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Cancer progression involves the gradual loss of a differentiated phenotype and acquisition of progenitor and stem-cell-like features. Here, we provide novel stemness indices for assessing the degree of oncogenic dedifferentiation. We used an innovative one-class logistic regression (OCLR) machine-learning algorithm to extract transcriptomic and epigenetic feature sets derived from non-transformed pluripotent stem cells and their differentiated progeny. Using OCLR, we were able to identify previously undiscovered biological mechanisms associated with the dedifferentiated oncogenic state. Analyses of the tumor microenvironment revealed unanticipated correlation of cancer stemness with immune checkpoint expression and infiltrating immune cells. We found that the dedifferentiated oncogenic phenotype was generally most prominent in metastatic tumors. Application of our stemness indices to single-cell data revealed patterns of intra-tumor molecular heterogeneity. Finally, the indices allowed for the identification of novel targets and possible targeted therapies aimed at tumor differentiation. Stemness features extracted from transcriptomic and epigenetic data from TCGA tumors reveal novel biological and clinical insight, as well as potential drug targets for anti-cancer therapies.

Contributions of null and hypomorphic alleles of Apc in mice produce both developmental and pathophysiological phenotypes. To ascribe the resulting genotype-to-phenotype relationship unambiguously to the Wnt/beta-catenin pathway, we challenged the allele combinations by genetically restricting intracellular beta-catenin expression in the corresponding compound mutant mice. Subsequent evaluation of the extent of resulting Tcf4-reporter activity in mouse embryo fibroblasts enabled genetic measurement of Wnt/beta-catenin signaling in the form of an allelic series of mouse mutants. Different permissive Wnt signaling thresholds appear to be required for the embryonic development of head structures, adult intestinal polyposis, hepatocellular carcinomas, liver zonation, and the development of natural killer cells. Furthermore, we identify a homozygous Apc allele combination with Wnt/beta-catenin signaling capacity similar to that in the germline of the Apc(min) mice, where somatic Apc loss-of-heterozygosity triggers intestinal polyposis, to distinguish whether co-morbidities in Apc(min) mice arise independently of intestinal tumorigenesis. Together, the present genotype phenotype analysis suggests tissue-specific response levels for the Wnt/beta-catenin pathway that regulate both physiological and pathophysiological conditions.

Gene expression profiling of beta-catenin, Cripto and Wnt3 mutant mouse embryos has been used to characterise the genetic networks that regulate early embryonic development. We have defined genes whose expression is regulated by beta-catenin during formation of the anteroposterior axis and the mesoderm, and have identified Cripto, which encodes a Nodal co-receptor, as a primary target of beta-catenin signals both in embryogenesis as well as in colon carcinoma cell lines and tissues. We have also defined groups of genes regulated by Wnt3/beta-catenin signalling during primitive streak and mesoderm formation. Our data assign a key role to beta-catenin upstream of two distinct gene expression programs during anteroposterior axis and mesoderm formation.

Gain of Wnt signaling through beta-catenin has been ascribed a critical function in the stimulation of hematopoietic stem cell self-renewal, whereas loss of beta-catenin is reportedly dispensable for hematopoiesis. Here we have used conditional mouse genetics and transplantation assays to demonstrate that constitutive activation of beta-catenin blocked multilineage differentiation, leading to the death of mice. Blood cell depletion was accompanied by failure of hematopoietic stem cells to repopulate irradiated hosts and to differentiate into mature cells. Activation of beta-catenin enforced cell cycle entry of hematopoietic stem cells, thus leading to exhaustion of the long-term stem cell pool. Our data suggest that fine-tuned Wnt stimulation is essential for hematopoiesis and is thus critical for therapeutic hematopoietic stem cell population expansion.

The human beta-catenin locus (CTNNB1) was mapped by in situ fluorescence analysis to band p21 on the short arm of chromosome 3, a region frequently affected by somatic alterations in a variety of tumors. PCR primers for the genomic amplification of beta-catenin sequences were selected on the basis of homology to exon 4 of the Drosophila armadillo gene. Analysis of a panel of somatic cell hybrids confirmed the localization of beta-catenin on human chromosome 3. Furthermore, exclusion mapping of three hybrids carrying defined fragments of the short arm of human chromosome 3 allowed us to determine the position of the CTNNB1 locus close to the marker D3S2 in 3p21.

BACKGROUND: Levels of the pro-tumorigenic prostaglandin PGE(2) are increased in colorectal cancer, previously attributed to increased synthesis through COX-2 upregulation and, more recently, to decreased catabolism. The functionally linked genes 15-prostaglandin dehydrogenase (15-PGDH) and the prostaglandin transporter PGT co-operate in prostaglandin degradation and are downregulated in colorectal cancer. We previously reported repression of 15-PGDH expression by the Wnt/beta-catenin pathway, commonly deregulated during early colorectal neoplasia. Here we asked whether beta-catenin also regulates PGT expression. METHODS: The effect of beta-catenin deletion in vivo was addressed by PGT immunostaining of beta-catenin(-/lox)-villin-cre-ERT2 mouse tissue. The effect of siRNA-mediated beta-catenin knockdown and dnTCF4 induction in vitro was addressed by semi-quantitative and quantitative real-time RT-PCR and immunoblotting. RESULTS: This study shows for the first time that deletion of beta-catenin in murine intestinal epithelium in vivo upregulates PGT protein, especially in the crypt epithelium. Furthermore, beta-catenin knockdown in vitro increases PGT expression in both colorectal adenoma- and carcinoma-derived cell lines, as does dnTCF4 induction in LS174T cells. CONCLUSIONS: These data suggest that beta-catenin employs a two-pronged approach to inhibiting prostaglandin turnover during colorectal neoplasia by repressing PGT expression in addition to 15-PGDH. Furthermore, our data highlight a potential mechanism that may contribute to the non-selective NSAID aspirin's chemopreventive efficacy. British Journal of Cancer (2012) 107, 1514-1517. doi:10.1038/bjc.2012.430 www.bjcancer.com Published online 2 October 2012 (C) 2012 Cancer Research UK

Studies of chimeric mice have disclosed that the stem cell hierarchy in the small intestinal epithelium is established during formation of its proliferative units (crypts of Lieberkuhn). This process involves a selection among several multipotential progenitors so that ultimately only one survives to supply descendants to the fully formed crypt. In this report, we examine the hypothesis that the level of beta-catenin (beta-cat)-mediated signaling is an important factor regulating this stem cell selection. In the canonical Wnt signaling pathway, beta-catenin can partner with Lef-1/Tcf high mobility group (HMG) box transcription factors to control gene expression. Both Lef-1 and Tcf-4 mRNAs are produced in the fetal mouse small intestine. Tcf-4 expression is sustained, whereas Lef-1 levels fall as crypt formation is completed during the first two postnatal weeks. A Tcf-4 gene knockout is known to block intestinal epithelial proliferation in late fetal life. Therefore, to test the hypothesis, we enhanced beta-catenin signaling in a chimeric mouse model in which the stem cell selection could be monitored. A fusion protein containing the HMG box domain of Lef-1 linked to the trans-activation domain of beta-catenin (Lef-1/beta-cat) was constructed to promote direct stimulation of signaling without being retained in the cytoplasm through interactions with E-cadherin and Apc/Axin. Lef-1/beta-cat was expressed in 129/Sv embryonic stem cell-derived small intestinal epithelial progenitors present in developing B6-ROSA26129/Sv chimeras. Lef-1/beta-cat stimulated expression of a known beta-catenin target (E-cadherin), suppressed expression of Apc and Axin, and induced apoptosis in 129/Sv but not in neighboring B6-ROSA26 epithelial cells. This apoptotic response was not associated with any detectable changes in cell division within the Lef-1/beta-cat-expressing epithelium. By the time crypt development was completed, all 129/Sv epithelial cells were lost. These results indicate that developmental changes in beta-catenin-mediated signaling can play an important role in establishing a stem cell hierarchy during crypt morphogenesis.

Recent studies implicate Wnt/beta-catenin signaling in lens differentiation (Stump, R. J., et al., 2003. A role for Wnt/beta-catenin signaling in lens epithelial differentiation. Dev Biol;259:48-61). Beta-catenin is a component of adherens junctions and functions as a transcriptional activator in canonical Wnt signaling. We investigated the effects of Cre/LoxP-mediated deletion of beta-catenin during lens development using two Cre lines that specifically deleted beta-catenin in whole lens or only in differentiated fibers, from E13.5. We found that beta-catenin was required in lens epithelium and during early fiber differentiation but appeared to be redundant in differentiated fiber cells. Complete loss of beta-catenin resulted in an abnormal and deficient epithelial layer with loss of E-cadherin and Pax6 expression as well as abnormal expression of c-Maf and p57(kip2) but not Prox1. There was also disrupted fiber cell differentiation, characterized by poor cell elongation, decreased beta-crystallin expression, epithelial cell cycle arrest at G(1)-S transition and premature cell cycle exit. Despite cell cycle arrest there was no induction of apoptosis. Mutant fiber cells displayed altered apical-basal polarity as evidenced by altered distribution of the tight junction protein, ZO1, disruption of apical actin filaments and abnormal deposition of extracellular matrix, resulting in a deficient lens capsule. Loss of beta-catenin also affected the formation of adhesion junctions as evidenced by dissociation of N-cadherin and F-actin localization in differentiating fiber cells. However, loss of beta-catenin from terminally differentiating fibers had no apparent effects on adhesion junctions between adjacent embryonic fibers. These data indicate that beta-catenin plays distinct functions during lens fiber differentiation and is involved in both Wnt signaling and adhesion-related mechanisms that regulate lens epithelium and early fiber differentiation.

beta-Catenin is an essential component of the canonical Wnt signaling system that controls decisive steps in development. We employed here two conditional beta-catenin mutant alleles to alter beta-catenin signaling in the central nervous system of mice: one allele to ablate beta-catenin and the second allele to express a constitutively active beta-catenin. The tissue mass of the spinal cord and brain is reduced after ablation of beta-catenin, and the neuronal precursor population is not maintained. In contrast, the spinal cord and brain of mice that express activated beta-catenin is much enlarged in mass, and the neuronal precursor population is increased in size. beta-Catenin signals are thus essential for the maintenance of proliferation of neuronal progenitors, controlling the size of the progenitor pool, and impinging on the decision of neuronal progenitors to proliferate or to differentiate.

P-cadherin expression is restricted to the basal layer of stratified epithelia including that of the mammary gland. Although evidence for an important role of P-cadherin in mammary morphogenesis and tumorigenesis is increasing, the mechanisms that regulate its expression are poorly understood. We show that in basal mammary epithelial cells, beta-catenin is associated with the P-cadherin promoter and activates its expression independently of LEF/TCF in a cell-type specific manner. Down-regulation of endogenous beta-catenin levels by RNA interference technique inhibited P-cadherin promoter activity. In vivo, in skin and mammary gland of mutant mice, activation of beta-catenin signalling correlates with up-regulation of P-cadherin expression. These data suggest that beta-catenin-dependent modulation of P-cadherin expression can contribute to the establishment of the basal phenotype.

To examine the consequences of repressing beta-catenin/Lef1 signalling in mouse epidermis, we expressed a DeltaNLef1 transgene, which lacks the beta-catenin binding site, under the control of the keratin 14 promoter. No skin abnormalities were detected before the first postnatal hair cycle. However, from 6 weeks of age, mice underwent progressive hair loss which correlated with the development of dermal cysts. The cysts were derived from the base of the hair follicles and expressed morphological and molecular markers of interfollicular epidermis. Adult mice developed spontaneous skin tumours, most of which exhibited sebaceous differentiation, which could be indicative of an origin in the upper part of the hair follicle. The transgene continued to be expressed in the tumours and beta-catenin signalling was still inhibited, as evidenced by absence of cyclin D1 expression. However, patched mRNA expression was upregulated, suggesting that the sonic hedgehog pathway might play a role in tumour formation. Based on our results and previous data on the consequences of activating beta-catenin/Lef1 signalling in postnatal keratinocytes, we conclude that the level of beta-catenin signalling determines whether keratinocytes differentiate into hair or interfollicular epidermis, and that perturbation of the pathway by overexpression of DeltaNLef1 can lead to skin tumour formation.

By conditional gene ablation in mice, we found that β-catenin, an essential downstream effector of canonical Wnt signaling, is a key regulator of formation of the apical ectodermal ridge (AER) and of the dorsal-ventral axis of the limbs. By generation of compound mutants, we also show that {beta}-catenin acts downstream of the BMP receptor IA in AER induction, but upstream or parallel in dorsal-ventral patterning. Thus, AER formation and dorsal-ventral patterning of limbs are tightly controlled by an intricate interplay between Wnt/{beta}-catenin and BMP receptor signaling.

It has been realized for some time that the loss of epithelial differentiation in carcinomas, which is accompanied by higher mobility and invasiveness of the tumor cells, is a consequence of reduced intercellular adhesion. A variety of recent reports have indicated that the primary cause for the 'scattering' of the cells in invasive carcinomas is a loss of the integrity of intercellular adherens junctions often involving loss of a functional cell-cell adhesion molecule E-cadherin. In the present review, permanent and transient molecular mechanisms are discussed which lead to the impairment of junctional integrity of cells and thus the progression of carcinomas toward a more metastatic state

Both beta-catenin and plakoglobin can stimulate the expression of Lef/Tcf target genes in vitro. beta-Catenin is known to associate with Lef/Tcf factors and to participate directly in transactivation in vivo, whereas the role of plakoglobin in transcriptional regulation has been less studied. To analyze the functions of plakoglobin in vivo, we generated transgenic mice expressing in the epidermis N-terminally truncated plakoglobin (DeltaN122-PG) lacking the glycogen synthase kinase 3beta phosphorylation sites and therefore protected against degradation (transgenic line K5-DeltaN122-PG). The expression of DeltaN122-PG led to the formation of additional hair germs, hyperplastic hair follicles, and noninvasive hair follicle tumors, a phenotype reminiscent of that induced by expression of N-terminally truncated beta-catenin. However, if expressed in beta-catenin-null epidermis, DeltaN122-PG did not induce new hair follicle germs and follicular tumors. Thus, DeltaN122-PG cannot substitute for beta-catenin in its signaling functions in vivo and the phenotype observed in K5-DeltaN122-PG mouse skin must be due to the aberrant activation of beta-catenin signaling. On the other hand, the expression of DeltaN122-PG in beta-catenin-null skin significantly increased the survival rate of mutant mice, rescued differentiation, and limited excessive proliferation in the interfollicular epidermis, suggesting that plakoglobin may be involved in the intracellular signaling events essential for epidermal differentiation.

The loss of epithelial differentiation in carcinomas, which is accompanied by higher mobility and invasiveness of the tumour cells, is often a consequence of reduced intercellular adhesion. The primary cause of the "scattering" of cells in invasive carcinomas appears to be a disturbance of the integrity of intercellular junctions, often involving the cell adhesion molecule E-cadherin. Permanent and transient molecular mechanisms can lead to the impairment of junction integrity of epithelial cells and thus to the progression of carcinomas towards a more invasive state. These include downregulation of E-cadherin expression and interaction between the adherens junction protein beta-catenin and the tumour suppressor gene product APC

Wnt/beta-catenin and NF-kappaB signaling mechanisms provide central controls in development and disease, but how these pathways intersect is unclear. Using hair follicle induction as a model system, we show that patterning of dermal Wnt/beta-catenin signaling requires epithelial beta- catenin activity. We find that Wnt/beta-catenin signaling is absolutely required for NF-kappaB activation, and that Edar is a direct Wnt target gene. Wnt/beta-catenin signaling is initially activated independently of EDA/EDAR/NF-kappaB activity in primary hair follicle primordia. However, Eda/Edar/NF-kappaB signaling is required to refine the pattern of Wnt/beta-catenin activity, and to maintain this activity at later stages of placode development. We show that maintenance of localized expression of Wnt10b and Wnt10a requires NF-kappaB signaling, providing a molecular explanation for the latter observation, and identify Wnt10b as a direct NF-kappaB target. These data reveal a complex interplay and interdependence of Wnt/beta-catenin and EDA/EDAR/NF-kappaB signaling pathways in initiation and maintenance of primary hair follicle placodes.

The Wnt signaling pathway is deregulated in over 90% of human colorectal cancers. beta-Catenin, the central signal transducer of the Wnt pathway, can directly modulate gene expression by interacting with transcription factors of the TCF/LEF family. In the present study we investigate the role of Wnt signaling in the homeostasis of intestinal epithelium by using tissue-specific, inducible beta-catenin gene ablation in adult mice. Block of Wnt/beta-catenin signaling resulted in rapid loss of transient-amplifying cells and crypt structures. Importantly, intestinal stem cells were induced to terminally differentiate upon deletion of beta-catenin, resulting in a complete block of intestinal homeostasis and fatal loss of intestinal function. Transcriptional profiling of mutant crypt mRNA isolated by laser capture microdissection confirmed those observations and allowed us to identify genes potentially responsible for the functional preservation of intestinal stem cells. Our data demonstrate an essential requirement of Wnt/beta-catenin signaling for the maintenance of the intestinal epithelium in the adult organism. This challenges attempts to target aberrant Wnt signaling as a new therapeutic strategy to treat colorectal cancer.

The armadillo-related protein beta-catenin has multiple functions in cardiac tissue homeostasis: stabilization of beta-catenin has been implicated in adult cardiac hypertrophy, and downregulation initiates heart formation in embryogenesis. The protein is also part of the cadherin/catenin complex at the cell membrane, where depletion might result in disturbed cell-cell interaction similar to N-cadherin knockout models. Here, we analyzed the in vivo role of beta-catenin in adult cardiac hypertrophy initiated by angiotensin II (Ang II). The cardiac-specific mifepristone-inducible alphaMHC-CrePR1 transgene was used to induce beta-catenin depletion (loxP-flanked exons 3 to 6, beta-cat(Deltaex3-6) mice) or stabilization (loxP-flanked exon 3, beta-cat(Deltaex3) mice). Levels of beta-catenin were altered both in membrane and nuclear extracts. Analysis of the beta-catenin target genes Axin2 and Tcf-4 confirmed increased beta-catenin-dependent transcription in beta-catenin stabilized mice. In both models, transgenic mice were viable and healthy at age 6 months. beta-Catenin appeared dispensable for cell membrane function. Ang II infusion induced cardiac hypertrophy both in wild-type mice and in mice with beta-catenin depletion. In contrast, mice with stabilized beta-catenin had decreased cross-sectional area at baseline and an abrogated hypertrophic response to Ang II infusion. Stabilizing beta-catenin led to impaired fractional shortening compared with control littermates after Ang II stimulation. This functional deterioration was associated with altered expression of the T-box proteins Tbx5 and Tbx20 at baseline and after Ang II stimulation. In addition, atrophy-related protein IGFBP5 was upregulated in beta-catenin-stabilized mice. These data suggest that beta-catenin downregulation is required for adaptive cardiac hypertrophy.

Mutations and deregulation of adenomatous polyposis coli (APC) and beta-catenin are implicated in specific cancers of the pancreas, but the role of Wnt pathway in normal pancreas development and homeostasis is unknown [1-4]. This article reports a comprehensive investigation of the activity and the role of the Wnt pathway in pancreas organogenesis. We have used two reporter lines to monitor canonical Wnt pathway activity during development and after birth and demonstrate activity in endocrine cells and in the mesenchyme. We have specifically deleted the beta-catenin gene in the epithelium of the pancreas and duodenum by using Pdx1-Cre mice. In agreement with Wnt pathway activity in pancreatic endocrine cells, we find a reduction in endocrine islet numbers. Our study reveals that beta-catenin deletion also affects cells in which Wnt pathway activity is not detected. Indeed, beta-catenin mutant cells have a competitive disadvantage during development that also affects the exocrine compartment. Moreover, the conditional knockout (KO) mice develop acute edematous pancreatitis perinatally due to the disruption of the epithelial structure of acini. These effects are likely to be due to the function of beta-catenin at the membrane. Mice later recover from pancreatitis and regenerate normal pancreas and duodenal villi from the wild-type (wt) cells that escape beta-catenin deletion.

Gab1 is a multiadaptor protein that has been shown to be required for multiple processes in embryonic development and oncogenic transformation. Gab1 functions by amplifying signal transduction downstream of various receptor tyrosine kinases through recruitment of multiple signaling effectors, including phosphatidylinositol 3-kinase and Shp2. Until now, the functional significance of individual interactions in vivo was not known. Here we have generated knockin mice that carry point mutations in either the P13K or Shp2 binding sites of Gab1. We show that different effector interactions with Gab1 play distinct biological roles downstream of Gab1 during the development of different organs. Recruitment of phosphatidylinositol 3-kinase by Gab1 is essential for EGF receptor-mediated embryonic eyelid closure and keratinocyte migration, and the Gab1-Shp2 interaction is crucial for Met receptor-directed placental development and muscle progenitor cell migration to the limbs. Furthermore, we investigate the dual association of Gab1 with the Met receptor. By analyzing knockin mice with mutations in the Grb2 or Met binding site of Gab1, we show that the requirements for Gab1 recruitment to Met varies in different biological contexts. Either the direct or the indirect interaction of Gab1 with Met is sufficient for Met-dependent muscle precursor cell migration, whereas both modes of interaction are required and neither is sufficient for placenta development, liver growth, and palatal shelf closure. These data demonstrate that Gab1 induces different biological responses through the recruitment of distinct effectors and that different modes of recruitment for Gab1 are required in different organs.

The canonical Wnt signaling pathway plays key roles in stem-cell maintenance, progenitor cell expansion, and lineage decisions. Transcriptional responses induced by Wnt depend on the association of either beta-catenin or gamma-catenin with lymphoid enhancer factor/T cell factor transcription factors. Here we show that hematopoiesis, including thymopoiesis, is normal in the combined absence of beta- and gamma-catenin. Double-deficient hematopoietic stem cells maintain long-term repopulation capacity and multilineage differentiation potential. Unexpectedly, 2 independent ex vivo reporter gene assays show that Wnt signal transmission is maintained in double-deficient hematopoietic stem cells, thymocytes, or peripheral T cells. In contrast, Wnt signaling is strongly reduced in thymocytes lacking TCF-1 or in nonhematopoietic cells devoid of beta-catenin. These data provide the first evidence that hematopoietic cells can transduce canonical Wnt signals in the combined absence of beta- and gamma-catenin.

The lungs are divided, both structurally and functionally, into two distinct components, the proximal airways, which conduct air, and the peripheral airways, which mediate gas exchange. The mechanisms that control the specification of these two structures during lung development are currently unknown. Here we show that beta-catenin signaling is required for the formation of the distal, but not the proximal, airways. When the gene for beta-catenin was conditionally excised in epithelial cells of the developing mouse lung prior to embryonic day 14.5, the proximal lung tubules grew and differentiated appropriately. The mice, however, died at birth because of respiratory failure. Analysis of the lungs by in situ hybridization and immunohistochemistry, using molecular markers of the epithelial and mesenchymal components of both proximal and peripheral airways, showed that the lungs were composed primarily of proximal airways. These observations establish, for the first time, both the sites and timing of specification of the proximal and peripheral airways in the developing lung, and that beta-catenin is one of the essential components of this specification.

Genetic and chemically induced neuronopathic mouse models of Gaucher disease were developed to facilitate understanding of the reversibility and/or progression of CNS involvement. The lethality of the skin permeability barrier defect of the complete gene knock out [gba, (glucocerebrosidase) GCase] was avoided by conditional reactivation of a low activity allele (D409H) in keratinocytes (kn-9H). In kn-9H mice, progressive CNS disease and massive glucosylceramide storage in tissues led to death from CNS involvement by the age of 14 days. Conduritol B epoxide (CBE, a covalent inhibitor of GCase) treatment (for 8-12 days) of wild type, D409H, D409V or V394L homozygotes recapitulated the CNS phenotype of the kn- 9H mice with seizures, tail arching, shaking, tremor, quadriparesis, extensive neuronal degeneration loss and apoptosis, and death by the age of 14 days. Minor CNS abnormalities occurred after daily CBE injections of 100mg/kg/day for 6 doses, but neuronal degeneration was progressive and glucosylceramide storage persisted in D409V homozygotes in the 2 to 5 months after CBE cessation; wild type and D409H mice had persistent neurological damage without progression. The persistent CNS deterioration, histologic abnormalities, and glucosylceramide storage in the CBE-treated D409V mice revealed a threshold level of GCase activity necessary for the prevention of progression of CNS involvement

Various structural components of intercellular junctions have recently been found to represent (or be related to) products of tumor-suppressor genes. The tumor-suppressor gene product adenomatous polyposis coli (APC) binds to beta 2-catenin (homologous to the product of Drosophila armadillo), which is cytoplasmically associated with the cell adhesion molecule E-cadherin

T cells encounter two main checkpoints during development in the thymus. These checkpoints are critically dependent on signals derived from the thymic microenvironment as well as from the pre-T cell receptor (pre-TCR) and the alphabeta TCR. Here we show that T cell-specific deletion of beta-catenin impaired T cell development at the beta-selection checkpoint, leading to a substantial decrease in splenic T cells. In addition, beta-catenin also seemed to be a target of TCR-CD3 signals in thymocytes and mature T cells. These data indicate that beta-catenin-mediated signals are required for normal T cell development.