Cloning of murine TCF-1, a T cell-specific transcription factor interacting with functional motifs in the CD3-epsilon and T cell receptor alpha enhancers

Optimizing in vitro T cell differentiation by using induced pluripotent stem cells with GFP-RUNX1 and mCherry-TCF7 labelling

In vitro T-cell differentiation from pluripotent stem cells (PSCs) could potentially provide an unlimited source of T cells for cancer immunotherapy, which, however is still hindered by the inefficient obtaining functionally-matured, terminally-differentiated T cells. Here, we established a fluorescence reporter human induced pluripotent stem cell (iPSC) line termed TCF7mCherryRUNX1GFP, in which the endogenous expression of RUNX1 and TCF7 are illustrated by the GFP and mCherry fluorescence, respectively. Utilizing TCF7mCherryRUNX1GFP, we defined that the feeder cells incorporating CXCL12-expressing OP9 cells with DL4-expressing OP9 cells at a 1:3 ratio (OP9-C1D3) significantly enhanced efficiency of CD8+ T cell differentiation from PSCs. Additionally, we engineered a chimeric antigen receptor (CAR) targeting EGFR into iPSCs. The CAR-T cells differentiated from these iPSCs using OP9-C1D3 feeders demonstrated effective cytotoxicity toward lung cancer cells. We anticipate this platform will help the in vitro HSPC and T cell differentiation optimization, serving the clinical demands of these cells.

The role of thymic epithelium in thymus development and age-related thymic involution

The establishment of an adaptive immune system is critical for protecting our bodies from neoplastic cancers and invading pathogens such as viruses and bacteria. As a primary lymphoid organ, the thymus generates lymphoid T cells that play a major role in the adaptive immune system. T cell generation in the thymus is controlled by interactions between thymocytes and other thymic cells, primarily thymic epithelial cells. Thus, the normal development and function of thymic epithelial cells are important for the generation of immunocompetent and self-tolerant T cells. On the other hand, the degeneration of the thymic epithelium due to thymic aging causes thymic involution, which is associated with the decline of adaptive immune function. Herein we summarize basic and current knowledge of the development and function of thymic epithelial cells and the mechanism of thymic involution. J. Med. Invest. 71 : 29-39, February, 2024.

Fine-tuning of β-catenin in mouse thymic epithelial cells is required for postnatal T-cell development

In the thymus, the thymic epithelium provides a microenvironment essential for the development of functionally competent and self-tolerant T cells. Previous findings showed that modulation of Wnt/β-catenin signaling in mouse thymic epithelial cells (TECs) disrupts embryonic thymus organogenesis. However, the role of β-catenin in TECs for postnatal T-cell development remains to be elucidated. Here, we analyzed gain-of-function (GOF) and loss-of-function (LOF) of β-catenin highly specific in mouse TECs. We found that GOF of β-catenin in TECs results in severe thymic dysplasia and T-cell deficiency beginning from the embryonic period. By contrast, LOF of β-catenin in TECs reduces the number of cortical TECs and thymocytes modestly and only postnatally. These results indicate that fine-tuning of β-catenin expression within a permissive range is required for TECs to generate an optimal microenvironment to support postnatal T-cell development.

Control of Lymphocyte Fate, Infection, and Tumor Immunity by TCF-1

T cell factor-1 (TCF-1), encoded by Tcf7, is a transcription factor and histone deacetylase (HDAC) essential for commitment to both the T cell and the innate lymphoid cell (ILC) lineages in mammals. In this review, we discuss the multifunctional role of TCF-1 in establishing these lineages and the requirement for TCF-1 throughout lineage differentiation and maintenance of lineage stability. We highlight recent reports showing promise for TCF-1 as a novel biomarker to identify recently characterized subsets of exhausted CD8⁺ T cells that may help to predict patient responses to immune checkpoint blockade (ICB).

Lymphoid Enhancer Factor 1 Contributes to Hepatocellular Carcinoma Progression Through Transcriptional Regulation of Epithelial-Mesenchymal Transition Regulators and Stemness Genes

Lymphoid enhancer factor 1 (LEF1) activity is associated with progression of several types of cancers. The role of LEF1 in progression of hepatocellular carcinoma (HCC) remains poorly known. We investigated LEF1 expression in HCC and its interactions with epithelial-mesenchymal transition (EMT) regulators (e.g., Snail, Slug, Twist) and stemness genes (e.g., octamer-binding transcription factor 4 [Oct4], sex determining region Y-box 2 [Sox2], Nanog homeobox [Nanog]). Microarray analysis was performed on resected tumor samples from patients with HCC with or without postoperative recurrence. LEF1 expression was associated with postoperative recurrence as validated by immunohistochemical staining in another HCC cohort. Among 74 patients, 44 displayed a relatively high percentage of LEF1 staining (>30% of HCC cells), which was associated with a reduced recurrence-free interval (P < 0.001) and overall survival (P = 0.009). In multivariate analysis, a high percentage of LEF1 staining was significantly associated with low albumin level (P = 0.035), Twist overexpression (P = 0.018), Snail overexpression (P = 0.064), co-expression of Twist and Snail (P = 0.054), and multinodular tumors (P = 0.025). Down-regulation of LEF1 by short hairpin RNA decreased tumor sphere formation, soft agar colony formation, and transwell invasiveness of HCC cell lines Mahlavu and PLC. Xenotransplant and tail vein injection experiments revealed that LEF1 down-regulation in Mahlavu reduced tumor size and metastasis. LEF1 up-regulation in Huh7 increased sphere formation, soft agar colony formation, and transwell invasiveness. LEF1 was shown to physically interact with and transcriptionally activate promoter regions of Oct4, Snail, Slug, and Twist. Furthermore, Oct4, Snail, and Twist transactivated LEF1 to form a regulatory positive-feedback loop. Conclusion: LEF1 plays a pivotal role in HCC progression through transcriptional regulation of Oct4 and EMT regulators.

Identification of LEF1 as a Susceptibility Locus for Kawasaki Disease in Patients Younger than 6 Months of Age

Kawasaki disease (KD) is an acute febrile vasculitis predominately affecting infants and children. The dominant incidence age of KD is from 6 months to 5 years of age, and the incidence is unusual in those younger than 6 months and older than 5 years of age. We tried to identify genetic variants specifically associated with KD in patients younger than 6 months or older than 5 years of age. We performed an age-stratified genome-wide association study using the Illumina HumanOmni1-Quad BeadChip data (296 cases vs. 1,000 controls) and a replication study (1,360 cases vs. 3,553 controls) in the Korean population. Among 26 candidate single nucleotide polymorphisms (SNPs) tested in replication study, only a rare nonsynonymous SNP (rs4365796: c.1106C＞T, p.Thr369Met) in the lymphoid enhancer binding factor 1 (LEF1) gene was very significantly associated with KD in patients younger than 6 months of age (odds ratio [OR], 3.07; p_combined = 1.10 × 10^-5), whereas no association of the same SNP was observed in any other age group of KD patients. The same SNP (rs4365796) in the LEF1 gene showed the same direction of risk effect in Japanese KD patients younger than 6 months of age, although the effect was not statistically significant (OR, 1.42; p = 0.397). This result indicates that the LEF1 gene may play an important role as a susceptibility gene specifically affecting KD patients younger than 6 months of age.

Cytokines, Transcription Factors, and the Initiation of T-Cell Development

Multipotent blood progenitor cells migrate into the thymus and initiate the T-cell differentiation program. T-cell progenitor cells gradually acquire T-cell characteristics while shedding their multipotentiality for alternative fates. This process is supported by extracellular signaling molecules, including Notch ligands and cytokines, provided by the thymic microenvironment. T-cell development is associated with dynamic change of gene regulatory networks of transcription factors, which interact with these environmental signals. Together with Notch or pre-T-cell-receptor (TCR) signaling, cytokines always control proliferation, survival, and differentiation of early T cells, but little is known regarding their cross talk with transcription factors. However, recent results suggest ways that cytokines expressed in distinct intrathymic niches can specifically modulate key transcription factors. This review discusses how stage-specific roles of cytokines and transcription factors can jointly guide development of early T cells.

β-catenin is required for taste bud cell renewal and behavioral taste perception in adult mice

Taste stimuli are transduced by taste buds and transmitted to the brain via afferent gustatory fibers. Renewal of taste receptor cells from actively dividing progenitors is finely tuned to maintain taste sensitivity throughout life. We show that conditional β-catenin deletion in mouse taste progenitors leads to rapid depletion of progenitors and Shh⁺ precursors, which in turn causes taste bud loss, followed by loss of gustatory nerve fibers. In addition, our data suggest LEF1, TCF7 and Wnt3 are involved in a Wnt pathway regulatory feedback loop that controls taste cell renewal in the circumvallate papilla epithelium. Unexpectedly, taste bud decline is greater in the anterior tongue and palate than in the posterior tongue. Mutant mice with this regional pattern of taste bud loss were unable to discern sweet at any concentration, but could distinguish bitter stimuli, albeit with reduced sensitivity. Our findings are consistent with published reports wherein anterior taste buds have higher sweet sensitivity while posterior taste buds are better tuned to bitter, and suggest β-catenin plays a greater role in renewal of anterior versus posterior taste buds.

By remaining relatively constant throughout adult life, the sense of taste helps keep the body healthy. However, taste perception can be disrupted by various environmental factors, including cancer therapies. Here, we show that Wnt/β-catenin signaling, a pathway known to control normal tissue maintenance and associated with the development of cancers, is required for taste cell renewal and behavioral taste sensitivity in mice. Our findings are significant as they suggest that chemotherapies targeting the Wnt pathway in cancerous tissues may cause taste dysfunction and further diminish the quality of life of patients.

TCF/LEF Transcription Factors: An Update from the Internet Resources

T-cell factor/lymphoid enhancer-binding factor (TCF/LEF) proteins (TCFs) from the High Mobility Group (HMG) box family act as the main downstream effectors of the Wnt signaling pathway. The mammalian TCF/LEF family comprises four nuclear factors designated TCF7, LEF1, TCF7L1, and TCF7L2 (also known as TCF1, LEF1, TCF3, and TCF4, respectively). The proteins display common structural features and are often expressed in overlapping patterns implying their redundancy. Such redundancy was indeed observed in gene targeting studies; however, individual family members also exhibit unique features that are not recapitulated by the related proteins. In the present viewpoint, we summarized our current knowledge about the specific features of individual TCFs, namely structural-functional studies, posttranslational modifications, interacting partners, and phenotypes obtained upon gene targeting in the mouse. In addition, we employed several publicly available databases and web tools to evaluate the expression patterns and production of gene-specific isoforms of the TCF/LEF family members in human cells and tissues.

Transcription Factor 7-like 2 Mediates Canonical Wnt/β-Catenin Signaling and c-Myc Upregulation in Heart Failure

BACKGROUND

How canonical Wnt/β-catenin signals in adult hearts, especially in different diseased states, remains unclear. The proto-oncogene, c-Myc, is a Wnt target and an early response gene during cardiac stress. It is not clear whether c-Myc is activated or how it is regulated during heart failure.

METHODS AND RESULTS

We investigated canonical Wnt/β-catenin signaling and how it regulated c-Myc expression in failing hearts of human ischemic heart disease, idiopathic dilated cardiomyopathy, and murine desmin-related cardiomyopathy. Our data demonstrated that canonical Wnt/β-catenin signaling was activated through nuclear accumulation of β-catenin in idiopathic dilated cardiomyopathy, ischemic heart disease, and murine desmin-related cardiomyopathy when compared with nonfailing controls and transcription factor 7-like 2 (TCF7L2) was the main β-catenin partner of the T-cell factor (TCF) family in adult hearts. We further revealed that c-Myc mRNA and protein levels were significantly elevated in failing hearts by real-time reverse transcription polymerase chain reaction, Western blotting, and immunohistochemical staining. Immunoprecipitation and confocal microscopy further showed that β-catenin interacted and colocalized with TCF7L2. More importantly, chromatin immunoprecipitation confirmed that β-catenin and TCF7L2 were recruited to the regulatory elements of c-Myc. This recruitment was associated with increased histone H3 acetylation and transcriptional upregulation of c-Myc. With lentiviral infection, TCF7L2 overexpression increased c-Myc expression and cardiomyocyte size, whereas shRNA-mediated knockdown of TCF7L2 suppressed c-Myc expression and cardiomyocyte growth in cultured neonatal rat cardiomyocytes.

CONCLUSIONS

This study indicates that TCF7L2 mediates canonic Wnt/β-catenin signaling and c-Myc upregulation during abnormal cardiac remodeling in heart failure and suppression of Wnt/β-catenin to c-Myc axis can be explored for preventing and treating heart failure.

TCF-1 upregulation identifies early innate lymphoid progenitors in the bone marrow

The cellular and molecular events that drive the early development of innate lymphoid cells (ILCs) remain poorly understood. We show that the transcription factor TCF-1 is required for the efficient generation of all known adult ILC subsets and their precursors. Using novel reporter mice, we identified a new subset of early ILC progenitors (EILPs) expressing high amounts of TCF-1. EILPs lacked efficient T and B lymphocyte potential but efficiently gave rise to NK cells and all known adult helper ILC lineages, indicating that they are the earliest ILC-committed progenitors identified so far. Our results suggest that upregulation of TCF-1 expression denotes the earliest stage of ILC fate specification. The discovery of EILPs provides a basis for deciphering additional signals that specify ILC fate.

Developmental gene networks: a triathlon on the course to T cell identity

Cells acquire their ultimate identities by activating combinations of transcription factors that initiate and sustain expression of the appropriate cell type-specific genes. T cell development depends on the progression of progenitor cells through three major phases, each of which is associated with distinct transcription factor ensembles that control the recruitment of these cells to the thymus, their proliferation, lineage commitment and responsiveness to T cell receptor signals, all before the allocation of cells to particular effector programmes. All three phases are essential for proper T cell development, as are the mechanisms that determine the boundaries between each phase. Cells that fail to shut off one set of regulators before the next gene network phase is activated are predisposed to leukaemic transformation.

A Comprehensive Overview of Skeletal Phenotypes Associated with Alterations in Wnt/β-catenin Signaling in Humans and Mice

The Wnt signaling pathway plays key roles in differentiation and development and alterations in this signaling pathway are causally associated with numerous human diseases. While several laboratories were examining roles for Wnt signaling in skeletal development during the 1990s, interest in the pathway rose exponentially when three key papers were published in 2001-2002. One report found that loss of the Wnt co-receptor, Low-density lipoprotein related protein-5 (LRP5), was the underlying genetic cause of the syndrome Osteoporosis pseudoglioma (OPPG). OPPG is characterized by early-onset osteoporosis causing increased susceptibility to debilitating fractures. Shortly thereafter, two groups reported that individuals carrying a specific point mutation in LRP5 (G171V) develop high-bone mass. Subsequent to this, the causative mechanisms for these observations heightened the need to understand the mechanisms by which Wnt signaling controlled bone development and homeostasis and encouraged significant investment from biotechnology and pharmaceutical companies to develop methods to activate Wnt signaling to increase bone mass to treat osteoporosis and other bone disease. In this review, we will briefly summarize the cellular mechanisms underlying Wnt signaling and discuss the observations related to OPPG and the high-bone mass disorders that heightened the appreciation of the role of Wnt signaling in normal bone development and homeostasis. We will then present a comprehensive overview of the core components of the pathway with an emphasis on the phenotypes associated with mice carrying genetically engineered mutations in these genes and clinical observations that further link alterations in the pathway to changes in human bone.

Wnt signaling in normal and malignant hematopoiesis

One of the most remarkable characteristics of stem cells is their ability to perpetuate themselves through self-renewal while concomitantly generating differentiated cells. In the hematopoietic system, stem cells balance these mechanisms to maintain steady-state hematopoiesis for the lifetime of the organism, and to effectively regenerate the system following injury. Defects in the proper control of self-renewal and differentiation can be potentially devastating and contribute to the development of malignancies. In this review, we trace the emerging role of Wnt signaling as a critical regulator of distinct aspects of self-renewal and differentiation, its contribution to the maintenance of homeostasis and regeneration, and how the pathway can be hijacked to promote leukemia development. A better understanding of these processes could pave the way to enhancing recovery after injury and to developing better therapeutic approaches for hematologic malignancies.

CD8α+ dendritic cell trans presentation of IL-15 to naive CD8+ T cells produces antigen-inexperienced T cells in the periphery with memory phenotype and function

Various populations of memory phenotype CD8(+) T cells have been described over the last 15-20 y, all of which possess elevated effector functions relative to naive phenotype cells. Using a technique for isolating Ag-specific cells from unprimed hosts, we recently identified a new subset of cells, specific for nominal Ag, but phenotypically and functionally similar to memory cells arising as a result of homeostatic proliferation. We show in this study that these virtual memory (VM) cells are independent of previously identified innate memory cells, arising as a result of their response to IL-15 trans presentation by lymphoid tissue-resident CD8α(+) dendritic cells in the periphery. The absence of IL-15, CD8(+) T cell expression of either CD122 or eomesodermin or of CD8a(+) dendritic cells all lead to the loss of VM cells in the host. Our results show that CD8(+) T cell homeostatic expansion is an active process within the nonlymphopenic environment, is mediated by IL-15, and produces Ag-inexperienced memory cells that retain the capacity to respond to nominal Ag with memory-like function. Preferential engagement of these VM T cells into a vaccine response could dramatically enhance the rate by which immune protection develops.

Canonical Wnt/β-catenin signaling in epicardial fibrosis of failed pediatric heart allografts with diastolic dysfunction

BACKGROUND

Failed pediatric heart allografts with diastolic dysfunction exhibit severe epicardial fibrosis. The molecular mechanism underlying this process is poorly understood. Canonical Wnt/β-catenin signaling plays an important role in epithelial-mesenchymal transition and is implicated in fibrosing diseases. In this study, we tested the hypothesis that canonical Wnt/β-catenin signaling is activated in epicardial fibrosis of end-stage dysfunctional pediatric allografts.

METHODS

Fourteen explanted heart grafts of 12 patients who had undergone 14 heart transplantations were used for immunohistochemical staining of β-catenin and its nuclear binding partners, T-cell factor/lymphoid enhancer factor family transcriptional factors. Fourteen age-matched native hearts from patients who had undergone first heart transplantation without evidence of epicardial fibrosis were used as controls.

RESULTS AND CONCLUSIONS

Epicardial fibroblasts from explanted allografts demonstrated nuclear accumulation of β-catenin. These cells also showed nuclear positivity for T-cell factor 4. No T-cell factor 3 expression was present in the epicardium. T-cell factor 1 and lymphoid enhancer factor 1 were observed in lymphocytes, but not in other cell types of the epicardium. These findings suggest an association between canonical Wnt/beta-catenin signaling and epicardial fibrosis of failed pediatric heart allografts. Should activation of this pathway be shown to be causal to epicardial fibrosis in this setting, then inhibition of this pathway may help to prevent this devastating process.

How do they do Wnt they do?: regulation of transcription by the Wnt/β-catenin pathway

Wnt/β-catenin signalling is known to play many roles in metazoan development and tissue homeostasis. Misregulation of the pathway has also been linked to many human diseases. In this review, specific aspects of the pathway's involvement in these processes are discussed, with an emphasis on how Wnt/β-catenin signalling regulates gene expression in a cell and temporally specific manner. The T-cell factor (TCF) family of transcription factors, which mediate a large portion of Wnt/β-catenin signalling, will be discussed in detail. Invertebrates contain a single TCF gene that contains two DNA-binding domains, the high mobility group (HMG) domain and the C-clamp, which increases the specificity of DNA binding. In vertebrates, the situation is more complex, with four TCF genes producing many isoforms that contain the HMG domain, but only some of which possess a C-clamp. Vertebrate TCFs have been reported to act in concert with many other transcription factors, which may explain how they obtain sufficient specificity for specific DNA sequences, as well as how they achieve a wide diversity of transcriptional outputs in different cells.

Dynamic expression of a LEF-EGFP Wnt reporter in mouse development and cancer

We have characterized a transgenic mouse line in which enhanced green fluorescent protein (EGFP) is expressed under the control of multimerized LEF-1 responsive elements. In embryos, EGFP was detected in known sites of Wnt activation, including the primitive streak, mesoderm, neural tube, somites, heart, limb buds, mammary placodes, and whisker follicles. In vitro cultured transgenic embryonic fibroblasts upregulated EGFP expression in response to activation of Wnt signaling by GSK3beta inhibition. Mammary tumor cell lines derived from female LEF-EGFP transgenic mice treated with the carcinogen 7, 12-dimethylbenz[a]anthracene (DMBA) also express EGFP. Thus, this transgenic line is useful for ex vivo and in vitro studies of Wnt signaling in development and cancer.

Antagonistic effect of the matricellular signaling protein CCN3 on TGF-beta- and Wnt-mediated fibrillinogenesis in systemic sclerosis and Marfan syndrome

Abnormal fibrillinogenesis is associated with connective tissue disorders (CTDs), including Marfan syndrome (MFS), systemic sclerosis (SSc) and Tight-skin (Tsk) mice. We have previously shown that TGF-beta and Wnt stimulate fibrillin-1 assembly and that fibrillin-1 and the developmental regulator CCN3 are both highly increased in Tsk skin. We investigated the role of CCN3 in abnormal fibrillinogenesis in Tsk mice, MFS, and SSc. Smad3 deletion in Tsk mice decreased CCN3 overexpression, suggesting that TGF-beta mediates at least part of the effect of Tsk fibrillin on CCN3 which is consistent with a synergistic effect of TGF-beta and Wnt in vitro on CCN3 expression. Disruption of fibrillin-1 assembly by MFS fibrillin decreased CCN3 expression and skin from patients with early diffuse SSc showed a strong correlation between increased CCN3 and fibrillin-1 expression, suggesting that CCN3 regulation by fibrillin-1 extends to these CTDs. Diffuse SSc skin and sera also showed evidence of increased Wnt activity, implicating a Wnt stimulus behind this correlation. CCN3 overexpression markedly repressed fibrillin-1 assembly and also blocked other TGFbeta- and Wnt-regulated profibrotic gene expression. Together, these data indicate that CCN3 counter-regulates positive signals from TGF-beta and Wnt for fibrillin fibrillogenesis and profibrotic gene expression.

Prenatal cadmium exposure dysregulates sonic hedgehog and Wnt/beta-catenin signaling in the thymus resulting in altered thymocyte development

Cadmium (Cd) is both an environmental pollutant and a component of cigarette smoke. Although evidence demonstrates that adult exposure to Cd causes changes in the immune system, there are limited reports in the literature of immunomodulatory effects of prenatal exposure to Cd. The sonic hedgehog (Shh) and Wnt/beta-catenin pathways are required for thymocyte maturation. Several studies have demonstrated that Cd exposure affects these pathways in different organ systems. This study was designed to investigate the effect of prenatal Cd exposure on thymocyte development, and to determine if these effects were linked to dysregulation of Shh and Wnt/beta-catenin pathways. Pregnant C57Bl/6 mice were exposed to an environmentally relevant dose (10 ppm) of Cd throughout pregnancy and effects on the thymus were assessed on the day of birth. Thymocyte phenotype was determined by flow cytometry. A Gli:luciferase reporter cell line was used to measure Shh signaling. Transcription of target genes and translation of key components of both signaling pathways were assessed using real-time RT-PCR and western blot, respectively. Prenatal Cd exposure increased the number of CD4(+) cells and a subpopulation of double-negative cells (DN; CD4(-)CD8(-)), DN4 (CD44(-)CD25(-)). Shh and Wnt/beta-catenin signaling were both decreased in the thymus. Target genes of Shh (Patched1 and Gli1) and Wnt/beta-catenin (c-fos, and c-myc) were affected differentially among thymocyte subpopulations. These findings suggest that prenatal exposure to Cd dysregulates two signaling pathways in the thymus, resulting in altered thymocyte development.

Constitutive WNT/beta-catenin signaling in murine Sertoli cells disrupts their differentiation and ability to support spermatogenesis

Sertoli and germ cell interactions are essential for spermatogenesis and, thus, male fertility. Sertoli cells provide a specialized microenvironment for spermatogonial stem cells to divide, allowing both self-renewal and spermatogenesis. In the present study, we used mice with a conditional activated allele of the beta-catenin gene (Ctnnb1(tm1Mmt)(/+)) in Sertoli cells expressing Cre recombinase driven by the anti-Müllerian hormone (AMH; also known as Müllerian-inhibiting substance) type II receptor promoter (Amhr2(tm3(cre)Bhr)(/+)) to show that constitutively activated beta-catenin leads to their continuous proliferation and compromised differentiation. Compared to controls, Sertoli cells in mature mutant mice continue to express high levels of both AMH and glial cell-derived neurotrophic factor (GDNF), which normally are expressed only in immature Sertoli cells. We also show evidence that LiCl treatment, which activates endogenous nuclear beta-catenin activity, regulates both AMH and GDNF expression at the transcriptional level. The epididymides were devoid of sperm in the Amhr2(tm3(cre)Bhr)(/+);Ctnnb1(tm1Mmt)(/+) mice at all ages examined. We show that the mutant mice are infertile because of defective differentiation of germ cells and increased apoptosis, both of which are characteristic of GDNF overexpression in Sertoli cells. Constitutive activation of beta-catenin in Amhr2-null mice showed the same histology, suggesting that the phenotype was the result of persistent overexpression of GDNF. These results show that dysregulated wingless-related MMTV integration site/beta-catenin signaling in Sertoli cells inhibits their postnatal differentiation, resulting in increased germ cell apoptosis and infertility.

Transcription Factor Expression in Cell Lines Derived from Natural Killer-Cell and Natural Killer-Like T-Cell Leukemia-Lymphoma

Although a number of transcription factors (TFs) have been identified that play a pivotal role in the development of hematopoietic lineages, only little is known about factors that may influence development and lineage commitment of natural killer (NK) or NK-like T (NKT)-cells. Obviously to fully appreciate the NK- and NKT-cell differentiation process, it is important to identify and characterize the TFs effecting the NK- and NKT-cell lineage. Furthermore, these TFs may play a role in NK- or NKT-cell leukemias, in which the normal differentiation program is presumably disturbed. The present study analyzed the expression of the following 13 TFs: AML1, CEBPA, E2A, ETS1, GATA1, GATA2, GATA3, IKAROS, IRF1, PAX5, PU1, TBET and TCF1 in 7 malignant NK-cell lines together with 5 malignant NKT-cell lines, 5 T-cell acute lymphoblastic leukemia (ALL) cell lines including 3 gamma/delta T-cell receptor (TCR) type and 2 alpha/beta TCR type, and 3 B-cell precursor (BCP) leukemia cell lines. AML1, E2A, ETS1, IKAROS and IRF1 were found to be positive for all cell lines tested whereas GATA1 turned out to be universally negative. CEBPA, PAX5 and PU1 were negative for all cell lines tested except in the three positive BCP-cell lines. GATA2 was positive for 3/5 T-cell lines but negative for the other cell lines. GATA3 was positive for 7/7 NK-, 4/5 NKT-, 5/5 T- and 2/3 BCP-cell lines. TBET was positive for all NK- and NKT-cell lines and negative for all T- and BCP-cell lines except one BCP-cell line. In contrast to the expression of TBET, TCF1 was negative for all NK- and NKT-cell lines, being positive for 4/5 T- and 1/3 BCP-cell lines. Expression analysis of TFs revealed that NK- and NKT-cell lines showed identical profiles, clearly distinct from those of the other T-ALL or BCP-ALL leukemia-derived cell lines..

Inhibition of Wnt signaling by the osteoblast-specific transcription factor Osterix

The recent identification of the genes responsible for several human genetic diseases affecting bone homeostasis and the characterization of mouse models for these diseases indicated that canonical Wnt signaling plays a critical role in the control of bone mass. Here, we report that the osteoblast-specific transcription factor Osterix (Osx), which is required for osteoblast differentiation, inhibits Wnt pathway activity. First, in calvarial cells of embryonic day (E)18.5 Osx-null embryos, expression of the Wnt antagonist Dkk1 was abolished, and that of Wnt target genes c-Myc and cyclin D1 was increased. Moreover, our studies demonstrated that Osx bound to and activated the Dkk1 promoter. In addition, Osx inhibited beta-catenin-induced Topflash reporter activity and beta-catenin-induced secondary axis formation in Xenopus embryos. Importantly, in calvaria of E18.5 Osx-null embryos harboring the TOPGAL reporter transgene, beta-galactosidase activity was increased, suggesting that Osx inhibited the Wnt pathway in osteoblasts in vivo. Our data further showed that Osx disrupted binding of Tcf to DNA, providing a likely mechanism for the inhibition by Osx of beta-catenin transcriptional activity. We also showed that Osx decreased osteoblast proliferation. Indeed, E18.5 Osx-null calvaria showed greater BrdU incorporation than wild-type calvaria and that Osx overexpression in C2C12 mesenchymal cells inhibited cell growth. Because Wnt signaling has a major role in stimulating osteoblast proliferation, we speculate that Osx-mediated inhibition of osteoblast proliferation is a consequence of the Osx-mediated control of Wnt/beta-catenin activity. Our results add a layer of control to Wnt/beta-catenin signaling in bone.

Integrated morphogen signal inputs in gammadelta versus alphabeta T-cell differentiation

Morphogens, a class of secreted proteins that regulate gene expression in a concentration-dependent manner, are responsible for directing nearly all lineage fate choices during embryogenesis. In the thymus, morphogen signal pathways consisting of WNT, Hedgehog, and the transforming growth factor-beta superfamily are active and have been implicated in various developmental processes including proliferation, survival, and differentiation of maturing thymocytes. Intriguingly, it has been inferred that some of these morphogen signal pathways differentially affect gammadelta and alphabeta T-cell development or maintenance, but their role in T-cell lineage commitment has not been directly probed. We have recently identified a modulator of morphogen signaling that significantly influences binary gammadelta versus alphabeta T-cell lineage diversification. In this review, we summarize functions of morphogens in the thymus and provide a highly speculative model of integrated morphogen signals, potentially directing the gammadelta versus alphabeta T-cell fate determination process.

Intracellular expression of the T-cell factor-1 RNA aptamer as an intramer

T-cell factor (TCF)-1 protein forms the transcriptional complex with beta-catenin and regulates the expression of diverse target genes during early development and carcinogenesis. We have selected previously an RNA aptamer that binds to the DNA-binding domain of TCF-1 and have shown that it interfered with binding of TCF-1 to its specific DNA recognition sequences in vitro. As an approach to modulate the transcription by TCF/beta-catenin complex in the cells, we have developed the RNA expression vector for stable expression of RNA aptamer inside of the mammalian cells. High level of RNA was expressed as an intramer in the fusion with the stable RNA transcript. The RNA intramer inhibited TCF/beta-catenin transcription activity as shown by luciferase assay. It also modulated the expression of TCF/beta-catenin target genes, such as cyclin D1 and matrix metalloproteinase-7, as predicted to be as an effective inhibitor of the TCF function. In addition, it efficiently reduced the growth rate and tumorigenic potential of HCT116 colon cancer cells. Such RNA intramer could lead to valuable gene therapeutics for TCF/beta-catenin-mediated carcinogenesis.

Differentiation-inducing factor-1 alters canonical Wnt signaling and suppresses alkaline phosphatase expression in osteoblast-like cell lines

Because DIF-1 has been shown to affect Wnt/beta-catenin signaling pathway, the effects of DIF-1 on osteoblast-like cell lines, SaOS-2 and MC3T3-E1, were examined. We found that DIF-1 inhibited this pathway, resulting in the suppression of ALP promoter activity through the TCF/LEF binding site.

INTRODUCTION

Differentiation-inducing factor-1 (DIF-1), a morphogen of Dictyostelium, inhibits cell proliferation and induces cell differentiation in several mammalian cells. Previous studies showed that DIF-1 activated glycogen synthase kinase-3beta, suggesting that this chemical could affect the Wnt/beta-catenin signaling pathway. This pathway has been shown to be involved in bone biology.

MATERIALS AND METHODS

We studied the effects of DIF-1 on SaOS-2 and MC3T3-E1, osteosarcoma cell lines widely used as a model system for ostoblastic cells and murine osteoblast-like cell line, respectively. Reporter gene assays were also carried out to examine the effect of DIF-1 on the Wnt/beta-catenin signaling pathway.

RESULTS

DIF-1 inhibited SaOS-2 proliferation and reduced alkaline phosphatase (ALP) activity in a concentration- and a time-dependent manner. The expression of ALP was markedly suppressed by DIF-1-treatment in protein and mRNA levels. DIF-1 also suppressed the expression of other osteoblast differentiation markers, including core binding factor alpha1, type I collagen, and osteocalcin, in protein and mRNA levels and inhibited osteoblast-mediated mineralization. Subsequently, we examined the effect of DIF-1 on the Wnt/beta-catenin signaling pathway. We found that DIF-1 suppressed the expression of beta-catenin protein and the activity of the reporter gene containing T-cell factor/lymphoid enhancer-binding factor (TCF/LEF) consensus binding sites. We examined the effect of DIF-1 on a reporter gene driven by the human ALP promoter and found that DIF-1 significantly reduced the ALP reporter gene activity through the TCF/LEF binding site (-1023/-1017 bp). Furthermore, the effect of DIF-1 on MC3T3-E1, a murine osteoblast-like cell line, was examined, and it was found that DIF-1 suppressed ALP mRNA expression by the reduction of the ALP reporter gene activity through the TCF/LEF binding site.

CONCLUSIONS

Our data suggest that DIF-1 inhibits Wnt/beta-catenin signaling, resulting in the suppression of ALP promoter activity. To our knowledge, this is the first report to analyze the role of the TCF/LEF binding site (-1023/-1017 bp) of the ALP gene promoter in osteoblast-like cell lines.

Notch and Wnt signaling in T-lymphocyte development and acute lymphoblastic leukemia

Many acute lymphoblastic leukemias can be considered as malignant counterparts of cells in the various stages of normal lymphoid development in bone marrow and thymus. T-cell development in the thymus is an ordered and tightly controlled process. Two evolutionary conserved signaling pathways, which were first discovered in Drosophila, control the earliest steps of T-cell development. These are the Notch and Wnt-signaling routes, which both are deregulated in several types of leukemias. In this review we discuss both pathways, with respect to their signaling mechanisms, functions during T-cell development and their roles in development of leukemias, especially T-cell acute lymphoblastic leukemia.

Wnt signaling in lymphopoiesis

Wnt signaling elicits changes in gene expression and cell physiology through beta-catenin and LEF1/TCF proteins. The signal transduction pathway regulates many cellular and developmental processes, including cell proliferation, cell fate decisions and differentiation. In cells that have been stimulated by a Wnt protein, cytoplasmic beta-catenin is stabilized and transferred to the nucleus, where it interacts with the nuclear mediators of Wnt signaling, the LEF1/TCF proteins, to elicit a transcriptional response. Loss-of-function and gain-of-function experiments in the mouse have provided insight into the role of this signaling pathway in lymphopoiesis. The self-renewal and maintenance of hematopoietic stem cells is regulated by Wnt signals. Differentiation of T cells and natural killer cells is blocked in the absence of LEF1/TCF proteins, and pro-B cell proliferation is regulated by Wnt signaling.

Inhibition of the DNA binding by the TCF-1 binding RNA aptamer

The DNA binding architectural protein, TCF, and the transcriptional activator, beta-catenin, form a complex that regulates the expression of diverse target genes during early development and carcinogenesis. As an approach to modulating transcription by this complex, we selected an RNA aptamer that binds to the DNA binding domain of TCF-1. The aptamer interfered with the binding of TCF-1 to its specific DNA recognition sequences in vitro and also inhibited DNA binding of cellular TCF-1. We also developed the truncated version of the aptamer for efficient delivery to the cells. Structural analysis of the truncated aptamer revealed that a stem-loop with an internal loop was responsible for the binding to TCF-1. Similar approach may well be applicable to other proteins, especially DNA binding transcription factors, in order to modulate their DNA binding and transcriptional activity in the cells.

Identifying polymorphisms in the Rattus norvegicus D3 dopamine receptor gene and regulatory region

The D(3) dopamine receptor has been implicated in several neuropsychiatric disorders, including schizophrenia, Parkinson's disease and addiction. Sequence variation in the D(3) gene can lead to subtle alteration in receptor structure or gene expression and thus to a different phenotype. In this study we examine the sequence variation in the D(3) gene in 96 rat strains and substrains. Interestingly, the analyses revealed 10 polymorphisms in the 5'flanking region and four polymorphisms in intronic regions of the gene. Moreover, two single nucleotide polymorphisms (SNPs) that result in amino acid changes were found in the last exon of the D(3) gene in the RNU/Mol strain. Additionally, bioinformatic analysis of the 5'flanking region and first intron of the gene revealed putative transcription factor binding sites that are conserved between mouse and human and are affected by the SNPs, possibly resulting in altered regulation of the subsequent transcription factor.

High-Resolution assessment of protein DNA binding affinity and selectivity utilizing a fluorescent intercalator displacement (FID) assay

Protein titration displacement of ethidium bromide bound to hairpin deoxyoligonucleotides containing any sequence of interest provides a well-defined titration curve (measuring the loss of fluorescence derived from the DNA bound ethidium bromide) that provides both absolute binding constants (K(a)) and stoichiometry of binding. This use of a fluorescent intercalator displacement (FID) assay for establishing protein DNA binding affinity and selectivity is demonstrated with the examination of the LEF-1 HMG domain binding to hairpin deoxyoligonucleotides containing its commonly accepted consensus sequence 5'-CTTTGWW (W=A or T) and those modified (5'-CTNTGWW) to examine sequences implicated in early studies (5'-CTNTG). The effectiveness of the FID assay coupled with its technically non-demanding experimental use makes it an attractive alternative or complement to selection screening, footprinting or affinity cleavage, and electrophoretic mobility shift assays for detecting, characterizing, and quantitating protein DNA binding affinity and selectivity.

Initiation and limitation of Ly-49A NK cell receptor acquisition by T cell factor-1

The establishment of clonally variable expression of MHC class I-specific receptors by NK cells is not well understood. The Ly-49A receptor is used by approximately 20% of NK cells, whereby most cells express either the maternal or paternal allele and few express simultaneously both alleles. We have previously shown that NK cells expressing Ly-49A were reduced or almost absent in mice harboring a single or no functional allele of the transcription factor T cell factor-1 (TCF-1), respectively. In this study, we show that enforced expression of TCF-1 in transgenic mice yields an expanded Ly-49A subset. Even though the frequencies of Ly-49A(+) NK cells varied as a function of the TCF-1 dosage, the relative abundance of mono- and biallelic Ly-49A cells was maintained. Mono- and biallelic Ly-49A NK cells were also observed in mice expressing exclusively a transgenic TCF-1, i.e., expressing a fixed amount of TCF-1 in all NK cells. These findings suggest that Ly-49A acquisition is a stochastic event due to limiting TCF-1 availability, rather than the consequence of clonally variable expression of the endogenous TCF-1 locus. Efficient Ly-49A acquisition depended on the expression of a TCF-1 isoform, which included a domain known to associate with the TCF-1 coactivator beta-catenin. Indeed, the proximal Ly-49A promoter was beta-catenin responsive in reporter gene assays. We thus propose that Ly-49A receptor expression is induced from a single allele in occasional NK cells due to a limitation in the amount of a transcription factor complex requiring TCF-1.

Caught up in a Wnt storm: Wnt signaling in cancer

The Wnt signaling pathway, named for its most upstream ligands, the Wnts, is involved in various differentiation events during embryonic development and leads to tumor formation when aberrantly activated. Molecular studies have pinpointed activating mutations of the Wnt signaling pathway as the cause of approximately 90% of colorectal cancer (CRC), and somewhat less frequently in cancers at other sites, such as hepatocellular carcinoma (HCC). Ironically, Wnts themselves are only rarely involved in the activation of the pathway during carcinogenesis. Mutations mimicking Wnt stimulation-generally inactivating APC mutations or activating beta-catenin mutations-result in nuclear accumulation of beta-catenin which subsequently complexes with T-cell factor/lymphoid enhancing factor (TCF/LEF) transcription factors to activate gene transcription. Recent data identifying target genes has revealed a genetic program regulated by beta-catenin/TCF controlling the transcription of a suite of genes promoting cellular proliferation and repressing differentiation during embryogenesis, carcinogenesis, and in the post-embryonic regulation of cell positioning in the intestinal crypts. This review considers the spectra of tumors arising from active Wnt signaling and attempts to place perspective on recent data that begin to elucidate the mechanisms prompting uncontrolled cell growth following induction of Wnt signaling.

Homeobox gene expression profile in human hematopoietic multipotent stem cells and T-cell progenitors: implications for human T-cell development

Class I homeobox (HOX) genes comprise a large family of transcription factors that have been implicated in normal and malignant hematopoiesis. However, data on their expression or function during T-cell development is limited. Using degenerated RT-PCR and Affymetrix microarray analysis, we analyzed the expression pattern of this gene family in human multipotent stem cells from fetal liver (FL) and adult bone marrow (ABM), and in T-cell progenitors from child thymus. We show that FL and ABM stem cells are similar in terms of HOX gene expression, but significant differences were observed between these two cell types and child thymocytes. As the most immature thymocytes are derived from immigrated FL and ABM stem cells, this indicates a drastic change in HOX gene expression upon entry into the thymus. Further analysis of HOX-A7, HOX-A9, HOX-A10, and HOX-A11 expression with specific RT-PCR in all thymocyte differentiation stages showed a sequential loss of 3' region HOX-A cluster genes during intrathymic T-cell development and an unexpected expression of HOX-A11, previously not recognized to play a role in hematopoiesis. Also HOX-B3 and HOX-C4 were expressed throughout thymocyte development. Overall, these data provide novel evidence for an important role of certain HOX genes in human T-cell development.

Tcf-1 expression during Xenopus development

We report the cloning and expression of Xenopus Tcf-1. The amino acid sequence of Tcf-1 of Xenopus laevis and Xenopus tropicalis is closely related to that of chicken, mouse and man. Thus, the family of Tcf/Lef proteins in the amphibian Xenopus comprises four members as in higher vertebrates. RT-PCR analysis revealed that Tcf-1 RNA encoding a beta-catenin binding isoform is maternally present as well as throughout early development. Different transcripts are expressed by alternative splicing. In cleavage and blastula stage embryos, Tcf-1 RNA is present at high levels in the animal hemisphere. During gastrulation Tcf-1 is differentially expressed with high levels in the animal cap and most of the marginal zone except for a narrow domain around the blastopore. At neurula stages expression is predominant in the neural plate. At tailbud stages expression is localized in specific areas of the brain, in the eyes, the otic vesicle, branchial arches and head mesenchyme, somites, tailbud, pronephros and pronephric duct.

Loss of expression of the WNT/beta-catenin-signaling pathway transcription factors lymphoid enhancer factor-1 (LEF-1) and T cell factor-1 (TCF-1) in a subset of peripheral T cell lymphomas

T cell factor-1 (TCF-1) and lymphoid enhancer factor-1 (LEF-1), members of the TCF/LEF family of transcription factors, play a significant role in T cell development and are expressed in thymocytes and peripheral CD3+ T cells. Previously, precursor T lymphoblastic leukemia/lymphoblastic lymphoma (T-ALL/LyL) was found to express TCF-1, and we find that 9 of 10 cases of T-ALL/LyL express LEF-1 as well as TCF-1, exhibiting uniform nuclear immunostaining for both transcription factors. In addition, a significant subset of cases of peripheral T cell lymphoma (PTCL), 39 of 81 cases (48%), are immunoreactive for LEF-1 and/or TCF-1, with 36 of 38 cases immunoreactive for both, indicating that these transcription factors are coordinately expressed in PTCL. The vast majority of LEF-1+ and/or TCF-1+ PTCL (34 of 39 or 87%) exhibit a composite Th1 T-cell-like immunophenotype, based on expression of Th1 T cell-associated, but not Th2 T cell-associated, chemokine receptors and activation markers. Of the Th1-like PTCL studied, 33 of 42 (79%) were immunoreactive for LEF-1 and 32 of 42 (76%) were immunoreactive for TCF-1, including most cases of angioimmunoblastic lymphoma and all cases of lymphoepithelioid lymphoma. Surprisingly, none of the 21 cases of Th2-like PTCL studied, all cases of anaplastic large cell lymphoma, were immunoreactive for LEF-1 or TCF-1 (P < 0.0001), suggesting that LEF-1 and TCF-1 transcription factor expression may be lost in Th2 T cells or Th2-like PTCL. LEF-1 and TCF-1 immunostaining can serve to identify specific subtypes of PTCL, and lends support to a bipartite model of PTCL development, based on expression of activation markers.

Wnt signaling in the thymus

Wnt proteins are secreted signaling molecules that regulate cell-to-cell interactions during embryogenesis in many different tissues and species. Wnt signaling is required for normal thymocyte development, most dramatically at the pro-T-cell stage, although recent reports also indicate a role for Wnt proteins in later stages of thymocyte differentiation. The Wnt cascade induces the interaction of the normally cytoplasmic cofactor beta-catenin with the nuclear Tcf and Lef transcription factors. Active Wnt signaling is an absolute requirement for T-cell development, as demonstrated by the complete block in thymocyte development observed in the absence of Tcf1 and Lef1, or in the presence of extracellular Wnt inhibitors.

WNT signaling and lymphocyte development

Developmental studies in model organisms have revealed that cell fate decisions are governed by only a handful of highly conserved signal transduction cascades. Recent data indicate that at least two of these, the Wnt and the Notch cascades, have been recruited by the vertebrate immune system to control early lymphopoiesis.

TOX: an HMG box protein implicated in the regulation of thymocyte selection

In the thymus, pre-T cell receptor (pre-TCR)--mediated signaling and then TCR-mediated signaling initiate changes in gene expression that result in the maturation of CD4 and CD8 lineage T cells from common precursors. Using gene chip technology, we isolated a murine gene, designated Tox, that encodes a member of the HMG (high-mobility group) box family of DNA-binding proteins. TOX expression is up-regulated by both pre-TCR and TCR activation of immature thymocytes but not by TCR activation of mature naïve T cells. Transgenic mice that express TOX show expanded CD8+ and reduced CD4+ single positive thymocyte subpopulations. We present evidence here that this phenotype results from a perturbation in lineage commitment due to reduced sensitivity to TCR-mediated signaling. This molecular marker of thymic selection events may therefore play a role in establishing the activation threshold of developing T cells and patterning changes in gene expression.

HOX-A10 regulates hematopoietic lineage commitment: evidence for a monocyte-specific transcription factor

Homeobox genes are well known for their crucial role during embryogenesis but have also been found to be critically involved in normal and leukemic hematopoiesis. Because most previous studies focused on the role of aberrant HOX gene expression in leukemogenesis and because HOX-A10 is expressed in human CD34(+) precursor cells, this study investigated whether HOX-A10 also plays a pivotal role in normal hematopoietic-lineage determination. The effect of enforced expression of this transcription factor on hematopoietic differentiation of highly purified human cord-blood progenitors was examined by using in vitro assays. In fetal thymic organ cultures, a dramatic reduction in cells expressing high levels of HOX-A10 was observed, along with absence of thymocytes positive for CD3(+) T-cell receptor alphabeta. Furthermore, in MS-5 stromal cell cultures, there was a 7-fold reduction in the number of natural killer cells and a 9-fold reduction in the number of B cells, thus showing a profound defect in differentiation toward the lymphoid lineage in HOX-A10-transduced progenitors. In contrast, the number of CD14(+) monocytic cells in the stromal cell culture was 6-fold higher, suggesting an enhanced differentiation toward the myeloid differentiation pathway of HOX-A10-transduced progenitors. However, there was a slight reduction in the number of CD15(+) granulocytic cells, which were blocked in their final maturation. These data show that HOX-A10 can act as an important key regulator of lineage determination in human hematopoietic progenitor cells.

Extinction of expression of the genes encoding haematopoietic cell-restricted transcription factors in T-lymphoma x fibroblast cell hybrids

We previously reported that expression of the T-cell receptor (TCR) alpha and lck genes is extinguished in hybrids between mouse T-lymphoma EL4 cells and mouse fibroblast B82 cells. In the present study, we found that the activities of the TCRalpha minimum enhancer and the lck promoter monitored by the luciferase or chloramphenicol acetyltransferase (CAT) assays were markedly inhibited in the hybrids. Expression of the TCF-1, LEF-1, GATA-3, Ikaros, c-myb and Fli-1 genes, which encode the haematopoietic cell-restricted transcription factors that appear to be responsible for the activities of the enhancer and the promoter, was fully extinguished or markedly suppressed in the hybrids. On the other hand, expression of the transcription factor genes observed in both parental cells, such as the AML1 and c-ets-1 genes, and that of the genes encoding ubiquitously expressed transcription factors, such as the E2A, CREB and c-ets-2 genes, was not significantly suppressed in the hybrids. These results suggest that the genes encoding haematopoietic cell-restricted transcription factors are targets for negative regulation in fibroblastic background and that the repression of these genes may consequently lead to suppression of the promoter and/or enhancer activities of several T-cell-specific structural genes in T-lymphoma x fibroblast cell hybrids.

The beta-catenin--TCF-1 pathway ensures CD4(+)CD8(+) thymocyte survival

The association of trans-acting T cell factors (TCFs) or lymphoid enhancer factor 1 (LEF-1) with their coactivator beta-catenin mediates transient transcriptional responses to extracellular Wnt signals. We show here that T cell maturation depends on the presence of the beta-catenin--binding domain in TCF-1. This domain is necessary to mediate the survival of immature CD4(+)CD8(+) double-positive (DP) thymocytes. Accelerated spontaneous thymocyte death in the absence of TCF-1 correlates with aberrantly low expression of the anti-apoptotic protein Bcl-x(L). Increasing anti-apoptotic effectors in thymocytes by the use of a Bcl-2 transgene rescued TCF-1-deficient DP thymocytes from apoptosis. Thus, TCF-1, upon association with beta-catenin, transiently ensures the survival of immature T cells, which enables them to generate and edit T cell receptor (TCR) alpha chains and attempt TCR-mediated positive selection.

Sry, Sox9 and mammalian sex determination

Sry is the Y-chromosomal gene that acts as a trigger for male development in mammalian embryos. This gene encodes a high mobility group (HMG) box transcription factor that is known to bind to specific target sequences in DNA and to cause a bend in the chromatin. DNA bending appears to be part of the mechanism by which Sry influences transcription of genes downstream in a cascade of gene regulation leading to maleness, but the factors that cooperate with, and the direct targets of, Sry remain to be identified. One gene known to be downstream from Sry in this cascade in Sox9, which encodes a transcription factor related to Sry by the HMG box. Like Sry, mutations in Sox9 disrupt male development, but unlike Sry, the role of Sox9 is not limited to mammals. This review focuses on what is known about the two genes and their likely modes of action, and draws together recent data relating to how they might interconnect with the network of gene activity implicated in testis determination in mammals.

Transcriptional Control of T Lymphocyte Differentiation

Initiation of gene transcription by transcription factors (TFs) is an important regulatory step in many developmental processes. The differentiation of T cell progenitors in the thymus is tightly controlled by signaling molecules, ultimately activating nuclear TFs that regulate the expression of T lineage-specific genes. During the last 2 years, significant progress has been made in our understanding of the signaling routes and TFs operating during the earliest stages of thymic differentiation at the CD4(-)CD8(-) double negative stage. Here we will review the TF families that play an important role in differentiation of thymocytes, particularly focusing on recent new information with respect to the Tcf, bHLH, GATA, and CBF/HES TF families.

T-cell factor-1 expression during human natural killer cell development and in circulating CD56(+) bright natural killer cells

Transcription factors are essential to govern differentiation along the lymphoid lineage from uncommitted hematopoietic stem cells. Although many of these transcription factors have putative roles based on murine knockout experiments, their function in human lymphoid development is less known and was studied further. Transcription factor expression in fresh and cultured adult human bone marrow and umbilical cord blood progenitors was evaluated. We found that fresh CD34(+)Lin(-) cells that are human leukocyte antigen (HLA)-DR(-) or CD38(-) constitutively express GATA-3 but not T-cell factor-1 (TCF-1) or Id-3. Culture with the murine fetal liver cell line AFT024 and defined cytokines was capable of inducing TCF-1 mRNA. However, no T-cell receptor gene rearrangement was identified in cultured progeny. Id-3, a basic helix loop helix factor with dominant negative function for T-cell differentiation transcription factors, also was upregulated and may explain unsuccessful T-cell maturation. To better understand the developmental link between natural killer (NK) cells derived from progenitors, we studied NK cell subsets circulating in blood. CD56(+bright), but not CD56(+dim), NK cells constitutively express TCF-1 by reverse transcriptase polymerase chain reaction and Western blot analysis. The TCF-1 isoform found in CD56(+bright) cells, which express lectin but not immunoglobulin class I recognizing inhibitory receptors, was identical to that induced in NK cell differentiation culture and was distinctly different from isoforms in T cells. These results suggest that TCF-1 does not target human killer immunoglobulin receptor genes, TCF-1 is uniquely expressed in circulating CD56(+bright) NK cells, and specific TCF-1 isoforms may play an important role in regulating NK differentiation from a common NK/T-cell progenitor.

Wnt signaling regulates B lymphocyte proliferation through a LEF-1 dependent mechanism

Lymphocyte enhancer factor-1 (LEF-1) is a member of the LEF-1/TCF family of transcription factors, which have been implicated in Wnt signaling and tumorigenesis. LEF-1 was originally identified in pre-B and T cells, but its function in B lymphocyte development remains unknown. Here we report that LEF-1-deficient mice exhibit defects in pro-B cell proliferation and survival in vitro and in vivo. We further show that Lef1-/- pro-B cells display elevated levels of fas and c-myc transcription, providing a potential mechanism for their increased sensitivity to apoptosis. Finally, we establish a link between Wnt signaling and normal B cell development by demonstrating that Wnt proteins are mitogenic for pro-B cells and that this effect is mediated by LEF-1.

Activation of the p38 mitogen-activated protein kinase pathway arrests cell cycle progression and differentiation of immature thymocytes in vivo

The development of T cells in the thymus is coordinated by cell-specific gene expression programs that involve multiple transcription factors and signaling pathways. Here, we show that the p38 mitogen-activated protein (MAP) kinase signaling pathway is strictly regulated during the differentiation of CD4(-)CD8(-) thymocytes. Persistent activation of p38 MAP kinase blocks fetal thymocyte development at the CD25(+)CD44(-) stage in vivo, and results in the lack of T cells in the peripheral immune system of adult mice. Inactivation of p38 MAP kinase is required for further differentiation of these cells into CD4(+)CD8(+) thymocytes. The arrest of cell cycle in mitosis is partially responsible for the blockade of differentiation. Therefore, the p38 MAP kinase pathway is a critical regulatory element of differentiation and proliferation during the early stages of in vivo thymocyte development.