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Trend analysis of the consumption of ready-made food in Belgium. This study aims to analyze the evolution of the consumption of ready-made food in Belgium and to discern any trends. The data used are expenditure made on convenience food from 1999 to 2009 (in euros) and socio-demographic characteristics, obtained from the Household Budget Survey undertaken annually by the Federal Public Service Economy (DGSIE). Statistical analyses (simple, multiple and binary logistic regressions) enable the study of consumption trends in terms of expenditure and percentage of consumers as well as the determination of consumer profiles. Convenience food is part of the eating habits of Belgian households, with more than nine out of ten households being consumers. Convenience food prepared from meat is the most frequently purchased. For all ready-made food, the variable of household size explains the most variability in consumption, followed by the variables of income and age.

With the objective of determining whether it would be possible to sustainably produce Jatropha curcas L. seeds on the marginal land situated close to the Senegal River, a 6-hectare pilot plantation was cultivated under drip irrigation between September 2007-November 2011, close to the village of Bokhol (Lat. 16°31'N, Long. 15°23'W). A series of tests were conducted on this plot, in order to identify the best cultivation methods for the area (date, density and method of planting, appropriate type of pruning, fertilisers to be applied, irrigation method, etc.). The average yields obtained at this site, after four years of cultivation (less than 500 kg.ha-1 of dry seed), using the best known production techniques, are significantly lower than anticipated, compared to the available figures for the irrigated cultivation of Jatropha in other parts of the world. The main causes of this failure are the plant's limited useful vegetation period of six months per year, instead of twelve, and the scale of attacks by a soilborne vascular disease, which destroyed over 60% of the plantation within four years.

Jatropha curcas L. seed oil is proven to be toxic to many microorganisms, insects and animals. Despite its toxicity, Jatropha is not pest and disease resistant. The following major pests and diseases affecting Jatropha in the lower valley of the Senegal river have been identified: the leaf miner Stomphastis thraustica (Meyrick, 1908) (Lepidoptera, Gracillariidae), the leaf and stem miner Pempelia morosalis (Saalmuller, 1880) (Lepidoptera, Pyralidae) and the shield-backed bug Calidea panaethiopica (Kirkaldy, 1909) (Heteroptera, Scutelleridae), which can cause flower and fruit abortion. Damage from these pests was particularly great during the second year after the plantations were set up (2009) and before later receding. Nevertheless, the worst attacks were caused by a vascular disease transmitted through the soil, which killed 65% of the plants in four years. It is mainly characterised by collar and root rot, which causes foliage to yellow and wilt, before the plant eventually dies. These threats should increase if larger areas are planted with Jatropha. Considering the scale of the damage caused by these attacks in Bokhol, the development of an integrated pest management programme adapted to the local context should be considered.

CD4 Th cells are organizers of the immune response, directing other immune cells to initiate and maintain effective humoral and cellular immunity. CD4 T cells differentiate into distinct Th effector or regulatory subsets in response to signals delivered to them during the course of infection. Ikaros is a transcription factor that is expressed in blood cells from the level of the hematopoietic stem cell. It is required for normal thymic T cell development and serves as a tumor suppressor, as lack of Ikaros in developing lymphoid cells results in leukemia. To study the role of Ikaros in CD4 T cell differentiation and function, an Ikaros conditional knockout mouse was developed such that Ikaros expression was deleted specifically in mature T cells, thus avoiding defects observed in germline Ikaros mutant mice. Using this model system, we have shown that in the absence of Ikaros, CD4 T cells are able to attain Th1, Th2, and Th17, but not inducible regulatory T, cell fates. However, they show enhanced expression of a cohort of proinflammatory cytokines, resulting in differentiation of Th17 cells with a phenotype that has been associated with autoimmunity and pathological inflammation. In addition, we define Ikaros as a repressor of the gene program associated with the response to type I IFNs, another key pathway whose deregulation is linked to autoimmunity. Taken together, these data definitively define Ikaros as a critical regulator at the center of the inflammatory response in T cells and highlight a potential role in suppressing autoimmunity., (Copyright © 2019 by The American Association of Immunologists, Inc.)

The Notch receptor is an evolutionarily highly conserved transmembrane protein essential to a wide spectrum of cellular systems, and its deregulation has been linked to a vast number of developmental disorders and malignancies. Regulated Notch function is critical for the generation of T-cells, in which abnormal Notch signaling results in leukemia. Notch activation through trans -activation of the receptor by one of its ligands expressed on adjacent cells has been well defined. In this canonical ligand-dependent pathway, Notch receptor undergoes conformational changes upon ligand engagement, stimulated by a pulling-force on the extracellular fragment of Notch that results from endocytosis of the receptor-bound ligand into the ligand-expressing cell. These conformational changes in the receptor allow for two consecutive proteolytic cleavage events to occur, which release the intracellular region of the receptor into the cytoplasm. It can then travel to the nucleus, where it induces gene transcription. However, there is accumulating evidence that other pathways may induce Notch signaling. A ligand-independent mechanism of Notch activation has been described in which receptor processing is initiated via cell-internal signals. These signals result in the internalization of Notch into endosomal compartments, where chemical changes existing in this microenvironment result in the conformational modifications required for receptor processing. This review will present mechanisms underlying both canonical ligand-dependent and non-canonical ligand-independent Notch activation pathways and discuss the latter in the context of Notch signaling in T-cells.

Key Points: Adenosine is a widespread neuromodulator in the mammalian brain, but whether it affects information processing in sensory system(s) remains largely unknown. Here we show that adenosine A 1 receptors hyperpolarize mitral cells, one class of principal neurons that propagate odour information from the olfactory bulb to higher brain areas, by activation of background K + channels. The adenosine-modulated background K + channels belong to the family of two-pore domain K + channels. Adenosine reduces spontaneous activity of mitral cells, whereas action potential firing evoked by synaptic input upon stimulation of sensory neurons is not affected, resulting in a higher ratio of evoked firing (signal) over spontaneous firing (noise) and hence an improved signal-to-noise ratio. The study shows for the first time that adenosine influences fine-tuning of the input-output relationship in sensory systems., Abstract: Neuromodulation by adenosine is of critical importance in many brain regions, but the role of adenosine in olfactory information processing has not been studied so far. We investigated the effects of adenosine on mitral cells, which are projection neurons of the olfactory bulb. Significant expression of A 1 and A 2A receptors was found in mitral cells, as demonstrated by in situ hybridization. Application of adenosine in acute olfactory bulb slices hyperpolarized mitral cells in wild-type but not in adenosine A 1 receptor knockout mice. Adenosine-induced hyperpolarization was mediated by background K + currents that were reduced by halothane and bupivacaine, which are known to inhibit two-pore domain K + (K2P) channels. In mitral cells, electrical stimulation of axons of olfactory sensory neurons evoked synaptic currents, which can be considered as input signals, while spontaneous firing independent of sensory input can be considered as noise. Synaptic currents were not affected by adenosine, while adenosine reduced spontaneous firing, leading to an increase in the signal-to-noise ratio of mitral cell firing. Our findings demonstrate that A 1 adenosine receptors activate two-pore domain K + channels, which increases the signal-to-noise ratio of the input-output relationship in mitral cells and thereby modulates information processing in the olfactory bulb., (© 2017 The Authors. The Journal of Physiology © 2017 The Physiological Society.)

The Notch receptor is an evolutionarily highly conserved transmembrane protein that is essential to a wide spectrum of cellular systems. Notch signaling is especially important to T cell development, and its deregulation leads to leukemia. Although not well characterized, it continues to play an integral role in peripheral T cells, in which a unique mode of Notch activation can occur. In contrast to canonical Notch activation initiated by adjacent ligand-expressing cells, TCR stimulation is sufficient to induce Notch signaling. However, the interactions between these two pathways have not been defined. In this article, we show that Notch activation occurs in peripheral T cells within a few hours post-TCR stimulation and is required for optimal T cell activation. Using a panel of inhibitors against components of the TCR signaling cascade, we demonstrate that Notch activation is facilitated through initiation of protein kinase C-induced ADAM activity. Moreover, our data suggest that internalization of Notch via endocytosis plays a role in this process. Although ligand-mediated Notch stimulation relies on mechanical pulling forces that disrupt the autoinhibitory domain of Notch, we hypothesized that, in T cells in the absence of ligands, these conformational changes are induced through chemical adjustments in the endosome, causing alleviation of autoinhibition and receptor activation. Thus, T cells may have evolved a unique method of Notch receptor activation, which is described for the first time, to our knowledge, in this article., (Copyright © 2018 by The American Association of Immunologists, Inc.)

Ikaros is a transcription factor that regulates lymphocyte development from the level of the haematopoietic stem cell. Lack of Ikaros reduces the ability of progenitor cells to commit to the T-cell lineage, resulting in reduced numbers of early thymic T-cell progenitors and mature T cells. Mature CD4 T cells that lack Ikaros have defects in proliferation, T helper cell differentiation, cytokine expression and the ability to become anergic. A role for Ikaros in the naive T cell has not yet been identified. The receptors interleukin-7 receptor α (IL-7Rα) and l-selectin are important for ensuring survival and proper homing of naive T cells, respectively. Here we show that lack of Ikaros leads to reduced expression of these receptors in naive T cells, which impacts their ability to home and survive in response to IL-7. We define the mechanism underlying this phenotype as a requirement for Ikaros in maintenance of expression of Foxo1, a transcriptional regulator that is required for their expression. We also demonstrate that CD4 T cells lacking Ikaros are significantly crippled in their ability to become induced regulatory T cells, a phenotype also linked to reduced Foxo1 expression. Finally, we show that restoring Ikaros function to Ikaros-deficient CD4 T cells increases levels of Foxo1 message. Together, these studies define, for the first time, a role for Ikaros in naive T cells and establish it as the first transcriptional regulator required for maintaining levels of Foxo1 gene expression in these cells., (© 2017 John Wiley & Sons Ltd.)

The transcription factor Ikaros regulates the development of hematopoietic cells. Ikaros-deficient animals fail to develop B cells and display a T-cell malignancy, which is correlated with altered Notch signaling. Recently, loss of Ikaros was associated with progression of myeloproliferative neoplasms to acute myeloid leukemia and increasing evidence shows that Ikaros is also critical for the regulation of myeloid development. Previous studies showed that Ikaros-deficient mice have increased megakaryopoiesis, but the molecular mechanism of this phenomenon remains unknown. Here, we show that Ikaros overexpression decreases NOTCH-induced megakaryocytic specification, and represses expression of several megakaryocytic genes including GATA-1 to block differentiation and terminal maturation. We also demonstrate that Ikaros expression is differentially regulated by GATA-2 and GATA-1 during megakaryocytic differentiation and reveal that the combined loss of Ikzf1 and Gata1 leads to synthetic lethality in vivo associated with prominent defects in erythroid cells and an expansion of megakaryocyte progenitors. Taken together, our observations demonstrate an important functional interplay between Ikaros, GATA factors, and the NOTCH signaling pathway in specification and homeostasis of the megakaryocyte lineage.

Ikaros is a transcriptional regulator critical for B- and T-cell development. Recently, it has been shown to play a central role in facilitating rearrangement of antigen-receptor genes in B cells. Whether or not it had a similar function in this process in T cells, however, was a mystery. In this issue of the European Journal of Immunology, a role for Ikaros in T-cell receptor (TCR) rearrangement and expression of TCR-α chain genes is revealed in the study by Collins et al. [Eur. J. Immunol. 2013. 43: 521-532]. Ikaros functions in this capacity as an "accessibility factor," facilitating increased TCR-α chain gene transcription and accessibility of the locus to promote rearrangement. Interestingly, this study has also revealed differences in the mechanisms by which Ikaros promotes antigen-receptor rearrangement in B versus T cells, thereby suggesting that Ikaros may have lineage-specific functions in coordinating antigen-receptor rearrangement., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Host hematopoietically derived APCs play a vital role in the initiation of GVH responses. However, the APC autonomous molecular mechanisms that are critical for the induction of GVHD are not known. We report here that the Ikaros-Notch axis in host hematopoietically derived APCs regulates the severity of acute GVHD across multiple clinically relevant murine models of experimental bone marrow transplantation. In the present study, Ikaros deficiency (Ik(-/-)) limited to host hematopoietically derived APCs enhanced donor T-cell expansion and intensified acute GVHD, as determined by survival and other GVHD-specific parameters. The Ik(-/-) conventional CD8(+) and CD8(-)CD11c(+) dendritic cells (DCs), the most potent APCs, showed no increase in the expression of activation markers or in response to TLR stimulation compared with wild-type controls. However, Ik(-/-) DCs demonstrated an enhanced stimulation of allogeneic T cells. Deficiency of Ikaros in the conventional CD8(+) and CD8(-)CD11c(+) DCs was associated with an increase in Notch signaling, the blockade of which mitigated the enhanced in vitro and in vivo allostimulatory capacity. Therefore, the Ikaros-Notch axis is a novel pathway that modulates DC biology in general, and targeting this pathway in host hematopoietically derived APCs may reduce GVHD.

Ikaros and Notch are transcriptional regulators essential for normal T cell development. Aberrant activation of Notch target genes is observed in Ikaros-deficient thymocytes as well as leukemia cell lines. However, it is not known whether Notch deregulation plays a preferential or obligatory role in the leukemia that arise in Ikaros null (Ik(-/-)) mice. To answer this question, the expression of the DNA-binding Notch target gene activator RBP-Jkappa was abrogated in Ik(-/-) double-positive thymocytes. This was accomplished through conditional inactivation using CD4-Cre transgenic mice containing floxed RBP-Jkappa alleles (RBPJ(fl/fl)). Ik(-/-) x RBPJ(fl/fl) x CD4-Cre(+) transgenic mice develop clonal T cell populations in the thymus that escape to the periphery, with similar kinetics and penetrance as their CD4-Cre(-) counterparts. The clonal populations do not display increased RBP-Jkappa expression compared with nontransformed thymocytes, suggesting there is no selection for clones that have not fully deleted RBP-Jkappa. However, RBPJ-deficient clonal populations do not expand as aggressively as their RBPJ-sufficient counterparts, suggesting a qualitative role for deregulated Notch target gene activation in the leukemogenic process. Finally, these studies show that RBP-Jkappa plays no role in Notch target gene repression in double-positive thymocytes but rather that it is Ikaros that is required for the repression of these genes at this critical stage of T cell development.

IL-10 is a regulatory cytokine critical for controlling inflammatory responses. Here we show that Ikaros, a zinc finger DNA-binding protein, plays an important role in the regulation of Il10 in murine CD4(+) T cells. Upon initial stimulation of the TCR, T cells deficient in Ikaros express significantly lower levels of IL-10 compared with wild-type T cells. In addition, under Th2 skewing conditions, which induce IL-10 production by wild-type T cells, Ikaros null T cells are unable to properly differentiate, producing only low levels of IL-10. Expression of a dominant-negative isoform of Ikaros in wild-type Th2 cells represses IL-10 production but does not significantly alter expression levels of the genes encoding the transcription factors GATA-3 and T-bet. Furthermore, expression of Ikaros in Ikaros null T cells restores expression of the Th2 cytokines IL-10 and IL-4 while reducing production of the Th1 cytokine, IFN-gamma. Coexpression of Ikaros and GATA-3 further increases IL-10 production, showing that these two factors have an additive effect on activating Il10 expression. Finally, we show that Ikaros binds to conserved regulatory regions of the Il10 gene locus in Th2 cells, supporting a direct role for Ikaros in Il10 expression. Thus, we provide evidence for Ikaros as a regulator of Il10 and Ifng gene expression and suggest a role for Ikaros in directing lineage-specific cytokine gene activation and repression.

Positive selection is a critical T cell developmental checkpoint that is driven by TCR signals. Enhanced positive selection toward the CD4 lineage occurs in the absence of Ikaros. One explanation for this phenotype is that Ikaros establishes the TCR signaling threshold that must be overcome for positive selection to occur. In the current study, this possibility is explored through the use of CD3zeta ITAM transgenic mice that express a CD3 zeta-chain with zero, one, or three ITAMs and an MHC class II (DO11.10)- or MHC class I (H-Y)-restricted TCR transgene. Using this system, we demonstrate that in the absence of Ikaros, thymocytes are able to mature into the CD4 lineage with reduced TCR signaling potential compared with that required to drive the maturation of wild-type thymocytes. We also demonstrate that maturation into the CD8 lineage is enhanced under conditions of reduced TCR signaling potential in the absence of Ikaros.

Ikaros, a hematopoietic transcription factor, has well defined effects on early lymphocyte development in the bone marrow and thymus. In this study we demonstrate that Ikaros is a positive regulator of Th2 cytokine gene expression in peripheral T cells. CD4+ T cells from naive Ikaros(null) mice cultured under Th2-skewing conditions express the Th1 cytokine IFN-gamma and have reduced IL-4, IL-5, and IL-13 expression. Ikaros directly associates with several Th2 locus regulatory regions in naive CD4+ T cells. The decreased ability to express Th2 cytokines in Ikaros(null)T cells corresponds with histone 3 hypoacetylation across the Th2 cytokine locus as well as decreased GATA3 and cMaf and increased T-bet and STAT1 expression. These data support a model whereby Ikaros directly activates Th2 gene expression by promoting local chromatin accessibility during CD4+ T cell differentiation and also acts indirectly to regulate expression of Th2- and Th1-specific transcription factors.

Both Ikaros and Notch are essential for normal T cell development. Collaborative mutations causing a reduction in Ikaros activity and an increase in Notch activation promote T cell leukemogenesis. Although the molecular mechanisms of this cooperation have been studied, its consequences in thymocyte development remain unexplored. In this study, we show that Ikaros regulates expression of a subset of Notch target genes, including Hes1, Deltex1, pTa, Gata3, and Runx1, in both Ikaros null T cell leukemia lines and Ikaros null primary thymocytes. In Ikaros null leukemia cells, Notch deregulation occurs at both the level of Notch receptor cleavage and expression of Notch target genes, because re-expression of Ikaros in these cells down-regulates Notch target gene expression without affecting levels of intracellular cleaved Notch. In addition, abnormal expression of Notch target genes is observed in Ikaros null double-positive thymocytes, in the absence of detectable intracellular cleaved Notch. Finally, we show that this role of Ikaros is specific to double-positive and single-positive thymocytes because derepression of Notch target gene expression is not observed in Ikaros null double-negative thymocytes or lineage-depleted bone marrow. Thus, in this study, we provide evidence that Ikaros and Notch play opposing roles in regulation of a subset of Notch target genes and that this role is restricted to developing thymocytes where Ikaros is required to appropriately regulate the Notch program as they progress through T cell development.

The transcription factor Ikaros is essential for B cell development. However, its molecular functions in B cell fate specification and commitment have remained elusive. We show here that the transcription factor EBF restored the generation of CD19(+) pro-B cells from Ikaros-deficient hematopoietic progenitors. Notably, these pro-B cells, despite having normal expression of the transcription factors EBF and Pax5, were not committed to the B cell fate. They also failed to recombine variable gene segments at the immunoglobulin heavy-chain locus. Ikaros promoted heavy-chain gene rearrangements by inducing expression of the recombination-activating genes as well as by controlling accessibility of the variable gene segments and compaction of the immunoglobulin heavy-chain locus. Thus, Ikaros is an obligate component of a network that regulates B cell fate commitment and immunoglobulin heavy-chain gene recombination.

Kupffer cells are resident macrophages in the liver and play a central role in the hepatic response to injury. Bile acids can impair macrophage function leading to decreased cytokine release. TGR5 is a novel, membrane-bound bile acid receptor, and it has been suggested that the immunosuppressive effect of bile acids can be mediated by TGR5. However, the function of TGR5 in Kupffer cells has not been studied and a direct link between TGR5 and cytokine production in macrophages has not been established. The present study demonstrates that TGR5 is localized in the plasma membrane of isolated Kupffer cells and is responsive to bile acids. Furthermore, bile acids inhibited LPS-induced cytokine expression in Kupffer cells via TGR5-cAMP dependent pathways. TGR5-immunoreactivity in Kupffer cells was increased in rat livers following bile-duct ligation, suggesting that TGR5 may play a protective role in obstructive cholestasis preventing excessive cytokine production thereby reducing liver injury.

Ikaros and Notch1, two regulators of gene transcription, are critically important at many stages of T cell development. Deregulation of Ikaros and Notch activities cooperate to promote T cell leukemogenesis, providing evidence that they function in converging pathways in developing T cells. In this report, a mechanism for Ikaros:Notch cooperativity is described, revealing a non-redundant role for Ikaros in regulating expression of the Notch target gene Hes1 in a leukemia T cell line. We provide evidence that Ikaros directly represses Hes1 in concert with the transcriptional repressor, RBP-Jkappa, allowing for cross-talk between Notch and Ikaros that impacts regulation of CD4 expression. Taken together, these data describe a potential mechanism for Ikaros' function during T cell development and define Ikaros as an obligate repressor of Hes1.

T cell activation results in dynamic remodeling of the chromatin at the IL2 promoter and induction of IL2 gene transcription. These processes are each dependent upon CD28 costimulation, but the molecular basis for this requirement is not clear. The IL2 promoter contains consensus-binding elements for Ikaros, a lymphocyte-specific zinc-finger DNA-binding protein that can regulate gene expression by recruiting chromatin-remodeling complexes. We find that native Ikaros in CD4(+) T cells exhibits sequence-specific binding to these elements in vitro, and interacts with the endogenous IL2 promoter in vivo, in a manner dependent upon its DNA-binding domain. This binding has important consequences on the regulation of the IL2 gene, because CD4(+) T cells with reduced Ikaros DNA-binding activity no longer require signals from the TCR or CD28 for histone acetylation at the endogenous IL2 promoter, and no longer require CD28 costimulation for expression of the IL2 gene. Furthermore, CD4(+) T cells with reduced Ikaros activity are resistant to clonal anergy induced by TCR ligation in the absence of either CD28 or IL-2R signals. These results establish Ikaros as a transcriptional repressor of the IL2 gene that functions through modulation of chromatin structure and has an obligate role in the induction of anergy.

Ikaros is a transcriptional regulator whose function is essential for B cell development. It is expressed in the hematopoietic stem cell (HSC) through the mature B cell stage. Using genetically engineered mice in which the endogenous Ikaros gene is disrupted, it has been shown that a lack of Ikaros leads to a block in B cell development and that its severe diminution results in a hyperresponsive B cell compartment. Ikaros expression within the HSC has led to speculation as to whether the role of Ikaros in B cell biology is largely accomplished prior to B cell specification. In addition, widespread expression of Ikaros in hematopoietic cells leads to the possibility that some or all of the observed defects are not B cell autonomous. In this report, we demonstrate that over-expression of a dominant interfering Ikaros isoform exclusively in B cells has profound effects on mature B cell function. We provide evidence that continued high-level expression of Ikaros is essential for homeostasis of peripheral lymphocytes and maintenance of B cell tolerance. We also show that deregulation of Ikaros activity does not rapidly result in B cell leukemogenesis as it does with 100% penetrance within the T cell lineage.

When exposed to a pathogen, a naive CD4(+) T cell is forced to make a cell fate decision that leads to a polarized population of Th1 IFN-gamma- or Th2 IL-4- producing cells. Although IL-4 has traditionally been considered a factor that promotes Th2 cell differentiation, recent evidence has demonstrated that the site and timing of IL-4 expression in an immune response determines its ultimate effects on CD4(+) T cell fate. Using a mast cell (MC) reconstitution model, we demonstrate that MC-derived IL-4 promoted Th1 responses in vivo. Furthermore, MCs from genetically disparate mouse strains varied in their potential for IL-4 expression. Independent of the activation mode, MCs from Th1-prone C57BL/6 mice exhibited a more robust Il4 response than did the Th2-prone strain Balb/c. The hierarchy of IL-4 expression potential was directly associated with the degree of basal chromatin accessibility at cis-regulatory elements conserved noncoding sequence-1 and V(A) enhancer within the Th2 locus. GATA1/2 and Ikaros, factors with opposing roles in chromatin remodeling, acted at these sites. We propose that GATA and Ikaros proteins coordinately fine-tune accessibility at the Il4 locus during development to variably regulate IL-4 expression. These events likely contribute to the genetically determined heterogeneity in Th1 responses that underlie susceptibility to many diseases.

Development is the process whereby a multipotent cell gives rise, through series of divisions, to progeny with successively restricted potentials. During T cell development, the process begins with a multipotent hematopoietic stem cell (HSC) in the bone marrow, moves to the thymus where early T cells or thymocytes pass through signal-initiated developmental checkpoints, and ends in the periphery where mature T cells reside. At each step along this developmental pathway, T lymphocyte progenitors must be able to turn genes on and off, creating a specialized program of gene expression, to allow further development. How is gene expression coordinated? This review will summarize what has been learned about the function of chromatin structure in generating a "blueprint" of gene expression during T cell development. This will include discussion of mechanisms of chromatin remodeling, histone modification, and heritable gene silencing. In many cases, these processes are carried out by multi-protein complexes whose components are largely ubiquitously expressed. The spatial and temporal specificity of these complexes is contributed by sequence specific DNA binding factors, some of which are cell type restricted in their expression. This review will summarize research underway to identify these key genetic "targeters." Taken together, the research reviewed here provides a glimpse into the importance of regulation of chromatin structure in T cell development and the "players" involved., ((c) 2005 Wiley-Liss, Inc.)

Ikaros is a hematopoietic cell-specific zinc finger DNA binding protein that plays an important role in lymphocyte development. Genetic disruption of Ikaros results in T-cell transformation. Ikaros null mice develop leukemia with 100% penetrance. It has been hypothesized that Ikaros controls gene expression through its association with chromatin remodeling complexes. The development of leukemia in Ikaros null mice suggests that Ikaros has the characteristics of a tumor suppressor gene. In this report, we show that the introduction of Ikaros into an established mouse Ikaros null T leukemia cell line leads to growth arrest at the G0/G1 stage of the cell cycle. This arrest is associated with up-regulation of the cell cycle-dependent kinase inhibitor p27kip1, the induction of expression of T-cell differentiation markers, and a global and specific increase in histone H3 acetylation status. These studies provide strong evidence that Ikaros possesses the properties of a bona fide tumor suppressor gene for the T-cell lineage and offer insight into the mechanism of Ikaros's tumor suppressive activity.

Previous evidence suggested that the hemopoietic-specific nuclear factor Ikaros regulates TCR signaling thresholds in mature T cells. In this study, we test the hypothesis that Ikaros also sets TCR signaling thresholds to regulate selection events and CD4 vs CD8 lineage determination in developing thymocytes. Ikaros null mice were crossed to three lines of TCR-transgenic mice, and positive selection, negative selection, and CD4 vs CD8 lineage decisions were analyzed. Mice expressing a polyclonal repertoire or a MHC class II-restricted TCR transgene exhibited enhanced positive selection toward the CD4 lineage. Moreover, in the absence of Ikaros, CD4 development can occur with decreased thresholds of TCR signaling. In addition, CD4 single-positive thymocytes were detected in MHC class I-restricted TCR-transgenic Ikaros null mice. To assess the role of Ikaros in negative selection, we analyzed deletion of T cells induced by conventional Ag or by endogenous superantigen. Surprisingly, negative selection was impaired in Ikaros null thymocytes despite evidence of high levels of TCR signal and no intrinsic defect in apoptosis ex vivo. To our knowledge, these data identify Ikaros as the first nuclear factor that plays a critical role in regulating negative selection as well as CD4 vs CD8 lineage decisions during positive selection.

T cell differentiation relies on pre-T cell receptor (TCR) and TCR signaling events that take place at successive steps of the pathway. Here, we show that two of these T cell differentiation checkpoints are regulated by Ikaros. In the absence of Ikaros, double negative thymocytes can differentiate to the double positive stage without expression of a pre-TCR complex. Subsequent events in T cell development mediated by TCR involving transition from the double positive to the single positive stage are also regulated by Ikaros. Nonetheless, in Ikaros-deficient thymocytes, the requirement of pre-TCR expression for expansion of immature thymocytes as they progress to the double positive stage is still maintained, and the T cell malignancies that invariably arise in the thymus of Ikaros-deficient mice are dependent on either pre-TCR or TCR signaling. We conclude that Ikaros regulates T cell differentiation, selection, and homeostasis by providing signaling thresholds for pre-TCR and TCR.

T cell activation involves the sustained accumulation of T cell receptor (TCR) and IL-2 receptor (IL-2R) mediated signaling events that promote cell cycle entry and progression. The Ikaros family of nuclear factors regulate this process by providing thresholds overcome by receptor signaling. T cells with reduced levels of Ikaros activity require fewer TCR engagement events for activation, exhibit a greater proliferative response to IL-2, and are less sensitive to inhibitors of TCR and IL-2R signaling. Upon T cell activation, Ikaros proteins localize in a higher-order chromatin structure where they colocalize with components of the DNA replication machinery. Proliferating T cells with reduced Ikaros activity display chromosome abnormalities. We propose that participation of Ikaros in higher-order chromatin structures controls cell cycle transitions and restricts DNA replication.

The Ikaros gene family encodes zinc finger DNA-binding proteins essential for lineage determination and control of proliferation in the lymphoid system. Here, we report that, in the nucleus of a T cell, a major fraction of Ikaros and Aiolos proteins associate with the DNA-dependent ATPase Mi-2 and histone deacetylases, in a 2 MD complex. This Ikaros-NURD complex is active in chromatin remodeling and histone deacetylation. Upon T cell activation, Ikaros recruits Mi-2/HDAC to regions of heterochromatin. These studies reveal that Ikaros proteins are capable of targeting chromatin remodeling and deacetylation complexes in vivo. We propose that the restructuring of chromatin is a key aspect of Ikaros function in lymphocyte differentiation.

The Ikaros gene, which encodes a family of hemopoietic-specific zinc finger proteins, is described as a central regulator of lymphocyte differentiation. During fetal development, it is required at the earliest stage of T cell and B cell specification. In the adult, however, lymphoid lineages rely on Ikaros at distinct phases of their development. Its activity is essential for the generation of B cell but not of T cell precursors, although the differentiation of the latter is not normal. A significant increase in CD4 thymocytes and their immediate precursors is detected, and because these cells lack markers that correlate with positive selection, a deregulation in their maturation process is suggested. Furthermore, Ikaros-null thymocytes hyperproliferate in response to T cell receptor (TCR) signaling; within days after their appearance in the thymus, clonally expanding populations are detected. Deregulated TCR-mediated responses and the fast kinetics of tumor development in these mutant thymocytes implicate Ikaros as a central tumor suppressor gene for the T cell lineage. In addition, lack of natural killer cells and selective defects in gamma delta T cells and dendritic antigen-presenting cells point to Ikaros as an essential factor for the establishment of early branchpoints of the T cell pathway. The dominant interference activity of Ikaros isoforms unable to bind DNA and their effects in lymphocyte development suggest that Ikaros works in concert with other factors. The role of Aiolos, a lymphoid-restricted and structurally related gene, in lymphoid differentiation is discussed. A model is proposed that defines Ikaros as the backbone of a complex regulatory protein network that controls cell fate decisions and regulates homeostasis in the hemo-lymphoid system. Changes in this regulatory network may reflect differentiation and proliferation adjustments made in hemo-lymphoid progenitors and precursors as they give rise to the cells of our immune system.

The Ikaros gene is essential for lymphoid lineage specification. As previously reported, mice homozygous for a mutation in the Ikaros DNA-binding domain fail to generate mature lymphocytes as well as their earliest described progenitors. In addition, our studies with mice heterozygous for this mutation establish the Ikaros gene as an essential regulator of T cell proliferation. Thymocytes display augmented TCR-mediated proliferative responses, and peripheral T cells are autoproliferative. A general lymphoproliferation precedes the T cell leukemia and lymphoma that rapidly develop in all heterozygotes. The first step toward leukemic transformation occurs within the maturing thymocyte population and is demarcated by clonal expansions and loss of the single Ikaros wild-type allele. From these studies, we propose that within developing and mature T lymphocytes, distinct thresholds of Ikaros activity are required to regulate proliferation. A decrease in Ikaros activity below the first threshold causes the rapid accumulation of T lymphoblasts, whereas a further decrease leads to neoplastic transformation.

The Ikaros gene encodes a family of early hematopoietic- and lymphocyte-restricted transcription factors. Mice homozygous for a germline mutation in the Ikaros DNA-binding domain lack not only T and B lymphocytes and natural killer cells but also their earliest defined progenitors. In contrast, the erythroid and myeloid lineages were intact in these mutant mice. We propose that Ikaros promotes differentiation of pluripotential hematopoietic stem cell(s) into the lymphocyte pathways. In the absence of a functional Ikaros gene, these stem cells are exclusively diverted into the erythroid and myeloid lineages.