Trimethylation and Acetylation of β-Catenin at Lysine 49 Represent Key Elements in ESC Pluripotency.

Wnt/β-catenin signaling is required for embryonic stem cell (ESC) pluripotency by inducing mesodermal differentiation and inhibiting neuronal differentiation; however, how β-catenin counter-regulates these differentiation pathways is unknown. Here, we show that lysine 49 (K49) of β-catenin is trimethylated (β-catMe3) by Ezh2 or acetylated (β-catAc) by Cbp. Significantly, β-catMe3 acts as a transcriptional co-repressor of the neuronal differentiation genes sox1 and sox3, whereas β-catAc acts as a transcriptional co-activator of the key mesodermal differentiation gene t-brachyury (t-bra).

Editor's Highlight: Identification and Characterization of Teratogenic Chemicals Using Embryonic Stem Cells Isolated From a Wnt/β-Catenin-Reporter Transgenic Mouse Line.

Embryonic stem cells (ESCs) are commonly used for the analysis of gene function in embryonic development and provide valuable models for human diseases. In recent years, ESCs have also become an attractive tool for toxicological testing, in particular for the identification of teratogenic compounds. We have recently described a Bmp-reporter ESC line as a new tool to identify teratogenic compounds and to characterize the molecular mechanisms mediating embryonic toxicity.

A Bmp Reporter Transgene Mouse Embryonic Stem Cell Model as a Tool to Identify and Characterize Chemical Teratogens.

Embryonic stem cells (ESCs) were first isolated from mouse embryos more than 30 years ago. They have proven invaluable not only in generating genetically modified mice that allow for analysis of gene function in tissue development and homeostasis but also as models for genetic disease. In addition, ESCs in vitro are finding inroads in pharmaceutical and toxicological testing, including the identification of teratogenic compounds.

Beta-catenin is vital for the integrity of mouse embryonic stem cells.

β-Catenin mediated Wnt-signaling is assumed to play a major function in embryonic stem cells in maintaining their stem cell character and the exit from this unique trait. The complexity of β-catenin action and conflicting results on the role of β-catenin in maintaining the pluripotent state have made it difficult to understand its precise cellular and molecular functions. To attempt this issue we have generated new genetically modified mouse embryonic stem cell lines allowing for the deletion of β-catenin in a controlled manner by taking advantage of the Cre-ER-T2 system and analyzed the effects in a narrow time window shortly after ablation.

Wnt3a-dependent and -independent protein interaction networks of chromatin-bound β-catenin in mouse embryonic stem cells.

Canonical Wnt signaling is repeatedly used during development to control cell fate, and it is often implicated in human cancer. β-catenin, the effector of Wnt signaling, has a dual function in the cell and is involved in both cell adhesion and transcription. Nuclear β-catenin controls transcription through association with transcription factors of the TCF family and the recruitment of epigenetic modifiers.

E-cadherin is required for the proper activation of the Lifr/Gp130 signaling pathway in mouse embryonic stem cells.

The leukemia inhibitory factor (Lif) signaling pathway is a crucial determinant for mouse embryonic stem (mES) cell self-renewal and pluripotency. One of the hallmarks of mES cells, their compact growth morphology, results from tight cell adhesion mediated through E-cadherin, β-catenin (Ctnnb1) and α-catenin with the actin cytoskeleton. β-catenin is also involved in canonical Wnt signaling, which has also been suggested to control mES cell stemness.

Differential requirements for β-catenin during mouse development.

Embryogenesis relies on the precise interplay of signaling cascades to activate tissue-specific differentiation programs. An important player in these morphogenetic processes is β-catenin, which is a central component of adherens junctions and canonical Wnt signaling. Lack of β-catenin is lethal before gastrulation, but mice heterozygous for β-catenin (Ctnnb1) develop as wild type.

Wnt/β-catenin signaling regulates telomerase in stem cells and cancer cells.

Telomerase activity controls telomere length and plays a pivotal role in stem cells, aging, and cancer. Here, we report a molecular link between Wnt/β-catenin signaling and the expression of the telomerase subunit Tert. β-Catenin-deficient mouse embryonic stem (ES) cells have short telomeres; conversely, ES cell expressing an activated form of β-catenin (β-cat(ΔEx3/+)) have long telomeres.

Replacement of E-cadherin by N-cadherin in the mammary gland leads to fibrocystic changes and tumor formation.

Introduction: E-cadherin (E-cad; cadherin 1) and N-cadherin (N-cad; cadherin 2) are the most prominent members of the cadherin family of cell adhesion molecules. Although they share many structural and functional features, they are expressed in an almost mutually exclusive manner in vivo.

Methods: To explore functional differences between the two cadherins in vivo, we recently generated a knock-in line in which N-cad is expressed from the E-cad locus.

Lineage specification of parietal epithelial cells requires β-catenin/Wnt signaling.

β-Catenin/Wnt signaling is essential during early inductive stages of kidney development, but its role during postinductive stages of nephron development and maturation is not well understood. In this study, we used Pax8Cre mice to target β-catenin deficiency to renal epithelial cells at the late S-shaped body stage and the developing collecting ducts. The conditional β-catenin knockout mice formed abnormal kidneys and had reduced renal function.

Biological and mathematical modeling of melanocyte development.

We aim to evaluate environmental and genetic effects on the expansion/proliferation of committed single cells during embryonic development, using melanoblasts as a paradigm to model this phenomenon. Melanoblasts are a specific type of cell that display extensive cellular proliferation during development. However, the events controlling melanoblast expansion are still poorly understood due to insufficient knowledge concerning their number and distribution in the various skin compartments.

Inhibition of glycogen synthase kinase-3 alleviates Tcf3 repression of the pluripotency network and increases embryonic stem cell resistance to differentiation.

Self-renewal of rodent embryonic stem cells is enhanced by partial inhibition of glycogen synthase kinase-3 (Gsk3; refs 1, 2). This effect has variously been attributed to stimulation of Wnt signalling by β-catenin, stabilization of Myc protein and global de-inhibition of anabolic processes. Here we demonstrate that β-catenin is not necessary for embryonic stem cell identity or expansion, but its absence eliminates the self-renewal response to Gsk3 inhibition.

N-cadherin can structurally substitute for E-cadherin during intestinal development but leads to polyp formation.

We conditionally substituted E-cadherin (E-cad; cadherin 1) with N-cadherin (N-cad; cadherin 2) during intestine development by generating mice in which an Ncad cDNA was knocked into the Ecad locus. Mutant mice were born, demonstrating that N-cad can structurally replace E-cad and establish proper organ architecture. After birth, mutant mice gradually developed a mutant phenotype in both the small and large intestine and died at ~2-3 weeks of age, probably due to malnutrition during the transition to solid food.

Nanog is required for primitive endoderm formation through a non-cell autonomous mechanism.

Early lineage segregation in mouse development results in two, either CDX2- or OCT4/NANOG-positive, cell populations. CDX2-positive cells form the trophectoderm (TE), OCT4/NANOG-positive cells the inner cell mass (ICM). In a second lineage decision ICM cells segregate into Epiblast (EPI) and primitive endoderm (PE).

Beta-catenin-mediated signaling and cell adhesion in postgastrulation mouse embryos.

beta-Catenin plays two major roles during the development of multicellular organisms. It is the downstream effector of the canonical Wnt signaling cascade, which is involved in many developmental processes and in tumor formation. Additionally, it is linked to classic cadherins and is required for the correct assembly and function of adherens junctions.

Abrogation of E-cadherin-mediated cell-cell contact in mouse embryonic stem cells results in reversible LIF-independent self-renewal.

We have previously demonstrated that differentiation of embryonic stem (ES) cells is associated with downregulation of cell surface E-cadherin. In this study, we assessed the function of E-cadherin in mouse ES cell pluripotency and differentiation. We show that inhibition of E-cadherin-mediated cell-cell contact in ES cells using gene knockout (Ecad(-/-)), RNA interference (EcadRNAi), or a transhomodimerization-inhibiting peptide (CHAVC) results in cellular proliferation and maintenance of an undifferentiated phenotype in fetal bovine serum-supplemented medium in the absence of leukemia inhibitory factor (LIF).

Cdx1::Cre allele for gene analysis in the extraembryonic ectoderm and the three germ layers of mice at mid-gastrulation.

Transgenic mice with a defined cell- or tissues-specific expression of Cre-recombinase are essential tools to study gene function. Here we report the generation and analysis of a transgenic mouse line (Cdx1::Cre) with restricted Cre-expression from Cdx1 regulatory elements. The expression of Cre-recombinase mimicked the endogenous expression pattern of Cdx1 at midgastrulation (from E7.

Neural progenitors of the postnatal and adult mouse forebrain retain the ability to self-replicate, form neurospheres, and undergo multipotent differentiation in vivo.

Somatic stem cells are reservoirs to replace lost cells or damaged tissue. Cells with neural stem cell (NSC) characteristics can be isolated from the postnatal mammalian brain into adulthood and expanded as neurospheres. We addressed the ability of these in vitro expanded putative NSCs to retain progenitor characteristics in vivo, in analogy to hematopoietic stem cells.

Postsynaptic and differential localization to neuronal subtypes of protocadherin beta16 in the mammalian central nervous system.

The formation of synapses is dependent on the expression of surface adhesion molecules that facilitate correct recognition, stabilization and function. The more than 60 clustered protocadherins (Pcdhalpha, Pcdhbeta and Pcdhgamma) identified in human and mouse have attracted considerable attention because of their clustered genomic organization and the potential role of alpha- and gamma-Pcdhs in allocating a neuronal surface code specifying synaptic connectivity. Here, we investigated whether beta-Pcdhs also contribute to these processes.

Simultaneous loss of beta- and gamma-catenin does not perturb hematopoiesis or lymphopoiesis.

Hematopietic stem cells (HSCs) maintain life-long hematopoiesis in the bone marrow via their ability to self-renew and to differentiate into all blood lineages. Although a central role for the canonical wnt signaling pathway has been suggested in HSC self-renewal as well as in the development of B and T cells, conditional deletion of beta-catenin (which is considered to be essential for Wnt signaling) has no effect on hematopoiesis or lymphopoiesis. Here, we address whether this discrepancy can be explained by a redundant and compensatory function of gamma-catenin, a close homolog of beta-catenin.

beta-Catenin regulates excitatory postsynaptic strength at hippocampal synapses.

The precise contribution of the cadherin-beta-catenin synapse adhesion complex in the functional and structural changes associated with the pre- and postsynaptic terminals remains unclear. Here we report a requirement for endogenous beta-catenin in regulating synaptic strength and dendritic spine morphology in cultured hippocampal pyramidal neurons. Ablating beta-catenin after the initiation of synaptogenesis in the postsynaptic neuron reduces the amplitude of spontaneous excitatory synaptic responses without a concurrent change in their frequency and synapse density.

Beta-catenin directly regulates Islet1 expression in cardiovascular progenitors and is required for multiple aspects of cardiogenesis.

Recent studies have demonstrated that the LIM homeodomain transcription factor Islet1 (Isl1) marks pluripotent cardiovascular progenitor cells and is required for proliferation, survival, and migration of recently defined second heart field progenitors. Factors that are upstream of Isl1 in cardiovascular progenitors have not yet been defined. Here we demonstrate that beta-catenin is required for Isl1 expression in cardiac progenitors, directly regulating the Isl1 promoter.

E-cadherin inhibits cell surface localization of the pro-migratory 5T4 oncofetal antigen in mouse embryonic stem cells.

Epithelial-mesenchymal transition (EMT) events occur during embryonic development and are important for the metastatic spread of epithelial tumors. We show here that spontaneous differentiation of mouse embryonic stem (ES) cells is associated with an E- to N-cadherin switch, up-regulation of E-cadherin repressor molecules (Snail and Slug proteins), gelatinase activity (matrix metalloproteinase [MMP]-2 and -9), and increased cellular motility, all characteristic EMT events. The 5T4 oncofetal antigen, previously shown to be associated with very early ES cell differentiation and altered motility, is also a part of this coordinated process.

Le(x) glycan mediates homotypic adhesion of embryonal cells independently from E-cadherin: a preliminary note.

Le(x) glycan and E-cadherin (Ecad) are co-expressed at embryonal stem (ES) cells and embryonal carcinoma (EC) cells. While the structure and function of Ecad mediating homotypic adhesion of these cells have been well established, evidence that Le(x) glycan also mediates such adhesion is weak, despite the fact that Le(x) oligosaccharide inhibits the compaction process. To provide stronger evidence, we knocked out Ecad gene in EC and ES cells to establish F9 Ecad (-/-) and D3M Ecad (-/-) cells, which highly express Le(x) glycan but do not express Ecad at all.