Functional GATA-3 binding sites within murine CD8 alpha upstream regulatory sequences

iNKT cells with high PLZF expression are recruited into the lung via CCL21-CCR7 signaling to facilitate the development of asthma tolerance in mice

Establishment of immune tolerance is crucial to protect humans against asthma. Promyelocytic leukemia zinc finger (PLZF) is an emerging suppressor of inflammatory responses. CCL21-CCR7 signaling mediates tolerance development. However, whether PLZF and CCL21-CCR7 are required for the development of asthma tolerance is unknown. Here, we found that Zbtb16 (coding PLZF) and Ccl21 were upregulated in OVA-induced asthma tolerance (OT) lungs by RNA-seq. PLZF physically interacted with GATA3 and its expression was higher in GATA3⁺ Th2 cells and ILC2s in OT lungs. Zbtb16-knockdown in lymphocytes promoted the differentiation of CD3e⁺ CD4⁺ T cells, particularly those producing IL-4 and IL-5. Moreover, iNKT cells with high expression of PLZF were recruited into the lungs via draining lymph nodes during tolerance. Blockade of CCL21-CCR7 signaling in OT mice decreased the PLZF⁺  cell population, abolished CCR7-induced PLZF⁺ iNKT recruitment to the lungs, enhanced Th2responses and exacerbated lung pathology. In OT mice, respiratory syncytial virus (RSV) infection impeded PLZF⁺  cell and CCR7⁺ PLZF⁺ iNKT cellrecruitment to the lungs and increased airway resistance. Collectively, these results indicate that PLZF could interact with GATA3 and restrain differentiation of IL-4- and IL-5-producing T cells, iNKT cells with high PLZF expression are recruited to the lungs via CCL21-CCR7 signaling to facilitate the development of asthma tolerance.

Clinical and molecular characteristics of MEF2D fusion-positive B-cell precursor acute lymphoblastic leukemia in childhood, including a novel translocation resulting in MEF2D-HNRNPH1 gene fusion

Fusion genes involving MEF2D have recently been identified in precursor B-cell acute lymphoblastic leukemia, mutually exclusive of the common risk stratifying genetic abnormalities, although their true incidence and associated clinical characteristics remain unknown. We identified 16 cases of acute lymphoblastic leukemia and 1 of lymphoma harboring MEF2D fusions, including MEF2D-BCL9 (n=10), MEF2D-HNRNPUL1 (n=6), and one novel MEF2D-HNRNPH1 fusion. The incidence of MEF2D fusions overall was 2.4% among consecutive precursor B-cell acute lymphoblastic leukemia patients enrolled onto a single clinical trial. They frequently showed a cytoplasmic μ chain-positive pre-B immunophenotype, and often expressed an aberrant CD5 antigen. Besides up- and down-regulation of HDAC9 and MEF2C, elevated GATA3 expression was also a characteristic feature of MEF2D fusion-positive patients. Mutations of PHF6, recurrent in T-cell acute lymphoblastic leukemia, also showed an unexpectedly high frequency (50%) in these patients. MEF2D fusion-positive patients were older (median age 9 years) with elevated WBC counts (median: 27,300/ml) at presentation and, as a result, were mostly classified as NCI high risk. Although they responded well to steroid treatment, MEF2D fusion-positive patients showed a significantly worse outcome, with 53.3% relapse and subsequent death. Stem cell transplantation was ineffective as salvage therapy. Interestingly, relapse was frequently associated with the presence of CDKN2A/CDKN2B gene deletions. Our observations indicate that MEF2D fusions comprise a distinct subgroup of precursor B-cell acute lymphoblastic leukemia with a characteristic immunophenotype and gene expression signature, associated with distinct clinical features.

The ubiquitin ligase SCFFBXW7α promotes GATA3 degradation

GATA3 is a key transcription factor in cell fate determination and its dysregulation has been implicated in various types of malignancies. However, how the abundance and function of GATA3 are regulated remains unclear. Here, we report that GATA3 is physically associated with FBXW7α, and FBXW7α destabilizes GATA3 through assembly of a SKP1-CUL1-F-box E3 ligase complex. Importantly, we showed that FBXW7α promotes GATA3 ubiquitination and degradation in a GSK3 dependent manner. Furthermore, we demonstrated that FBXW7α inhibits breast cancer cells survival through destabilizing GATA3, and the expression level of FBXW7α is negatively correlated with that of GATA3 in breast cancer samples. This study indicated that FBXW7α is a critical negative regulator of GATA3 and revealed a pathway for the maintenance of GATA3 abundance in breast cancer cells.

EP300-ZNF384 fusion gene product up-regulates GATA3 gene expression and induces hematopoietic stem cell gene expression signature in B-cell precursor acute lymphoblastic leukemia cells

ZNF384-related fusion genes are associated with a distinct subgroup of B-cell precursor acute lymphoblastic leukemias in childhood, with a frequency of approximately 3-4%. We previously identified a novel EP300-ZNF384 fusion gene. Patients with the ZNF384-related fusion gene exhibit a hematopoietic stem cell (HSC) gene expression signature and characteristic immunophenotype with negative or low expression of CD10 and aberrant expression of myeloid antigens, such as CD33 and CD13. However, the molecular basis of this pathogenesis remains completely unknown. In the present study, we examined the biological effects of EP300-ZNF384 expression induced by retrovirus-mediated gene transduction in an REH B-cell precursor acute lymphoblastic leukemia cell line, and observed the acquisition of the HSC gene expression signature and an up-regulation of GATA3 gene expression, as assessed by microarray analysis. In contrast, the gene expression profile induced by wild-type ZNF384 in REH cells was significantly different from that by EP300-ZNF384 expression. Together with the results of reporter assays, which revealed the enhancement of GATA3-promoter activity by EP300-ZNF384 expression, these findings suggest that EP300-ZNF384 mediates GATA3 gene expression and may be involved in the acquisition of the HSC gene expression signature and characteristic immunophenotype in B-cell precursor acute lymphoblastic leukemia cells.

GATA family transcriptional factors: emerging suspects in hematologic disorders

GATA transcription factors are zinc finger DNA binding proteins that regulate transcription during development and cell differentiation. The three important GATA transcription factors GATA1, GATA2 and GATA3 play essential roles in the development and maintenance of hematopoietic systems. GATA1 is required for the erythroid and megakaryocytic commitment during hematopoiesis. GATA2 is crucial for the proliferation and survival of early hematopoietic cells, and is also involved in lineage specific transcriptional regulation as the dynamic partner of GATA1. GATA3 plays an essential role in T lymphoid cell development and immune regulation. As a result, mutations in genes encoding the GATA transcription factors or alteration in the protein expression level or their function have been linked to a variety of human hematologic disorders. In this review, we summarized the current knowledge regarding the disrupted biologic function of GATA in various hematologic disorders.

Epigenetic plasticity of Cd8a locus during CD8(+) T-cell development and effector differentiation and reprogramming

Modulation of CD8 coreceptor levels can profoundly affect T-cell sensitivity to antigen. Here we show that the heritable downregulation of CD8 during type 2 polarization of murine CD8⁺ effector T cells in vitro and in vivo is associated with CpG methylation of several regions of the Cd8a locus. These epigenetic modifications are maintained long-term in vivo following adoptive transfer. Even after extended type 2 polarization, however, some CD8^low effector cells respond to interferon-γ by re-expressing CD8 and a type 1 cytokine profile in association with partial Cd8a demethylation. Cd8a methylation signatures in naive, polarized and repolarized cells are distinct from those observed during the initiation, maintenance and silencing of CD8 expression by developing T cells in the thymus. This persistent capacity for epigenetic reprogramming of coreceptor levels on effector CD8⁺ T cells enables the heritable tuning of antigen sensitivity in parallel with changes in type 1/type 2 cytokine balance.

CD8 expression levels on peripheral CD8+ T cells are regulated during development and effector differentiation. Here, the authors show that methylation patterns at the Cd8a locus, whose product is essential for surface CD8 expression, can change during T-cell development, activation, cytokine polarization and reprogramming.

DNA methylation and regulation of the CD8A after duck hepatitis virus type 1 infection

Background

Cluster of differentiation 8 (CD8) is expressed in cytotoxic T cells, where it functions as a co-receptor for the T-cell receptor by binding to major histocompatibility complex class I (MHCI) proteins, which present peptides on the cell surface. CD8A is critical for cell-mediated immune defense and T-cell development. CD8A transcription is controlled by several cis-acting elements and trans-acting elements and is also regulated by DNA methylation. However, the epigenetic regulation of CD8A in the duck and its relationship with virus infection are still unclear.

Results

We investigated the epigenetic transcriptional regulatory mechanisms, such as DNA methylation, for the expression of the CD8A and further evaluated the contribution of such epigenetic regulatory mechanisms to DHV-I infection in the duck. Real-time quantitative polymerase chain reaction (RT-qPCR) revealed the highest level of CD8A expression to be in the thymus, followed by the lungs, spleen, and liver, and the levels of CD8A expression were very low in the kidney, cerebrum, cerebellum, and muscle in the duck. RT-qPCR also demonstrated that the CD8A mRNA was down-regulated significantly in morbid ducklings treated with DHV-1 and up-regulated significantly in non-morbid ducklings in all the tissues tested. In addition, hypermethylation of CD8A was detected in the morbid ducklings, whereas relatively low methylation of CD8A was evident in the non-morbid ducklings. The CD8A mRNA level was negatively associated with the CpG methylation level of CD8A and global methylation status.

Conclusions

We concluded that the mRNA level of the CD8A was negatively associated with the CpG methylation level of CD8A and global methylation status in the duck, suggesting that the hypermethylation of CD8A may be associated with DHV-1 infection. The first two CpG sites of the CD8A promoter region could be considered as epigenetic biomarkers for resistance breeding against duckling hepatitis disease in the duck.

From the cradle to the grave: activities of GATA-3 throughout T-cell development and differentiation

GATA family transcription factors play multiple vital roles in hematopoiesis in many cell lineages, and in particular, T cells require GATA-3 for execution of several developmental steps. Transcriptional activation of the Gata3 gene is observed throughout T-cell development and differentiation in a stage-specific fashion. GATA-3 has been described as a master regulator of T-helper 2 (Th2) cell differentiation in mature CD4(+) T cells. During T-cell development in the thymus, its roles in the CD4 versus CD8 lineage choice and at the β-selection checkpoint are the best characterized. In contrast, its importance prior to β-selection has been obscured both by the developmental heterogeneity of double negative (DN) 1 thymocytes and the paucity of early T-lineage progenitors (ETPs), a subpopulation of DN1 cells that contains the most immature thymic progenitors that retain potent T-lineage developmental potential. By examining multiple lines of in vivo evidence procured through the analysis of Gata3 mutant mice, we have recently demonstrated that GATA-3 is additionally required at the earliest stage of thymopoiesis for the development of the ETP population. Here, we review the characterized functions of GATA-3 at each stage of T-cell development and discuss hypothetical molecular pathways that mediate these functions.

The L2a element is a mouse CD8 silencer that interacts with MAR-binding proteins SATB1 and CDP

Previous transgenic-reporter and targeted-deletion studies indicate that the subset-specific expression of CD8αβ heterodimers is controlled by multiple enhancer activities, since no silencer elements had been found within the locus. We have identified such a silencer as L2a, a previously characterized ∼ 220 bp nuclear matrix associating region (MAR) located ∼ 4.5 kb upstream of CD8α. L2a transgenes driven by the E8(I) enhancer showed no reporter expression in thymic subsets or T cells in splenic, inguinal and mesenteric lymph node peripheral T cells. Deletion of L2a resulted in significant reporter de-repression, even in the CD4(+)CD8(+) double positive (DP) thymocyte population. L2a contains binding sites for two MAR-interacting proteins, SATB1 and CDP. We found that that binding of these factors was markedly influenced by the content and spacing of L2a sub-motifs (L and S) and that SATB1 binds preferentially to the L motif both in vitro and in vivo. A small fraction of the transgenic CD8 single positive (SP) thymocytes and peripheral CD8(+) T cells bypassed L2a-silencing to give rise to variegated expression of the transgenic reporter. Crossing the L2a-containing transgene onto a SATB1 knockdown background enhanced variegated expression, suggesting that SATB1 is critical in overcoming L2a-silenced transcription.

Interferon-gamma and interleukin-4 reciprocally regulate CD8 expression in CD8+ T cells

The CD8 co-receptor can modulate CD8(+) T cell function through its contributions to T cell receptor (TCR) binding and signaling. Here we show that IFN-gamma and IL-4 exert opposing effects on the expression of CD8alpha mRNA and surface CD8 protein during CD8(+) T cell activation. IL-4 caused down-regulation of surface CD8 on ovalbumin (OVA)(257-264)-specific TCR-transgenic OT-I CD8(+) T cells activated with OVA(257-264)-coated antigen presenting cells or polyclonal stimuli, and on wild type CD8(+) T cells activated with polyclonal stimuli. This effect was enhanced in each case when the cells lacked a functional IFN-gamma or IFN-gamma R gene. When WT or IFN-gamma-deficient OT-I CD8(+) T cells were analyzed 9 days after co-injection with control or IL-4-expressing OVA(+) tumor cells into RAG-2(-/-)gamma c(-/-) mice, CD8 levels were highest on WT donor cells from mice that received the control tumor and lowest on IFN-gamma-deficient donor cells from mice that received the IL-4-expressing tumor. The latter CD8(low) cells displayed markedly impaired binding of OVA(257-264)/MHC tetramers and peptide/MHC-dependent degranulation. The data reveal an unexpected role for IFN-gamma in tuning the CD8 co-receptor during primary CD8(+) T cell activation both in vitro and in vivo.

SATB1 is required for CD8 coreceptor reversal

Intrathymic signals induce the differentiation of immature CD4(+)CD8(+) double positive (DP) thymocytes into mature CD4(+) or CD8(+) single positive (SP) T cells. The transcriptional mechanism by which CD8 lineage is determined is not fully understood. The best evidence, which favors the kinetic signaling/coreceptor reversal model, indicates that signaled DP thymocytes terminate CD8 transcription prior to their subsequent re-initiation of CD8 transcription and ultimate differentiation into CD8SP T cells. We and others have shown that CD8 lineage commitment is severely perturbed in mice in which expression of the transcription factor SATB1 is either conventionally knocked out or T cell-specifically knocked down. Here, we demonstrate that, as with normal thymocytes, cultured SATB1-deficient DP thymocytes inactivate CD8 coreceptor transcription following receipt of signals (PMA plus ionomycin) that mimic TCR-mediated positive selection. However, this terminated CD8 transcription is not re-initiated by signals (IL-7) conducive to CD8 differentiation in SATB1-deficient DP. We show that SATB1 specifically binds to a cis-regulatory element within the CD8 enhancer (E8(III)) known to be required for coreceptor reversal. A requirement in CD8 coreceptor reversal identifies SATB1 as an essential trans-regulator of CD8 lineage fate, whose action may be mediated via recruitment to the E8(III) DP enhancer.

Regulation of the GATA3 promoter by human T-cell lymphotropic virus type I Tax protein

The Human T-cell leukemia virus type I (HTLV-I) non-structural protein Tax plays a crucial role in cellular transformation. It activates the transcription factors of various cellular genes and interacts with cellular proteins. There is limited data available on the interaction between specific T-cell transcription factor GATA3 and Tax. Implications for the significance of GATA3 in T-cell development and function, T helper2 (Th2) differentiation, and a role of GATA3 during the immune response have been reported. To determine the effect of the Tax protein on GATA3 gene expression, we investigated the interaction between this protein and the GATA3 promoter and repressor regions. Results demonstrated an interaction between Tax and the GATA3 promoter via the transcription factor Sp1 and a role for Tax in the negative regulation of GATA3 expression, through its interaction with the repressor ZEB. This interaction may be involved in the pathophysiology of adult T-cell leukemia/lymphoma (ATL) and tropical spastic paraparesis/HTLV-I-associated myelopathy (TSP/HAM).

Dual Functions of Runx Proteins for Reactivating CD8 and Silencing CD4 at the Commitment Process into CD8 Thymocytes

To understand how CD8 expression is regulated during the transition process from CD4+8+ (CD4 and CD8 double positive, DP) to CD4-8+ (CD8 single positive, CD8SP) cells in the thymus, the involvement of Runx proteins in the alteration of chromatin configuration was investigated. Using the chromatin immunoprecipitation assay, we first demonstrated that Runx proteins bind to the stage-specific CD8 enhancer, as well as the CD4 silencer, in CD8SP thymocytes. Among Runx family members, Runx3 expression was initiated in DP thymocytes receiving a positive selection signal and increased in concert with differentiation to the CD8SP stage. Furthermore, reactivation of the CD8 gene, as well as CD4 silencing, was suppressed in positively selected thymocytes of Runx dominant-negative transgenic mice. These results suggest that Runx proteins, especially Runx3, are involved in lineage specification of CD8 T cells and provide important information for understanding the mechanism for the mutually exclusive expression of coreceptors in mature thymocytes.

Critical roles for transcription factor GATA-3 in thymocyte development

The transcription factor GATA-3 is expressed at every stage of thymic development, but its role in thymocyte differentiation is unknown. The fact that RAG chimeric animals lacking GATA-3 cannot generate early thymocytes from common lymphoid progenitors has thus far precluded investigation of the function of GATA-3 in the thymus. To address this, we generated mice deficient in GATA-3 at early and late stages of thymic differentiation. Our studies revealed that GATA-3 is involved in beta selection and is indispensable for single-positive CD4 thymocyte development. Thus, our data demonstrate that the coordinated and regulated expression of GATA-3 at each stage of thymic development is critical for the generation of mature T cells.

Morpholino antisense oligonucleotide-mediated gene knockdown during thymocyte development reveals role for Runx3 transcription factor in CD4 silencing during development of CD4-/CD8+ thymocytes

During thymic T cell development, immature CD4(+)/CD8(+) thymocytes develop into either CD4(+)/CD8(-) helper or CD4(-)/CD8(+) CTLs. The molecular mechanisms governing the complex selection and differentiation steps during thymic T cell development are not well understood. Here we developed a novel approach to investigate gene function during thymocyte development. We transfected ex vivo isolated immature thymocytes with gene-specific morpholino antisense oligonucleotides and induced differentiation in cell or organ cultures. A morpholino oligonucleotide specific for CD8alpha strongly reduces CD8 expression. To our knowledge, this is the first demonstrated gene knockdown by morpholino oligonucleotides in primary lymphocytes. Using this approach, we show here that the transcription factor Runx3 is involved in silencing of CD4 expression during CD8 T cell differentiation. Runx3 protein expression appears late in thymocyte differentiation and is confined to mature CD8 single-positive thymocytes, whereas Runx3 mRNA is transcribed in mature CD4 and CD8 thymocytes. Therefore, Runx3 protein expression is regulated at a post-transcriptional level. The knockdown of Runx3 protein expression through morpholino oligonucleotides inhibited the development of CD4(-)/CD8(+) T cells. Instead, mature cells with a CD4(+)/CD8(+) phenotype accumulated. Potential Runx binding sites were identified in the CD4 gene silencer element, which are bound by Runx protein in EMSAs. Mutagenesis of potential Runx binding sites in the CD4 gene silencer abolished silencing activity in a reporter gene assay, indicating that Runx3 is involved in CD4 gene silencing. The experimental approach developed here should be valuable for the functional analysis of other candidate genes in T cell differentiation.

An important regulatory role for CD4+CD8 alpha alpha T cells in the intestinal epithelial layer in the prevention of inflammatory bowel disease

The normal immunoregulatory mechanisms that maintain homeostasis in the intestinal mucosa, despite continuous provocation by environmental antigens, are jeopardized in inflammatory bowel diseases. Although previous studies have suggested that intestinal intraepithelial lymphocytes prevent spontaneous intestinal inflammation, there is limited knowledge about the characteristics of regulatory cells in the intestinal intraepithelial lymphocytes population. Here we show that CD4(+)CD8 alpha alpha(+) double-positive cells present in the intestinal intraepithelial lymphocytes population can suppress T helper 1-induced intestinal inflammation in an IL-10-dependent fashion. CD4(+) T cells stimulated along the Th2 but not the Th1 lineage, when transferred to RAG-1-/- mice, acquire CD8 alpha alpha expression on reaching the intestinal epithelium, and on arrival there, augment their production of IL-10. We show that a precursor CD4(+) T cell after limited, but not repeated, stimulation by IL-4 is able to become a double-positive-regulatory cell on exposure to the intestinal microenvironment in mice. Both CD8 alpha alpha acquisition and IL-10 production depend critically on the NF-kappa B-GATA-3-axis that we have previously shown is essential for differentiation to the Th2 phenotype and for the induction of airway inflammation. Our studies identify a mechanism for the generation of regulatory T cells in the intestine that may play an important role in controlling inflammatory bowel disease.

Transient IL-7/IL-7R signaling provides a mechanism for feedback inhibition of immunoglobulin heavy chain gene rearrangements

Production of immunoglobulin heavy chain (IgH) protein feeds back to terminate further V(H) gene recombination, a phenomenon also referred to as allelic exclusion. Here we provide evidence to support the proposition that allelic exclusion is the consequence of terminating signals that activate V(H) genes for recombination. For the largest V(H)J558 family of genes, this occurs by attenuating IL-7/IL-7R signals in pre-B cells. Loss of these signals reverts the V(H) locus to a chromatin state that is associated with hypoacetylated histones and is less accessible to nucleases. Furthermore, hyperacetylation and accessibility of unrearranged V(H) genes can be restored in allelically excluded splenic B cells by activating this pathway. Thus, transient signals mediate V(H) gene activation and inactivation during development.

GATA-2 and GATA-2/ER display opposing activities in the development and differentiation of blood progenitors

GATA-2 is a zinc finger transcription factor essential for the development of hematopoiesis. While GATA-2 is generally considered to play an important role in the biology of hematopoietic stem and progenitor cells, its function within these compartments is not well understood. Here we have employed both conditional expression of GATA-2 and conditional activation of a GATA-2/estrogen receptor (ER) chimera to examine the effect of enforced GATA-2 expression in the development and differentiation of hematopoietic progenitors from murine embryonic stem cells. Consistent with the phenotype of GATA-2 null animals, conditional expression of GATA-2 from a tetracycline-inducible promoter enhanced the production of hematopoietic progenitors. Conditional activation of a GATA-2/ER chimera produced essentially opposite effects to those observed with conditional GATA-2 expression. GATA-2 and GATA-2/ER differ in their binding activities and transcriptional interactions from other hematopoietic-associated transcription factors such as c-Myb and PU.1. While we have exploited these differences in activity to explore the transcriptional networks underlying hematopoietic cell fate determination, our results suggest that care should be taken in interpreting results obtained using only chimeric proteins.

Identification of a candidate regulatory region in the human CD8 gene complex by colocalization of DNase I hypersensitive sites and matrix attachment regions which bind SATB1 and GATA-3

To locate elements regulating the human CD8 gene complex, we mapped nuclear matrix attachment regions (MARs) and DNase I hypersensitive (HS) sites over a 100-kb region that included the CD8B gene, the intergenic region, and the CD8A gene. MARs facilitate long-range chromatin remodeling required for enhancer activity and have been found closely linked to several lymphoid enhancers. Within the human CD8 gene complex, we identified six DNase HS clusters, four strong MARs, and several weaker MARs. Three of the strong MARs were closely linked to two tissue-specific DNase HS clusters (III and IV) at the 3' end of the CD8B gene. To further establish the importance of this region, we obtained 19 kb of sequence and screened for potential binding sites for the MAR-binding protein, SATB1, and for GATA-3, both of which are critical for T cell development. By gel shift analysis we identified two strong SATB1 binding sites, located 4.5 kb apart, in strong MARs. We also detected strong GATA-3 binding to an oligonucleotide containing two GATA-3 motifs located at an HS site in cluster IV. This clustering of DNase HS sites and MARs capable of binding SATB1 and GATA-3 at the 3' end of the CD8B gene suggests that this region is an epigenetic regulator of CD8 expression.

A clonal culture system demonstrates that IL-4 induces a subpopulation of noncytolytic T cells with low CD8, perforin, and granzyme expression

Immune deviation of cytolytic T cell function, induced by type 2 cytokines like IL-4, is an attractive concept to explain failure of the immune system in some diseases. However, this concept is challenged by previous conflicting results on whether type 2 cytokine-producing CD8(+) T cells are cytolytic. Therefore, we have analyzed the relationship between cytolytic activity and cytokine production among large numbers of primary CD8(+) T cell clones. Single murine CD8(+) T cells of naive phenotype were activated at high efficiency with immobilized Abs to CD3, CD8, and CD11a in the presence of IL-2 (neutral conditions) or IL-2, IL-4, and anti-IFN-gamma Ab (type 2-polarizing conditions) for 8-9 days. Under neutral conditions, most clones produced IFN-gamma without IL-4 and were cytolytic. Under type 2-polarizing conditions, most clones produced IFN-gamma and IL-4 but displayed variable cytolytic activity and CD8 expression. Separation on the basis of surface CD8 levels revealed that, compared with CD8(high) cells from the same cultures, CD8(low) cells were poorly cytolytic and expressed low levels of perforin mRNA and protein and granzyme A, B, and C mRNA. A similar, smaller population of noncytolytic CD8(low) cells was identified among CD8(+) T cells activated in mixed lymphocyte reaction with IL-4. Variable efficiency of generation of the noncytolytic cells may account for the differing results of earlier studies. We conclude that IL-4 promotes the development of a noncytolytic CD8(low) T cell phenotype that might be important in tumor- or pathogen-induced immune deviation.

Stepwise activation of the immunoglobulin mu heavy chain gene locus

The immunoglobulin heavy chain (IgH) gene locus spans several megabases. We show that IgH activation during B-cell differentiation, as measured by histone acetylation, occurs in discrete, independently regulated domains. Initially, a 120 kb domain of germline DNA is hyperacetylated, that extends from D(FL16.1), the 5'-most D(H) gene segment, to the intergenic region between Cmu and Cdelta. Germline V(H) genes were not hyperacetylated at this stage, which accounts for D(H) to J(H) recombination occurring first during B-cell development. Subsequent activation of the V(H) locus happens in at least three differentially regulated domains: an interleukin-7-regulated domain consisting of the 5' J558 family, an intermediate domain and the 3' V(H) genes, which are hyperacetylated in response to DJ(H) recombination. These observations lead to mechanisms for two well-documented phenomena in B-cell ontogeny: the sequential rearrangement of D(H) followed by V(H) gene segments, and the preferential recombination of D(H)-proximal V(H) genes in pro-B cells. We suggest that stepwise activation may be a general mechanism by which large segments of the genome are prepared for expression.

Enforced expression of GATA-3 severely reduces human thymic cellularity

Following bone marrow transplantation, patients often suffer from immune incompetence by reduced or late T cell development. Moreover, adult bone marrow stem cells have a lower capacity to generate T cells compared with fetal liver- and umbilical cord blood-derived progenitors. Therefore, enhancing thymic-dependent T cell generation might hold great therapeutic potential. GATA-3 is a transcription factor that is essential in T cell development. In this study we examined the therapeutic potential of GATA-3 to enhance T cell generation by overexpressing GATA-3 in T cell progenitors followed by fetal thymic organ culture (FTOC). We observed that early during FTOC, there was an enhanced differentiation toward the double positive stage of T cell development. From day 10 of FTOC, however, overexpression of GATA-3 induced a severe reduction in thymic cellularity, which probably correlates with the absence of a functional TCR-beta chain. We further show that the frequency of apoptosis was increased in GATA-3-transduced thymocytes. Despite the absence of a functional TCR-beta chain, GATA-3 transduced progenitors were able to differentiate into CD8beta(+) double positive thymocytes. This study shows that a strictly regulated expression of GATA-3 is essential for normal T cell development and this puts severe restrictions on the potential therapeutic use of continuously overexpressed GATA-3.

Transcriptional regulation of hemopoiesis

The regulation of blood cell formation, or hemopoiesis, is central to the replenishment of mature effector cells of innate and acquired immune responses. These cells fulfil specific roles in the host defense against invading pathogens, and in the maintenance of homeostasis. The development of hemopoietic cells is under stringent control from extracellular and intracellular stimuli that result in the activation of specific downstream signaling cascades. Ultimately, all signal transduction pathways converge at the level of gene expression where positive and negative modulators of transcription interact to delineate the pattern of gene expression and the overall cellular hemopoietic response. Transcription factors, therefore, represent a nodal point of hemopoietic control through the integration of the various signaling pathways and subsequent modulation of the transcriptional machinery. Transcription factors can act both positively and negatively to regulate the expression of a wide range of hemopoiesis-relevant genes including growth factors and their receptors, other transcription factors, as well as various molecules important for the function of developing cells. The expression of these genes is dependent on the complex interactions between transcription factors, co-regulatory molecules, and specific binding sequences on the DNA. Recent advances in various vertebrate and invertebrate systems emphasize the importance of transcription factors for hemopoiesis control and the evolutionary conservation of several of such mechanisms. In this review we outline some of the key issues frequently identified in studies of the transcriptional regulation of hemopoietic gene expression. In teleosts, we expect that the characterization of several of these transcription factors and their regulatory mechanisms will complement recent advances in a number of fish systems where identification of cytokine and other hemopoiesis-relevant factors are currently under investigation.

Enforced expression of GATA-3 during T cell development inhibits maturation of CD8 single-positive cells and induces thymic lymphoma in transgenic mice

The zinc finger transcription factor GATA-3 is of critical importance for early T cell development and commitment of Th2 cells. To study the role of GATA-3 in early T cell development, we analyzed and modified GATA-3 expression in vivo. In mice carrying a targeted insertion of a lacZ reporter on one allele, we found that GATA-3 transcription in CD4(+)CD8(+) double-positive thymocytes correlated with the onset of positive selection events, i.e., TCRalphabeta up-regulation and CD69 expression. LacZ expression remained high ( approximately 80% of cells) during maturation of CD4 single-positive (SP) cells in the thymus, but in developing CD8 SP cells the fraction of lacZ-expressing cells decreased to <20%. We modified this pattern by enforced GATA-3 expression driven by the CD2 locus control region, which provides transcription of GATA-3 throughout T cell development. In two independent CD2-GATA3-transgenic lines, approximately 50% of the mice developed thymic lymphoblastoid tumors that were CD4(+)CD8(+/low) and mostly CD3(+). In tumor-free CD2-GATA3-transgenic mice, the total numbers of CD8 SP cells in the thymus were within normal ranges, but their maturation was hampered, as indicated by increased apoptosis of CD8 SP cells and a selective deficiency of mature CD69(low)HSA(low) CD8 SP cells. In the spleen and lymph nodes, the numbers of CD8(+) T cells were significantly reduced. These findings indicate that GATA-3 supports development of the CD4 lineage and inhibits maturation of CD8 SP cells in the thymus.

Kinetics of GATA-3 gene expression in early polarizing and committed human T cells

Different transcription factors have been shown to control the transition of naive T cells into T helper 1 (Th1)/Th2 subsets. The T-cell-specific transcription factor GATA-3 is known to be selectively expressed in murine developing Th2 cells and to exert a positive action on Th2-specific cytokine production. Investigating GATA-3 gene regulation in human T cells we have found that naive T cells highly express GATA-3, and during early T2 or T1 polarization, respectively, they either maintain or quickly down-regulate expression. In developing T2 cells, as well as in committed Th2 cell lines and clones, we found a positive correlation among GATA-3, interleukin (IL)-5 and IL-4 gene expression kinetics, supporting the positive action of GATA-3 on Th2-specific cytokine production. A possible relationship between GATA-3 gene expression and the down-regulation of the IL-12 receptor (beta2-chain; IL-12Rbeta2) gene was evident only in the early phases of T2 polarization (within 24 hr), and not demonstrated at later times. During T-cell commitment the presence of IL-4 in the culture was essential to maintain or enhance GATA-3 transcription, while IL-12 was not necessary for full repression of GATA-3. Finally, we showed selective GATA-3 up-regulation in human Th2 cell lines and clones and the maintainance of a low basal level of GATA-3 expression in Th1 cells upon activation.

Acetylation of GATA-3 affects T-cell survival and homing to secondary lymphoid organs

Acetylation of a transcription factor has recently been shown to play a significant role in gene regulation. Here we show that GATA-3 is acetylated in T cells and that a mutation introduced into amino acids 305-307 (KRR-GATA3) creates local hypoacetylation in GATA-3. Remarkably, KRR-GATA3 possesses the most potent suppressive effect when compared with other mutants that are disrupted in putative acetylation targets. Expressing this mutant in peripheral T cells results in defective T-cell homing to systemic lymphnodes, and prolonged T-cell survival after activation. These findings have significant implications in that the acetylation state of GATA-3 affects its physiological function in the immune system and, more importantly, provides evidence for the novel role of GATA-3 in T-cell survival and homing to secondary lymphoid organs.

ROG, repressor of GATA, regulates the expression of cytokine genes

GATA-3 is a T cell-specific transcription factor and is essential for the development of the T cell lineage. Recently, it was shown that the expression of GATA-3 is further induced in CD4+ helper T cells upon differentiation into type 2 but not type 1 effector cells. Here, we report the molecular cloning of a GATA-3 interacting protein, repressor of GATA (ROG). ROG is a lymphoid-specific gene and is rapidly induced in Th cells upon stimulation with anti-CD3. In in vitro assays, ROG represses the GATA-3-induced transactivation. Furthermore, overexpression of ROG in Th clones inhibits the production of Th cytokines. Taken together, our results suggest that ROG might play a critical role in regulating the differentiation and activation of Th cells.

The regulation of CD4 and CD8 coreceptor gene expression during T cell development

The two major subsets of T lymphocytes in the peripheral immune system, the helper and cytotoxic T cells, are defined by their expression of either the CD4 or the CD8 glycoproteins, respectively. Expression of these molecules, which serve as coreceptors by interacting specifically with either MHC class II or class I molecules, also defines discrete stages of T cell development within the thymus. Thus, CD4+ and CD8+ single-positive (SP) thymocytes arise from common progenitor double positive (DP) cells that express both CD4 and CD8, during a process known as positive selection. The molecular mechanisms underlying the developmental choice toward the helper or cytotoxic lineage remain poorly understood. Because regulation of coreceptor gene expression appears to be coupled to the phenotypic choice of the differentiating T cell, it is likely that shared signaling pathways direct CD4 and CD8 transcription and the development of an uncommited DP thymocyte toward either the helper or cytotoxic lineage. Therefore, an understanding of how CD4 and CD8 expression is regulated will not only provide insights into transcriptional control mechanisms in T cells, but may also result in the identification of molecular factors that are involved in lineage choices during T cell development. In this review, we summarize recent progress that has been made toward an understanding of how CD4 and CD8 gene expression is regulated.

Transcriptional regulation of T lymphocyte development and function

The development and function of T lymphocytes are regulated tightly by signal transduction pathways that include specific cell-surface receptors, intracellular signaling molecules, and nuclear transcription factors. Since 1988, several families of functionally important T cell transcription factors have been identified. These include the Ikaros, LKLF, and GATA3 zinc-finger proteins; the Ets, CREB/ATF, and NF-kappa B/Rel/NFAT transcription factors; the Stat proteins; and HMG box transcription factors such as LEF1, TCF1, and Sox4. In this review, we summarize our current understanding of the transcriptional regulation of T cell development and function with particular emphasis on the results of recent gene targeting and transgenic experiments. In addition to increasing our understanding of the molecular pathways that regulate T cell development and function, these results have suggested novel targets for genetic and pharmacological manipulation of T cell immunity.

Molecular regulation of cytokine gene expression during the immune response

Cytokine expression by immune system cells plays an important role in the regulation of the immune response. On first encounter with antigen, naive CD4+ T helper (Th) cells differentiate into cytokine-producing effector cells. Two types of effector cells characterized by their distinct expression of cytokine profiles have been described. Th1 cells produce IL-2 and IFN-gamma, whereas Th2 cells produce IL-4, IL-5, IL-6, IL-10, and IL-13. In many pathological situations, the balance between Th1 and Th2 immune responses determines the outcome of diverse immunologically mediated clinical syndromes including infectious, autoimmune, and allergic diseases. However, the molecular basis for the tissue-specific expression of Th1/Th2-like cytokines has remained elusive. In this review we evaluate the possible in vivo role of different transcription factors and transcriptional mechanisms in T cell differentiation and the immune response.

Hierarchical interactions of control elements determine CD8alpha gene expression in subsets of thymocytes and peripheral T cells

CD4 and CD8 are crucial for the development and function of T cells. An intergenic deoxyribonuclease I hypersensitive site region (cluster CIII) directs expression in mature CD8 T cells only. Here, we show that two further independent regions from the CD8 gene locus in conjunction with cluster CIII restore transgene expression in appropriate immature thymocytes. Deletion of two of the intergenic cluster CIII DNaseI-HSS in homozygous mutant mice affects expression of CD8alphaalpha homodimers on intraepithelial T cells (IEL), particularly on the gammadeltaTCR+ subset. Surprisingly, none of the thymocyte or peripheral alphabetaTCR T cell subsets are affected by this mutation, indicating hierarchical activation of these elements within the different T cell subsets.

Distinct Stage-Specific cis-Active Transcriptional Mechanisms Control Expression of T Cell Coreceptor CD8α at Double- and Single-Positive Stages of Thymic Development

Developing thymocytes that give rise to CD8+ (cytotoxic) and CD4+ (helper) αβ-TCR T lymphocytes go through progressive stages of expression of coreceptors CD8 and CD4 from being negative for both (the double-negative stage), to coexpressing both (the double-positive (DP) stage), to a mutually exclusive sublineage-specific expression of one or the other (the single-positive (SP) stage). To delineate the mechanisms underlying regulation of CD8 during these developmental transitions, we have examined expression of a series of mouse CD8α gene constructs in developing T cells of conventional and CD8α “knock-out” transgenic mice. Our results indicate that cis-active transcriptional control sequences essential for stage- and sublineage-specific expression lie within a 5′ 40-kb segment of the CD8 locus, ∼12 kb upstream of the CD8α gene. Studies to characterize and sublocalize these cis sequences showed that a 17-kb 5′ subfragment is able to direct expression of the CD8α gene up to the CD3intermediate DP stage but not in more mature DP or SP cells. These results indicate that stage-specific expression of CD8α in developing T cells is mediated by the differential activity of multiple functionally distinct cis-active transcriptional control mechanisms. It will be important to determine the relationship of “switching” between these cis mechanisms and selection.

Regulatory Elements in the Promoter of a Murine TCRD V Gene Segment

TCRD V segments rearrange in an ordered fashion during human and murine thymic development. Recombination requires the accessibility of substrate gene segments, and transcriptional enhancers and promoters have been shown to regulate the accessible chromatin configuration. We therefore investigated the regulation of TCRD V rearrangements by characterizing the promoter of the first TCRD V segment to be rearranged, DV101S1, under the influence of its own enhancer. Sequences required for full promoter activity were identified by transient transfections of normal and mutated promoters into a human γδ lymphoma, and necessary elements fall between −86 and +66 nt, relative to the major transcription start site. They include a cAMP responsive element (CRE) at −62, an Ets site at −39, a TATA box at −26, the major transcriptional start site sequence (−8 to −5 and −2 to +11), and a downstream sequence (+12 to +33). Gel shift analyses and in vitro DNase I footprinting showed that nuclear proteins bind to the functionally relevant CRE, Ets, +1 to +10 sequence, and the +17 to +21 sequence. Nuclear proteins also bind to an E box at −52, and GATA-3 binds to a GATA motif at −5, as shown by Ab ablation-supershift experiments, but mutations that abrogated protein binding to these sites failed to affect DV101S1 promoter activity. We conclude that not all protein-binding sites within the DV101S1 minimal promoter are important for enhancer driven TCRD gene transcription. Further, the possibility remains that the GATA and E box sites function in enhancer independent DV101S1 germline transcription.

An enhancer that directs lineage-specific expression of CD8 in positively selected thymocytes and mature T cells

Positive selection of CD4+CD8+ T cells to the CD4+CD8- helper and CD4- CD8+ cytotoxic lineages is a multistep process that involves complex regulation of coreceptor gene expression. By analyzing expression of a reporter gene in transgenic mice, we have identified a DNA segment, located between the murine CD8beta and CD8alpha genes, that has enhancer activity restricted to CD8 lineage cells. Remarkably, this enhancer functions in thymocytes undergoing positive selection to the CD4-CD8+ phenotype but not in immature double-positive thymocytes. The enhancer also functions in gut intraepithelial lymphocytes that express CD8alpha but not CD8beta, suggesting that it is specific for CD8alpha expression. The tight correlation between activation of this enhancer and the final step in positive selection has important implications for understanding the mechanism of lineage commitment in thymocytes.

A region in the CD8 gene locus that directs expression to the mature CD8 T cell subset in transgenic mice

The coreceptors CD4 and CD8 play a crucial role during thymocyte development and T cell effector function, and their expression is developmentally regulated. To determine the underlying molecular mechanisms of CD8 gene regulation we cloned the murine CD8 gene locus from genomic libraries and analyzed this region for deoxyribonuclease (DNase I) hypersensitive sites (HSS). Here we report, using transgenic mice, deletion analysis of one of the identified clusters of DNase I hypersensitivity, consisting of three DNase I-HSS and located in the intergenic region between the CD8alpha and CD8beta genes. Our data show that at least two of the DNase I-HSS constituting this cluster are individually sufficient to direct CD8alpha or heterologous transgene expression to the mature CD8 single-positive T cell subset and that this expression coincides temporally with the appearance of positively selected T cells.

Temporal and spatial control of murine GATA-3 transcription by promoter-proximal regulatory elements

GATA-3 is expressed in a temporally dynamic manner and fulfills vital functions during vertebrate fetal development. Homozygous mGATA-3 mutant embryos die at midgestation, thus complicating the analysis of its contribution to the development of specific cell fates in the many tissues where it is expressed during embryogenesis. We show here that the elements controlling GATA-3 regulation can be precisely refined, using transgenic mice, to discrete cis-acting domains: within 6 kb surrounding the transcriptional initiation site, separate sequences were found to control the expression of mGATA-3 in early muscle masses, in a subset of PNS neurons, in the genital tubercle, and in the branchial arches. The branchial arch regulatory element is particularly robust and was refined to a discrete enhancer sequence lying between nt -2832 and -2462 from the transcription initiation site. The enhancer contains potential binding sites for many well-characterized transcription factors, suggesting that mGATA-3 transcriptional activity may be regulated by these proteins (or related family members) in the mesenchyme of the arches that contribute to formation of the jaw. These studies show that discrete regulatory elements required for the elaboration of complex developmental programs can be individually localized, suggesting that the developmentally transient expression of individual transcription factors collaboratively contributes to the temporal and spatial pattern of cellular differentiation leading to the formation of adult anatomy.

Interaction of the nuclear matrix-associated region (MAR)-binding proteins, SATB1 and CDP/Cux, with a MAR element (L2a) in an upstream regulatory region of the mouse CD8a gene

Matrix-associated regions (MARs), AT-rich DNA segments that have an affinity for the nuclear matrix, have been shown to play a role in transcriptional regulation of eukaryotic genes. The present study demonstrates that a DNA element, called L2a, which has been implicated in the transcriptional regulation of the mouse CD8a gene encoding an important T cell coreceptor, is a MAR. Moreover, the identities of two nuclear proteins, L2a-P1 and L2a-P2, previously shown to bind to the L2a element, have been determined. The L2a-P1 protein found to be present in all CD8-positive T cell lines tested is SATB1, a known MAR-binding protein. The widely expressed L2a-P2 protein is CDP/Cux, a MAR-binding protein that has been associated with repression of gene transcription. Interaction of both proteins with the L2a element was studied using the missing nucleoside approach, DNase I footprinting, and electrophoretic mobility shift assays with wild type and mutant L2a elements. The data suggest that CDP/Cux bound to the L2a element is displaced by binding of SATB1 and the accompanying conformational change in the DNA lying between the primary binding sites of SATB1 and CDP/Cux. We suggest that displacement of CDP/Cux by SATB1 favors transcription of the CD8a gene, possibly by enhancing or altering its association with the nuclear matrix.

Transcription Factor GATA-2 Is Required for Proliferation/Survival of Early Hematopoietic Cells and Mast Cell Formation, But Not for Erythroid and Myeloid Terminal Differentiation

The zinc-finger transcription factor GATA-2 plays a critical role in maintaining the pool of early hematopoietic cells. To define its specific functions in the proliferation, survival, and differentiation of hematopoietic cells, we analyzed the hematopoietic potential of GATA-2−/− cells in in vitro culture systems for proliferation and maintenance of uncommitted progenitors or differentiation of specific lineages. From a two-step in vitro differentiation assay of embryonic stem cells and in vitro culture of yolk sac cells, we demonstrate that GATA-2 is required for the expansion of multipotential hematopoietic progenitors and the formation of mast cells, but dispensable for the terminal differentiation of erythroid cells and macrophages. The rare GATA-2−/− multipotential progenitors that survive proliferate poorly and generate small colonies with extensive cell death, implying that GATA-2 may play a role in both the proliferation and survival of early hematopoietic cells. To explore possible mechanisms resulting in the hematopoietic defects of GATA-2−/− cells, we interbred mutant mouse strains to assess the effects of p53 loss on the behavior of GATA-2−/− hematopoietic cells. Analysis of GATA-2−/−/p53−/− compound-mutant embryos shows that the absence of p53 partially restores the number of total GATA-2−/− hematopoietic cells, and therefore suggests a potential link between GATA-2 and p53 pathways.

Transcription Factor GATA-2 Is Required for Proliferation/Survival of Early Hematopoietic Cells and Mast Cell Formation, But Not for Erythroid and Myeloid Terminal Differentiation

The zinc-finger transcription factor GATA-2 plays a critical role in maintaining the pool of early hematopoietic cells. To define its specific functions in the proliferation, survival, and differentiation of hematopoietic cells, we analyzed the hematopoietic potential of GATA-2−/− cells in in vitro culture systems for proliferation and maintenance of uncommitted progenitors or differentiation of specific lineages. From a two-step in vitro differentiation assay of embryonic stem cells and in vitro culture of yolk sac cells, we demonstrate that GATA-2 is required for the expansion of multipotential hematopoietic progenitors and the formation of mast cells, but dispensable for the terminal differentiation of erythroid cells and macrophages. The rare GATA-2−/− multipotential progenitors that survive proliferate poorly and generate small colonies with extensive cell death, implying that GATA-2 may play a role in both the proliferation and survival of early hematopoietic cells. To explore possible mechanisms resulting in the hematopoietic defects of GATA-2−/− cells, we interbred mutant mouse strains to assess the effects of p53 loss on the behavior of GATA-2−/− hematopoietic cells. Analysis of GATA-2−/−/p53−/− compound-mutant embryos shows that the absence of p53 partially restores the number of total GATA-2−/− hematopoietic cells, and therefore suggests a potential link between GATA-2 and p53 pathways.

Involvement of transcription factors TCF-1 and GATA-3 in the initiation of the earliest step of T cell development in the thymus

Flow cytometric and immunocytochemical analyses of murine fetal thymus (FT) cells with antibodies to various surface markers and transcription factors reveal that the synthesis of TCF-1 and GATA-3 protein begins simultaneously in a fraction of the most immature population of FT cells, which have the phenotype of CD4-CD8-CD44+CD25-. No TCF-1-producing cells is found in the fetal liver (FL). In CD44+CD25- FT cells, the production of TCF-1 is immediately followed by intracellular expression of CD3 epsilon. It is also found that the T cell development from FL, but not FT, progenitors in the FT organ culture system is severely inhibited by the addition of antisense oligonucleotides for either TCF-1 or GATA-3. These results strongly suggest that TCF-1 and GATA-3 play essential roles in the initiation of the earliest steps of T cell development in the thymus.

Characterization of the mouse CD8 beta chain-encoding gene promoter region

We identified a regulatory region of the mouse CD8 beta chain-encoding gene (CD8b) promoter. The CD8b 5' upstream sequence could not drive the expression of the bacterial chloramphenicol acetyltransferase (CAT) gene without T-cell receptor or SV40 enhancer elements. The results of transient transfection assays indicated that the dominant transcription-activating element within the CD8b-promoter is located at -45 to -40 base pairs (CCGCCC) from the transcriptional initiation site. Elimination of this element, by deletion or specific point mutation, significantly reduced transcriptional activity from this promoter. The sequence of this core region corresponds to a GC box motif known to act as a binding site for a ubiquitously expressed transcriptional activator, Sp1. However, the promoter activity appeared to be T-cell-specific, and the gel retardation assay using the core sequence as a probe revealed formation of complexes with multiple nuclear factors, one of them being specific to T lineage cells. These data suggest that the CD8b promoter requires a cis-acting element as well as several nuclear factors for full-range, tissue-specific transcription.

Regulation of Drosophila yolk protein genes by an ovary-specific GATA factor

The divergently transcribed yolk protein genes (Yp1 and Yp2) of Drosophila melanogaster are expressed only in adult females, in fat body tissue and in ovarian follicle cells. Using an in vitro transcription assay, we have identified a single 12-bp DNA element that activates transcription from the promoters of both Yp genes. In vivo, this regulatory element is tissue specific: it activates transcription of Yp1 and Yp2 reporter genes in follicle cells but has no detectable effect in fat body or other tissues. The sequence of the element consists of two recognition sites for the GATA family of transcription factors. We show that among the Drosophila genes known to encode GATA factors, only dGATAb is expressed in ovaries. The single transcript that we detect in ovaries is alternatively spliced or initiated to produce an ovary-specific isoform of the protein. Bacterially expressed dGATAb binds to the 12-bp element; a similar binding activity is also present in the Kc0 nuclear extracts used for in vitro transcription assays. These in vitro and in vivo results lead us to propose that dGATAb makes several developmentally regulated products, one of which is a follicle cell-specific protein activating transcription of Yp1 and Yp2 from a known regulatory element.

The GATA-3 gene is expressed during human kidney embryogenesis

GATA-3 is a transcription factor involved in the differentiation of T lymphocytes and additionally expressed in several chicken and mouse embryonic tissues. Using in situ hybridization, we found that the human GATA-3 gene is selectively expressed in the developing kidney. GATA-3 mRNA is first detected in the Wolffian duct from the time of its emergence in the embryonic intermediate mesoderm and further expressed in the collecting ducts of the mesonephros until its involution. In the metanephros, GATA-3 is expressed in the ureteric bud where it is constitutively transcribed, throughout development, along the branching process that gives rise to the whole collecting system of the definitive kidney. Besides the Wolffian duct and derivatives, we also report the expression of GATA-3 gene in the glomerular mesangium and adjacent endocapillary cells, in both meso- and metanephros. This early and specific expression of the GATA-3 gene suggests a role for this transcription factor in the differentiation of the human kidney.

Hematopoietic lineage commitment: role of transcription factors

This review focuses on the roles of transcription factors in hematopoietic lineage commitment. A brief introduction to lineage commitment and asymmetric cell division is followed by a discussion of several methods used to identify transcription factors important in specifying hematopoietic cell types. Next is presented a discussion of the use of embryonic stem cells in the analysis of hematopoietic gene expression and the use of targeted gene disruption to analyze the role of transcription factors in hematopoiesis. Finally, the status of our current knowledge concerning the roles of transcription factors in the commitment to erythroid, myeloid and lymphoid cell types is summarized.

GATA-3 dominant negative mutant. Functional redundancy of the T cell receptor alpha and beta enhancers

The GATA family of transcription factors regulates a wide variety of genes, including those involved in differentiation of erythrocytes and T lymphocytes. We report here the creation of a dominant negative mutant of GATA-3, KRR, which effectively blocks wild-type GATA-1, GATA-2, and GATA-3 transactivation when co-expressed in transient assays. KRR was generated by site-directed mutagenesis while investigating a putative activation domain of GATA-3, located between its two zinc fingers. The GATA-3 KRR mutation does not affect expression, nuclear translocation, or the ability to bind to a consensus GATA sequence. KRR can suppress the activity of the minimal T cell receptor (TCR) alpha and beta enhancers by 12- and 3.4-fold, respectively. However, KRR did not have a significant effect on the activity of larger TCR-alpha and -beta enhancer fragments. Thus, functional redundancy in the TCR-alpha and -beta enhancers can compensate for the loss of GATA-3 activity.

Elf-1 binds to a critical element in a second CD4 enhancer

The coordinated expression of CD4 and CD8 during T-cell development is tightly coupled with the maturation state of the T cell. Additionally, the mutually exclusive expression of these receptors in mature T cells is representative of the functional T-cell subclasses (CD4+ helper T cells versus CD8+ cytotoxic T cells). We have studied the regulation CD4 gene transcription during T-cell development in an attempt to gain an understanding of the molecular mechanisms involved in T-cell development and differentiation. Here we present the identification of a second transcriptional enhancer in the murine CD4 locus 24 kb upstream of the CD4 promoter. This enhancer is active in mature T cells and is especially active in CD4+ helper T cells. A number of nuclear proteins bind to elements in the minimal CD4 enhancer that includes consensus sites for AP-1, Sp1, Gata, and Ets transcription factor families. We find that the Ets consensus site is crucial for enhancer activity and that the recently identified Ets factor, Elf-1, which is expressed at high levels in T cells and involved in the regulation of several other T-cell-specific genes, is a dominant protein in T-cell nuclear extracts that binds to this site.

Elf-1 binds to a critical element in a second CD4 enhancer

The coordinated expression of CD4 and CD8 during T-cell development is tightly coupled with the maturation state of the T cell. Additionally, the mutually exclusive expression of these receptors in mature T cells is representative of the functional T-cell subclasses (CD4+ helper T cells versus CD8+ cytotoxic T cells). We have studied the regulation CD4 gene transcription during T-cell development in an attempt to gain an understanding of the molecular mechanisms involved in T-cell development and differentiation. Here we present the identification of a second transcriptional enhancer in the murine CD4 locus 24 kb upstream of the CD4 promoter. This enhancer is active in mature T cells and is especially active in CD4+ helper T cells. A number of nuclear proteins bind to elements in the minimal CD4 enhancer that includes consensus sites for AP-1, Sp1, Gata, and Ets transcription factor families. We find that the Ets consensus site is crucial for enhancer activity and that the recently identified Ets factor, Elf-1, which is expressed at high levels in T cells and involved in the regulation of several other T-cell-specific genes, is a dominant protein in T-cell nuclear extracts that binds to this site.

Embryonic expression and cloning of the murine GATA-3 gene

We describe the embryonic expression pattern as well as the cloning and initial transcriptional regulatory analysis of the murine (m) GATA-3 gene. In situ hybridization shows that mGATA-3 mRNA accumulation is temporally and spatially regulated during early development: although found most abundantly in the placenta prior to 10 days of embryogenesis, mGATA-3 expression becomes restricted to specific cells within the embryonic central nervous system (in the mesencephalon, diencephalon, pons and inner ear) later in gestation. GATA-3 also shows a restricted expression pattern in the peripheral nervous system, including terminally differentiating cells in the cranial and sympathetic ganglia. In addition to this distinct pattern in the nervous system, mGATA-3 is also expressed in the embryonic kidney and the thymic rudiment, and further analysis showed that it is expressed throughout T lymphocyte differentiation. To begin to investigate how this complex gene expression pattern is elicited, cloning and transcriptional regulatory analyses of the mGATA-3 gene were initiated. At least two regulatory elements (one positive and one negative) appear to be required for appropriate tissue-restricted regulation after transfection of mGATA-3-directed reporter genes into cells that naturally express GATA-3 (T lymphocytes and neuroblastoma cells). Furthermore, this same region of the locus confers developmentally appropriate expression in transgenic mice, but only in a subset of the tissues that naturally express the gene.