Wnt-mediated down-regulation of Sp1 target genes by a transcriptional repressor Sp5

The transcription factor Zic4 promotes tentacle formation and prevents epithelial transdifferentiation in Hydra

The molecular mechanisms that maintain cellular identities and prevent dedifferentiation or transdifferentiation remain mysterious. However, both processes are transiently used during animal regeneration. Therefore, organisms that regenerate their organs, appendages, or even their whole body offer a fruitful paradigm to investigate the regulation of cell fate stability. Here, we used Hydra as a model system and show that Zic4, whose expression is controlled by Wnt3/β-catenin signaling and the Sp5 transcription factor, plays a key role in tentacle formation and tentacle maintenance. Reducing Zic4 expression suffices to induce transdifferentiation of tentacle epithelial cells into foot epithelial cells. This switch requires the reentry of tentacle battery cells into the cell cycle without cell division and is accompanied by degeneration of nematocytes embedded in these cells. These results indicate that maintenance of cell fate by a Wnt-controlled mechanism is a key process both during homeostasis and during regeneration.

Pax2a, Sp5a and Sp5l act downstream of Fgf and Wnt to coordinate sensory-neural patterning in the inner ear

In zebrafish, sensory epithelia and neuroblasts of the inner ear form simultaneously in abutting medial and lateral domains, respectively, in the floor of the otic vesicle. Previous studies support regulatory roles for Fgf and Wnt, but how signaling is coordinated is poorly understood. We investigated this problem using pharmacological and transgenic methods to alter Fgf or Wnt signaling from early placodal stages to evaluate later changes in growth and patterning. Blocking Fgf at any stage reduces proliferation of otic tissue and terminates both sensory and neural specification. Wnt promotes proliferation in the otic vesicle but is not required for sensory or neural development. However, sustained overactivation of Wnt laterally expands sensory epithelia and blocks neurogenesis. pax2a, sp5a and sp5l are coregulated by Fgf and Wnt and show overlapping expression in the otic placode and vesicle. Gain- and loss-of-function studies show that these genes are together required for Wnt's suppression of neurogenesis, as well as some aspects of sensory development. Thus, pax2a, sp5a and sp5l are critical for mediating Fgf and Wnt signaling to promote spatially localized sensory and neural development.

SOX transcription factors direct TCF-independent WNT/β-catenin responsive transcription to govern cell fate in human pluripotent stem cells

WNT/β-catenin signaling controls gene expression across biological contexts from development and stem cell homeostasis to diseases including cancer. How β-catenin is recruited to distinct enhancers to activate context-specific transcription is unclear, given that most WNT/ß-catenin-responsive transcription is thought to be mediated by TCF/LEF transcription factors (TFs). With time-resolved multi-omic analyses, we show that SOX TFs can direct lineage-specific WNT-responsive transcription during the differentiation of human pluripotent stem cells (hPSCs) into definitive endoderm and neuromesodermal progenitors. We demonstrate that SOX17 and SOX2 are required to recruit β-catenin to lineage-specific WNT-responsive enhancers, many of which are not occupied by TCFs. At TCF-independent enhancers, SOX TFs establish a permissive chromatin landscape and recruit a WNT-enhanceosome complex to activate SOX/ß-catenin-dependent transcription. Given that SOX TFs and the WNT pathway are critical for specification of most cell types, these results have broad mechanistic implications for the specificity of WNT responses across developmental and disease contexts.

Identification of putative enhancer-like elements predicts regulatory networks active in planarian adult stem cells

Planarians have become an established model system to study regeneration and stem cells, but the regulatory elements in the genome remain almost entirely undescribed. Here, by integrating epigenetic and expression data we use multiple sources of evidence to predict enhancer elements active in the adult stem cell populations that drive regeneration. We have used ChIP-seq data to identify genomic regions with histone modifications consistent with enhancer activity, and ATAC-seq data to identify accessible chromatin. Overlapping these signals allowed for the identification of a set of high-confidence candidate enhancers predicted to be active in planarian adult stem cells. These enhancers are enriched for predicted transcription factor (TF) binding sites for TFs and TF families expressed in planarian adult stem cells. Footprinting analyses provided further evidence that these potential TF binding sites are likely to be occupied in adult stem cells. We integrated these analyses to build testable hypotheses for the regulatory function of TFs in stem cells, both with respect to how pluripotency might be regulated, and to how lineage differentiation programs are controlled. We found that our predicted GRNs were independently supported by existing TF RNAi/RNA-seq datasets, providing further evidence that our work predicts active enhancers that regulate adult stem cells and regenerative mechanisms.

Decomposing a deterministic path to mesenchymal niche formation by two intersecting morphogen gradients

Organ formation requires integrating signals to coordinate proliferation, specify cell fates, and shape tissue. Tracing these events and signals remains a challenge, as intermediate states across many critical transitions are unresolvable over real time and space. Here, we designed a unique computational approach to decompose a non-linear differentiation process into key components to resolve the signals and cell behaviors that drive a rapid transition, using the hair follicle dermal condensate as a model. Combining scRNA sequencing with genetic perturbation, we reveal that proliferative Dkk1+ progenitors transiently amplify to become quiescent dermal condensate cells by the mere spatiotemporal patterning of Wnt/β-catenin and SHH signaling gradients. Together, they deterministically coordinate a rapid transition from proliferation to quiescence, cell fate specification, and morphogenesis. Moreover, genetically repatterning these gradients reproduces these events autonomously in "slow motion" across more intermediates that resolve the process. This analysis unravels two morphogen gradients that intersect to coordinate events of organogenesis.

A Regulatory Program for Initiation of Wnt Signaling during Posterior Regeneration

Whole-body regeneration relies on the re-establishment of body axes for patterning of new tissue. Wnt signaling is required to correctly regenerate tissues along the primary axis in many animals. However, the causal mechanisms that first launch Wnt signaling during regeneration are poorly characterized. We use the acoel worm Hofstenia miamia to identify processes that initiate Wnt signaling during posterior regeneration and find that the ligand wnt-3 is upregulated early in posterior-facing wounds. Functional studies reveal that wnt-3 is required to regenerate posterior tissues. wnt-3 is expressed in stem cells, it is needed for their proliferation, and its function is stem cell dependent. Chromatin accessibility data reveal that wnt-3 activation requires input from the general wound response. In addition, the expression of a different Wnt ligand, wnt-1, before amputation is required for wound-induced activation of wnt-3. Our study establishes a gene regulatory network for initiating Wnt signaling in posterior tissues in a bilaterian.

A regulatory sub-circuit downstream of Wnt signaling controls developmental transitions in neural crest formation

The process of cell fate commitment involves sequential changes in the gene expression profiles of embryonic progenitors. This is exemplified in the development of the neural crest, a migratory stem cell population derived from the ectoderm of vertebrate embryos. During neural crest formation, cells transition through distinct transcriptional states in a stepwise manner. The mechanisms underpinning these shifts in cell identity are still poorly understood. Here we employ enhancer analysis to identify a genetic sub-circuit that controls developmental transitions in the nascent neural crest. This sub-circuit links Wnt target genes in an incoherent feedforward loop that controls the sequential activation of genes in the neural crest lineage. By examining the cis-regulatory apparatus of Wnt effector gene AXUD1, we found that multipotency factor SP5 directly promotes neural plate border identity, while inhibiting premature expression of specification genes. Our results highlight the importance of repressive interactions in the neural crest gene regulatory network and illustrate how genes activated by the same upstream signal become temporally segregated during progressive fate restriction.

Extracellular vesicle-enclosed miR-486-5p mediates wound healing with adipose-derived stem cells by promoting angiogenesis

Adipose‐derived stem cells (ASC) are said to have a pivotal role in wound healing. Specifically, ASC‐secreted extracellular vesicles (EV) carry diverse cargos such as microRNAs (miRNAs) to participate in the ASC‐based therapies. Considering its effects, we aimed to investigate the role of ASC‐EVs in the cutaneous wound healing accompanied with the study on the specific cargo‐medicated effects on wound healing. Two full‐thickness excisional skin wounds were created on mouse dorsum, and wound healing was recorded at the indicated time points followed by histological analysis and immunofluorescence staining for CD31 and α‐SMA. Human skin fibroblasts (HSFs) and human microvascular endothelial cells (HMECs) were co‐cultured with EVs isolated from ASC (ASC‐EVs), respectively, followed by the evaluation of their viability and mobility using CCK‐8, scratch test and transwell migration assays. Matrigel‐based angiogenesis assays were performed to evaluate vessel‐like tube formation by HMECs in vitro. ASC‐EVs accelerated the healing of full‐thickness skin wounds, increased re‐epithelialization and reduced scar thickness whilst enhanced collagen synthesis and angiogenesis in murine models. However, miR‐486‐5p antagomir abrogated the ASC‐EVs‐induced effects. Intriguingly, miR‐486‐5p was found to be highly enriched in ASC‐EVs, exhibiting an increase in viability and mobility of HSFs and HMECs and enhanced the angiogenic activities of HMECs. Notably, we also demonstrated that ASC‐EVs‐secreted miR‐486‐5p achieved the aforesaid effects through its target gene Sp5. Hence, our results suggest that miR‐486‐5p released by ASC‐EVs could be a critical mediator to develop an ASC‐based therapeutic strategy for wound healing.

A genome-wide view of the de-differentiation of central nervous system endothelial cells in culture

Vascular endothelial cells (ECs) derived from the central nervous system (CNS) variably lose their unique barrier properties during in vitro culture, hindering the development of robust assays for blood-brain barrier (BBB) function, including drug permeability and extrusion assays. In previous work (Sabbagh et al., 2018) we characterized transcriptional and accessible chromatin landscapes of acutely isolated mouse CNS ECs. In this report, we compare transcriptional and accessible chromatin landscapes of acutely isolated mouse CNS ECs versus mouse CNS ECs in short-term in vitro culture. We observe that standard culture conditions are associated with a rapid and selective loss of BBB transcripts and chromatin features, as well as a greatly reduced level of beta-catenin signaling. Interestingly, forced expression of a stabilized derivative of beta-catenin, which in vivo leads to a partial conversion of non-BBB CNS ECs to a BBB-like state, has little or no effect on gene expression or chromatin accessibility in vitro.

Wnt Glycation Inhibits Canonical Signaling

Glycation occurs as a non-enzymatic reaction between amino and thiol groups of proteins, lipids, and nucleotides with reducing sugars or α-dicarbonyl metabolites. The chemical reaction underlying is the Maillard reaction leading to the formation of a heterogeneous group of compounds named advanced glycation end products (AGEs). Deleterious effects have been observed to accompany glycation such as alterations of protein structure and function resulting in crosslinking and accumulation of insoluble protein aggregates. A substantial body of evidence associates glycation with aging. Wnt signaling plays a fundamental role in stem cell biology as well as in regeneration and repair mechanisms. Emerging evidence implicates that changes in Wnt/β-catenin pathway activity contribute to the aging process. Here, we investigated the effect of glycation of Wnt3a on its signaling activity. Methods: Glycation was induced by treatment of Wnt3a-conditioned medium (CM) with glyoxal (GO). Effects on Wnt3a signaling activity were analyzed by Topflash/Fopflash reporter gene assay, co-immunoprecipitation, and quantitative RT-PCR. Results: Our data show that GO-treatment results in glycation of Wnt3a. Glycated Wnt3a suppresses β-catenin transcriptional activity in reporter gene assays, reduced binding of β-catenin to T-cell factor 4 (TCF-4) and extenuated transcription of Wnt/β-catenin target genes. Conclusions: GO-induced glycation impairs Wnt3a signaling function.

A small set of conserved genes, including sp5 and Hox, are activated by Wnt signaling in the posterior of planarians and acoels

Wnt signaling regulates primary body axis formation across the Metazoa, with high Wnt signaling specifying posterior identity. Whether a common Wnt-driven transcriptional program accomplishes this broad role is poorly understood. We identified genes acutely affected after Wnt signaling inhibition in the posterior of two regenerative species, the planarian Schmidtea mediterranea and the acoel Hofstenia miamia, which are separated by >550 million years of evolution. Wnt signaling was found to maintain positional information in muscle and regional gene expression in multiple differentiated cell types. sp5, Hox genes, and Wnt pathway components are down-regulated rapidly after β-catenin RNAi in both species. Brachyury, a vertebrate Wnt target, also displays Wnt-dependent expression in Hofstenia. sp5 inhibits trunk gene expression in the tail of planarians and acoels, promoting separate tail-trunk body domains. A planarian posterior Hox gene, Post-2d, promotes normal tail regeneration. We propose that common regulation of a small gene set–Hox, sp5, and Brachyury–might underlie the widespread utilization of Wnt signaling in primary axis patterning across the Bilateria.

How animals form and maintain their body axes is a fundamental topic in developmental biology. Wnt signaling is an important regulator of head-tail axis formation across animals, with high Wnt signaling specifying tail identity. In this study, we use two species that are separated by more than 550 million years of evolution, planarians and acoels, to find genes regulated by Wnt signaling in the tail broadly in the Bilateria. We identified a small conserved set of Wnt-regulated genes, including the transcription factor-encoding genes sp5 and Hox. This suggests that regulation of this gene set might be a key function of Wnt signaling in the tails of bilaterally symmetric animals. Inhibition of a planarian posterior Hox gene, Post-2d, by RNAi caused tail-regeneration defects. Inhibition of sp5 by RNAi revealed that it functions to restrict the expression of trunk genes in the tail of planarians and acoels. Since Wnt signaling activates both trunk and tail patterning gene expression in planarians, this suggests a mechanism by which Wnt signaling can establish separate trunk-tail body domains through regulation of sp5.

Wnt Signaling in Neural Crest Ontogenesis and Oncogenesis

Neural crest (NC) cells are a temporary population of multipotent stem cells that generate a diverse array of cell types, including craniofacial bone and cartilage, smooth muscle cells, melanocytes, and peripheral neurons and glia during embryonic development. Defective neural crest development can cause severe and common structural birth defects, such as craniofacial anomalies and congenital heart disease. In the early vertebrate embryos, NC cells emerge from the dorsal edge of the neural tube during neurulation and then migrate extensively throughout the anterior-posterior body axis to generate numerous derivatives. Wnt signaling plays essential roles in embryonic development and cancer. This review summarizes current understanding of Wnt signaling in NC cell induction, delamination, migration, multipotency, and fate determination, as well as in NC-derived cancers.

An evolutionarily-conserved Wnt3/β-catenin/Sp5 feedback loop restricts head organizer activity in Hydra

Polyps of the cnidarian Hydra maintain their adult anatomy through two developmental organizers, the head organizer located apically and the foot organizer basally. The head organizer is made of two antagonistic cross-reacting components, an activator, driving apical differentiation and an inhibitor, preventing ectopic head formation. Here we characterize the head inhibitor by comparing planarian genes down-regulated when β-catenin is silenced to Hydra genes displaying a graded apical-to-basal expression and an up-regulation during head regeneration. We identify Sp5 as a transcription factor that fulfills the head inhibitor properties: leading to a robust multiheaded phenotype when knocked-down in Hydra, acting as a transcriptional repressor of Wnt3 and positively regulated by Wnt/β-catenin signaling. Hydra and zebrafish Sp5 repress Wnt3 promoter activity while Hydra Sp5 also activates its own expression, likely via β-catenin/TCF interaction. This work identifies Sp5 as a potent feedback loop inhibitor of Wnt/β-catenin signaling, a function conserved across eumetazoan evolution.

Hydra regenerate various body parts on amputation by activation of the appropriate organiser, but how head formation is controlled is unclear. Here, the authors identify the transcription factor Sp5 as restricting head formation, by being activated by beta-catenin and then acting as a repressor of Wnt3.

Amphioxus Sp5 is a member of a conserved Specificity Protein complement and is modulated by Wnt/β-catenin signalling

A cluster of three Specificity Protein (Sp) genes (Sp1-4, Sp5 and Sp6-9) is thought to be ancestral in both chordates and the wider Eumetazoa. Sp5 and Sp6-9 gene groups are associated with embryonic growth zones, such as tailbuds, and are both Wnt/β-catenin signalling pathway members and targets. Currently, there are conflicting reports as to the number and identity of Sp genes in the cephalochordates, the sister group to the vertebrates and urochordates. We confirm the SP complement of Branchiostoma belcheri and Branchiostoma lanceolatum, as well as their genomic arrangement, protein domain structure and residue frequency. We assay Sp5 expression in B. lanceolatum embryos, and determine its response to pharmacologically increased β-catenin signalling. Branchiostoma possesses three Sp genes, located on the same genomic scaffold. Phylogenetic and domain structure analyses are consistent with their identification as SP1-4, SP5 and SP6-9, although SP1-4 contains a novel glutamine-rich N-terminal region. SP5 is expressed in axial mesoderm and neurectoderm, and marks the cerebral vesicle and presumptive pharynx. Early exposure to increased β-catenin caused ubiquitous SP5 expression in late gastrula, while later treatment at gastrula stages reduced SP5 expression in the posterior growth zone during axis elongation. Amphioxus possess a typical invertebrate eumetazoan SP complement, and SP5 expression in embryos is well conserved with vertebrate homologues. Its expression in the tailbud, a posterior growth zone, is consistent with expression seen in other bilaterians. Branchiostoma SP5 shows a dynamic response to Wnt/β-catenin signalling.

Malic Enzyme 1 (ME1) is pro-oncogenic in ApcMin/+ mice

Cytosolic Malic Enzyme (ME1) provides reduced NADP for anabolism and maintenance of redox status. To examine the role of ME1 in tumor genesis of the gastrointestinal tract, we crossed mice having augmented intestinal epithelial expression of ME1 (ME1-Tg mice) with ApcMin/+ mice to obtain male ApcMin/+/ME1-Tg mice. ME1 protein levels were significantly greater within gut epithelium and adenomas of male ApcMin/+/ME1-Tg than ApcMin/+ mice. Male ApcMin/+/ME1-Tg mice had larger and greater numbers of adenomas in the small intestine (jejunum and ileum) than male ApcMin/+ mice. Male ApcMin/+/ME1-Tg mice exhibited greater small intestine crypt depth and villus length in non-adenoma regions, correspondent with increased KLF9 protein abundance in crypts and lamina propria. Small intestines of male ApcMin/+/ME1-Tg mice also had enhanced levels of Sp5 mRNA, suggesting Wnt/β-catenin pathway activation. A small molecule inhibitor of ME1 suppressed growth of human CRC cells in vitro, but had little effect on normal rat intestinal epithelial cells. Targeting of ME1 may add to the armentarium of therapies for cancers of the gastrointestinal tract.

Multiple functions of p27 in cell cycle, apoptosis, epigenetic modification and transcriptional regulation for the control of cell growth: A double-edged sword protein

The cell cycle is controlled by precise mechanisms to prevent malignancies such as cancer, and the cell needs these tight and advanced controls. Cyclin dependent kinase inhibitor p27 (also known as KIP₁) is a factor that inhibits the progression of the cell cycle by using specific molecular mechanisms. The inhibitory effect of p27 on the cell cycle is mediated by CDKs inhibition. Other important functions of p27 include cell proliferation, cell differentiation and apoptosis. Post- translational modification of p27 by phosphorylation and ubiquitination respectively regulates interaction between p27 and cyclin/CDK complex and degradation of p27. In this review, we focus on the multiple function of p27 in cell cycle regulation, apoptosis, epigenetic modifications and post- translational modification, and briefly discuss the mechanisms and factors that have important roles in p27 functions.

Screening of Potential Genes and Transcription Factors of Postoperative Cognitive Dysfunction via Bioinformatics Methods

Background

The aim of this study was to explore the potential genes and transcription factors involved in postoperative cognitive dysfunction (POCD) via bioinformatics analysis.

Material/Methods

GSE95070 miRNA expression profiles were downloaded from Gene Expression Omnibus database, which included five hippocampal tissues from POCD mice and controls. Moreover, the differentially expressed miRNAs (DEMs) between the two groups were identified. In addition, the target genes of DEMs were predicted using Targetscan 7.1, followed by protein-protein interaction (PPI) network construction, functional enrichment analysis, pathway analysis, and prediction of transcription factors (TFs) targeting the potential targets.

Results

A total of eight DEMs were obtained, and 823 target genes were predicted, including 170 POCD-associated genes. Furthermore, potential key genes in the network were remarkably enriched in focal adhesion, protein digestion and absorption, ECM-receptor interaction, and Wnt and MAPK signaling pathways.

Conclusions

Most potential target genes were involved in the regulation of TFs, including LEF1, SP1, and AP4, which may exert strong impact on the development of POCD.

Sp5 negatively regulates the proliferation of HCT116 cells by upregulating the transcription of p27

The Wnt signaling pathway is aberrantly activated in the majority of human colorectal tumors. β-catenin, a key component of the Wnt signaling pathway, interacts with the T-cell factor/lymphoid enhancer-binding factor family of transcription factors and activates transcription of Wnt target genes. Sp5 is one of the Wnt target genes, and its expression is commonly upregulated in colon cancer cells. The present study demonstrates that the expression of Sp5 is not upregulated in the colon cancer cell line HCT116, in which Wnt signaling is constitutively activated. Furthermore, the results demonstrate that Sp5 has the potential to inhibit cell proliferation through upregulation of the cell cycle inhibitor p27. These findings suggest that HCT116 cells downregulate Sp5 to avoid p27-mediated growth arrest.

The WNT target SP5 negatively regulates WNT transcriptional programs in human pluripotent stem cells

The WNT/β-catenin signaling pathway is a prominent player in many developmental processes, including gastrulation, anterior-posterior axis specification, organ and tissue development, and homeostasis. Here, we use human pluripotent stem cells (hPSCs) to study the dynamics of the transcriptional response to exogenous activation of the WNT pathway. We describe a mechanism involving the WNT target gene SP5 that leads to termination of the transcriptional program initiated by WNT signaling. Integration of gene expression profiles of wild-type and SP5 mutant cells with genome-wide SP5 binding events reveals that SP5 acts to diminish expression of genes previously activated by the WNT pathway. Furthermore, we show that activation of SP5 by WNT signaling is most robust in cells with developmental potential, such as stem cells. These findings indicate a mechanism by which the developmental WNT signaling pathway reins in expression of transcriptional programs.

Early Transcriptional Changes Induced by Wnt/β-Catenin Signaling in Hippocampal Neurons

Wnt/β-catenin signaling modulates brain development and function and its deregulation underlies pathological changes occurring in neurodegenerative and neurodevelopmental disorders. Since one of the main effects of Wnt/β-catenin signaling is the modulation of target genes, in the present work we examined global transcriptional changes induced by short-term Wnt3a treatment (4 h) in primary cultures of rat hippocampal neurons. RNAseq experiments allowed the identification of 170 differentially expressed genes, including known Wnt/β-catenin target genes such as Notum, Axin2, and Lef1, as well as novel potential candidates Fam84a, Stk32a, and Itga9. Main biological processes enriched with differentially expressed genes included neural precursor (GO:0061364, p-adjusted = 2.5 × 10⁻⁷), forebrain development (GO:0030900, p-adjusted = 7.3 × 10⁻⁷), and stem cell differentiation (GO:0048863 p-adjusted = 7.3 × 10⁻⁷). Likewise, following activation of the signaling cascade, the expression of a significant number of genes with transcription factor activity (GO:0043565, p-adjusted = 4.1 × 10⁻⁶) was induced. We also studied molecular networks enriched upon Wnt3a activation and detected three highly significant expression modules involved in glycerolipid metabolic process (GO:0046486, p-adjusted = 4.5 × 10⁻¹⁹), learning or memory (GO:0007611, p-adjusted = 4.0 × 10⁻⁵), and neurotransmitter secretion (GO:0007269, p-adjusted = 5.3 × 10⁻¹²). Our results indicate that Wnt/β-catenin mediated transcription controls multiple biological processes related to neuronal structure and activity that are affected in synaptic dysfunction disorders.

Manipulating Wnt signaling at different subcellular levels affects the fate of neonatal neural stem/progenitor cells

The canonical Wnt signaling pathway plays an important role in embryogenesis, and the establishment of neurogenic niches. It is involved in proliferation and differentiation of neural progenitors, since elevated Wnt/β-catenin signaling promotes differentiation of neural stem/progenitor cells (NS/PCs¹) towards neuroblasts. Nevertheless, it remains elusive how the differentiation program of neural progenitors is influenced by the Wnt signaling output. Using transgenic mouse models, we found that in vitro activation of Wnt signaling resulted in higher expression of β-catenin protein and Wnt/β-catenin target genes, while Wnt signaling inhibition resulted in the reverse effect. Within differentiated cells, we identified three electrophysiologically and immunocytochemically distinct cell types, whose incidence was markedly affected by the Wnt signaling output. Activation of the pathway suppressed gliogenesis, and promoted differentiation of NS/PCs towards a neuronal phenotype, while its inhibition led to suppressed neurogenesis and increased counts of cells of glial phenotype. Moreover, Wnt signaling hyperactivation resulted in an increased incidence of cells expressing outwardly rectifying K⁺ currents, together with inwardly rectifying Na⁺ currents, a typical current pattern of immature neurons, while blocking the pathway led to the opposite effect. Taken together, our data indicate that the Wnt signaling pathway orchestrates neonatal NS/PCs differentiation towards cells with neuronal characteristics, which might be important for nervous tissue regeneration during central nervous system disorders. Furthermore, the transgenic mouse strains used in this study may serve as a convenient tool to manipulate β-catenin-dependent signaling in neural progenitors in the neonatal brain.

A human neurodevelopmental model for Williams syndrome

Williams syndrome is a genetic neurodevelopmental disorder characterized by an uncommon hypersociability and a mosaic of retained and compromised linguistic and cognitive abilities. Nearly all clinically diagnosed individuals with Williams syndrome lack precisely the same set of genes, with breakpoints in chromosome band 7q11.23 (refs 1-5). The contribution of specific genes to the neuroanatomical and functional alterations, leading to behavioural pathologies in humans, remains largely unexplored. Here we investigate neural progenitor cells and cortical neurons derived from Williams syndrome and typically developing induced pluripotent stem cells. Neural progenitor cells in Williams syndrome have an increased doubling time and apoptosis compared with typically developing neural progenitor cells. Using an individual with atypical Williams syndrome, we narrowed this cellular phenotype to a single gene candidate, frizzled 9 (FZD9). At the neuronal stage, layer V/VI cortical neurons derived from Williams syndrome were characterized by longer total dendrites, increased numbers of spines and synapses, aberrant calcium oscillation and altered network connectivity. Morphometric alterations observed in neurons from Williams syndrome were validated after Golgi staining of post-mortem layer V/VI cortical neurons. This model of human induced pluripotent stem cells fills the current knowledge gap in the cellular biology of Williams syndrome and could lead to further insights into the molecular mechanism underlying the disorder and the human social brain.

Tcf7l1 protects the anterior neural fold from adopting the neural crest fate

The neural crest (NC) is crucial for the evolutionary diversification of vertebrates. NC cells are induced at the neural plate border by the coordinated action of several signaling pathways, including Wnt/β-catenin. NC cells are normally generated in the posterior neural plate border, whereas the anterior neural fold is devoid of NC cells. Using the mouse model, we show here that active repression of Wnt/β-catenin signaling is required for maintenance of neuroepithelial identity in the anterior neural fold and for inhibition of NC induction. Conditional inactivation of Tcf7l1, a transcriptional repressor of Wnt target genes, leads to aberrant activation of Wnt/β-catenin signaling in the anterior neuroectoderm and its conversion into NC. This reduces the developing prosencephalon without affecting the anterior-posterior neural character. Thus, Tcf7l1 defines the border between the NC and the prospective forebrain via restriction of the Wnt/β-catenin signaling gradient.

Sp5 and Sp8 recruit β-catenin and Tcf1-Lef1 to select enhancers to activate Wnt target gene transcription

The ancient, highly conserved, Wnt signaling pathway regulates cell fate in all metazoans. We have previously shown that combined null mutations of the specificity protein (Sp) 1/Klf-like zinc-finger transcription factors Sp5 and Sp8 (i.e., Sp5/8) result in an embryonic phenotype identical to that observed when core components of the Wnt/β-catenin pathway are mutated; however, their role in Wnt signal transduction is unknown. Here, we show in mouse embryos and differentiating embryonic stem cells that Sp5/8 are gene-specific transcriptional coactivators in the Wnt/β-catenin pathway. Sp5/8 bind directly to GC boxes in Wnt target gene enhancers and to adjacent, or distally positioned, chromatin-bound T-cell factor (Tcf) 1/lymphoid enhancer factor (Lef) 1 to facilitate recruitment of β-catenin to target gene enhancers. Because Sp5 is itself directly activated by Wnt signals, we propose that Sp5 is a Wnt/β-catenin pathway-specific transcript on factor that functions in a feed-forward loop to robustly activate select Wnt target genes.

A novel role for the tumour suppressor Nitrilase1 modulating the Wnt/β-catenin signalling pathway

Nitrilase1 was classified as a tumour suppressor in association with the fragile histidine-triad protein Fhit. However, knowledge about nitrilase1 and its tumour suppressor function is still limited. Whereas nitrilase1 and Fhit are discrete proteins in mammals, they are merged in Drosophila melanogaster and Caenorhabditis elegans. According to the Rosetta-Stone hypothesis, proteins encoded as fusion proteins in one organism and as separate proteins in another organism may act in the same signalling pathway. Although a direct interaction of human nitrilase1 and Fhit has not been shown, our previous finding that Fhit interacts with β-catenin and represses its transcriptional activity in the canonical Wnt pathway suggested that human nitrilase1 also modulates Wnt signalling. In fact, human nitrilase1 forms a complex with β-catenin and LEF-1/TCF-4, represses β-catenin-mediated transcription and shows an additive effect together with Fhit. Knockdown of human nitrilase1 enhances Wnt target gene expression. Moreover, our experiments show that β-catenin competes away human nitrilase1 from LEF-1/TCF and thereby contributes to the activation of Wnt-target gene transcription. Inhibitory activity of human nitrilase1 on vertebrate Wnt signalling was confirmed by repression of Wnt-induced double axis formation in Xenopus embryogenesis. In line with this finding, the Drosophila fusion protein Drosophila NitFhit directly binds to Armadillo and represses the Wingless pathway in reporter gene assays. Genetic experiments confirmed the repressive activity of Drosophila NitFhit on Wingless signalling in the Drosophila wing imaginal disc. In addition, colorectal tumour microarray analysis revealed a significantly reduced expression of human nitrilase1 in poorly differentiated tumours. Taken together, repression of the canonical Wnt pathway represents a new mechanism for the human nitrilase1 tumour suppressor function.

Transcriptome response to heat stress in a chicken hepatocellular carcinoma cell line

Heat stress triggers an evolutionarily conserved set of responses in cells. The transcriptome responds to hyperthermia by altering expression of genes to adapt the cell or organism to survive the heat challenge. RNA-seq technology allows rapid identification of environmentally responsive genes on a large scale. In this study, we have used RNA-seq to identify heat stress responsive genes in the chicken male white leghorn hepatocellular (LMH) cell line. The transcripts of 812 genes were responsive to heat stress (p < 0.01) with 235 genes upregulated and 577 downregulated following 2.5 h of heat stress. Among the upregulated were genes whose products function as chaperones, along with genes affecting collagen synthesis and deposition, transcription factors, chromatin remodelers, and genes modulating the WNT and TGF-beta pathways. Predominant among the downregulated genes were ones that affect DNA replication and repair along with chromosomal segregation. Many of the genes identified in this study have not been previously implicated in the heat stress response. These data extend our understanding of the transcriptome response to heat stress with many of the identified biological processes and pathways likely to function in adapting cells and organisms to hyperthermic stress. Furthermore, this study should provide important insight to future efforts attempting to improve species abilities to withstand heat stress through genome-wide association studies and breeding.

Wnt/β-catenin signaling regulates sequential fate decisions of murine cortical precursor cells

The fate of neural progenitor cells (NPCs) is determined by a complex interplay of intrinsic programs and extrinsic signals, very few of which are known. β-Catenin transduces extracellular Wnt signals, but also maintains adherens junctions integrity. Here, we identify for the first time the contribution of β-catenin transcriptional activity as opposed to its adhesion role in the development of the cerebral cortex by combining a novel β-catenin mutant allele with conditional inactivation approaches. Wnt/β-catenin signaling ablation leads to premature NPC differentiation, but, in addition, to a change in progenitor cell cycle kinetics and an increase in basally dividing progenitors. Interestingly, Wnt/β-catenin signaling affects the sequential fate switch of progenitors, leading to a shortened neurogenic period with decreased number of both deep and upper-layer neurons and later, to precocious astrogenesis. Indeed, a genome-wide analysis highlighted the premature activation of a corticogenesis differentiation program in the Wnt/β-catenin signaling-ablated cortex. Thus, β-catenin signaling controls the expression of a set of genes that appear to act downstream of canonical Wnt signaling to regulate the stage-specific production of appropriate progenitor numbers, neuronal subpopulations, and astroglia in the forebrain.

Adenomatous polyposis coli protein deletion leads to cognitive and autism-like disabilities

Intellectual disabilities (IDs) and autism spectrum disorders link to human APC inactivating gene mutations. However, little is known about adenomatous polyposis coli's (APC's) role in the mammalian brain. This study is the first direct test of the impact of APC loss on central synapses, cognition and behavior. Using our newly generated APC conditional knock-out (cKO) mouse, we show that deletion of this single gene in forebrain neurons leads to a multisyndromic neurodevelopmental disorder. APC cKO mice, compared with wild-type littermates, exhibit learning and memory impairments, and autistic-like behaviors (increased repetitive behaviors, reduced social interest). To begin to elucidate neuronal changes caused by APC loss, we focused on the hippocampus, a key brain region for cognitive function. APC cKO mice display increased synaptic spine density, and altered synaptic function (increased frequency of miniature excitatory synaptic currents, modestly enhanced long-term potentiation). In addition, we found excessive β-catenin levels and associated changes in canonical Wnt target gene expression and N-cadherin synaptic adhesion complexes, including reduced levels of presenilin1. Our findings identify some novel functional and molecular changes not observed previously in other genetic mutant mouse models of co-morbid cognitive and autistic-like disabilities. This work thereby has important implications for potential therapeutic targets and the impact of their modulation. We provide new insights into molecular perturbations and cell types that are relevant to human ID and autism. In addition, our data elucidate a novel role for APC in the mammalian brain as a hub that links to and regulates synaptic adhesion and signal transduction pathways critical for normal cognition and behavior.

Mouse IDGenes: a reference database for genetic interactions in the developing mouse brain

The study of developmental processes in the mouse and other vertebrates includes the understanding of patterning along the anterior–posterior, dorsal–ventral and medial– lateral axis. Specifically, neural development is also of great clinical relevance because several human neuropsychiatric disorders such as schizophrenia, autism disorders or drug addiction and also brain malformations are thought to have neurodevelopmental origins, i.e. pathogenesis initiates during childhood and adolescence. Impacts during early neurodevelopment might also predispose to late-onset neurodegenerative disorders, such as Parkinson’s disease. The neural tube develops from its precursor tissue, the neural plate, in a patterning process that is determined by compartmentalization into morphogenetic units, the action of local signaling centers and a well-defined and locally restricted expression of genes and their interactions. While public databases provide gene expression data with spatio-temporal resolution, they usually neglect the genetic interactions that govern neural development. Here, we introduce Mouse IDGenes, a reference database for genetic interactions in the developing mouse brain. The database is highly curated and offers detailed information about gene expressions and the genetic interactions at the developing mid-/hindbrain boundary. To showcase the predictive power of interaction data, we infer new Wnt/β-catenin target genes by machine learning and validate one of them experimentally. The database is updated regularly. Moreover, it can easily be extended by the research community. Mouse IDGenes will contribute as an important resource to the research on mouse brain development, not exclusively by offering data retrieval, but also by allowing data input.

Database URL:http://mouseidgenes.helmholtz-muenchen.de.

The cortical hem regulates the size and patterning of neocortex

The cortical hem, a source of Wingless-related (WNT) and bone morphogenetic protein (BMP) signaling in the dorsomedial telencephalon, is the embryonic organizer for the hippocampus. Whether the hem is a major regulator of cortical patterning outside the hippocampus has not been investigated. We examined regional organization across the entire cerebral cortex in mice genetically engineered to lack the hem. Indicating that the hem regulates dorsoventral patterning in the cortical hemisphere, the neocortex, particularly dorsomedial neocortex, was reduced in size in late-stage hem-ablated embryos, whereas cortex ventrolateral to the neocortex expanded dorsally. Unexpectedly, hem ablation also perturbed regional patterning along the rostrocaudal axis of neocortex. Rostral neocortical domains identified by characteristic gene expression were expanded, and caudal domains diminished. A similar shift occurs when fibroblast growth factor (FGF) 8 is increased at the rostral telencephalic organizer, yet the FGF8 source was unchanged in hem-ablated brains. Rather we found that hem WNT or BMP signals, or both, have opposite effects to those of FGF8 in regulating transcription factors that control the size and position of neocortical areas. When the hem is ablated a necessary balance is perturbed, and cerebral cortex is rostralized. Our findings reveal a much broader role for the hem in cortical development than previously recognized, and emphasize that two major signaling centers interact antagonistically to pattern cerebral cortex.

TGF-β-activated kinase 1 (TAK1) signaling regulates TGF-β-induced WNT-5A expression in airway smooth muscle cells via Sp1 and β-catenin

WNT-5A, a key player in embryonic development and post-natal homeostasis, has been associated with a myriad of pathological conditions including malignant, fibroproliferative and inflammatory disorders. Previously, we have identified WNT-5A as a transcriptional target of TGF-β in airway smooth muscle cells and demonstrated its function as a mediator of airway remodeling. Here, we investigated the molecular mechanisms underlying TGF-β-induced WNT-5A expression. We show that TGF-β-activated kinase 1 (TAK1) is a critical mediator of WNT-5A expression as its pharmacological inhibition or siRNA-mediated silencing reduced TGF-β induction of WNT-5A. Furthermore, we show that TAK1 engages p38 and c-Jun N-terminal kinase (JNK) signaling which redundantly participates in WNT-5A induction as only simultaneous, but not individual, inhibition of p38 and JNK suppressed TGF-β-induced WNT-5A expression. Remarkably, we demonstrate a central role of β-catenin in TGF-β-induced WNT-5A expression. Regulated by TAK1, β-catenin is required for WNT-5A induction as its silencing repressed WNT-5A expression whereas a constitutively active mutant augmented basal WNT-5A abundance. Furthermore, we identify Sp1 as the transcription factor for WNT-5A and demonstrate its interaction with β-catenin. We discover that Sp1 is recruited to the WNT-5A promoter in a TGF-β-induced and TAK1-regulated manner. Collectively, our findings describe a TAK1-dependent, β-catenin- and Sp1-mediated signaling cascade activated downstream of TGF-β which regulates WNT-5A induction.

Wnt and lithium: a common destiny in the therapy of nervous system pathologies?

Wnt signaling is required for neurogenesis, the fate of neural progenitors, the formation of neuronal circuits during development, neuron positioning and polarization, axon and dendrite development and finally for synaptogenesis. This signaling pathway is also implicated in the generation and differentiation of glial cells. In this review, we describe the mechanisms of action of Wnt signaling pathways and their implication in the development and correct functioning of the nervous system. We also illustrate how a dysregulated Wnt pathway could lead to psychiatric, neurodegenerative and demyelinating pathologies. Lithium, used for the treatment of bipolar disease, inhibits GSK3β, a central enzyme of the Wnt/β-catenin pathway. Thus, lithium could, to some extent, mimic Wnt pathway. We highlight the possible dialogue between lithium therapy and modulation of Wnt pathway in the treatment of the diseases of the nervous system.

A mesodermal factor, T, specifies mouse germ cell fate by directly activating germline determinants

Germ cells ensure reproduction and heredity. In mice, primordial germ cells (PGCs), the precursors for spermatozoa and oocytes, are induced in pluripotent epiblast by BMP4 and WNT3, yet the underlying mechanism remains unclear. Here, using an in vitro PGC specification system, we show that WNT3 induces many transcription factors associated with mesoderm in epiblast-like cells through β-CATENIN. Among these, T (BRACHYURY), a classical and conserved mesodermal factor, was essential for robust activation of Blimp1 and Prdm14, two of the germline determinants. T, but not SMAD1 or TCF1, binds distinct regulatory elements of both Blimp1 and Prdm14 and directly upregulates these genes, delineating the downstream PGC program. Without BMP4, a program induced by WNT3 prevents T from activating Blimp1 and Prdm14, demonstrating a permissive role of BMP4 in PGC specification. These findings establish the key signaling mechanism for, and a fundamental role of a mesodermal factor in, mammalian PGC specification.

The combined hyperlipidemia caused by impaired Wnt-LRP6 signaling is reversed by Wnt3a rescue

The underlying molecular genetic basis of combined hyperlipidemia, the most common atherogenic lipid disorder, is poorly characterized. Rare, nonconservative mutations in the Wnt coreceptor, LRP6, underlie autosomal dominant atherosclerosis, combined hyperlipidemia, and fatty liver disease. Mice with LRP6(R611C) mutation similarly developed elevated plasma LDL and TG levels and fatty liver. Further investigation showed that LRP6(R611C) mutation triggers hepatic de novo lipogenesis, lipid and cholesterol biosynthesis, and apoB secretion by an Sp1-dependent activation of IGF1, AKT, and both mTORC1 and mTORC2. These pathways were normalized after in vitro treatment of primary hepatocytes from LRP6(R611C) mice with either the IGF1R antagonist PPP, rapamycin, or rmWnt3a. Strikingly, in vivo administration of rmWnt3a to LRP6(R611C) mice normalized the altered expression of enzymes of DNL and cholesterol biosynthesis, and restored plasma TG and LDL levels to normal. These findings identify Wnt signaling as a regulator of plasma lipids and a target for treatment of hyperlipidemia.

Transcriptional profiling of Wnt3a mutants identifies Sp transcription factors as essential effectors of the Wnt/β-catenin pathway in neuromesodermal stem cells

Neuromesodermal (NM) stem cells reside in the primitive streak (PS) of gastrulating vertebrate embryos and generate precursors of the spinal cord and musculoskeletal system. Although Wnt3a/β-catenin signaling is crucial for NM stem cell maintenance and differentiation, few key transcriptional effectors have been identified. Through a concerted transcriptional profiling and genetic approach we have determined that two Zn²⁺-finger transcription factors, Sp5 and Sp8, are regulated by Wnt3a in the PS, and are essential for neural and musculoskeletal patterning. These results identify Sp5 and Sp8 as pivotal downstream effectors of Wnt3a, and suggest that they are essential for the self-renewal and differentiation of NM stem cells.

Role of Sp5 as an essential early regulator of neural crest specification in xenopus

BACKGROUND

The neural crest (NC) is a multipotent embryonic cell population, which is induced by an integration of secreted signals including BMP, Wnt, and FGF and, subsequently, NC cell fates are specified by a regulatory network of specific transcription factors. This study was undertaken to identify a role of Sp5 transcription factor in vertebrates.

RESULTS

Xenopus Sp5 is expressed in the prospective neural crest regions from gastrulation through the tadpole stages in early development. Knockdown of Sp5 caused severe defects in craniofacial cartilage, pigmentation, and dorsal fin. Gain- and loss-of-function of Sp5 led to up- and down-regulation of the expression of NC markers in the neural fold, respectively. In contrast, Sp5 had no effect on neural induction and patterning. Sp5 regulated the expression of neural plate border (NPB) specifiers, Msx1 and Pax3, and these regulatory factors recovered the expression of NC marker in the Sp5-deficient embryos. Depletion of Sp5 impaired NC induction by Wnt/β-catenin or FGF signal, whereas its co-expression rescued NC markers in embryos in which either signal was blocked.

CONCLUSIONS

These results suggest that Sp5 functions as a critical early factor in the genetic cascade to regulate NC induction downstream of Wnt and FGF pathways.

Ectopic activation of the canonical wnt signaling pathway affects ectodermal patterning along the primary axis during larval development in the anthozoan Nematostella vectensis

The primary axis of cnidarians runs from the oral pole to the apical tuft and defines the major body axis of both the planula larva and adult polyp. In the anthozoan cnidarian Nematostella vectensis, the primary oral-aboral (O-Ab) axis first develops during the early embryonic stage. Here, we present evidence that pharmaceutical activators of canonical wnt signaling affect molecular patterning along the primary axis of Nematostella. Although not overtly morphologically complex, molecular investigations in Nematostella reveal that the O-Ab axis is demarcated by the expression of differentially localized signaling molecules and transcription factors that may serve roles in establishing distinct ectodermal domains. We have further characterized the larval epithelium by determining the position of a nested set of molecular boundaries, utilizing several newly characterized as well as previously reported epithelial markers along the primary axis. We have assayed shifts in their position in control embryos and in embryos treated with the pharmacological agents alsterpaullone and azakenpaullone, Gsk3β inhibitors that act as canonical wnt agonists, and the Wnt antagonist iCRT14, following gastrulation. Agonist drug treatments result in an absence of aboral markers, a shift in the expression boundaries of oral markers toward the aboral pole, and changes in the position of differentially localized populations of neurons in a dose-dependent manner, while antagonist treatment had the opposite effect. These experiments are consistent with canonical wnt signaling playing a role in an orally localized wnt signaling center. These findings suggest that in Nematostella, wnt signaling mediates O-Ab ectodermal patterning across a surprisingly complex epithelium in planula stages following gastrulation in addition to previously described roles for the wnt signaling pathway in endomesoderm specification during gastrulation and overall animal-vegetal patterning at earlier stages of anthozoan development.

Modeling neural crest induction, melanocyte specification, and disease-related pigmentation defects in hESCs and patient-specific iPSCs

Melanocytes are pigment-producing cells of neural crest (NC) origin that are responsible for protecting the skin against UV irradiation. Pluripotent stem cell (PSC) technology offers a promising approach for studying human melanocyte development and disease. Here, we report that timed exposure to activators of WNT, BMP, and EDN3 signaling triggers the sequential induction of NC and melanocyte precursor fates under dual-SMAD-inhibition conditions. Using a SOX10::GFP human embryonic stem cell (hESC) reporter line, we demonstrate that the temporal onset of WNT activation is particularly critical for human NC induction. Subsequent maturation of hESC-derived melanocytes yields pure populations that match the molecular and functional properties of adult melanocytes. Melanocytes from Hermansky-Pudlak syndrome and Chediak-Higashi syndrome patient-specific induced PSCs (iPSCs) faithfully reproduce the ultrastructural features of disease-associated pigmentation defects. Our data define a highly specific requirement for WNT signaling during NC induction and enable the generation of pure populations of human iPSC-derived melanocytes for faithful modeling of pigmentation disorders.

Expression of Sp3 and VEGF in hepatocellular carcinoma and their correlation

AIM: To investigate the expression of transcription factor Sp3 and vascular endothelial growth factor (VEGF) in hepatocellular carcinoma (HCC) and their correlation.

METHODS: Immunohistochemical method was used to detect the expression of Sp3 and VEGF in 111 cases of HCC and tumor-adjacent liver tissue. The correlations between Sp3 and VEGF expression, and between these two indices and clinicopathologic characteristics of HCC were analyzed.

RESULTS: The positive rate of moderate or strong Sp3 expression in HCC was significantly higher than that in tumor-adjacent liver tissue (82.9% vs 29.7%, P = 0.000). There is a positive correlation between Sp3 and VEGF expression in HCC (r = 0.352, P = 0.000). Both Sp3 and VEGF expression was related with tumor differentiation. In addition, expression of Sp3 was related with tumor size, and expression of VEGF was related with TNM stage. The prognosis of cases with high Sp3 expression was poorer than those with low Sp3 expression (P = 0.041).

CONCLUSION: Sp3 is expected to be an index for diagnosis of HCC. Combined detection of Sp3 and VEGF expression may be used to evaluate the malignant degree of HCC.

Investigation of TBR1 Hemizygosity: Four Individuals with 2q24 Microdeletions

TBR1 encodes a transcription factor with critical roles in corticogenesis, including cortical neuron migration and axon pathfinding, establishment of regional and laminar identity of cortical neurons, and control of glutamatergic neuronal cell fate. Based upon TBR1's role in cortical development, we sought to investigate TBR1 hemizygosity in individuals referred for genetic evaluation of intellectual disability and developmental delay. We describe 4 patients with microdeletions identified by molecular cytogenetic techniques, encompassing TBR1 and spanning 2q24.1q31.1, ranging in size from 2.17 to 12.34 Mb. Only the patient with the largest deletion had a possible cortical malformation. Mild ventriculomegaly is the only common brain anomaly, present in all patients; a Chiari I malformation is seen in 2 patients, and mega cisterna magna is seen in a third. Our findings are consistent with Tbr1 mouse models showing that hemizygosity of the gene requires additional genetic factors for the manifestation of severe structural brain malformations. Other syndromic features are present in these patients, including autism spectrum disorders, ocular colobomas, and craniosynostosis, features that are likely affected by the deletion of genes other than TBR1.

A WNT/p21 circuit directed by the C-clamp, a sequence-specific DNA binding domain in TCFs

The lymphoid enhancer factor 1/T cell factor (LEF/TCF) family of transcription factors are downstream effectors of the WNT signaling pathway, which drives colon tumorigenesis. LEF/TCFs have a DNA sequence-specific high-mobility group (HMG) box that binds Wnt response elements (WREs). The "E tail" isoforms of TCFs are alternatively spliced to include a second DNA binding domain called the C-clamp. We show that induction of a dominant negative C-clamp version of TCF1 (dnTCF1E) induces p21 expression and a stall in the growth of DLD1 colon cancer cells. Induction of a C-clamp mutant did not efficiently induce p21, nor did it stall cell growth. Microarray analysis revealed that induction of p21 by wild-type dnTCF1E (dnTCF1E(WT)) correlated with a decrease in expression of multiple p21 suppressors that act at multiple levels from transcription (SP5, YAP1, and RUNX1), RNA stability (MSI2), and protein stability (CUL4A). We show that the C-clamp is a sequence-specific DNA binding domain that can make contacts with 5'-RCCG-3' elements upstream or downstream of WREs. The C-clamp-RCCG interaction was critical for TCF1E-mediated transcriptional control of p21-connected target gene promoters. Our results indicate that a rapid-response WNT/p21 circuit is driven by C-clamp target gene selection.

Comparison of the gene expression profiles from normal and Fgfrl1 deficient mouse kidneys reveals downstream targets of Fgfrl1 signaling

Fgfrl1 (fibroblast growth factor receptor-like 1) is a transmembrane receptor that is essential for the development of the metanephric kidney. It is expressed in all nascent nephrogenic structures and in the ureteric bud. Fgfrl1 null mice fail to develop the metanephric kidneys. Mutant kidney rudiments show a dramatic reduction of ureteric branching and a lack of mesenchymal-to-epithelial transition. Here, we compared the expression profiles of wildtype and Fgfrl1 mutant kidneys to identify genes that act downstream of Fgfrl1 signaling during the early steps of nephron formation. We detected 56 differentially expressed transcripts with 2-fold or greater reduction, among them many genes involved in Fgf, Wnt, Bmp, Notch, and Six/Eya/Dach signaling. We validated the microarray data by qPCR and whole-mount in situ hybridization and showed the expression pattern of candidate genes in normal kidneys. Some of these genes might play an important role during early nephron formation. Our study should help to define the minimal set of genes that is required to form a functional nephron.

Transcriptional analysis of Gli3 mutants identifies Wnt target genes in the developing hippocampus

Early development of the hippocampus, which is essential for spatial memory and learning, is controlled by secreted signaling molecules of the Wnt gene family and by Wnt/β-catenin signaling. Despite its importance, little is known, however, about Wnt-regulated genes during hippocampal development. Here, we used the Gli3 mutant mouse extra-toes (Xt(J)), in which Wnt gene expression in the forebrain is severely affected, as a tool in a microarray analyses to identify potential Wnt target genes. This approach revealed 53 candidate genes with restricted or graded expression patterns in the dorsomedial telencephalon. We identified conserved Tcf/Lef-binding sites in telencephalon-specific enhancers of several of these genes, including Dmrt3, Gli3, Nfia, and Wnt8b. Binding of Lef1 to these sites was confirmed using electrophoretic mobility shift assays. Mutations in these Tcf/Lef-binding sites disrupted or reduced enhancer activity in vivo. Moreover, ectopic activation of Wnt/β-catenin signaling in an ex vivo explant system led to increased telencephalic expression of these genes. Finally, conditional inactivation of Gli3 results in defective hippocampal growth. Collectively, these data strongly suggest that we have identified a set of direct Wnt target genes in the developing hippocampus and provide inside into the genetic hierarchy underlying Wnt-regulated hippocampal development.

Developmental functions for the Caenorhabditis elegans Sp protein SPTF-3

Sp factors are important for animal development and the transcriptional regulation of a wide variety of genes. How they influence the developmental decisions of individual cells within the organism, however, is poorly understood. To better understand the developmental functions for Sp transcription factors, we have characterized the functions of Caenorhabditis elegans SPTF-3 using RNAi knockdown and a non-null, hypomorphic mutant allele. We find that disruption of sptf-3 confers a variety of developmental defects, including defects in development of the egg-laying system, oocyte production, and embryonic morphogenesis. sptf-3 mutants exhibit defects in vulval lineage polarity, a phenotype previously only observed in mutants defective in Wnt signaling. We show that the embryonic function of sptf-3 is dependent on germline activity, arguing that the gene has an important maternal contribution to embryonic development. An evaluation of reporter gene expression suggests that SPTF-3 exhibits specificity, in that it can influence the expression of a given gene in some cells but not others, and that SPTF-3 participates in the maintenance of gene expression states in differentiated cells. We propose SPTF-3 provides a good model to study the in vivo functions for Sp transcription factors during animal development.

Transcription factors Sp1 and Sp4 regulate TRPV1 gene expression in rat sensory neurons

Background

The capsaicin receptor, transient receptor potential vanilloid type -1 (TRPV1) directs complex roles in signal transduction including the detection of noxious stimuli arising from cellular injury and inflammation. Under pathophysiologic conditions, TRPV1 mRNA and receptor protein expression are elevated in dorsal root ganglion (DRG) neurons for weeks to months and is associated with hyperalgesia. Building on our previous isolation of a promoter system for the rat TRPV1 gene, we investigated the proximal TRPV1 P2-promoter by first identifying candidate Sp1-like transcription factors bound in vivo to the P2-promoter using chromatin immunoprecipitation (ChIP) assay. We then performed deletion analysis of GC-box binding sites, and quantified promoter activity under conditions of Sp1 / Sp4 over-expression versus inhibition/knockdown. mRNA encoding Sp1, Sp4 and TRPV1 were quantified by qRT-PCR under conditions of Sp1/Sp4 over-expression or siRNA mediated knockdown in cultured DRG neurons.

Results

Using ChIP analysis of DRG tissue, we demonstrated that Sp1 and Sp4 are bound to the candidate GC-box site region within the endogenous TRPV1 P2-promoter. Deletion of GC-box "a" or "a + b" within the P2- promoter resulted in a complete loss of transcriptional activity indicating that GC-box "a" was the critical site for promoter activation. Co-transfection of Sp1 increased P2-promoter activity in cultured DRG neurons whereas mithramycin-a, an inhibitor of Sp1-like function, dose dependently blocked NGF and Sp1-dependent promoter activity in PC12 cells. Co-transfection of siRNA directed against Sp1 or Sp4 decreased promoter activity in DRG neurons and NGF treated PC12 cells. Finally, electroporation of Sp1 or Sp4 cDNA into cultures of DRG neurons directed an increase in Sp1/Sp4 mRNA and importantly an increase in TRPV1 mRNA. Conversely, combined si-RNA directed knockdown of Sp1/Sp4 resulted in a decrease in TRPV1 mRNA.

Conclusion

Based on these studies, we now propose a model of TRPV1 expression that is dependent on Sp1-like transcription factors with Sp4 playing a predominant role in activating TRPV1 RNA transcription in DRG neurons. Given that increases of TRPV1 expression have been implicated in a wide range of pathophysiologic states including persistent painful conditions, blockade of Sp1-like transcription factors represents a novel direction in therapeutic strategies.

Expression and functional analysis of Dkk1 during early gonadal development

WNT signalling plays a central role in mammalian sex determination by promoting ovarian development and repressing aspects of testis development in the early gonad. Dickkopf homolog 1 (DKK1) is a WNT signalling antagonist that plays critical roles in multiple developmental systems by modulating WNT activity. Here, we examined the role of DKK1 in mouse sex determination and early gonadal development. Dkk1 mRNA was upregulated sex-specifically during testis differentiation, suggesting that DKK1 could repress WNT signalling in the developing testis. However, we observed overtly normal testis development in Dkk1-null XY gonads, and found no significant upregulation of Axin2 or Sp5 that would indicate increased canonical WNT signalling. Nor did we find significant differences in expression of key markers of testis and ovarian development. We propose that DKK1 may play a protective role that is not unmasked by loss-of-function in the absence of other stressors.

Differential gene expression signatures between colorectal cancers with and without KRAS mutations: crosstalk between the KRAS pathway and other signalling pathways

PURPOSE

KRAS mutation is an important predictive marker in determining resistance to anti-Epidermal Growth Factor Receptor (EGFR) antibody therapies. In order to clarify whether not only KRAS related signalling pathways but also other signalling pathways are altered in patients with colorectal cancers (CRCs) with KRAS mutations, we examined the differences in the gene expression signatures between CRCs with and without KRAS mutation.

PATIENTS AND METHODS

One-hundred and thirteen patients who underwent a surgical resection of a primary CRC were examined. KRAS mutational status was determined using the Peptide Nucleic Acid (PNA)-clamp real-time polymerase chain reaction (PCR) TaqMan assay. Gene expression profiles were compared between CRCs with and without KRAS mutation using the Human Genome GeneChip array U133.

RESULTS

Among 113 CRCs, KRAS mutations were present in 35 tumours (31%). We identified 30 genes (probes) that were differentially expressed between CRCs with and without KRAS mutation (False Discovery Rate (FDR), p<0.01), by which we were able to predict the KRAS status with an accuracy of 90.3%. Thirty discriminating genes included TC21, paired-like homeodomain 1 (PITX1), Sprouty-2, dickkopf homologue 4 (DKK-4), SET and MYND domain containing 3 (SMYD3), mitogen-activated protein kinase kinase kinase 14 (MAP3K14) and c-mer Proto-oncogene tyrosine kinase (MerTK). These genes were related to not only KRAS related signalling pathway but also to other signalling pathways, such as the Wnt-signalling pathway, the NF-kappa B activation pathway and the TGF-beta signalling pathway.

CONCLUSIONS

KRAS mutant CRCs exhibited a distinct gene expression signature different from wild-type KRAS CRCs. Using human CRC samples, we were able to show that there is crosstalk between the KRAS-mediated pathway and other signalling pathways. These results are necessary to be taken into account in establishing chemotherapeutic strategies for patients with anti-EGFR-refractory KRAS mutant CRCs.

In vitro differentiation of mouse embryonic stem cells into neurons of the dorsal forebrain

Pluripotent embryonic stem cells (ESCs) are able to differentiate into all cell types in the organism including cortical neurons. To follow the dynamic generation of progenitors of the dorsal forebrain in vitro, we generated ESCs from D6-GFP mice in which GFP marks neocortical progenitors and neurons after embryonic day (E) 10.5. We used several cell culture protocols for differentiation of ESCs into progenitors and neurons of the dorsal forebrain. In cell culture, GFP-positive cells were induced under differentiation conditions in quickly formed embryoid bodies (qEBs) after 10–12 day incubation. Activation of Wnt signaling during ESC differentiation further stimulated generation of D6-GFP-positive cortical cells. In contrast, differentiation protocols using normal embryoid bodies (nEBs) yielded only a few D6-GFP-positive cells. Gene expression analysis revealed that multiple components of the canonical Wnt signaling pathway were expressed during the development of embryoid bodies. As shown by immunohistochemistry and quantitative qRT-PCR, D6-GFP-positive cells from qEBs expressed genes that are characteristic for the dorsal forebrain such as Pax6, Dach1, Tbr1, Tbr2, or Sox5. qEBs culture allowed the formation of a D6-GFP positive pseudo-polarized neuroepithelium with the characteristic presence of N-cadherin at the apical pole resembling the structure of the developing neocortex.

FGF4 and FGF8 comprise the wavefront activity that controls somitogenesis

Somites form along the embryonic axis by sequential segmentation from the presomitic mesoderm (PSM) and differentiate into the segmented vertebral column as well as other unsegmented tissues. Somites are thought to form via the intersection of two activities known as the clock and the wavefront. Previous work has suggested that fibroblast growth factor (FGF) activity may be the wavefront signal, which maintains the PSM in an undifferentiated state. However, it is unclear which (if any) of the FGFs expressed in the PSM comprise this activity, as removal of any one gene is insufficient to disrupt early somitogenesis. Here we show that when both Fgf4 and Fgf8 are deleted in the PSM, expression of most PSM genes is absent, including cycling genes, WNT pathway genes, and markers of undifferentiated PSM. Significantly, markers of nascent somite cell fate expand throughout the PSM, demonstrating the premature differentiation of this entire tissue, a highly unusual phenotype indicative of the loss of wavefront activity. When WNT signaling is restored in mutants, PSM progenitor markers are partially restored but premature differentiation of the PSM still occurs, demonstrating that FGF signaling operates independently of WNT signaling. This study provides genetic evidence that FGFs are the wavefront signal and identifies the specific FGF ligands that encode this activity. Furthermore, these data show that FGF action maintains WNT signaling, and that both signaling pathways are required in parallel to maintain PSM progenitor tissue.