The developmental biology of Dishevelled: an enigmatic protein governing cell fate and cell polarity

Magnesium and embryonic development

Important for energy metabolism, neurotransmission, bone stability, and other cellular functions, Mg(2+) has well-established and undisputedly critical roles in adult tissues. Its contributions to early embryonic development are less clearly understood. For decades it has been known that gestational Mg(2+) deficiency in rodents produces teratogenic effects. More recent studies have linked deficiency in this vital cation to birth defects in humans, including spina bifida, a neural fold closure defect in humans that occurs at an average rate of 1 per 1000 pregnancies. The first suggestion that Mg(2+) may be playing a more specific role in early development arose from studies of the TRPM7 and TRPM6 ion channels. TRPM7 and TRPM6 are divalent-selective ion channels in possession of their own kinase domains that have been implicated in the control of Mg(2+) homeostasis in vertebrates. Disruption of the functions of these ion channels in mice as well as in frogs interferes with gastrulation, a pivotal process during early embryonic development that executes the emergence of the body plan and closure of the neural tube. Surprisingly, gastrulation defects produced by depletion of TRPM7 can be prevented by Mg(2+) supplementation, indicating an essential role for Mg(2+) in gastrulation and neural fold closure. The aim of this review is to summarize the data emerging from molecular genetic, biochemical and electrophysiological studies of TRPM6 and TRPM7 and provide a model of how Mg(2+), through these unique channel-kinases, may be impacting early embryonic development.

Ubiquitin ligase HUWE1 regulates axon branching through the Wnt/β-catenin pathway in a Drosophila model for intellectual disability

We recently reported that duplication of the E3 ubiquitin ligase HUWE1 results in intellectual disability (ID) in male patients. However, the underlying molecular mechanism remains unknown. We used Drosophila melanogaster as a model to investigate the effect of increased HUWE1 levels on the developing nervous system. Similar to the observed levels in patients we overexpressed the HUWE1 mRNA about 2-fold in the fly. The development of the mushroom body and neuromuscular junctions were not altered, and basal neurotransmission was unaffected. These data are in agreement with normal learning and memory in the courtship conditioning paradigm. However, a disturbed branching phenotype at the axon terminals of the dorsal cluster neurons (DCN) was detected. Interestingly, overexpression of HUWE1 was found to decrease the protein levels of dishevelled (dsh) by 50%. As dsh as well as Fz2 mutant flies showed the same disturbed DCN branching phenotype, and the constitutive active homolog of β-catenin, armadillo, could partially rescue this phenotype, our data strongly suggest that increased dosage of HUWE1 compromises the Wnt/β-catenin pathway possibly by enhancing the degradation of dsh.

Differential regulation of disheveled in a novel vegetal cortical domain in sea urchin eggs and embryos: implications for the localized activation of canonical Wnt signaling

Pattern formation along the animal-vegetal (AV) axis in sea urchin embryos is initiated when canonical Wnt (cWnt) signaling is activated in vegetal blastomeres. The mechanisms that restrict cWnt signaling to vegetal blastomeres are not well understood, but there is increasing evidence that the egg's vegetal cortex plays a critical role in this process by mediating localized "activation" of Disheveled (Dsh). To investigate how Dsh activity is regulated along the AV axis, sea urchin-specific Dsh antibodies were used to examine expression, subcellular localization, and post-translational modification of Dsh during development. Dsh is broadly expressed during early sea urchin development, but immunolocalization studies revealed that this protein is enriched in a punctate pattern in a novel vegetal cortical domain (VCD) in the egg. Vegetal blastomeres inherit this VCD during embryogenesis, and at the 60-cell stage Dsh puncta are seen in all cells that display nuclear β-catenin. Analysis of Dsh post-translational modification using two-dimensional Western blot analysis revealed that compared to Dsh pools in the bulk cytoplasm, this protein is differentially modified in the VCD and in the 16-cell stage micromeres that partially inherit this domain. Dsh localization to the VCD is not directly affected by disruption of microfilaments and microtubules, but unexpectedly, microfilament disruption led to degradation of all the Dsh pools in unfertilized eggs over a period of incubation suggesting that microfilament integrity is required for maintaining Dsh stability. These results demonstrate that a pool of differentially modified Dsh in the VCD is selectively inherited by the vegetal blastomeres that activate cWnt signaling in early embryos, and suggests that this domain functions as a scaffold for localized Dsh activation. Localized cWnt activation regulates AV axis patterning in many metazoan embryos. Hence, it is possible that the VCD is an evolutionarily conserved cytoarchitectural domain that specifies the AV axis in metazoan ova.

Cornelia de Lange Syndrome: NIPBL haploinsufficiency downregulates canonical Wnt pathway in zebrafish embryos and patients fibroblasts

Cornelia de Lange Syndrome is a severe genetic disorder characterized by malformations affecting multiple systems, with a common feature of severe mental retardation. Genetic variants within four genes (NIPBL (Nipped-B-like), SMC1A, SMC3, and HDAC8) are believed to be responsible for the majority of cases; all these genes encode proteins that are part of the 'cohesin complex'. Cohesins exhibit two temporally separated major roles in cells: one controlling the cell cycle and the other involved in regulating the gene expression. The present study focuses on the role of the zebrafish nipblb paralog during neural development, examining its expression in the central nervous system, and analyzing the consequences of nipblb loss of function. Neural development was impaired by the knockdown of nipblb in zebrafish. nipblb-loss-of-function embryos presented with increased apoptosis in the developing neural tissues, downregulation of canonical Wnt pathway genes, and subsequent decreased Cyclin D1 (Ccnd1) levels. Importantly, the same pattern of canonical WNT pathway and CCND1 downregulation was observed in NIPBL-mutated patient-specific fibroblasts. Finally, chemical activation of the pathway in nipblb-loss-of-function embryos rescued the adverse phenotype and restored the physiological levels of cell death.

Genome-wide network analysis of Wnt signaling in three pediatric cancers

Genomic structural alteration is common in pediatric cancers, and analysis of data generated by the Pediatric Cancer Genome Project reveals such tumor-related alterations in many Wnt signaling–associated genes. Most pediatric cancers are thought to arise within developing tissues that undergo substantial expansion during early organ formation, growth and maturation, and Wnt signaling plays an important role in this development. We examined three pediatric tumors—medullobastoma, early T-cell precursor acute lymphoblastic leukemia, and retinoblastoma—that show multiple genomic structural variations within Wnt signaling pathways. We mathematically modeled this pathway to investigate the effects of cancer-related structural variations on Wnt signaling. Surprisingly, we found that an outcome measure of canonical Wnt signaling was consistently similar in matched cancer cells and normal cells, even in the context of different cancers, different mutations, and different Wnt-related genes. Our results suggest that the cancer cells maintain a normal level of Wnt signaling by developing multiple mutations.

Deubiquitination of Dishevelled by Usp14 is required for Wnt signaling

Dishevelled (Dvl) is a key regulator of Wnt signaling both in the canonical and non-canonical pathways. Here we report the identification of a regulatory domain of ubiquitination (RDU) in the C-terminus of Dvl. Mutations in the RDU resulted in accumulation of polyubiquitinated forms of Dvl, which were mainly K63 linked. Small interfering RNA-based screening identified Usp14 as a mediator of Dvl deubiquitination. Genetic and chemical suppression of Usp14 activity caused an increase in Dvl polyubiquitination and significantly impaired downstream Wnt signaling. These data suggest that Usp14 functions as a positive regulator of the Wnt signaling pathway. Consistently, tissue microarray analysis of colon cancer revealed a strong correlation between the levels of Usp14 and β-catenin, which suggests an oncogenic role for Usp14 via enhancement of Wnt/β-catenin signaling.

Microarray analysis of gene expression profiles of Schistosoma japonicum derived from less-susceptible host water buffalo and susceptible host goat

Background

Water buffalo and goats are natural hosts for S. japonicum in endemic areas of China. The susceptibility of these two hosts to schistosome infection is different, as water buffalo are less conducive to S. japonicum growth and development. To identify genes that may affect schistosome development and survival, we compared gene expression profiles of schistosomes derived from these two natural hosts using high-throughput microarray technology.

Results

The worm recovery rate was lower and the length and width of worms from water buffalo were smaller compared to those from goats following S. japonicum infection for 7 weeks. Besides obvious morphological difference between the schistosomes derived from the two hosts, differences were also observed by scanning and transmission electron microscopy. Microarray analysis showed differentially expressed gene patterns for parasites from the two hosts, which revealed that genes related to lipid and nucleotide metabolism, as well as protein folding, sorting, and degradation were upregulated, while others associated with signal transduction, endocrine function, development, immune function, endocytosis, and amino acid/carbohydrate/glycan metabolism were downregulated in schistosomes from water buffalo. KEGG pathway analysis deduced that the differentially expressed genes mainly involved lipid metabolism, the MAPK and ErbB signaling pathways, progesterone-mediated oocyte maturation, dorso-ventral axis formation, reproduction, and endocytosis, etc.

Conclusion

The microarray gene analysis in schistosomes derived from water buffalo and goats provide a useful platform to disclose differences determining S. japonicum host compatibility to better understand the interplay between natural hosts and parasites, and identify schistosome target genes associated with susceptibility to screen vaccine candidates.

Integrative genomics analysis identifies candidate drivers at 3q26-29 amplicon in squamous cell carcinoma of the lung

PURPOSE

Chromosome 3q26-29 is a critical region of genomic amplification in lung squamous cell carcinomas (SCC). Identification of candidate drivers in this region could help uncover new mechanisms in the pathogenesis and potentially new targets in SCC of the lung.

EXPERIMENTAL DESIGN

We conducted a meta-analysis of seven independent datasets containing a total of 593 human primary SCC samples to identify consensus candidate drivers in 3q26-29 amplicon. Through integrating protein-protein interaction network information, we further filtered for candidates that may function together in a network. Computationally predicted candidates were validated using RNA interference (RNAi) knockdown and cell viability assays. Clinical relevance of the experimentally supported drivers was evaluated in an independent cohort of 52 lung SCC patients using survival analysis.

RESULTS

The meta-analysis identified 20 consensus candidates, among which four (SENP2, DCUN1D1, DVL3, and UBXN7) are involved in a small protein-protein interaction network. Knocking down any of the four proteins led to cell growth inhibition of the 3q26-29-amplified SCC. Moreover, knocking down of SENP2 resulted in the most significant cell growth inhibition and downregulation of DCUN1D1 and DVL3. Importantly, a gene expression signature composed of SENP2, DCUN1D1, and DVL3 stratified patients into subgroups with different response to adjuvant chemotherapy.

CONCLUSION

Together, our findings show that SENP2, DCUN1D1, and DVL3 are candidate driver genes in the 3q26-29 amplicon of SCC, providing novel insights into the molecular mechanisms of disease progression and may have significant implication in the management of SCC of the lung.

Naked cuticle Drosophila 1 expression in histologic subtypes of small adenocarcinoma of the lung

Background

Naked cuticle Drosophila 1 (NKD1) has been related to non-small cell lung cancer in that decreased NKD1 levels have been associated with both poor prognosis and increased invasive quality.

Methods

Forty cases of lung adenocarcinoma staged as Tis or T1a were selected. Cases were subclassified into adenocarcinoma in situ (AIS), minimally invasive adenocarcinoma (MIA), and small adenocarcinoma (SAD). Immunohistochemical studies for NKD1 were performed.

Results

Forty samples comprised five cases of AIS (12.5%), eight of MIA (20.0%), and 27 of SAD (67.5%). AIS and MIA showed no lymph node metastasis and 100% disease-free survival, whereas among 27 patients with SAD, 2 (7.4%) had lymph node metastasis, and 3 (11.1%) died from the disease. Among the 40 cases, NKD1-reduced expression was detected in 8 (20%) samples, whereas normal expression was found in 15 (37.5%) and overexpression in 17 (42.5%). Loss of NKD1 expression was significantly associated with lymph node metastasis (p=0.001). All cases with predominant papillary pattern showed overexpression of NKD1 (p=0.026).

Conclusions

Among MIA and SAD, MIA had better outcomes than SAD. Down-regulated NKD1 expression was closely associated with nodal metastasis, and overexpression was associated with papillary predominant adenocarcinoma.

Emerging role of primary cilia as mechanosensors in osteocytes

The primary cilium is a solitary, immotile microtubule-based extension present on nearly every mammalian cell. This organelle has established mechanosensory roles in several contexts including kidney, liver, and the embryonic node. Mechanical load deflects the cilium, triggering biochemical responses. Defects in cilium function have been associated with numerous human diseases. Recent research has implicated the primary cilium as a mechanosensor in bone. In this review, we discuss the cilium, the growing evidence for its mechanosensory role in bone, and areas of future study.

Xenopus laevis nucleotide binding protein 1 (xNubp1) is important for convergent extension movements and controls ciliogenesis via regulation of the actin cytoskeleton

Nucleotide binding protein 1 (Nubp1) is a highly conserved phosphate loop (P-loop) ATPase involved in diverse processes including iron-sulfur protein assembly, centrosome duplication and lung development. Here, we report the cloning, expression and functional characterization of Xenopus laevis Nubp1. We show that xNubp1 is expressed maternally, displays elevated expression in neural tissues and is required for convergent extension movements and neural tube closure. In addition, xNubp1knockdown leads to defective ciliogenesis of the multi-ciliated cells of the epidermis as well as the monociliated cells of the gastrocoel roof plate. Specifically, xNubp1 is required for basal body migration, spacing and docking in multi-ciliated cells and basal body positioning and axoneme elongation in monociliated gastrocoel roof plate cells. Live imaging of the different pools of actin and basal body migration during the process of ciliated cell intercalation revealed that two independent pools of actin are present from the onset of cell intercalation; an internal network surrounding the basal bodies, anchoring them to the cell cortex and an apical pool of punctate actin which eventually matures into the characteristic apical actin network. We show that xNubp1 colocalizes with the apical actin network of multiciliated cells and that problems in basal body transport in xNubp1 morphants are associated with defects of the internal network of actin, while spacing and polarity issues are due to a failure of the apical and sub-apical actin pools to mature into a network. Effects of xNubp1 knockdown on the actin cytoskeleton are independent of RhoA localization and activation, suggesting that xNubp1 may have a direct role in the regulation of the actin cytoskeleton.

Dishevelled-2 silencing reduces androgen-dependent prostate tumor cell proliferation and migration and expression of Wnt-3a and matrix metalloproteinases

To identify Dishevelled-2 (Dvl2) is a prostate cancer-associated gene and analyze the effects on the growth and invasive capacity of human prostate cancer (PCa) cells. Dvl2 mRNA expression was measured in PCa cell lines and tissue samples, by real-time reverse transcription PCR (qRT-PCR). Immunohistochemistry was used to examine the distribution of Dvl2 in PCa specimens. Silencing Dvl2 in LNCaP cells, proliferation was measured by the CCK-8 assay, cell motility and invasiveness by scratch wound and transwell migration assays, and Wnt-3a, AR, and matrix metalloproteinase (MMP) expression by western blotting. Dvl2 was overexpressed in LNCaP cells compared with the AI PCa lines DU-145 and PC-3, as well as in the majority of PCa tissue specimens examined by qRT-PCR (14/27, 51.9 %). Dvl2 expression was low in all 10 BPH specimens, weakly positive in 26/104 AD PCa specimens (23.8 %), positive in 60/104 AD PCa specimens (55 %), and strongly positive in all 5 AI PCa specimens. Dvl2 expression was significantly correlated with combined Gleason score (p = 0.02), lymph node metastasis (p = 0.005), and TNM stage (p = 0.015). Silencing of Dvl2 mRNA expression significantly reduced LNCaP cell proliferation, motility, invasiveness and Wnt-3a, AR, MMP-2, and MMP-9 expression. Dvl2 may increase PCa growth and metastasis potential, possibly by upregulating Wnt-3a, AR, and MMP expression. Silencing Dvl2 expression may be an effective treatment strategy for PCa.

Different thresholds of Wnt-Frizzled 7 signaling coordinate proliferation, morphogenesis and fate of endoderm progenitor cells

Wnt signaling has multiple dynamic roles during development of the gastrointestinal and respiratory systems. Differential Wnt signaling is thought to be a critical step in Xenopus endoderm patterning such that during late gastrula and early somite stages of embryogenesis, Wnt activity must be suppressed in the anterior to allow the specification of foregut progenitors. However, the foregut endoderm also expresses the Wnt-receptor Frizzled 7 (Fzd7) as well as several Wnt ligands suggesting that the current model may be too simple. In this study, we show that Fzd7 is required to transduce a low level of Wnt signaling that is essential to maintain foregut progenitors. Foregut-specific Fzd7-depletion from the Xenopus foregut resulted in liver and pancreas agenesis. Fzd7-depleted embryos failed to maintain the foregut progenitor marker hhex and exhibited decreased proliferation; in addition the foregut cells were enlarged with a randomized orientation. We show that in the foregut Fzd7 signals via both the Wnt/β-catenin and Wnt/JNK pathways and that different thresholds of Wnt-Fzd7 activity coordinate progenitor cell fate, proliferation and morphogenesis.

RNA helicase DDX3 is a regulatory subunit of casein kinase 1 in Wnt-β-catenin signaling

Casein kinase 1 (CK1) members play key roles in numerous biological processes. They are considered "rogue" kinases, because their enzymatic activity appears unregulated. Contrary to this notion, we have identified the DEAD-box RNA helicase DDX3 as a regulator of the Wnt-β-catenin network, where it acts as a regulatory subunit of CK1ε: In a Wnt-dependent manner, DDX3 binds CK1ε and directly stimulates its kinase activity, and promotes phosphorylation of the scaffold protein dishevelled. DDX3 is required for Wnt-β-catenin signaling in mammalian cells and during Xenopus and Caenorhabditis elegans development. The results also suggest that the kinase-stimulatory function extends to other DDX and CK1 members, opening fresh perspectives for one of the longest-studied protein kinase families.

HECT domain-containing E3 ubiquitin ligase NEDD4L negatively regulates Wnt signaling by targeting dishevelled for proteasomal degradation

Wnt signaling plays a pivotal role in embryogenesis and tissue homeostasis. Dishevelled (Dvl) is a central mediator for both Wnt/β-catenin and Wnt/planar cell polarity pathways. NEDD4L, an E3 ubiquitin ligase, has been shown to regulate ion channel activity, cell signaling, and cell polarity. Here, we report a novel role of NEDD4L in the regulation of Wnt signaling. NEDD4L induces Dvl2 polyubiquitination and targets Dvl2 for proteasomal degradation. Interestingly, the NEDD4L-mediated ubiquitination of Dvl2 is Lys-6, Lys-27, and Lys-29 linked but not typical Lys-48-linked ubiquitination. Consistent with the role of Dvl in both Wnt/β-catenin and Wnt/planar cell polarity signaling, NEDD4L regulates the cellular β-catenin level and Rac1, RhoA, and JNK activities. We have further identified a hierarchical regulation that Wnt5a induces JNK-mediated phosphorylation of NEDD4L, which in turn promotes its ability to degrade Dvl2. Finally, we show that NEDD4L inhibits Dvl2-induced axis duplication in Xenopus embryos. Our work thus demonstrates that NEDD4L is a negative feedback regulator of Wnt signaling.

Origin and evolution of dishevelled

Dishevelled (Dsh or Dvl) is an important signaling protein, playing a key role in Wnt signaling and relaying cellular information for several developmental pathways. Dsh is highly conserved among metazoans and has expanded into a multigene family in most bilaterian lineages, including vertebrates, planarians, and nematodes. These orthologs, where explored, are known to have considerable overlap in function, but evidence for functional specialization continues to mount. We performed a comparative analysis of Dsh across animals to explore protein architecture and identify conserved and divergent features that could provide insight into functional specialization with an emphasis on invertebrates, especially nematodes. We find evidence of dynamic evolution of Dsh, particularly among nematodes, with taxa varying in ortholog number from one to three. We identify a new domain specific to some nematode lineages and find an unexpected nuclear localization signal conserved in many Dsh orthologs. Our findings raise questions of protein evolution in general and provide clues as to how animals have dealt with the complex intricacies of having a protein, such as Dsh, act as a central messenger hub connected to many different and vitally important pathways. We discuss our findings in the context of functional specialization and bring many testable hypotheses to light.

Dishevelled limits Notch signalling through inhibition of CSL

Notch and Wnt are highly conserved signalling pathways that are used repeatedly throughout animal development to generate a diverse array of cell types. However, they often have opposing effects on cell-fate decisions with each pathway promoting an alternate outcome. Commonly, a cell receiving both signals exhibits only Wnt pathway activity. This suggests that Wnt inhibits Notch activity to promote a Wnt-ON/Notch-OFF output; but what might underpin this Notch regulation is not understood. Here, we show that Wnt acts via Dishevelled to inhibit Notch signalling, and that this crosstalk regulates cell-fate specification in vivo during Xenopus development. Mechanistically, Dishevelled binds and directly inhibits CSL transcription factors downstream of Notch receptors, reducing their activity. Furthermore, our data suggest that this crosstalk mechanism is conserved between vertebrate and invertebrate homologues. Thus, we identify a dual function for Dishevelled as an inhibitor of Notch signalling and an activator of the Wnt pathway that sharpens the distinction between opposing Wnt and Notch responses, allowing for robust cell-fate decisions.

The PCP effector Fuzzy controls cilial assembly and signaling by recruiting Rab8 and Dishevelled to the primary cilium

During vertebrate development, the PCP pathway controls multiple cellular processes. Loss of the gene for the PCP effector Fuzzy affects formation of primary cilia via mostly unknown mechanisms. We report that Fuzzy localizes to the primary cilia and orchestrates delivery of Rab8 and Dishevelled to the primary cilium; loss of Fuzzy affects cilia-dependent signaling.

The planar cell polarity (PCP) pathway controls multiple cellular processes during vertebrate development. Recently the PCP pathway was implicated in ciliogenesis and in ciliary function. The primary cilium is an apically projecting solitary organelle that is generated via polarized intracellular trafficking. Because it acts as a signaling nexus, defects in ciliogenesis or cilial function cause multiple congenital anomalies in vertebrates. Loss of the PCP effector Fuzzy affects PCP signaling and formation of primary cilia; however, the mechanisms underlying these processes are largely unknown. Here we report that Fuzzy localizes to the basal body and ciliary axoneme and is essential for ciliogenesis by delivering Rab8 to the basal body and primary cilium. Fuzzy appears to control subcellular localization of the core PCP protein Dishevelled, recruiting it to Rab8-positive vesicles and to the basal body and cilium. We show that loss of Fuzzy results in inhibition of PCP signaling and hyperactivation of the canonical WNT pathway. We propose a mechanism by which Fuzzy participates in ciliogenesis and affects both canonical WNT and PCP signaling.

Collective epithelial and mesenchymal cell migration during gastrulation

Gastrulation, the process that puts the three major germlayers, the ectoderm, mesoderm and endoderm in their correct topological position in the developing embryo, is characterised by extensive highly organised collective cell migration of epithelial and mesenchymal cells. We discuss current knowledge and insights in the mechanisms controlling these cell behaviours during gastrulation in the chick embryo. We discuss several ideas that have been proposed to explain the observed large scale vortex movements of epithelial cells in the epiblast during formation of the primitive streak. We review current insights in the control and execution of the epithelial to mesenchymal transition (EMT) underlying the formation of the hypoblast and the ingression of the mesendoderm cells through the streak. We discuss the mechanisms by which the mesendoderm cells move, the nature and dynamics of the signals that guide these movements, as well as the interplay between signalling and movement that result in tissue patterning and morphogenesis. We argue that instructive cell-cell signaling and directed chemotactic movement responses to these signals are instrumental in the execution of all phases of gastrulation.

Role of the Wnt-Frizzled system in cardiac pathophysiology: a rapidly developing, poorly understood area with enormous potential

Abstract  The Wnt-Frizzled (Fzd) G-protein-coupled receptor system, involving 19 distinct Wnt ligands and 10 Fzd receptors, plays key roles in the development and functioning of many organ systems. There is increasing evidence that Wnt-Fzd signalling is important in regulating cardiac function. Wnt-Fzd signalling primarily involves a canonical pathway, with dishevelled-1-dependent nuclear translocation of β-catenin that derepresses Wnt-sensitive gene transcription, but can also include non-canonical pathways via phospholipase-C/Ca(2+) mobilization and dishevelled-protein activation of small GTPases. Wnt-Fzd effects vary with specific ligand/receptor interactions and associated downstream pathways. This paper reviews the biochemistry and physiology of the Wnt-Fzd complex, and presents current knowledge of Wnt signalling in cardiac remodelling processes such as hypertrophy and fibrosis, as well as disease states such as myocardial infarction (MI), heart failure and arrhythmias. Wnt signalling is activated during hypertrophy; inhibiting Wnt signalling by activating glycogen synthase kinase attenuates the hypertrophic response. Wnt signalling has complex and time-dependent actions post-MI, so that either beneficial or harmful effects might result from Wnt-directed interventions. Stem cell biology, a promising area for therapeutic intervention, is highly regulated by Wnt signalling. The Wnt system regulates fibroblast function, and is prominently altered in arrhythmogenic ventricular cardiomyopathy, a familial disease involving excess deposition of fibroadipose tissue. Wnt signalling controls connexin43 expression, thereby contributing to the regulation of cardiac electrical stability and arrhythmia generation. Although much has been learned about Wnt-Fzd signalling in hypertrophy and infarction, its role is poorly understood for a broad range of other heart disorders. Much more needs to be learned for its contributions to be fully appreciated, and to permit more effective exploitation of its enormous potential in therapeutic development.

Tiam1 regulates the Wnt/Dvl/Rac1 signaling pathway and the differentiation of midbrain dopaminergic neurons

Understanding the mechanisms that drive the differentiation of dopaminergic (DA) neurons is crucial for successful development of novel therapies for Parkinson's disease, in which DA neurons progressively degenerate. However, the mechanisms underlying the differentiation-promoting effects of Wnt5a on DA precursors are poorly understood. Here, we present the molecular and functional characterization of a signaling pathway downstream of Wnt5a, the Wnt/Dvl/Rac1 pathway. First, we characterize the interaction between Rac1 and Dvl and identify the N-terminal part of Dvl3 as necessary for Rac1 binding. Next, we show that Tiam1, a Rac1 guanosine exchange factor (GEF), is expressed in the ventral midbrain, interacts with Dvl, facilitates Dvl-Rac1 interaction, and is required for Dvl- or Wnt5a-induced activation of Rac1. Moreover, we show that Wnt5a promotes whereas casein kinase 1 (CK1), a negative regulator of the Wnt/Dvl/Rac1 pathway, abolishes the interactions between Dvl and Tiam1. Finally, using ventral midbrain neurosphere cultures, we demonstrate that the generation of DA neurons in culture is impaired after Tiam1 knockdown, indicating that Tiam1 is required for midbrain DA differentiation. In summary, our data identify Tiam1 as a novel regulator of DA neuron development and as a Dvl-associated and Rac1-specific GEF acting in the Wnt/Dvl/Rac1 pathway.

Novel mutations including deletions of the entire OFD1 gene in 30 families with type 1 orofaciodigital syndrome: a study of the extensive clinical variability

OFD1, now recognized as a ciliopathy, is characterized by malformations of the face, oral cavity and digits, and is transmitted as an X-linked condition with lethality in males. Mutations in OFD1 also cause X-linked Joubert syndrome (JBTS10) and Simpson-Golabi-Behmel syndrome type 2 (SGBS2). We have studied 55 sporadic and six familial cases of suspected OFD1. Comprehensive mutation analysis in OFD1 revealed mutations in 37 female patients from 30 families; 22 mutations have not been previously described including two heterozygous deletions spanning OFD1 and neighbouring genes. Analysis of clinical findings in patients with mutations revealed that oral features are the most reliable diagnostic criteria. A first, detailed evaluation of brain MRIs from seven patients with cognitive defects illustrated extensive variability with the complete brain phenotype consisting of complete agenesis of the corpus callosum, large single or multiple interhemispheric cysts, striking cortical infolding of gyri, ventriculomegaly, mild molar tooth malformation and moderate to severe cerebellar vermis hypoplasia. Although the OFD1 gene apparently escapes X-inactivation, skewed inactivation was observed in seven of 14 patients. The direction of skewing did not correlate with disease severity, reinforcing the hypothesis that additional factors contribute to the extensive intrafamilial variability.

Wnt signal transduction pathways

The Wnt signaling pathway is an ancient and evolutionarily conserved pathway that regulates crucial aspects of cell fate determination, cell migration, cell polarity, neural patterning and organogenesis during embryonic development. The Wnts are secreted glycoproteins and comprise a large family of nineteen proteins in humans hinting to a daunting complexity of signaling regulation, function and biological output. To date major signaling branches downstream of the Fz receptor have been identified including a canonical or Wnt/beta-catenin dependent pathway and the non-canonical or beta-catenin-independent pathway which can be further divided into the Planar Cell Polarity and the Wnt/Ca(2+) pathways, and these branches are being actively dissected at the molecular and biochemical levels. In this review, we will summarize the most recent advances in our understanding of these Wnt signaling pathways and the role of these pathways in regulating key events during embryonic patterning and morphogenesis.

Structure-function dissection of the frizzled receptor in Drosophila melanogaster suggests different mechanisms of action in planar polarity and canonical Wnt signaling

Members of the Frizzled family of sevenpass transmembrane receptors signal via the canonical Wnt pathway and also via noncanonical pathways of which the best characterized is the planar polarity pathway. Activation of both canonical and planar polarity signaling requires interaction between Frizzled receptors and cytoplasmic proteins of the Dishevelled family; however, there has been some dispute regarding whether the Frizzled-Dishevelled interactions are the same in both cases. Studies looking at mutated forms of Dishevelled suggested that stable recruitment of Dishevelled to membranes by Frizzled was required only for planar polarity activity, implying that qualitatively different Frizzled-Dishevelled interactions underlie canonical signaling. Conversely, studies looking at the sequence requirements of Frizzled receptors in the fruit fly Drosophila melanogaster for canonical and planar polarity signaling have concluded that there is most likely a common mechanism of action. To understand better Frizzled receptor function, we have carried out a large-scale mutagenesis in Drosophila to isolate novel mutations in frizzled that affect planar polarity activity and have identified a group of missense mutations in cytosolic-facing regions of the Frizzled receptor that block Dishevelled recruitment. Interestingly, although some of these affect both planar polarity and canonical activity, as previously reported for similar lesions, we find a subset that affect only planar polarity activity. These results support the view that qualitatively different Frizzled-Dishevelled interactions underlie planar polarity and canonical Wnt signaling.

The importance of Wnt signalling for neurodegeneration in Parkinson's disease

PD (Parkinson's disease) is a devastating progressive motor disorder with no available cure. Over the last two decades, an increasing number of genetic defects have been found that cause familial and idiopathic forms of PD. In parallel, the importance of Wnt signalling pathways for the healthy functioning of the adult brain and the dysregulation of these pathways in neurodegenerative disease has become apparent. Cell biological functions disrupted in PD are partially controlled by Wnt signalling pathways and proteins encoded by PARK genes have been shown to modify Wnt signalling. This suggests the prospect of targeting Wnt signalling pathways to modify PD progression.

Genetic analysis of disheveled 2 and disheveled 3 in human neural tube defects

Neural tube defects are severe malformations affecting 1/1,000 live births. The planar cell polarity pathway controls the neural tube closure and has been implicated in the pathogenesis of neural tube defects both in animal models and human cohorts. In mouse disruption of Dvl2 alone (Dvl2^−/−) or Dvl2 and Dvl3 (Dvl2^−/−; Dvl3^+/−, Dvl2^+/−; Dvl3^−/−) results in incomplete neurulation, suggesting a role for Disheveled in neural tube closure. Disheveled is a multifunctional protein that is involved in both the canonical Wnt signaling and the noncanonical planar cell polarity pathway. In this study, we analyzed the role of the human orthologs DVL2 and DVL3 in a cohort of 473 patients with neural tube defects. Rare variants were genotyped in 639 ethnically matched controls. We identified seven rare missense mutations that were absent in all controls analyzed. Two of these mutations, p.Tyr667Cys and p.Ala53Val, identified in DVL2 were predicted to be detrimental in silico. Significantly, a 1-bp insertion (c.1801_1802insG) in exon 15 of DVL2 predicted to lead to the truncation of the protein was identified in a patient with a complex form of caudal agenesis. In summary, we demonstrate a possible role for rare variants in DVL2 gene as risk factors for neural tube defects.

An integrated proteomics and metabolomics approach for defining oncofetal biomarkers in the colorectal cancer

OBJECTIVE

The present study was designed to search for potential diagnostic biomarkers in the serum of colorectal cancer (CRC).

BACKGROUND

CRC is the third most common cancer worldwide, and its prognosis is poor at early stages. A panel of novel biomarkers is urgently needed for early diagnosis of CRC.

METHODS

An integrated proteomics and metabolomics approach was performed to define oncofetal biomarkers in CRC by protein and metabolite profiling of serum samples from CRC patients, healthy control adults, and fetus. The differentially expressed proteins were identified by a 2-D DIGE (2-Dimensional Difference Gel Electrophoresis) coupled with a Finnigan LTQ-based proteomics approach. Meanwhile, the serum metabolome was analyzed using gas chromatography-mass spectrometry integrated with a commercial mass spectral library for peak identification.

RESULTS

Of the 28 identified proteins and the 34 analyzed metabolites, only 5 protein spots and 6 metabolites were significantly increased or decreased in both CRC and fetal serum groups compared with the healthy adult group. Data from supervised predictive models allowed a separation of 93.5% of CRC patients from the healthy controls using the 6 metabolites. Finally, correlation analysis was applied to establish quantitative linkages between the 5 individual metabolite 3-hydroxybutyric acid, L-valine, L-threonine, 1-deoxyglucose, and glycine and the 5 individual proteins MACF1, APOH, A2M, IGL@, and VDB. Furthermore, 10 potential oncofetal biomarkers were characterized and their potential for CRC diagnosis was validated.

CONCLUSION

The integrated approach we developed will promote the translation of biomarkers with clinical value into routine clinical practice.

The Dishevelled-associating protein Daple controls the non-canonical Wnt/Rac pathway and cell motility

Dishevelled is the common mediator of canonical and non-canonical Wnt signalling pathways, which are important for embryonic development, tissue maintenance and cancer progression. In the non-canonical Wnt signalling pathway, the Rho family of small GTPases acting downstream of Dishevelled has essential roles in cell migration. The mechanisms by which the non-canonical Wnt signalling pathway regulates Rac activation remain unknown. Here we show that Daple (Dishevelled-associating protein with a high frequency of leucine residues) regulates Wnt5a-mediated activation of Rac and formation of lamellipodia through interaction with Dishevelled. Daple increases the association of Dishevelled with an isoform of atypical protein kinase C, consequently promoting Rac activation. Accordingly, Daple deficiency impairs migration of fibroblasts and epithelial cells during wound healing in vivo. These findings indicate that Daple interacts with Dishevelled to direct the Dishevelled/protein kinase λ protein complex to activate Rac, which in turn mediates the non-canonical Wnt signalling pathway required for cell migration.

Signaling crosstalk between TGFβ and Dishevelled/Par1b

Crosstalk of signaling pathways is critical during metazoan development and adult tissue homeostasis. Even though the transforming growth factor-beta (TGFβ) transduction cascade is rather simple, in vivo responsiveness to TGFβ ligands is tightly regulated at several steps. As such, TGFβ represents a paradigm for how the activity of one signaling system is modulated by others. Here, we report an unsuspected regulatory step involving Dishevelled (Dvl) and Par1b (also known as MARK2). Dvl and Par1b cooperate to enable TGFβ/bone morphogenetic protein (BMP) signaling in Xenopus mesoderm development and TGFβ responsiveness in mammalian cells. Mechanistically, the assembly of the Par1b/Dvl3/Smad4 complex is fostered by Wnt5a. The association of Smad4 to Dvl/Par1 prevents its inhibitory ubiquitination by ectodermin (also known as transcriptional intermediary factor 1 gamma or tripartite motif protein 33). We propose that this crosstalk is relevant to coordinate TGFβ responses with Wnt-noncanonical and polarity pathways.

Wnt signaling in mammalian development: lessons from mouse genetics

Wnts are evolutionarily conserved signaling ligands critical for animal development. Genetic engineering in the mouse has enabled investigators to acquire a detailed activation profile of the β-catenin-dependent canonical Wnt pathway during mouse development, and to manipulate Wnt pathway activities with great spatial and temporal precision. Together, these studies have not only revealed important functions of Wnt signaling at multiple stages of early mouse development, but also elucidated how the Wnt pathway interacts with other pathways to form signaling networks that confer the unique features of mammalian embryogenesis. Additionally, the planar cell polarity pathway has emerged as an essential β-catenin independent noncanonical Wnt pathway that coordinates cell polarity and regulates tissue morphogenesis in various mammalian developmental processes. Importantly, studies of Wnt signaling in mouse development have also revealed important pathogenic mechanisms of several congenital disorders in humans.

Wnt/planar cell polarity signaling in the regulation of convergent extension movements during Xenopus gastrulation

The Wnt/planar cell polarity (PCP) signaling pathway plays a critical role in wing, eye, neural tube defects, and sensory bristle development of Drosophila and vertebrate development. Recently, the Wnt/PCP pathway has been known to regulate convergent extension (CE) movements that are essential for establishing the three germ layers and body axis during early vertebrate development. Here, we describe detailed practical procedures required for the particular studies in Xenopus CE movements.

Disruption of Wnt planar cell polarity signaling by aberrant accumulation of the MetAP-2 substrate Rab37

Identification of methionine aminopeptidase-2 (MetAP-2) as the molecular target of the antiangiogenic compound TNP-470 has sparked interest in N-terminal Met excision's (NME) role in endothelial cell biology. In this regard, we recently demonstrated that MetAP-2 inhibition suppresses Wnt planar cell polarity (PCP) signaling and that endothelial cells depend on this pathway for normal function. Despite this advance, the substrate(s) whose activity is altered upon MetAP-2 inhibition, resulting in loss of Wnt PCP signaling, is not known. Here we identify the small G protein Rab37 as a MetAP-2-specific substrate that accumulates in the presence of TNP-470. A functional role for aberrant Rab37 accumulation in TNP-470's mode of action is demonstrated using a Rab37 point mutant that is resistant to NME, because expression of this mutant phenocopies the effects of MetAP-2 inhibition on Wnt PCP signaling-dependent processes.

Novel regulators of planar cell polarity: a genetic analysis in Drosophila

Planar cell polarity (PCP) is a common feature of many epithelia and epithelial organs. Although progress has been made in the dissection of molecular mechanisms regulating PCP, many questions remain. Here we describe a screen to identify novel PCP regulators in Drosophila. We employed mild gain-of-function (GOF) phenotypes of two cytoplasmic Frizzled (Fz)/PCP core components, Diego (Dgo) and Prickle (Pk), and screened these against the DrosDel genome-wide deficiency collection for dominant modifiers. Positive genomic regions were rescreened and narrowed down with smaller overlapping deficiencies from the Exelixis collection and RNAi-mediated knockdown applied to individual genes. This approach isolated new regulators of PCP, which were confirmed with loss-of-function analyses displaying PCP defects in the eye and/or wing. Furthermore, knockdown of a subset was also sensitive to dgo dosage or dominantly modified a dishevelled (dsh) GOF phenotype, supporting a role in Fz/PCP-mediated polarity establishment. Among the new "PCP" genes we identified several kinases, enzymes required for lipid modification, scaffolding proteins, and genes involved in substrate modification and/or degradation. Interestingly, one of them is a member of the Meckel-Gruber syndrome factors, associated with human ciliopathies, suggesting an important role for cell polarity in nonciliated cells.

Daam2 is required for dorsal patterning via modulation of canonical Wnt signaling in the developing spinal cord

The Daam family of proteins consists of Daam1 and Daam2. Although Daam1 participates in noncanonical Wnt signaling during gastrulation, Daam2 function remains completely uncharacterized. Here we describe the role of Daam2 in canonical Wnt signal transduction during spinal cord development. Loss-of-function studies revealed that Daam2 is required for dorsal progenitor identities and canonical Wnt signaling. These phenotypes are rescued by β-catenin, demonstrating that Daam2 functions in dorsal patterning through the canonical Wnt pathway. Complementary gain-of-function studies demonstrate that Daam2 amplifies Wnt signaling by potentiating ligand activation. Biochemical examination found that Daam2 association with Dvl3 is required for Wnt activity and dorsal patterning. Moreover, Daam2 stabilizes Dvl3/Axin2 binding, resulting in enhanced intracellular assembly of Dvl3/Axin2 complexes. These studies demonstrate that Daam2 modulates the formation of Wnt receptor complexes, revealing new insight into the functional diversity of Daam proteins and how canonical Wnt signaling contributes to pattern formation in the developing spinal cord.

The many roles of PTK7: a versatile regulator of cell-cell communication

PTK7 (protein tyrosine kinase 7) is an evolutionarily conserved transmembrane receptor with functions in various processes ranging from embryonic morphogenesis to epidermal wound repair. Here, we review recent findings indicating that PTK7 is a versatile co-receptor that functions as a molecular switch in Wnt, Semaphorin/Plexin and VEGF signaling pathways. We focus in particular on the role of PTK7 in Wnt signaling, as recent data indicate that PTK7 acts as a Wnt co-receptor, which activates the planar cell polarity pathway, but inhibits canonical Wnt signaling.

Activation and function of small GTPases Rho, Rac, and Cdc42 during gastrulation

Gastrulation is comprised of a series of cell polarization and directional cell migration events that establish the physical body plan of the embryo. One of the major ligand-based pathways that has emerged to play crucial roles in the regulation of gastrulation is the non-canonical Wnt signaling pathway. This aspect of Wnt signaling is comprised of a number of signaling branches that are subsequently integrated for the regulation of changes to the actin cytoskeleton during cell polarization and cell migration during vertebrate gastrulation. The Rho family of small GTPases are activated and required for non-canonical Wnt signaling during gastrulation, and in this chapter, we describe biochemical assays for the detection of Wnt-mediated activation of Rho, Rac, and Cdc42 in both mammalian cells and Xenopus embryo explants.

Wnt signalling antagonizes stress granule assembly through a Dishevelled-dependent mechanism

Cells often respond to diverse environmental stresses by inducing stress granules (SGs) as an adaptive mechanism. SGs are generally assembled as a result of aggregation of mRNAs stalled in a translational pre-initiation complex, mediated by a set of RNA-binding proteins such as G3BP and TIA-1. SGs may serve as triage centres for storage, translation re-initiation or degradation of specific mRNAs. However, the mechanism involved in the modulation of their assembly/disassembly is unclear. Here we report that Wnt signalling negatively regulates SG assembly through Dishevelled (Dvl), a cytoplasmic Wnt effector. Overexpression of Dvl2, an isoform of Dvl, leads to impairment of SG assembly through a DEP domain dependent mechanism. Intriguingly, the Dvl2 mutant K446M, which corresponds to an analogous mutation in Drosophila Dishevelled DEP domain (dsh¹) that results in defective PCP pathway, fails to antagonize SG assembly. Furthermore, we show that Dvl2 exerts the antagonistic effect on SG assembly through a mechanism involving Rac1-mediated inhibition of RhoA. Dvl2 interacts with G3BP, a downstream component of Ras signalling involved in SG assembly, and functional analysis suggests a model wherein the Dvl-Rac1-RhoA axis regulates G3BP's SG-nucleating activity. Collectively, these results define an antagonistic effect of Wnt signalling on SG assembly, and reveal a novel role for Wnt/Dvl pathway in the modulation of mRNA functions.

Functional conservation of Nematostella Wnts in canonical and noncanonical Wnt-signaling

Cnidarians surprise by the completeness of Wnt gene subfamilies (11) expressed in an overlapping pattern along the anterior-posterior axis. While the functional conservation of canonical Wnt-signaling components in cnidarian gastrulation and organizer formation is evident, a role of Nematostella Wnts in noncanonical Wnt-signaling has not been shown so far. In Xenopus, noncanonical Wnt-5a/Ror2 and Wnt-11 (PCP) signaling are distinguishable by different morphant phenotypes. They differ in PAPC regulation, cell polarization, cell protrusion formation, and the so far not reported reorientation of the microtubules. Based on these readouts, we investigated the evolutionary conservation of Wnt-11 and Wnt-5a function in rescue experiments with Nematostella orthologs and Xenopus morphants. Our results revealed that NvWnt-5 and -11 exhibited distinct noncanonical Wnt activities by disturbing convergent extension movements. However, NvWnt-5 rescued XWnt-11 and NvWnt-11 specifically XWnt-5a depleted embryos. This unexpected 'inverse' activity suggests that specific structures in Wnt ligands are important for receptor complex recognition in Wnt-signaling. Although we can only speculate on the identity of the underlying recognition motifs, it is likely that these crucial structural features have already been established in the common ancestor of cnidarians and vertebrates and were conserved throughout metazoan evolution.

Identification of neuroglobin-interacting proteins using yeast two-hybrid screening

Neuroglobin (Ngb) is a globin protein that is highly and specifically expressed in brain neurons. A large volume of evidence has proven that Ngb is a neuroprotective molecule against hypoxic/ischemic brain injury and other related neurological disorder; however, the underlying mechanisms remain poorly understood. Aiming to provide more clues in understanding the molecular mechanisms of Ngb's neuroprotection, we performed yeast two-hybrid screening to search for proteins that interact with Ngb. From a mouse brain cDNA library, we found totally 36 proteins that potentially interact with Ngb, and 10 of them were each identified in multiple positive clones. The shared sequences within these multiple clones are more likely to be Ngb-interacting domains. In primary cultured mouse cortical neurons, immuno-precipitation was performed to confirm the interactions of selected proteins with Ngb. The discovered Ngb-interacting proteins in this study include those involved in energy metabolism, mitochondria function, and signaling pathways for cell survival and proliferation. Our findings provide molecular targets for investigating protein interaction-based biological functions and neuroprotective mechanisms of Ngb.

Planar cell polarity signaling pathway in congenital heart diseases

Congenital heart disease (CHD) is a common cardiac disorder in humans. Despite many advances in the understanding of CHD and the identification of many associated genes, the fundamental etiology for the majority of cases remains unclear. The planar cell polarity (PCP) signaling pathway, responsible for tissue polarity in Drosophila and gastrulation movements and cardiogenesis in vertebrates, has been shown to play multiple roles during cardiac differentiation and development. The disrupted function of PCP signaling is connected to some CHDs. Here, we summarize our current understanding of how PCP factors affect the pathogenesis of CHD.

Expression of Wnt signaling components during Xenopus pronephros development

BACKGROUND

The formation of the vertebrate kidney is tightly regulated and relies on multiple evolutionarily conserved inductive events. These are present in the complex metanephric kidney of higher vertebrates, but also in the more primitive pronephric kidney functional in the larval stages of amphibians and fish. Wnts have long been viewed as central in this process. Canonical β-Catenin-dependent Wnt signaling establishes kidney progenitors and non-canonical β-Catenin-independent Wnt signaling participate in the morphogenetic processes that form the highly sophisticated nephron structure. While some individual Wnt signaling components have been studied extensively in the kidney, the overall pathway has not yet been analyzed in depth.

METHODOLOGY/PRINCIPAL FINDINGS

Here we report a detailed expression analysis of all Wnt ligands, receptors and several downstream Wnt effectors during pronephros development in Xenopus laevis using in situ hybridization. Out of 19 Wnt ligands, only three, Wnt4, Wnt9a and Wnt11, are specifically expressed in the pronephros. Others such as Wnt8a are present, but in a broader domain comprising adjacent tissues in addition to the kidney. The same paradigm is observed for the Wnt receptors and its downstream signaling components. Fzd1, Fzd4, Fzd6, Fzd7, Fzd8 as well as Celsr1 and Prickle1 show distinct expression domains in the pronephric kidney, whereas the non-traditional Wnt receptors, Ror2 and Ryk, as well as the majority of the effector molecules are rather ubiquitous. In addition to this spatial regulation, the timing of expression is also tightly regulated. In particular, non-canonical Wnt signaling seems to be restricted to later stages of pronephros development.

CONCLUSION/SIGNIFICANCE

Together these data suggest a complex cross talk between canonical and non-canonical Wnt signaling is required to establish a functional pronephric kidney.

Dickkopf1--a new player in modelling the Wnt pathway

The Wnt signaling pathway transducing the stabilization of β-catenin is essential for metazoan embryo development and is misregulated in many diseases such as cancers. In recent years models have been proposed for the Wnt signaling pathway during the segmentation process in developing embryos. Many of these include negative feedback loops where Axin2 plays a key role. However, Axin2 null mice show no segmentation phenotype. We therefore propose a new model where the negative feedback involves Dkk1 rather than Axin2. We show that this model can exhibit the same type of oscillations as the previous models with Axin2 and as observed in experiments. We show that a spatial Wnt gradient can consistently convert this temporal periodicity into the spatial periodicity of somites, provided the oscillations in new cells arising in the presomitic mesoderm are synchronized with the oscillations of older cells. We further investigate the hypothesis that a change in the Wnt level in the tail bud during the later stages of somitogenesis can lengthen the time period of the oscillations and hence the size and separation of the later somites.

Dishevelled 2 signaling promotes self-renewal and tumorigenicity in human gliomas

Glioblastoma multiforme is the most common glioma variant in adults and is highly malignant. Tumors are thought to harbor a subpopulation of stem-like cancer cells, with the bulk resembling neural progenitor-like cells that are unable to fully differentiate. Although multiple pathways are known to be involved in glioma tumorigenesis, the role of Wnt signaling has been poorly described. Here, we show that Dishevelled 2 (Dvl2), a key component of the Wnt signaling pathway, is overexpressed in human gliomas. RNA interference-mediated depletion of Dvl2 blocked proliferation and promoted the differentiation of cultured human glioma cell lines and primary, patient-derived glioma cells. In addition, Dvl2 depletion inhibited tumor formation after intracranial injection of glioblastoma cells in immunodeficient mice. Inhibition of canonical Wnt/β-catenin signaling also blocked proliferation, but unlike Dvl2 depletion, did not induce differentiation. Finally, Wnt5a, a noncanonical Wnt ligand, was also required for glioma cell proliferation. The data therefore suggest that both canonical and noncanonical Wnt signaling pathways downstream of Dvl2 cooperate to maintain the proliferative capacity of human glioblastomas.

Planar cell polarity: coordinating morphogenetic cell behaviors with embryonic polarity

Planar cell polarization entails establishment of cellular asymmetries within the tissue plane. An evolutionarily conserved planar cell polarity (PCP) signaling system employs intra- and intercellular feedback interactions between its core components, including Frizzled, Van Gogh, Flamingo, Prickle, and Dishevelled, to establish their characteristic asymmetric intracellular distributions and coordinate planar polarity of cell populations. By translating global patterning information into asymmetries of cell membranes and intracellular organelles, PCP signaling coordinates morphogenetic behaviors of individual cells and cell populations with the embryonic polarity. In vertebrates, by polarizing cilia in the node/Kupffer's vesicle, PCP signaling links the anteroposterior to left-right embryonic polarity.

Functional dissection of phosphorylation of Disheveled in Drosophila

Disheveled/Dsh proteins (Dvl in mammals) are core components of both Wnt/Wg-signaling pathways: canonical β-catenin signaling and Frizzled (Fz)-planar cell polarity (PCP) signaling. Although Dsh is a key cytoplasmic component of both Wnt/Fz-pathways, regulation of its signaling specificity is not well understood. Dsh is phosphorylated, but the functional significance of its phosphorylation remains unclear. We have systematically investigated the phosphorylation of Dsh by combining mass-spectrometry analyses, biochemical studies, and in vivo genetic methods in Drosophila. Our approaches identified multiple phospho-residues of Dsh in vivo. Our data define three novel and unexpected conclusions: (1) strikingly and in contrast to common assumptions, all conserved serines/threonines are non-essential for Dsh function in either pathway; (2) phosphorylation of conserved Tyrosine473 in the DEP domain is critical for PCP-signaling - Dsh(Y473F) behaves like a PCP-specific allele; and (3) defects associated with the PCP specific dsh(1) allele, Dsh(K417M), located within a putative Protein Kinase C consensus site, are likely due to a post-translational modification requirement of Lys417, rather than phosphorylation nearby. In summary, our combined data indicate that while many Ser/Thr and Tyr residues are indeed phosphorylated in vivo, strikingly most of these phosphorylation events are not critical for Dsh function with the exception of DshY473.