCACGC (χ2 = 6.58; p = 0.010) with myocardial infarction, while hypercholesterolaemia (χ2 = 3.86; p = 0.050) and hLDLC (χ2 = 4.94; p = 0.026) shared the AACCCATGT, and AACCCATGTC was associated with hLDLC (χ2 = 4.83; p = 0.028). A 10-mer GACCCGCGCC (χ2 = 7.59; p = 0.006) was associated with obesity (1,631 vs 2,362), and the GACACACCC (χ2 = 4.05; p = 0.044) was implicated in type 2 diabetes mellitus 2,378 vs 1,900).

CONCLUSION

Our study implicates GATA4 in CAD and its metabolic risk traits. The finding also points to the possible involvement of yet undefined entities related to GATA4 transcription activity or gene regulatory pathways in events leading to these cardiovascular disorders.

Contribution of GATA1 dysfunction to multi-step leukemogenesis

In mammals, hematopoietic homeostasis is maintained by a fine-tuned balance among the self-renewal, proliferation, differentiation and survival of hematopoietic stem cells and their progenies. Each process is also supported by the delicate balance of the expression of multiple genes specific to each process. GATA1 is a transcription factor that comprehensively regulates the genes that are important for the development of erythroid and megakaryocytic cells. Accumulating evidence supports the notion that defects in GATA1 function are intimately linked to hematopoietic disorders. In particular, the somatic mutation of the GATA1 gene, which leads to the production of N-terminally truncated GATA1, contributes to the genesis of transient myeloproliferative disorder and acute megakaryoblastic leukemia in infants with Down syndrome. Similarly, a mutation in the GATA1 regulatory region that reduces GATA1 expression is involved in the onset of erythroid leukemia in mice. In both cases, the accumulation of immature progenitor cells caused by GATA1 dysregulation underlies the pathogenesis of the leukemia. This review provides a summary of multi-step leukemogenesis with a focus on GATA1 dysfunction.

The transcription factor Sox4 is a downstream target of signaling by the cytokine TGF-β and suppresses T(H)2 differentiation

Sox4 is a transcription factor that regulates various developmental processes. Here we show that Sox4 was induced by TGF-β and negatively regulated the transcription factor GATA-3, the master regulator of function of T helper type 2 (T(H)2) cells, by two distinct mechanisms. First, Sox4 bound directly to GATA-3, preventing its binding to GATA-3 consensus DNA sequences. Second, Sox4 bound to the promoter region of the gene encoding interleukin 5 (IL-5), a T(H)2 cytokine, and prevented binding of GATA-3 to this promoter. T(H)2 cell-driven airway inflammation was modulated by alterations in Sox4 expression. Thus, Sox4 acted as a downstream target of TGF-β to inhibit GATA-3 function, T(H)2 differentiation and T(H)2 cell-mediated inflammation.

Mature erythrocyte membrane homeostasis is compromised by loss of the GATA1-FOG1 interaction

GATA1 plays essential roles in erythroid gene expression. The N-terminal finger of GATA1 (GATA1-Nf) is important for association with FOG1. Substitution mutations in GATA1-Nf, such as GATA1V205M that diminish the GATA1-FOG1 association, have been identified in human thrombocytopenia and anemia cases. A mouse model of human thrombocytopenia has been established using a transgenic complementation rescue approach; GATA1-deficient mice were successfully rescued from embryonic lethality by excess expression of GATA1V205G, but rescued adult mice suffered from severe thrombocytopenia. In this study, we examined GATA1-deficient mice rescued with GATA1V205G at a comparable level to endogenous GATA1. Mice rescued with this level of GATA1V205G rarely survive to adulthood. Rescued newborns suffered from severe anemia and jaundice accompanied with anisocytosis and spherocytosis. Expression of Slc4a1, Spna1, and Aqp1 genes (encoding the membrane proteins band-3, α-spectrin, and aquaporin-1, respectively) were strikingly diminished, whereas expression of other canonical GATA1-target genes, such as Alas2, were little affected. Lack of these membrane proteins provoked perturbation of membrane skeleton. Importantly, the red cells exhibited increased reactive oxygen species accumulation. These results thus demonstrate that the loss of the GATA1-FOG1 interaction causes a unique combination of membrane protein deficiency and disturbs the function of GATA1 in maintaining erythroid homeostasis.

Molecular characterizations and functional assessments of GATA-3 and its splice variant in Atlantic cod (Gadus morhua L.)

GATA-3 is a master transcription factor of the Th2 cells. We have identified GATA-3 cDNA and its splice variant in Atlantic cod. Cod GATA-3 (GmGATA-3) has a 1320 b p open reading frame encoding a polypeptide of 440 amino acids with two zinc finger domains that are well conserved within teleosts and higher vertebrates. The GATA-3 cDNA splice variant without zinc finger domains was shown to contain an 828 b p open reading frame encoding a polypeptide of 276 amino acids. Both GATA-3 proteins fused with RFP-tag were identified in or close to the nuclei 48 h after the plasmids were transfected in CHSE-214 cells. The full length GATA-3 with two zinc finger domains has a transcriptional function confirmed by transfection with GATA-3 reporter vector along with expression constructs of GATA-3 plasmids in CHSE-214 cells, whereas the GATA-3 splice variant without zinc finger domain did not enhance the activity of the GATA-3 reporter vector, and no interference was found between these two GATA-3 variants. RT-PCR analysis revealed that the two Atlantic cod GATA-3 variants were strongly expressed in the gills and infection with live Vibrio anguillarum induced the spleen expression of both GmGATA-3L and GmGATA-3S. Unexpectedly, PMA increased the expression of the GATA-3 splice variant in vivo and especially in vitro, with an increase of more than 100,000-fold in head kidney leukocytes at 24 and 48 h. On the other hand, there were no significant increases at the transcript level of full length GATA-3 between Poly I:C and β-glucan treatment groups compared to controls.

Friend of GATA (FOG) interacts with the nucleosome remodeling and deacetylase complex (NuRD) to support primitive erythropoiesis in Xenopus laevis

Friend of GATA (FOG) plays many diverse roles in adult and embryonic hematopoiesis, however the mechanisms by which it functions and the roles of potential interaction partners are not completely understood. Previous work has shown that overexpression of FOG in Xenopus laevis causes loss of blood suggesting that in contrast to its role in mammals, FOG might normally function to repress erythropoiesis in this species. Using loss-of-function analysis, we demonstrate that FOG is essential to support primitive red blood cell (RBC) development in Xenopus. Moreover, we show that it is specifically required to prevent excess apoptosis of circulating primitive RBCs and that in the absence of FOG, the pro-apoptotic gene Bim-1 is strongly upregulated. To identify domains of FOG that are essential for blood development and, conversely, to begin to understand the mechanism by which overexpressed FOG represses primitive erythropoiesis, we asked whether FOG mutants that are unable to interact with known co-factors retain their ability to rescue blood formation in FOG morphants and whether they repress erythropoiesis when overexpressed in wild type embryos. We find that interaction of FOG with the Nucleosome Remodeling and Deacetylase complex (NuRD), but not with C-terminal Binding Protein, is essential for normal primitive RBC development. In contrast, overexpression of all mutant and wild type constructs causes a comparable repression of primitive erythropoiesis. Together, our data suggest that a requirement for FOG and its interaction with NuRD during primitive erythropoiesis are conserved in Xenopus and that loss of blood upon FOG overexpression is due to a dominant-interfering effect.

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.

Transcriptional interactions between the pannier isoforms and the cofactor U-shaped during neural development in Drosophila

The pannier (pnr) gene of Drosophila melanogaster encodes two isoforms that belong to the family of GATA transcription factors. The isoforms share an expression domain in the wing discs where they exhibit distinct functions during regulation of the proneural achaete/scute (ac/sc) genes. We previously identified two regions in the pnr locus that drive reporter expression in transgenic lines in patterns that recapitulate the essential features of expression of the two isoforms. Here, we identify promoter regions driving isoform expression, showing that pnr-α regulatory sequences are close to the transcription start site while pnr-β expression requires functional interactions between proximal and distal regulatory elements. We find that the promoter domains necessary for reporter expression also mediate autoregulation of Pnr-β and repression of pnr-α by Pnr-β. The cofactor U-shaped (Ush), which is known to down-regulate the function of Pnr during thorax patterning postranscriptionally, in addition represses pnr-β required for ac/sc activation. Moreover, Ush negatively regulates its own expression, while the pnr isoforms positively regulate ush. Our study uncovers complex transcriptional interactions between the pnr isoforms and the cofactor Ush that may be important for regulation of proneural expression and thorax patterning.

ARR19 (androgen receptor corepressor of 19 kDa), an antisteroidogenic factor, is regulated by GATA-1 in testicular Leydig cells

ARR19 (androgen receptor corepressor of 19 kDa), which encodes for a leucine-rich protein, is expressed abundantly in the testis. Further analyses revealed that ARR19 was expressed in Leydig cells, and its expression was differentially regulated during Leydig cell development. Adenovirus-mediated overexpression of ARR19 in Leydig cells inhibited testicular steroidogenesis, down-regulating the expression of steroidogenic enzymes, which suggests that ARR19 is an antisteroidogenic factor. Interestingly, cAMP/luteinizing hormone attenuated ARR19 expression in a fashion similar to that of GATA-1, which was previously reported to be down-regulated by cAMP. Sequence analysis of the Arr19 promoter revealed the presence of two putative GATA-1 binding motifs. Further analyses with 5' deletion and point mutants of putative GATA-1 binding motifs showed that these GATA-1 binding sites were critical for high promoter activity. CREB-binding protein coactivated GATA-1 and markedly increased the activity of the Arr19 promoter. Both GATA-1 and CREB-binding proteins occupied the GATA-1 motifs within the Arr19 promoter, which was repressed by cAMP treatment. Altogether, these findings demonstrate that ARR19 is the target gene of GATA-1 and suggest that ARR19 gene expression in testicular Leydig cells is regulated by luteinizing hormone/cAMP signaling via the control of GATA-1 expression, resulting in the control of testicular steroidogenesis.

NMR spectroscopy as a tool for the rapid assessment of the conformation of GST-fusion proteins

Glutathione-S-transferase (GST)-fusion proteins are used extensively for structural, biochemical, and functional analyses. Although the conformation of the target protein is of critical importance, confirmation of the folded state of the target is often not undertaken or is cumbersome because of the requirement to first remove the GST tag. Here, we demonstrate that it is possible to record conventional (15)N-HSQC NMR spectra of small GST-fusion proteins and that the observed signals arise almost exclusively from the target protein. This approach constitutes a rapid and straightforward means of assessing the conformation of a GST-fusion protein without having to cleave the GST and should prove valuable, both to biochemists seeking to check the conformation of their proteins prior to functional studies and to structural biologists screening protein constructs for suitability as targets for structural studies.

Lymphoid enhancer factor interacts with GATA-3 and controls its function in T helper type 2 cells

GATA-3 is the master transcription factor for T helper 2 (Th2) cell differentiation and is critical for the expression of Th2 cytokines. Little is known, however, about the nature of the functional molecular complexes of GATA-3. We identified a high-mobility group (HMG)-box type transcription factor, lymphoid enhancer factor 1 (LEF-1), in the GATA-3 complex present in Th2 cells using a Flag-calmodulin-binding peptide (CBP)-tag based proteomics method. The interaction between GATA-3 and LEF-1 was confirmed by co-immunoprecipitation experiments using LEF-1-introduced T-cell lineage TG40 cells. The HMG-box domain of LEF-1 and two zinc finger domains of GATA-3 were found to be important for the physical association. The introduction of LEF-1 into developing Th2 cells resulted in the suppression of Th2 cytokine production. The suppression was significantly lower in the cells into which a HMG-box-deleted LEF-1 mutant was introduced. Moreover, LEF-1 inhibited the binding activity of GATA-3 to the interleukin (IL)-5 promoter. These results suggest that LEF-1 is involved in the GATA-3 complex, while also regulating the GATA-3 function, such as the induction of Th2 cytokine expression via the inhibition of the DNA-binding activity of GATA-3.

GATA3 mRNA in ginbuna crucian carp (Carassius auratus langsdorfii): cDNA cloning, splice variants and expression analysis

GATA3, a transcriptional activator, plays a critical role in the development of T-cells and differentiation to T helper type 2 cells. To date, no information is available on the role of GATA3 in the teleost immune system. We identified full-length cDNA and alternatively spliced variants of ginbuna crucian carp GATA3 (gbGATA3). The gbGATA3 gene is transcribed into multiple splice variants lacking either one or both zinc finger domains, although the sequences of both domains are fully conserved between ginbuna and other vertebrates. We found that alternative splice site and stop codon in gbGATA3 intron 3, located between exons that separately encode the two zinc finger domains, are conserved among teleosts, suggesting that teleost GATA3 gene can be translated into multiple isoforms. RT-PCR analysis revealed that the gbGATA3 is strongly expressed in the brain, thymus and gill of unstimulated fish. Moreover, gbGATA3 expression was detected in surface-IgM-negative lymphocytes among kidney cells sorted by FACS. Real-time PCR demonstrated that expression levels of full-length gbGATA3 and the splice variants differed with tissue type, but full length was always the predominantly expressed form. These results suggest that gbGATA3, including its splice variants, is involved in teleost T-cell function.

Gata4 and Hnf1alpha are partially required for the expression of specific intestinal genes during development

The terminal differentiation phases of intestinal development in mice occur during cytodifferentiation and the weaning transition. Lactase-phlorizin hydrolase (LPH), liver fatty acid binding protein (Fabp1), and sucrase-isomaltase (SI) are well-characterized markers of these transitions. With the use of gene inactivation models in mature mouse jejunum, we have previously shown that a member of the zinc finger transcription factor family (Gata4) and hepatocyte nuclear factor-1alpha (Hnf1alpha) are each indispensable for LPH and Fabp1 gene expression but are both dispensable for SI gene expression. In the present study, we used these models to test the hypothesis that Gata4 and Hnf1alpha regulate LPH, Fabp1, and SI gene expression during development, specifically focusing on cytodifferentiation and the weaning transition. Inactivation of Gata4 had no effect on LPH gene expression during either cytodifferentiation or suckling, whereas inactivation of Hnf1alpha resulted in a 50% reduction in LPH gene expression during these same time intervals. Inactivation of Gata4 or Hnf1alpha had a partial effect ( approximately 50% reduction) on Fabp1 gene expression during cytodifferentiation and suckling but no effect on SI gene expression at any time during development. Throughout the suckling period, we found a surprising and dramatic reduction in Gata4 and Hnf1alpha protein in the nuclei of absorptive enterocytes of the jejunum despite high levels of their mRNAs. Finally, we show that neither Gata4 nor Hnf1alpha mediates the glucocorticoid-induced precocious maturation of the intestine but rather are downstream targets of this process. Together, these data demonstrate that specific intestinal genes have differential requirements for Gata4 and Hnf1alpha that are dependent on the developmental time frame in which they are expressed.

Critical YxKxHxxxRP motif in the C-terminal region of GATA3 for its DNA binding and function

A zinc finger transcription factor, GATA3, plays an essential role in the development of T cells and the functional differentiation into type 2 Th cells. Two transactivation domains and two zinc finger regions are known to be important for the GATA3 function, whereas the role for other regions remains unclear. In this study we demonstrated that a conserved YxKxHxxxRP motif (aa 345-354) adjacent to the C-terminal zinc finger domain of GATA3 plays a critical in its DNA binding and functions, including transcriptional activity, the ability to induce chromatin remodeling of the Th2 cytokine gene loci, and Th2 cell differentiation. A single point mutation of the key amino acid (Y, K, H, R, and P) in the motif abrogated GATA3 functions. A computer simulation analysis based on the solution structure of the chicken GATA1/DNA complex supported the importance of this motif in GATA3 DNA binding. Thus, we identified a novel conserved YxKxHxxxRP motif adjacent to the C-terminal zinc finger domain of GATA3 that is indispensable for GATA3 DNA binding and functions.

Point mutations in two EVI1 Zn fingers abolish EVI1-GATA1 interaction and allow erythroid differentiation of murine bone marrow cells

EVI1 is an aggressive nuclear oncoprotein deregulated by recurring chromosomal abnormalities in myelodysplastic syndrome (MDS). The expression of the corresponding gene is a very poor prognostic marker for MDS patients and is associated with severe defects of the erythroid lineage. We have recently shown that the constitutive expression of EVI1 in murine bone marrow results in a fatal disease with features characteristic of MDS, including anemia, dyserythropoiesis, and dysmegakaryopoiesis. These lineages are regulated by the DNA-binding transcription factor GATA1. EVI1 has two zinc finger domains containing seven motifs at the N terminus and three motifs at the C terminus. Supported by results of assays utilizing synthetic DNA promoters, it was earlier proposed that erythroid-lineage repression by EVI1 is based on the ability of this protein to compete with GATA1 for DNA-binding sites, resulting in repression of gene activation by GATA1. Here, however, we show that EVI1 is unable to bind to classic GATA1 sites. To understand the mechanism utilized by EVI1 to repress erythropoiesis, we used a combination of biochemical assays, mutation analyses, and in vitro bone marrow differentiation. The results indicate that EVI1 interacts directly with the GATA1 protein rather than the DNA sequence. We further show that this protein-protein interaction blocks efficient recognition or binding to DNA by GATA1. Point mutations that disrupt the geometry of two zinc fingers of EVI1 abolish the protein-protein interaction, leading to normal erythroid differentiation of normal murine bone marrow in vitro.

Dyserythropoietic anemia and thrombocytopenia due to a novel mutation in GATA-1

Hematopoiesis is a complex process regulated by nuclear proteins that coordinate lineage-specific patterns of gene expression. Targeted mutagenesis has revealed critical roles for the X-linked transcription factor GATA-1 in erythrocyte and megakaryocyte differentiation. GATA-1 has two zinc fingers essential for normal function. The C-terminal finger is necessary for DNA binding. The N-terminal finger mediates interaction with FOG-1, a cofactor for GATA-1. Mutations in the N-terminal zinc finger of GATA-1 result in abnormal hematopoiesis. Here we report a family with a novel single base mutation that results in an amino acid substitution (Gly208Arg) within the highly conserved portion of the GATA-1 N-terminal finger domain, leading to dyserythropoietic anemia and macrothrombocytopenia. Another mutation described at the same codon (208) has been found to be associated with thrombocytopenia only. Our data support and extend the effect of the amino acid substitution at codon 208 on GATA-1 function not only regarding megakaryocyte but also regarding erythroid development.

GATA-1: one protein, many partners

GATA-1, the founding member of the GATA transcription factor family, is essential for cell maturation and differentiation within the erythroid and megakaryocytic lineages. GATA-1 regulates the expression of many genes within these lineages and its functionality depends upon its ability to bind both DNA and protein partners. Disruption of either of these functions causes severe hematopoietic dysfunction and results in blood disorders, such as thrombocytopenia and anemia. Within this review, we will focus on the structural aspects of GATA-1 with regard to interactions with its many partners and the identification of several mutations that disrupt these interactions.

Assessment of the robustness of a serendipitous zinc binding fold: mutagenesis and protein grafting

Zinc binding motifs have received much attention in the area of protein design. Here, we have tested the suitability of a recently discovered nonnative zinc binding structure as a protein design scaffold. A series of multiple alanine mutants was created to investigate the minimal requirements for folding, and solution structures of these mutants showed that the original fold was maintained, despite changes in approximately 50% of the sequence. We next attempted to transplant binding faces from chosen bimolecular interactions onto one of these mutants, and many of the resulting "chimeras" were shown to adopt a native-like fold. These results both highlight the robust nature of small zinc binding domains and underscore the complexity of designing functional proteins, even using such small, highly ordered scaffolds as templates.

GATA1 in normal and malignant hematopoiesis

In the late 1980s, several research groups independently discovered the founding member of the GATA family of transcription factors, GATA-1. Each group had evidence that GATA-1 played an important role in erythroid gene expression, but little did they know that it would turn out to be a key regulator of development of not only red blood cells, but of several other hematopoietic cell types as well. Furthermore, few would have guessed that missense mutations in GATA1 would cause inherited blood disorders, while acquired mutations would be found associated with essentially all cases of acute megakaryoblastic leukemia (AMKL) in children with Down syndrome (DS). With respect to the latter disorder, the presence of a GATA1 mutation is now arguably the defining feature of this leukemia. In this review, I will summarize our current knowledge of the role of GATA-1 in normal development, and discuss how mutations in GATA1 lead to abnormal and malignant hematopoiesis.

Differentiation status dependent function of FOG-1

The molecular interactions between transcription factors and cofactors play crucial roles in various biological processes, including haematopoiesis. FOG-1 is a cognate cofactor of GATA-1, and the FOG-1/GATA-1 complex is essential for the haematopoietic differentiation of erythroid cells and megakaryocytes. In order to elucidate the biological functions of FOG-1 in the different contexts of cell differentiation, we analysed the effects of FOG-1 expression on haematopoietic cell differentiation, using a combination of in vitro differentiation of mouse embryonic stem (ES) cells and conditional gene expression. FOG-1 suppressed the proliferation of primitive and definitive erythroid cells in all stages of differentiation. However, FOG-1 inhibited and enhanced megakaryopoiesis in the early and late differentiation stages, respectively, through different molecular mechanisms. In addition, FOG-1 inhibited the proliferation of ES cells, the molecular mechanism of which differs from those of erythroid and megakaryocytic cells. These results suggest that FOG-1 functions in a cell differentiation context-dependent manner.

Characterization of GATA3 Mutations in the Hypoparathyroidism, Deafness, and Renal Dysplasia (HDR) Syndrome

The hypoparathyroidism, deafness, and renal dysplasia (HDR) syndrome is an autosomal dominant disorder caused by mutations of the dual zinc finger transcription factor, GATA3. The C-terminal zinc finger (ZnF2) binds DNA, whereas the N-terminal finger (ZnF1) stabilizes this DNA binding and interacts with other zinc finger proteins, such as the Friends of GATA (FOG). We have investigated seven HDR probands and their families for GATA3 abnormalities and have identified two nonsense mutations (Glu-228 --> Stop and Arg-367 --> Stop); two intragenic deletions that result in frameshifts from codons 201 and 355 with premature terminations at codons 205 and 370, respectively; one acceptor splice site mutation that leads to a frameshift from codon 351 and a premature termination at codon 367; and two missense mutations (Cys-318 --> Arg and Asn-320 --> Lys). The functional effects of these mutations, together with a previously reported GATA3 ZnF1 mutation and seven other engineered ZnF1 mutations, were assessed by electrophoretic mobility shift, dissociation, yeast two-hybrid and glutathione S-transferase pull-down assays. Mutations involving GATA3 ZnF2 or adjacent basic amino acids resulted in a loss of DNA binding, but those of ZnF1 either lead to a loss of interaction with specific FOG2 ZnFs or altered DNA-binding affinity. These findings are consistent with the proposed three-dimensional model of ZnF1, which has separate DNA and protein binding surfaces. Thus, our results, which expand the spectrum of HDR-associated GATA3 mutations and report the first acceptor splice site mutation, help to elucidate the molecular mechanisms that alter the function of this zinc finger transcription factor and its role in causing this developmental anomaly.

Mutations of ZFPM2/FOG2 gene in sporadic cases of tetralogy of Fallot

Two out of 47 patients with sporadic tetralogy of Fallot (TOF), the most common cyanotic conotruncal heart defect (CTD), showed heterozygous missense mutations of the ZFPM2/FOG2 gene. Knockout mice carrying mutations in the ZFPM2/FOG2 gene have similarly been found to exhibit TOF. While both mutant ZFPM2/FOG2 proteins, E30G (c.88A>G) and S657G (c.1968A>G), retain the ability to bind the partner protein GATA4 and repress GATA4 mediated gene activation, the S657G, but not the E30G, mutation is subtly impaired in this function. ZFPM2/FOG2 gene mutations may contribute to some sporadic cases of TOF.

The GATA family of transcription factors in Arabidopsis and rice

GATA transcription factors are a group of DNA binding proteins broadly distributed in eukaryotes. The GATA factors DNA binding domain is a class IV zinc finger motif in the form CX(2)CX(17-20)CX(2)C followed by a basic region. In plants, GATA DNA motifs have been implicated in light-dependent and nitrate-dependent control of transcription. Herein, we show that the Arabidopsis and the rice (Oryza sativa) genomes present 29 and 28 loci, respectively, that encode for putative GATA factors. A phylogenetic analysis of the 57 GATA factors encoding genes, as well as the study of their intron-exon structure, indicates the existence of seven subfamilies of GATA genes. Some of these subfamilies are represented in both species but others are exclusive for one of them. In addition to the GATA zinc finger motif, polypeptides of the different subfamilies are characterized by the presence of additional domains such as an acidic domain, a CCT (CONSTANS, CO-like, and TOC1) domain, or a transposase-like domain also found in FAR1 and FHY3. Subfamily VI comprises genes that encode putative bi-zinc finger polypeptides, also found in metazoan and fungi, and a tri-zinc finger protein which has not been previously reported in eukaryotes. The phylogeny of the GATA zinc finger motif, excluding flanking regions, evidenced the existence of four classes of GATA zinc fingers, three of them containing 18 residues in the zinc finger loop and one containing a 20-residue loop. Our results support multiple models of evolution of the GATA gene family in plants including gene duplication and exon shuffling.

Inherited thrombocytopenias: toward a molecular understanding of disorders of platelet production

PURPOSE OF REVIEW

To review the defined syndromes of inherited thrombocytopenia and discuss new genetic data for several disorders that shed light on the process of megakaryopoiesis.

RECENT FINDINGS

The genes responsible for several inherited thrombocytopenias have been recently discovered, including congenital amegakaryocytic leukemia, amegakaryocytic thrombocytopenia with radio-ulnar synostosis, familial platelet syndrome with predisposition to acute myelogenous leukemia, Paris-Trousseau, Wiskott-Aldrich syndrome, and the May-Hegglin, Sebastian, Epstein, and Fechner syndromes. These clinical syndromes, combined with studies in mouse and in vitro models, reveal the importance of these genes for normal hematopoiesis.

SUMMARY

Although inherited syndromes of thrombocytopenia are rare, characterization of mutations in these disorders has contributed greatly to our understanding of megakaryocyte and platelet development. A systematic registry of congenitally thrombocytopenic individuals would almost certainly lead to new genetic discoveries.

Interaction with GATA transcription factors provides a mechanism for cell-specific effects of c-Fos

c-Fos is a multifunctional transcription factor that is involved in cellular proliferation, differentiation and apoptosis. c-Fos is rapidly induced by a variety of hormones, growth factors and other extracellular stimuli, resulting in cell-specific responses. One potential mechanism underlying the cell-specific effects of c-Fos may be its ability to regulate gene expression through interaction with tissue-restricted transcription factors. We report here that c-Fos interacts with the cell-specific GATA proteins to potentiate their ability to transactivate target promoters, via GATA-binding sites. c-Fos is recruited to GATA proteins through direct interaction with their N-terminal activation domain. Neither the leucine zipper nor the DNA-binding domain of c-Fos is required for physical interaction with GATA proteins. Instead, a C-terminal domain located between amino acids 235 and 296, which is conserved in FosB but not in the nontransforming Fos family members, FosB/SF or Fra-1, is essential for c-Fos-GATA interaction. These data suggest that c-Fos may act as an inducible cofactor for cell-specific transcription factors and unravel a novel mechanism for transcriptional regulation by c-Fos, independent of the well-studied AP-1 pathway. The results also raise the possibility that dysregulated interaction with cell-specific transcription factors may be an important component in cellular transformation by nuclear oncogenes.

Nuclear magnetic resonance structures of the zinc finger domain of human DNA polymerase-α

The carboxy terminus of the human DNA polymerase-alpha contains a zinc finger motif. Three-dimensional structures of this motif containing 38 amino acid residues, W L I C E E P T C R N R T R H L P L Q F S R T G P L C P A C M K A T L Q P E, were determined by nuclear magnetic resonance (NMR) spectroscopy. The structures reveal an alpha-helix-like domain at the amino terminus, extending 13 residues from L2 through H15 with an interruption at the sixth residue. The helix region is followed by three turns (H15-L18, T23-L26 and L26-A29), all of which involve proline. The first turn appears to be type III, judging by the dihedral angles. The second and third turns appear to be atypical. A second, shorter helix is formed at the carboxy terminus extending from C30 through L35. A fourth type III turn starting at L35 was also observed in the structure. Proline serves as the third residue of all the turns. Four cysteine residues, two located at the beginning of the helix at the N-terminus and two at the carboxy end, are coordinated to Zn(II), facilitating the formation of a loop. One of the cysteines at the carboxy terminus is part of the atypical turn, while the other is the part of the short helix. These structural features are consistent with the circular dichroism (CD) measurements which indicate the presence of 45% helix, 11% beta turns and 19% non-ordered secondary structures. The zinc finger motif described here is different from those observed for C(4), C(2)H(2), and C(2)HC modules reported in the literature. In particular, polymerase-alpha structures exhibit helix-turn-helix motif while most zinc finger proteins show anti-parallel sheet and helix. Several residues capable of binding DNA, T, R, N, and H are located in the helical region. These structural features imply that the zinc finger motif is most likely involved in binding DNA prior to replication, presumably through the helical region. These results are discussed in the context of other eukaryotic and prokaryotic DNA polymerases belonging to the polymerase B family.

Drosophila lola encodes a family of BTB-transcription regulators with highly variable C-terminal domains containing zinc finger motifs

Alternative splicing is an important mechanism contributing to the increased proteome diversity in higher eukaryotes. We have explored the alternative splicing events in the Drosophila longitudinals lacking (lola) gene by means of 5' RACE, 3' RACE, genome sequence searches, and EST sequencing. We demonstrated that the lola locus is comprised of 32 exons spanning over 60 kb, and encodes a total of 80 alternatively spliced variants consisting of 5' and 3' variable sequences and constitutive common exons. All the variants shared a common sequence (exons 5-8) encoding the N-terminal region containing the BTB domain, but both the 5' and 3' ends were variable. There were four promoters responsible for the variation in the 5' end (exons 1-4). Alternative splicing was involved in the variation in the 3' end corresponding to the C-terminal variable region, which was encoded by one or two exons that were selected from 20 groups of exons in a mutually exclusive manner (exons 9-32). Seventeen of the 20 isoforms contained C(2)H(2)-like zinc finger motifs in the C-terminal variable region. Analyses of the 3' variant-specific cDNA pools revealed that all combinations of 5' and 3' variable sequences were expressed in both the embryonic and third instar larval stages. Since the BTB domain mediates dimerization, lola encodes a family of transcription regulators with a large variety of DNA- or protein-binding specificities, and could be involved in various developmental processes, including the embryonic neural pathfindings. We also showed that the structures of Lola isoforms were highly conserved in Drosophila pseudoobscura.

Protein-protein interaction between Fli-1 and GATA-1 mediates synergistic expression of megakaryocyte-specific genes through cooperative DNA binding

Friend leukemia integration 1 (Fli-1) is a member of the Ets family of transcriptional activators that has been shown to be an important regulator during megakaryocytic differentiation. We undertook a two-hybrid screen of a K562 cDNA library to identify transcription factors that interacted with Fli-1 and were potential regulators of megakaryocyte development. Here we report the physical interaction of Fli-1 with GATA-1, a well-characterized, zinc finger transcription factor critical for both erythroid and megakaryocytic differentiation. We map the minimal domains required for the interaction and show that the zinc fingers of GATA-1 interact with the Ets domain of Fli-1. GATA-1 has previously been shown to interact with the Ets domain of the Fli-1-related protein PU.1, and the two proteins appear to inhibit each other's activity. In contrast, we demonstrate that GATA-1 and Fli-1 synergistically activate the megakaryocyte-specific promoters GPIX and GPIbalpha in transient transfections. Quantitative electrophoretic mobility shift assays using oligonucleotides derived from the GPIX promoter containing Ets and GATA binding motifs reveal that Fli-1 and GATA-1 exhibit cooperative DNA binding in which the binding of GATA-1 to DNA is increased approximately 26-fold in the presence of Fli-1 (from 4.2 to 0.16 nM), providing a mechanism for the observed transcriptional synergy. To test the effect on endogenous genes, we stably overexpressed Fli-1 in K562 cells, a line rich in GATA-1. Overexpression of Fli-1 induced the expression of the endogenous GPIX and GPIbalpha genes as measured by Northern blot and fluorescence-activated cell sorter analysis. This work suggests that Fli-1 and GATA-1 work together to activate the expression of genes associated with the terminal differentiation of megakaryocytes.

Selective dimerization of a C2H2 zinc finger subfamily

The C2H2 zinc finger is the most prevalent protein motif in the mammalian proteome. Two C2H2 fingers in Ikaros are dedicated to homotypic interactions between family members. We show here that these fingers comprise a bona fide dimerization domain. Dimerization is highly selective, however, as homologous domains from the TRPS-1 and Drosophila Hunchback proteins support homodimerization, but not heterodimerization with Ikaros. Ikaros-Hunchback selectivity is determined by 11 residues concentrated within the alpha-helical regions typically involved in base recognition. Preferential homodimerization of one chimeric protein predicts a parallel dimer interface and establishes the feasibility of creating novel dimer specificities. These results demonstrate that the C2H2 motif provides a versatile platform for both sequence-specific protein-nucleic acid interactions and highly specific dimerization.

Two isoforms of Serpent containing either one or two GATA zinc fingers have different roles in Drosophila haematopoiesis

serpent (srp) encodes a GATA transcription factor essential for haematopoiesis in Drosophila. Previously, Srp was shown to contain a single GATA zinc finger of C-terminal type. Here we show that srp encodes different isoforms, generated by alternative splicing, that contain either only a C-finger (SrpC) or both a C- and an N-finger (SrpNC). The presence of the N-finger stabilizes the interaction of Srp with palindromic GATA sites and allows interaction with the Friend of GATA factor U-shaped (Ush). We have examined the respective functions of SrpC and SrpNC during embryonic haematopoiesis. Both isoforms individually rescue blood cell formation that is lacking in an srp null mutation. Interestingly, while SrpC and SrpNC activate some genes in a similar manner, they regulate others differently. Interaction between SrpNC and Ush is responsible for some but not all aspects of the distinct activities of SrpC and SrpNC. Our results suggest that the inclusion or exclusion of the N-finger in the naturally occurring isoforms of Srp can provide an effective means of extending the versatility of srp function during development.

Characterization of the conserved interaction between GATA and FOG family proteins

The N-terminal zinc finger (ZnF) from GATA transcription factors mediates interactions with FOG family proteins. In FOG proteins, the interacting domains are also ZnFs; these domains are related to classical CCHH fingers but have an His --> Cys substitution at the final zinc-ligating position. Here we demonstrate that different CCHC fingers in the FOG family protein U-shaped contact the N-terminal ZnF of GATA-1 in the same fashion although with different affinities. We also show that these interactions are of moderate affinity, which is interesting given the presumed low concentrations of these proteins in the nucleus. Furthermore, we demonstrate that the variant CCHC topology enhances binding affinity, although the His --> Cys change is not essential for the formation of a stably folded domain. To ascertain the structural basis for the contribution of the CCHC arrangement, we have determined the structure of a CCHH mutant of finger nine from U-shaped. The structure is very similar overall to the wild-type domain, with subtle differences at the C terminus that result in loss of the interaction in vivo. Taken together, these results suggest that the CCHC zinc binding topology is required for the integrity of GATA-FOG interactions and that weak interactions can play important roles in vivo.

Combinatorial expression of GATA4, Nkx2-5, and serum response factor directs early cardiac gene activity

Herein, the restricted expression of serum response factors (SRF) closely overlapped with Nkx2-5 and GATA4 transcripts in early chick embryos coinciding with the earliest appearance of cardiac alpha-actin (alphaCA) transcripts and nascent myocardial cells. The combinatorial expression of SRF, a MADS box factor Nkx2-5 (a NK4 homeodomain), and/or GATA4, a dual C4 zinc finger protein, in heterologous CV1 fibroblasts and Schneider 2 insect cells demonstrated synergistic induction of alphaCA promoter activity. These three factors induced endogenous alphaCA mRNA over a 100-fold in murine embryonic stem cells. In addition, the DNA-binding defective mutant Nkx2-5pm efficiently coactivated the alphaCA promoter in the presence of SRF and GATA4 in the presence of all four SREs and was substantially weakened when individual SREs were mutated and or serially deleted. In contrast, the introduction of SRFpm, a SRF DNA-binding mutant, blocked the activation with all of the alphaCA promoter constructions. These assays indicated a dependence upon cooperative SRF binding for facilitating the recruitment of Nkx2-5 and GATA4 to the alphaCA promoter. Furthermore, the recruitment of Nkx2-5 and GATA4 by SRF was observed to strongly enhance SRF DNA binding affinity. This mechanism allowed for the formation of higher ordered alphaCA promoter DNA binding complexes, led to a model of SRF physical association with Nkx2-5 and GATA4.