Dishevelled phosphorylation, subcellular localization and multimerization regulate its role in early embryogenesis

Coupling and uncoupling of midline morphogenesis and cell flow in amniote gastrulation

Large-scale cell flow characterizes gastrulation in animal development. In amniote gastrulation, particularly in avian gastrula, a bilateral vortex-like counter-rotating cell flow, called 'polonaise movements', appears along the midline. Here, through experimental manipulations, we addressed relationships between the polonaise movements and morphogenesis of the primitive streak, the earliest midline structure in amniotes. Suppression of the Wnt/planar cell polarity (PCP) signaling pathway maintains the polonaise movements along a deformed primitive streak. Mitotic arrest leads to diminished extension and development of the primitive streak and maintains the early phase of the polonaise movements. Ectopically induced Vg1, an axis-inducing morphogen, generates the polonaise movements, aligned to the induced midline, but disturbs the stereotypical cell flow pattern at the authentic midline. Despite the altered cell flow, induction and extension of the primitive streak are preserved along both authentic and induced midlines. Finally, we show that ectopic axis-inducing morphogen, Vg1, is capable of initiating the polonaise movements without concomitant PS extension under mitotic arrest conditions. These results are consistent with a model wherein primitive streak morphogenesis is required for the maintenance of the polonaise movements, but the polonaise movements are not necessarily responsible for primitive streak morphogenesis. Our data describe a previously undefined relationship between the large-scale cell flow and midline morphogenesis in gastrulation.

Coupling and uncoupling of midline morphogenesis and cell flow in amniote gastrulation

Large-scale cell flow characterizes gastrulation in animal development. In amniote gastrulation, particularly in avian gastrula, a bilateral vortex-like counter-rotating cell flow, called 'polonaise movements', appears along the midline. Here, through experimental manipulations, we addressed relationships between the polonaise movements and morphogenesis of the primitive streak, the earliest midline structure in amniotes. Suppression of the Wnt/planar cell polarity (PCP) signaling pathway maintains the polonaise movements along a deformed primitive streak. Mitotic arrest leads to diminished extension and development of the primitive streak and maintains the early phase of the polonaise movements. Ectopically induced Vg1, an axis-inducing morphogen, generates the polonaise movements, aligned to the induced midline, but disturbs the stereotypical cell flow pattern at the authentic midline. Despite the altered cell flow, induction and extension of the primitive streak are preserved along both authentic and induced midlines. Finally, we show that ectopic axis-inducing morphogen, Vg1, is capable of initiating the polonaise movements without concomitant PS extension under mitotic arrest conditions. These results are consistent with a model wherein primitive streak morphogenesis is required for the maintenance of the polonaise movements, but the polonaise movements are not necessarily responsible for primitive streak morphogenesis. Our data describe a previously undefined relationship between the large-scale cell flow and midline morphogenesis in gastrulation.

Non-canonical non-genomic morphogen signaling in anucleate platelets: a critical determinant of prothrombotic function in circulation

Circulating platelets derived from bone marrow megakaryocytes play a central role in thrombosis and hemostasis. Despite being anucleate, platelets express several proteins known to have nuclear niche. These include transcription factors and steroid receptors whose non-genomic functions are being elucidated in platelets. Quite remarkably, components of some of the best-studied morphogen pathways, namely Notch, Sonic Hedgehog (Shh), and Wnt have also been described in recent years in platelets, which regulate platelet function in the context of thrombosis as well as influence their survival. Shh and Notch pathways in stimulated platelets establish feed-forward loops of autocrine/juxtacrine/paracrine non-canonical signaling that helps perpetuate thrombosis. On the other hand, non-canonical Wnt signaling is part of a negative feedback loop for restricting platelet activation and possibly limiting thrombus growth. The present review will provide an overview of these signaling pathways in general. We will then briefly discuss the non-genomic roles of transcription factors and steroid receptors in platelet activation. This will be followed by an elaborate description of morphogen signaling in platelets with a focus on their bearing on platelet activation leading to hemostasis and thrombosis as well as their potential for therapeutic targeting in thrombotic disorders.

Dishevelled: An emerging therapeutic oncogene in human cancers

Cancer is a multifaceted and complex disorder characterized by uncontrolled rates of cell proliferation and its ability to spread and attack other organs. Emerging data indicated several pathways and molecular targets are engaged in cancer progression. Among them, the Wnt signaling pathway was shown to have a crucial role in cancer onset and progression. Dishevelled (DVL) acts in a branch point of canonical and non-canonical Wnt pathway. DVL not only acts in the cytoplasm to inactivate the destruction complex of β-catenin but is also transported into the nucleus to affect the transcription of target genes. Available data revealed that the expression levels of DVL increased in cell and clinical specimens of various cancers, proposing that it may have an oncogenic role. DVL promoted cell invasion, migration, cell cycle, survival, proliferation, 3D-spheroid formation, stemness, and epithelial mesenchymal transition (EMT) and it suppressed cell apoptosis. The higher levels of DVL is associated with the clinicopathological characteristic of cancer-affected patients, including lymph node metastasis, tumor grade, histological type, and age. In addition, the higher levels of DVL could be a promising diagnostic and prognostic biomarker in cancer as well as it could be a mediator in cancer chemoresistance to Methotrexate, paclitaxel, and 5-fluorouracil. This study aimed to investigate the underlying molecular mechanism of DVL in cancer pathogenesis as well as to explore its importance in cancer diagnosis and prognosis as well as its role as a mediator in cancer chemotherapy.

Prickle and Ror modulate Dishevelled-Vangl interaction to regulate non-canonical Wnt signaling during convergent extension

Convergent extension (CE) is a fundamental morphogenetic process where oriented cell behaviors lead to polarized extension of diverse tissues. In vertebrates, regulation of CE requires both non-canonical Wnt, its co-receptor Ror, and "core members" of the planar cell polarity (PCP) pathway. PCP was originally identified as a mechanism to coordinate the cellular polarity in the plane of static epithelium, where core proteins Frizzled (Fz)/ Dishevelled (Dvl) and Van Gogh-like (Vangl)/ Prickel (Pk) partition to opposing cell cortex. But how core PCP proteins interact with each other to mediate non-canonical Wnt/ Ror signaling during CE is not clear. We found previously that during CE, Vangl cell-autonomously recruits Dvl to the plasma membrane but simultaneously keeps Dvl inactive. In this study, we show that non-canonical Wnt induces Dvl to transition from Vangl to Fz. PK inhibits the transition, and functionally synergize with Vangl to suppress Dvl during CE. Conversely, Ror is required for the transition, and functionally antagonizes Vangl. Biochemically, Vangl interacts directly with both Ror and Dvl. Ror and Dvl do not bind directly, but can be cofractionated with Vangl. We propose that Pk assists Vangl to function as an unconventional adaptor that brings Dvl and Ror into a complex to serves two functions: 1) simultaneously preventing both Dvl and Ror from ectopically activating non-canonical Wnt signaling; and 2) relaying Dvl to Fz for signaling activation upon non-canonical Wnt induced dimerization of Fz and Ror.

Many faces and functions of GSKIP: a temporospatial regulation view

Glycogen synthase kinase 3 (GSK3)-β (GSK3β) interaction protein (GSKIP) is one of the smallest A-kinase anchoring proteins that possesses a binding site for GSK3β. Recently, our group identified the protein kinase A (PKA)-GSKIP-GSK3β-X axis; knowledge of this axis may help us decipher the many roles of GSKIP and perhaps help explain the evolutionary reason behind the interaction between GSK3β and PKA. In this review, we highlight the critical and multifaceted role of GSKIP in facilitating PKA kinase activity and its function as a scaffolding protein in signaling pathways. We also highlight how these pivotal PKA and GSK3 kinases can control context-specific functions and interact with multiple target proteins, such as β-catenin, Drp1, Tau, and other proteins. GSKIP is a key regulator of multiple mechanisms because of not only its location at certain subcellular compartments but also its serial changes during the developmental process. Moreover, the involvement of critical upstream regulatory signaling pathways in GSKIP signaling in various cancers, such as miRNA (microRNA) and lncRNA (long noncoding RNA), may help in the identification of therapeutic targets in the era of precision medicine and personalized therapy. Finally, we emphasize on the model of the early stage of pathogenesis of Alzheimer Disease (AD). Although the model requires validation, it can serve as a basis for diagnostic biomarkers development and drug discovery for early-stage AD.

Selective function of the PDZ domain of Dishevelled in noncanonical Wnt signalling

Dishevelled is a cytoplasmic hub that transduces Wnt signals to cytoplasmic effectors, which can be broadly characterised as canonical (β-catenin dependent) and noncanonical, to specify cell fates and behaviours during development. To transduce canonical Wnt signals, Dishevelled binds to the intracellular face of Frizzled through its DEP domain and polymerises through its DIX domain to assemble dynamic signalosomes. Dishevelled also contains a PDZ domain, whose function remains controversial. Here, we use genome editing to delete the PDZ domain-encoding region from Drosophila dishevelled. Canonical Wingless signalling is entirely normal in these deletion mutants; however, they show defects in multiple contexts controlled by noncanonical Wnt signalling, such as planar polarity. We use nuclear magnetic resonance spectroscopy to identify bona fide PDZ-binding motifs at the C termini of different polarity proteins. Although deletions of these motifs proved aphenotypic in adults, we detected changes in the proximodistal distribution of the polarity protein Flamingo (also known as Starry night) in pupal wings that suggest a modulatory role of these motifs in polarity signalling. We also provide new genetic evidence that planar polarity relies on the DEP-dependent recruitment of Dishevelled to the plasma membrane by Frizzled.

The Wnt Pathway: From Signaling Mechanisms to Synthetic Modulators

The Wnt pathway is central to a host of developmental and disease-related processes. The remarkable conservation of this intercellular signaling cascade throughout metazoan lineages indicates that it coevolved with multicellularity to regulate the generation and spatial arrangement of distinct cell types. By regulating cell fate specification, mitotic activity, and cell polarity, Wnt signaling orchestrates development and tissue homeostasis, and its dysregulation is implicated in developmental defects, cancer, and degenerative disorders. We review advances in our understanding of this key pathway, from Wnt protein production and secretion to relay of the signal in the cytoplasm of the receiving cell. We discuss the evolutionary history of this pathway as well as endogenous and synthetic modulators of its activity. Finally, we highlight remaining gaps in our knowledge of Wnt signal transduction and avenues for future research. Expected final online publication date for the Annual Review of Biochemistry, Volume 91 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Exploring the roles of FGF/MAPK and cVG1/GDF signalling on mesendoderm induction and convergent extension during chick primitive streak formation

During primitive streak formation in the chick embryo, cells undergo mesendoderm specification and convergent extension at the same time and in the same cells. Previous work has implicated cVG1 (GDF3) as a key factor for induction of primitive streak identity and positioning the primitive streak, whereas FGF signalling was implicated in regulating cell intercalation via regulation of components of the WNT-planar cell polarity (PCP) pathway. FGF has also been reported to be able to induce a primitive streak (but lacking the most axial derivatives such as notochord/prechordal mesendoderm). These signals emanate from different cell populations in the embryo, so how do they interact to ensure that the same cells undergo both cell intercalation and acquire primitive streak identity? Here we begin to address this question by examining in more detail the ability of the two classes of signals in regulating the two developmental events. Using misexpression of inducers and/or exposure to inhibitors and in situ hybridisation, we study how these two signals regulate expression of Brachyury (TBXT) and PRICKLE1 as markers for the primitive streak and the PCP, respectively. We find that both signals can induce both properties, but while FGF seems to be required for induction of the streak by cVG1, it is not necessary for induction of PRICKLE1. The results are consistent with cVG1 being a common regulator for both primitive streak identity and the initiation of convergent extension that leads to streak elongation.

An emergent Wnt5a/YAP/TAZ regulatory circuit and its possible role in cancer

Wnt5a is a ligand that plays several roles in development, homeostasis, and disease. A growing body of evidence indicates that Wnt5a is involved in cancer progression. Despite extensive research in this field, our knowledge about how Wnt5a is precisely involved in cancer is still incomplete. It is usually thought that certain combinations of Frizzled receptors and co-receptors might explain the observed effects of Wnt5a either as a tumor suppressor or by promoting migration and invasion. While accepting this 'receptor context' model, this review proposes that Wnt5a is integrated within a larger regulatory circuit involving β-catenin, YAP/TAZ, and LATS1/2. Remarkably, WNT5A and YAP1 are transcriptionally regulated by the Hippo and Wnt pathways, respectively, and might form a regulatory circuit acting through LATS kinases and secreted Wnt/β-catenin inhibitors, including Wnt5a itself. Therefore, understanding the precise role of Wnt5a and YAP in cancer requires a systems biology perspective.

Regulation of Dishevelled DEP domain swapping by conserved phosphorylation sites

Wnt signals bind to Frizzled receptors to trigger canonical and noncanonical signaling responses that control cell fates during animal development and tissue homeostasis. All Wnt signals are relayed by the hub protein Dishevelled. During canonical (β-catenin-dependent) signaling, Dishevelled assembles signalosomes via dynamic head-to-tail polymerization of its Dishevelled and Axin (DIX) domain, which are cross-linked by its Dishevelled, Egl-10, and Pleckstrin (DEP) domain through a conformational switch from monomer to domain-swapped dimer. The domain-swapped conformation of DEP masks the site through which Dishevelled binds to Frizzled, implying that DEP domain swapping results in the detachment of Dishevelled from Frizzled. This would be incompatible with noncanonical Wnt signaling, which relies on long-term association between Dishevelled and Frizzled. It is therefore likely that DEP domain swapping is differentially regulated during canonical and noncanonical Wnt signaling. Here, we use NMR spectroscopy and cell-based assays to uncover intermolecular contacts in the DEP dimer that are essential for its stability and for Dishevelled function in relaying canonical Wnt signals. These contacts are mediated by an intrinsically structured sequence spanning a conserved phosphorylation site upstream of the DEP domain that serves to clamp down the swapped N-terminal α-helix onto the structural core of a reciprocal DEP molecule in the domain-swapped configuration. Mutations of this phosphorylation site and its cognate surface on the reciprocal DEP core attenuate DEP-dependent dimerization of Dishevelled and its canonical signaling activity in cells without impeding its binding to Frizzled. We propose that phosphorylation of this crucial residue could be employed to switch off canonical Wnt signaling.

Decoding Dishevelled-Mediated Wnt Signaling in Vertebrate Early Development

Dishevelled proteins are key players of Wnt signaling pathways. They transduce Wnt signals and perform cellular functions through distinct conserved domains. Due to the presence of multiple paralogs, the abundant accumulation of maternal transcripts, and the activation of distinct Wnt pathways, their regulatory roles during vertebrate early development and the mechanism by which they dictate the pathway specificity have been enigmatic and attracted much attention in the past decades. Extensive studies in different animal models have provided significant insights into the structure-function relationship of conserved Dishevelled domains in Wnt signaling and the implications of Dishevelled isoforms in early developmental processes. Notably, intra- and inter-molecular interactions and Dishevelled dosage may be important in modulating the specificity of Wnt signaling. There are also distinct and redundant functions among Dishevelled isoforms in development and disease, which may result from differential spatiotemporal expression patterns and biochemical properties and post-translational modifications. This review presents the advances and perspectives in understanding Dishevelled-mediated Wnt signaling during gastrulation and neurulation in vertebrate early embryos.

DVL mutations identified from human neural tube defects and Dandy-Walker malformation obstruct the Wnt signaling pathway

Wnt signaling pathways, including the canonical Wnt/β-catenin pathway, planar cell polarity pathway, and Wnt/Ca²⁺ signaling pathway, play important roles in neural development during embryonic stages. The DVL genes encode the hub proteins for Wnt signaling pathways. The mutations in DVL2 and DVL3 were identified from patients with neural tube defects (NTDs), but their functions in the pathogenesis of human neural diseases remain elusive. Here, we sequenced the coding regions of three DVL genes in 176 stillborn or miscarried fetuses with NTDs or Dandy-Walker malformation (DWM) and 480 adult controls from a Han Chinese population. Four rare mutations were identified: DVL1 p.R558H, DVL1 p.R606C, DVL2 p.R633W, and DVL3 p.R222Q. To assess the effect of these mutations on NTDs and DWM, various functional analyses such as luciferase reporter assay, stress fiber formation, and in vivo teratogenic assay were performed. The results showed that the DVL2 p.R633W mutation destabilized DVL2 protein and upregulated activities for all three Wnt signalings (Wnt/β-catenin signaling, Wnt/planar cell polarity signaling, and Wnt/Ca²⁺ signaling) in mammalian cells. In contrast, DVL1 mutants (DVL1 p.R558H and DVL1 p.R606C) decreased canonical Wnt/β-catenin signaling but increased the activity of Wnt/Ca²⁺ signaling, and DVL3 p.R222Q only decreased the activity of Wnt/Ca²⁺ signaling. We also found that only the DVL2 p.R633W mutant displayed more severe teratogenicity in zebrafish embryos than wild-type DVL2. Our study demonstrates that these four rare DVL mutations, especially DVL2 p.R633W, may contribute to human neural diseases such as NTDs and DWM by obstructing Wnt signaling pathways.

The Rho guanine nucleotide exchange factor Trio is required for neural crest cell migration and interacts with Dishevelled

Directional migration during embryogenesis and tumor progression faces the challenge that numerous external signals need to converge to precisely control cell movement. The Rho guanine exchange factor (GEF) Trio is especially well suited to relay signals, as it features distinct catalytic domains to activate Rho GTPases. Here, we show that Trio is required for Xenopus cranial neural crest (NC) cell migration and cartilage formation. Trio cell-autonomously controls protrusion formation of NC cells and Trio morphant NC cells show a blebbing phenotype. Interestingly, the Trio GEF2 domain is sufficient to rescue protrusion formation and migration of Trio morphant NC cells. We show that this domain interacts with the DEP/C-terminus of Dishevelled (DVL). DVL - but not a deletion construct lacking the DEP domain - is able to rescue protrusion formation and migration of Trio morphant NC cells. This is likely mediated by activation of Rac1, as we find that DVL rescues Rac1 activity in Trio morphant embryos. Thus, our data provide evidence for a novel signaling pathway, whereby Trio controls protrusion formation of cranial NC cells by interacting with DVL to activate Rac1.

Dishevelled-1 regulated apoptosis through NF-κB in cerebral ischemia/reperfusion injury in rats

Dishevelled-1(DVL-1) has been reported associated with the regulation of cell polarity and neuronal function. However, the effect of DVL-1 in cerebral ischemia-reperfusion injury of rats remains poorly understood. In this study, we give evidence that the level of DVL-1 is increased after a middle cerebral artery occlusion/reperfusion model (MCAO) in rats, with a peak at 12 h. On the side, knockdown of DVL-1 may relieve I/R damage and restrain apoptosis after MCAO model in rats. In the part of mechanism, DVL-1 could regulate apoptosis through NF-κB. These results suggest that DVL-1 may be a potential target in I/R injury in rats.

PDZ Domains as Drug Targets

Protein-protein interactions within protein networks shape the human interactome, which often is promoted by specialized protein interaction modules, such as the postsynaptic density-95 (PSD-95), discs-large, zona occludens 1 (ZO-1) (PDZ) domains. PDZ domains play a role in several cellular functions, from cell-cell communication and polarization, to regulation of protein transport and protein metabolism. PDZ domain proteins are also crucial in the formation and stability of protein complexes, establishing an important bridge between extracellular stimuli detected by transmembrane receptors and intracellular responses. PDZ domains have been suggested as promising drug targets in several diseases, ranging from neurological and oncological disorders to viral infections. In this review, the authors describe structural and genetic aspects of PDZ-containing proteins and discuss the current status of the development of small-molecule and peptide modulators of PDZ domains. An overview of potential new therapeutic interventions in PDZ-mediated protein networks is also provided.

Dishevelled-3 conformation dynamics analyzed by FRET-based biosensors reveals a key role of casein kinase 1

Dishevelled (DVL) is the key component of the Wnt signaling pathway. Currently, DVL conformational dynamics under native conditions is unknown. To overcome this limitation, we develop the Fluorescein Arsenical Hairpin Binder- (FlAsH-) based FRET in vivo approach to study DVL conformation in living cells. Using this single-cell FRET approach, we demonstrate that (i) Wnt ligands induce open DVL conformation, (ii) DVL variants that are predominantly open, show more even subcellular localization and more efficient membrane recruitment by Frizzled (FZD) and (iii) Casein kinase 1 ɛ (CK1ɛ) has a key regulatory function in DVL conformational dynamics. In silico modeling and in vitro biophysical methods explain how CK1ɛ-specific phosphorylation events control DVL conformations via modulation of the PDZ domain and its interaction with DVL C-terminus. In summary, our study describes an experimental tool for DVL conformational sampling in living cells and elucidates the essential regulatory role of CK1ɛ in DVL conformational dynamics.

Whole genome variant association across 100 dogs identifies a frame shift mutation in DISHEVELLED 2 which contributes to Robinow-like syndrome in Bulldogs and related screw tail dog breeds

Domestic dog breeds exhibit remarkable morphological variations that result from centuries of artificial selection and breeding. Identifying the genetic changes that contribute to these variations could provide critical insights into the molecular basis of tissue and organismal morphogenesis. Bulldogs, French Bulldogs and Boston Terriers share many morphological and disease-predisposition traits, including brachycephalic skull morphology, widely set eyes and short stature. Unlike other brachycephalic dogs, these breeds also exhibit vertebral malformations that result in a truncated, kinked tail (screw tail). Whole genome sequencing of 100 dogs from 21 breeds identified 12.4 million bi-allelic variants that met inclusion criteria. Whole Genome Association of these variants with the breed defining phenotype of screw tail was performed using 10 cases and 84 controls and identified a frameshift mutation in the WNT pathway gene DISHEVELLED 2 (DVL2) (Chr5: 32195043_32195044del, p = 4.37 X 10-37) as the most strongly associated variant in the canine genome. This DVL2 variant was fixed in Bulldogs and French Bulldogs and had a high allele frequency (0.94) in Boston Terriers. The DVL2 variant segregated with thoracic and caudal vertebral column malformations in a recessive manner with incomplete and variable penetrance for thoracic vertebral malformations between different breeds. Importantly, analogous frameshift mutations in the human DVL1 and DVL3 genes cause Robinow syndrome, a congenital disorder characterized by similar craniofacial, limb and vertebral malformations. Analysis of the canine DVL2 variant protein showed that its ability to undergo WNT-induced phosphorylation is reduced, suggesting that altered WNT signaling may contribute to the Robinow-like syndrome in the screwtail breeds.

Wnt signaling dynamics in head and neck squamous cell cancer tumor-stroma interactions

Wnt pathway activation maintains the cancer stem cell (CSC) phenotype and promotes tumor progression, making it an attractive target for anti-cancer therapy. Wnt signaling at the tumor and tumor microenvironment (TME) front have not been investigated in depth in head and neck squamous cell carcinoma (HNSCC). In a cohort of 48 HNSCCs, increased Wnt signaling, including Wnt genes (AXIN2, LGR6, WISP1) and stem cell factors (RET, SOX5, KIT), were associated with a more advanced clinical stage. Key Wnt pathway proteins were most abundant at the cancer epithelial-stromal boundary. To investigate these observations, we generated three pairs of cancer-cancer associated fibroblast (CAF) cell lines derived from the same HNSCC patients. 3D co-culture of cancer spheres and CAFs mimicked these in vivo interactions, and using these we observed increased expression of Wnt genes (eg, WNT3A, WNT7A, WNT16) in both compartments. Of these Wnt ligands, we found Wnt3a, and less consistently Wnt16, activated Wnt signaling in both cancer cells and CAFs. Wnt activation increased CSC characteristics like sphere formation and invasiveness, which was further regulated by the presence of CAFs. Time lapse microscopy also revealed preferential Wnt activation of cancer cells. Wnt inhibitors, OMP-18R5 and OMP-54F28, significantly reduced growth of HNSCC patient-derived xenografts and suppressed Wnt activation at the tumor epithelial-stromal boundary. Taken together, our findings suggest that Wnt signaling is initiated in cancer cells which then activate CAFs, and in turn perpetuate a paracrine signaling loop. This suggests that targeting Wnt signaling in the TME is essential.

Planar Cell Polarity Signaling in Mammalian Cardiac Morphogenesis

The mammalian heart is the first organ to form and is critical for embryonic survival and development. With an occurrence of 1%, congenital heart defects (CHDs) are also the most common birth defects in humans, and major cause of childhood morbidity and mortality (Hoffman and Kaplan in J Am Coll Cardiol 39(12):1890-1900, 2002; Samanek in Cardiol Young 10(3):179-185, 2000). Understanding how the heart forms will not only help to determine the etiology and to design diagnostic and therapeutic approaches for CHDs, but may also provide insight into regenerative medicine to repair injured adult hearts. Mammalian heart development requires precise orchestration of growth, differentiation, and morphogenesis to remodel a simple linear heart tube into an intricate, four-chambered heart with properly connected pulmonary artery and aorta, a structural basis for establishing the pulmonary and systemic circulation. Here we will review the recent advance in our understanding of how the planar cell polarity pathway, a highly conserved morphogenetic engine in vertebrates, regulates polarized morphogenetic processes to contribute to both the arterial and venous poles development of the heart.

TMEM59 potentiates Wnt signaling by promoting signalosome formation

Wnt/β-catenin signaling is crucial for adult homeostasis and stem cell maintenance, and its dysregulation is strongly associated to cancer. Upon Wnt binding, Wnt receptors assemble into large complexes called signalosomes that provide a platform for interactions with downstream effector proteins. The assembly and regulation of these signalosomes remains largely elusive. Here, we use internally tagged Wnt ligands as a tool to isolate and analyze the composition and regulation of endogenous Wnt receptor complexes. We identify a positive regulator of Wnt signaling that facilitates signalosome formation by promoting intramembrane receptor interactions. Our results reveal that the assembly of multiprotein Wnt signalosomes proceeds along well-ordered steps and involves regulated intramembrane interactions.

Wnt/β-catenin signaling controls development and adult tissue homeostasis by regulating cell proliferation and cell fate decisions. Wnt binding to its receptors Frizzled (FZD) and low-density lipoprotein-related 6 (LRP6) at the cell surface initiates a signaling cascade that leads to the transcription of Wnt target genes. Upon Wnt binding, the receptors assemble into large complexes called signalosomes that provide a platform for interactions with downstream effector proteins. The molecular basis of signalosome formation and regulation remains elusive, largely due to the lack of tools to analyze its endogenous components. Here, we use internally tagged Wnt3a proteins to isolate and characterize activated, endogenous Wnt receptor complexes by mass spectrometry-based proteomics. We identify the single-span membrane protein TMEM59 as an interactor of FZD and LRP6 and a positive regulator of Wnt signaling. Mechanistically, TMEM59 promotes the formation of multimeric Wnt–FZD assemblies via intramembrane interactions. Subsequently, these Wnt–FZD–TMEM59 clusters merge with LRP6 to form mature Wnt signalosomes. We conclude that the assembly of multiprotein Wnt signalosomes proceeds along well-ordered steps that involve regulated intramembrane interactions.

Targeting the Dvl-1/β-arrestin2/JNK3 interaction disrupts Wnt5a-JNK3 signaling and protects hippocampal CA1 neurons during cerebral ischemia reperfusion

It is well known that Wnt5a activation plays a pivotal role in brain injury and β-arrestin2 induces c-Jun N-terminal kinase (JNK3) activation is involved in neuronal cell death. Nonetheless, the relationship between Wnt5a and JNK3 remains unexplored during cerebral ischemia/reperfusion (I/R). In the present study, we tested the hypothesis that Wnt5a-mediated JNK3 activation via the Wnt5a-Dvl-1-β-arrestin2-JNK3 signaling pathway was correlated with I/R brain injury. We found that cerebral I/R could enhance the assembly of the Dvl-1-β-arrestin2-JNK3 signaling module, Dvl-1 phosphorylation and JNK3 activation. Activated JNK3 could phosphorylate the transcription factor c-Jun, prompt caspase-3 activation and ultimately lead to neuronal cell death. To further explore specifically Wnt5a mediated JNK3 pathway activation in neuronal injury, we used Foxy-5 (a peptide that mimics the effects of Wnt5a) and Box5 (a Wnt5a antagonist) both in vitro and in vivo. AS-β-arrestin2 (an antisense oligonucleotide against β-arrestin2) and RRSLHL (a small peptide that competes with β-arrestin2 for binding to JNK3) were applied to confirm the positive signal transduction effect of the Dvl-1-β-arrestin2-JNK3 signaling module during cerebral I/R. Furthermore, Box5 and the RRSLHL peptide were found to play protective roles in neuronal death both in vivo global and focal cerebral I/R rat models and in vitro oxygen glucose deprivation (OGD) neural cells. In summary, our results indicate that Wnt5a-mediated JNK3 activation participates in I/R brain injury by targeting the Dvl-1-β-arrestin2/JNK3 interaction. Our results also point to the possibility that disrupting Wnt5a-JNK3 signaling pathway may provide a new approach for stroke therapy.

The Nkd EF-hand domain modulates divergent wnt signaling outputs in zebrafish

Wnt proteins regulate diverse biological responses by initiating two general outcomes: β-catenin-dependent transcription and β-catenin-independent activation of signaling cascades, the latter including modulation of calcium and regulation of cytoskeletal dynamics (Planar Cell Polarity, PCP). It has been difficult to elucidate the mechanisms by which Wnt signals are directed to effect one or the other outcome due to shared signaling proteins between the β-catenin-dependent and -independent pathways, such as the Dishevelled binding protein Naked. While all Naked paralogs contain a putative calcium-binding domain, the EF-Hand, Drosophila Naked does not bind calcium. Here we find a lineage-specific evolutionary change within the Drosophila Naked EF-hand that is not shared with other insects or vertebrates. We demonstrate the necessary role of the EF-hand for Nkd localization changes in calcium fluxing cells and using in vivo assays, we identify a role for the zebrafish Naked EF-hand in PCP but not in β-catenin antagonism. In contrast, Drosophila-like Nkd does not function in PCP, but is a robust antagonist of Wnt/β-catenin signaling. This work reveals that the zebrafish Nkd1 EF-hand is essential to balance Wnt signaling inputs and modulate the appropriate outputs, while the Drosophila-like EF-Hand primarily functions in β-catenin signaling.

The N-Terminal Part of the Dishevelled DEP Domain Is Required for Wnt/β-Catenin Signaling in Mammalian Cells

Dishevelled (DVL) proteins are key mediators of the Wnt/β-catenin signaling pathway. All DVL proteins contain three conserved domains: DIX, PDZ, and DEP. There is a consensus in the field that the DIX domain is critical for Wnt/β-catenin signaling, but contradictory evidence regarding the function of the DEP domain exists. It has been difficult, until recently, to test the importance of the DEP domain rigorously because of the interference with endogenous DVL, expressed in all Wnt-responsive cell lines. In this study, we took advantage of DVL knockout (DVL1/DVL2/DVL3 triple knockout) cells fully deficient in Wnt3a-induced signaling events and performed a series of rescue experiments. Using these complementation assays, we analyzed the role of individual DVL isoforms. Further domain mapping of DVL1 showed that both the DVL1 DEP domain and especially its N-terminal region are required and sufficient for Wnt3a-induced phosphorylation of LRP6 and TopFlash reporter activation. On the contrary, multiple DEP domain mutants deficient in the planar cell polarity (PCP) pathway could fully rescue the Wnt3a response. This study provides conclusive evidence that the DVL DEP domain is essential for Wnt/β-catenin signaling in mammalian cells and establishes an experimental system suitable for further functional testing of DVL.

Peroxiredoxin1, a novel regulator of pronephros development, influences retinoic acid and Wnt signaling by controlling ROS levels

Peroxiredoxin1 (Prdx1) is an antioxidant enzyme belonging to the peroxiredoxin family of proteins. Prdx1 catalyzes the reduction of H₂O₂ and alkyl hydroperoxide and plays an important role in different biological processes. Prdx1 also participates in various age-related diseases and cancers. In this study, we investigated the role of Prdx1 in pronephros development during embryogenesis. Prdx1 knockdown markedly inhibited proximal tubule formation in the pronephros and significantly increased the cellular levels of reactive oxygen species (ROS), which impaired primary cilia formation. Additionally, treatment with ROS (H₂O₂) severely disrupted proximal tubule formation, whereas Prdx1 overexpression reversed the ROS-mediated inhibition in proximal tubule formation. Epistatic analysis revealed that Prdx1 has a crucial role in retinoic acid and Wnt signaling pathways during pronephrogenesis. In conclusion, Prdx1 facilitates proximal tubule formation during pronephrogenesis by regulating ROS levels.

Structural basis for Ccd1 auto-inhibition in the Wnt pathway through homomerization of the DIX domain

Wnt signaling plays an important role in governing cell fate decisions. Coiled-coil-DIX1 (Ccd1), Dishevelled (Dvl), and Axin are signaling proteins that regulate the canonical pathway by controlling the stability of a key signal transducer β-catenin. These proteins contain the DIX domain with a ubiquitin-like fold, which mediates their interaction in the β-catenin destruction complex through dynamic head-to-tail polymerization. Despite high sequence similarities, mammalian Ccd1 shows weaker stimulation of β-catenin transcriptional activity compared with zebrafish (z) Ccd1 in cultured cells. Here, we show that the mouse (m) Ccd1 DIX domain displays weaker ability for homopolymerization than that of zCcd1. Furthermore, X-ray crystallographic analysis of mCcd1 and zCcd1 DIX domains revealed that mCcd1 was assembled into a double-helical filament by the insertion of the β1-β2 loop into the head-to-tail interface, whereas zCcd1 formed a typical single-helical polymer similar to Dvl1 and Axin. The mutation in the contact interface of mCcd1 double-helical polymer changed the hydrodynamic properties of mCcd1 so that it acquired the ability to induce Wnt-specific transcriptional activity similar to zCcd1. These findings suggest a novel regulatory mechanism by which mCcd1 modulates Wnt signaling through auto-inhibition of dynamic head-to-tail homopolymerization.

Autoinhibition of Dishevelled protein regulated by its extreme C terminus plays a distinct role in Wnt/β-catenin and Wnt/planar cell polarity (PCP) signaling pathways

Dishevelled (Dvl) is a key intracellular signaling molecule that mediates the activation of divergent Wnt pathways. It contains three highly conserved domains known as DIX, PDZ, and DEP, the functions of which have been well characterized in β-catenin-dependent canonical and β-catenin-independent noncanonical Wnt signaling. The C-terminal region is also highly conserved from invertebrates to vertebrates. However, its function in regulating the activation of different Wnt signals remains unclear. We reported previously that Dvl conformational change triggered by the highly conserved PDZ-binding C terminus is important for the pathway specificity. Here we provide further evidence demonstrating that binding of the C terminus to the PDZ domain results in Dvl autoinhibition in the Wnt signaling pathways. Therefore, the forced binding of the C terminus to the PDZ domain reduces the activity of Dvl in noncanonical Wnt signaling, whereas obstruction of this interaction releases Dvl autoinhibition, impairs its functional interaction with LRP6 in canonical Wnt signaling, and increases its specificity in noncanonical Wnt signaling, which is closely correlated with an enhanced Dvl membrane localization. Our findings highlight the importance of the C terminus in keeping Dvl in an appropriate autoinhibited state, accessible for regulation by other partners to switch pathway specificity. Particularly, the C-terminally tagged Dvl fusion proteins that have been widely used to study the function and cellular localization of Dvl may not truly represent the wild-type Dvl because those proteins cannot be autoinhibited.

A novel role of the organizer gene Goosecoid as an inhibitor of Wnt/PCP-mediated convergent extension in Xenopus and mouse

Goosecoid (Gsc) expression marks the primary embryonic organizer in vertebrates and beyond. While functions have been assigned during later embryogenesis, the role of Gsc in the organizer has remained enigmatic. Using conditional gain-of-function approaches in Xenopus and mouse to maintain Gsc expression in the organizer and along the axial midline, neural tube closure defects (NTDs) arose and dorsal extension was compromised. Both phenotypes represent convergent extension (CE) defects, arising from impaired Wnt/planar cell polarity (PCP) signaling. Dvl2 recruitment to the cell membrane was inhibited by Gsc in Xenopus animal cap assays and key Wnt/PCP factors (RhoA, Vangl2, Prickle, Wnt11) rescued Gsc-mediated NTDs. Re-evaluation of endogenous Gsc functions in MO-mediated gene knockdown frog and knockout mouse embryos unearthed PCP/CE-related phenotypes as well, including cartilage defects in Xenopus and misalignment of inner ear hair cells in mouse. Our results assign a novel function to Gsc as an inhibitor of Wnt/PCP-mediated CE. We propose that in the organizer Gsc represses CE as well: Gsc-expressing prechordal cells, which leave the organizer first, migrate and do not undergo CE like the Gsc-negative notochordal cells, which subsequently emerge from the organizer. In this model, Gsc provides a switch between cell migration and CE, i.e. cell intercalation.

Vertebrate Axial Patterning: From Egg to Asymmetry

The emergence of the bilateral embryonic body axis from a symmetrical egg has been a long-standing question in developmental biology. Historical and modern experiments point to an initial symmetry-breaking event leading to localized Wnt and Nodal growth factor signaling and subsequent induction and formation of a self-regulating dorsal "organizer." This organizer forms at the site of notochord cell internalization and expresses primarily Bone Morphogenetic Protein (BMP) growth factor antagonists that establish a spatiotemporal gradient of BMP signaling across the embryo, directing initial cell differentiation and morphogenesis. Although the basics of this model have been known for some time, many of the molecular and cellular details have only recently been elucidated and the extent that these events remain conserved throughout vertebrate evolution remains unclear. This chapter summarizes historical perspectives as well as recent molecular and genetic advances regarding: (1) the mechanisms that regulate symmetry-breaking in the vertebrate egg and early embryo, (2) the pathways that are activated by these events, in particular the Wnt pathway, and the role of these pathways in the formation and function of the organizer, and (3) how these pathways also mediate anteroposterior patterning and axial morphogenesis. Emphasis is placed on comparative aspects of the egg-to-embryo transition across vertebrates and their evolution. The future prospects for work regarding self-organization and gene regulatory networks in the context of early axis formation are also discussed.

Essential role of the Dishevelled DEP domain in a Wnt-dependent human-cell-based complementation assay

Dishevelled (DVL) assembles Wnt signalosomes through dynamic head-to-tail polymerisation by means of its DIX domain. It thus transduces Wnt signals to cytoplasmic effectors including β-catenin, to control cell fates during normal development, tissue homeostasis and also in cancer. To date, most functional studies of Dishevelled relied on its Wnt-independent signalling activity resulting from overexpression, which is sufficient to trigger polymerisation, bypassing the requirement for Wnt signals. Here, we generate a human cell line devoid of endogenous Dishevelled (DVL1- DVL3), which lacks Wnt signal transduction to β-catenin. However, Wnt responses can be restored by DVL2 stably re-expressed at near-endogenous levels. Using this assay to test mutant DVL2, we show that its DEP domain is essential, whereas its PDZ domain is dispensable, for signalling to β-catenin. Our results imply two mutually exclusive functions of the DEP domain in Wnt signal transduction - binding to Frizzled to recruit Dishevelled to the receptor complex, and dimerising to cross-link DIX domain polymers for signalosome assembly. Our assay avoids the caveats associated with overexpressing Dishevelled, and provides a powerful tool for rigorous functional tests of this pivotal human signalling protein.

Wnt Signalosome Assembly by DEP Domain Swapping of Dishevelled

Extracellular signals are often transduced by dynamic signaling complexes ("signalosomes") assembled by oligomerizing hub proteins following their recruitment to signal-activated transmembrane receptors. A paradigm is the Wnt signalosome, which is assembled by Dishevelled via reversible head-to-tail polymerization by its DIX domain. Its activity causes stabilization of β-catenin, a Wnt effector with pivotal roles in animal development and cancer. How Wnt triggers signalosome assembly is unknown. Here, we use structural analysis, as well as biophysical and cell-based assays, to show that the DEP domain of Dishevelled undergoes a conformational switch, from monomeric to swapped dimer, to trigger DIX-dependent polymerization and signaling to β-catenin. This occurs in two steps: binding of monomeric DEP to Frizzled followed by DEP domain swapping triggered by its high local concentration upon Wnt-induced recruitment into clathrin-coated pits. DEP domain swapping confers directional bias on signaling, and the dimerization provides cross-linking between Dishevelled polymers, illustrating a key principle underlying signalosome formation.

Silica Nanoparticles Target a Wnt Signal Transducer for Degradation and Impair Embryonic Development in Zebrafish

Many types of biocompatible nanomaterials have proven of low cytotoxicity and hold great promise for various applications in nanomedicine. Whereas they generally do not cause apparent organ toxicity or tissue damage in adult animals, it is yet to determine their biological consequences in more general contexts. In this study, we investigate how silica nanoparticles (NPs) affect cellular activities and functions under several physiological or pathological conditions. Although silica NPs are generally regarded as "inert" nanocarriers and widely employed in biomedical studies, we find that they actively affect Wnt signaling in various types of cell lines, diminishing its anti-adipogenic effect in preadipocytes and pro-invasive effect in breast cancer cells, and more significantly, impair Wnt-regulated embryonic development in Zebrafish. We further demonstrate that intracellular silica NPs block Wnt signal transduction in a way resembling signaling molecules. Specifically, silica NPs target the Dvl protein, a key component of Wnt signaling cascade, for lysosomal degradation. As Wnt signaling play significant roles in embryonic development and adipogenesis, the observed physiological effects beyond toxicity imply potential risk of obesity, or developmental defects in somitogenesis and osteogenesis upon exposure to silica NPs. In addition, given the clinical implications of Wnt signaling in tumorigenesis and cancer metastasis, our work also establishes for the first time a molecular link between nanomaterials and the Wnt signaling pathway, which opens new door for novel applications of unmodified silica NPs in targeted therapy for cancers and other critical illness.

PAK5 is auto-activated by a central domain that promotes kinase oligomerization

The present study shows for the first time that self-association of PAK5 in vivo underlies its high basal activity, which contrasts with the inactive state of cellular PAK4. Such PAK5 self-association interferes with the engagement of the auto-inhibitory (AID) with the catalytic domain.

The Dishevelled Protein Family: Still Rather a Mystery After Over 20 Years of Molecular Studies

Dishevelled (Dsh) is a key component of Wnt-signaling pathways and possibly also has other functional requirements. Dsh appears to be a key factor to interpret Wnt signals coming via the Wnt-receptor family, the Frizzled proteins, from the plasma membrane and route them into the correct intracellular pathways. However, how Dsh is regulated to relay signal flow to specific and distinct cellular responses upon interaction with the same Wnt-receptor family remains very poorly understood.

Disinhibition of the HECT E3 ubiquitin ligase WWP2 by polymerized Dishevelled

Dishevelled is a pivot in Wnt signal transduction, controlling both β-catenin-dependent transcription to specify proliferative cell fates, and cell polarity and other non-nuclear events in post-mitotic cells. In response to Wnt signals, or when present at high levels, Dishevelled forms signalosomes by dynamic polymerization. Its levels are controlled by ubiquitylation, mediated by various ubiquitin ligases, including NEDD4 family members that bind to a conserved PPxY motif in Dishevelled (mammalian Dvl1-3). Here, we show that Dvl2 binds to the ubiquitin ligase WWP2 and unlocks its ligase activity from autoinhibition. This disinhibition of WWP2 depends on several features of Dvl2 including its PPxY motif and to a lesser extent its DEP domain, but crucially on the ability of Dvl2 to polymerize, indicating that WWP2 is activated in Wnt signalosomes. We show that Notch intracellular domains are substrates for Dvl-activated WWP2 and their transcriptional activity is consequently reduced, providing a molecular mechanism for cross-talk between Wnt and Notch signalling. These regulatory interactions are conserved in Drosophila whose WWP2 orthologue, Suppressor-of-deltex, downregulates Notch signalling upon activation by Dishevelled in developing wing tissue. Attentuation of Notch signalling by Dishevelled signalosomes could be important during the transition of cells from the proliferative to the post-mitotic state.

The Formin DAAM Functions as Molecular Effector of the Planar Cell Polarity Pathway during Axonal Development in Drosophila

Recent studies established that the planar cell polarity (PCP) pathway is critical for various aspects of nervous system development and function, including axonal guidance. Although it seems clear that PCP signaling regulates actin dynamics, the mechanisms through which this occurs remain elusive. Here, we establish a functional link between the PCP system and one specific actin regulator, the formin DAAM, which has previously been shown to be required for embryonic axonal morphogenesis and filopodia formation in the growth cone. We show that dDAAM also plays a pivotal role during axonal growth and guidance in the adult Drosophila mushroom body, a brain center for learning and memory. By using a combination of genetic and biochemical assays, we demonstrate that Wnt5 and the PCP signaling proteins Frizzled, Strabismus, and Dishevelled act in concert with the small GTPase Rac1 to activate the actin assembly functions of dDAAM essential for correct targeting of mushroom body axons. Collectively, these data suggest that dDAAM is used as a major molecular effector of the PCP guidance pathway. By uncovering a signaling system from the Wnt5 guidance cue to an actin assembly factor, we propose that the Wnt5/PCP navigation system is linked by dDAAM to the regulation of the growth cone actin cytoskeleton, and thereby growth cone behavior, in a direct way.

GATA2 regulates Wnt signaling to promote primitive red blood cell fate

Primitive erythropoiesis is regulated in a non cell-autonomous fashion across evolution from frogs to mammals. In Xenopus laevis, signals from the overlying ectoderm are required to induce the mesoderm to adopt an erythroid fate. Previous studies in our lab identified the transcription factor GATA2 as a key regulator of this ectodermal signal. To identify GATA2 target genes in the ectoderm required for red blood cell formation in the mesoderm, we used microarray analysis to compare gene expression in ectoderm from GATA2 depleted and wild type embryos. Our analysis identified components of the non-canonical and canonical Wnt pathways as being reciprocally up- and down-regulated downstream of GATA2 in both mesoderm and ectoderm. We show that up-regulation of canonical Wnt signaling during gastrulation blocks commitment to a hematopoietic fate while down-regulation of non-canonical Wnt signaling impairs erythroid differentiation. Our results are consistent with a model in which GATA2 contributes to inhibition of canonical Wnt signaling, thereby permitting progenitors to exit the cell cycle and commit to a hematopoietic fate. Subsequently, activation of non-canonical Wnt signaling plays a later role in enabling these progenitors to differentiate as mature red blood cells.

Xenopus Pkdcc1 and Pkdcc2 Are Two New Tyrosine Kinases Involved in the Regulation of JNK Dependent Wnt/PCP Signaling Pathway

Protein Kinase Domain Containing, Cytoplasmic (PKDCC) is a protein kinase which has been implicated in longitudinal bone growth through regulation of chondrocytes formation. Nevertheless, the mechanism by which this occurs remains unknown. Here, we identified two new members of the PKDCC family, Pkdcc1 and Pkdcc2 from Xenopus laevis. Interestingly, our knockdown experiments revealed that these two proteins are both involved on blastopore and neural tube closure during gastrula and neurula stages, respectively. In vertebrates, tissue polarity and cell movement observed during gastrulation and neural tube closure are controlled by Wnt/Planar Cell Polarity (PCP) molecular pathway. Our results showed that Pkdcc1 and Pkdcc2 promote the recruitment of Dvl to the plasma membrane. But surprisingly, they revealed different roles in the induction of a luciferase reporter under the control of Atf2 promoter. While Pkdcc1 induces Atf2 expression, Pkdcc2 does not, and furthermore inhibits its normal induction by Wnt11 and Wnt5a. Altogether our data show, for the first time, that members of the PKDCC family are involved in the regulation of JNK dependent Wnt/PCP signaling pathway.

Wnt Signalling Promotes Actin Dynamics during Axon Remodelling through the Actin-Binding Protein Eps8

Upon arrival at their synaptic targets, axons slow down their growth and extensively remodel before the assembly of presynaptic boutons. Wnt proteins are target-derived secreted factors that promote axonal remodelling and synaptic assembly. In the developing spinal cord, Wnts secreted by motor neurons promote axonal remodelling of NT-3 responsive dorsal root ganglia neurons. Axon remodelling induced by Wnts is characterised by growth cone pausing and enlargement, processes that depend on the re-organisation of microtubules. However, the contribution of the actin cytoskeleton has remained unexplored. Here, we demonstrate that Wnt3a regulates the actin cytoskeleton by rapidly inducing F-actin accumulation in growth cones from rodent DRG neurons through the scaffold protein Dishevelled-1 (Dvl1) and the serine-threonine kinase Gsk3β. Importantly, these changes in actin cytoskeleton occurs before enlargement of the growth cones is evident. Time-lapse imaging shows that Wnt3a increases lamellar protrusion and filopodia velocity. In addition, pharmacological inhibition of actin assembly demonstrates that Wnt3a increases actin dynamics. Through a yeast-two hybrid screen, we identified the actin-binding protein Eps8 as a direct interactor of Dvl1, a scaffold protein crucial for the Wnt signalling pathway. Gain of function of Eps8 mimics Wnt-mediated axon remodelling, whereas Eps8 silencing blocks the axon remodelling activity of Wnt3a. Importantly, blockade of the Dvl1-Eps8 interaction completely abolishes Wnt3a-mediated axonal remodelling. These findings demonstrate a novel role for Wnt-Dvl1 signalling through Eps8 in the regulation of axonal remodeling.

PAPC mediates self/non-self-distinction during Snail1-dependent tissue separation

In Xenopus and zebrafish gastrulae, PAPC attenuates planar cell polarity signaling and controls formation of an adhesive, yet flexible, contact at the ectoderm–mesoderm boundary.

Cleft-like boundaries represent a type of cell sorting boundary characterized by the presence of a physical gap between tissues. We studied the cleft-like ectoderm–mesoderm boundary in Xenopus laevis and zebrafish gastrulae. We identified the transcription factor Snail1 as being essential for tissue separation, showed that its expression in the mesoderm depends on noncanonical Wnt signaling, and demonstrated that it enables paraxial protocadherin (PAPC) to promote tissue separation through two novel functions. First, PAPC attenuates planar cell polarity signaling at the ectoderm–mesoderm boundary to lower cell adhesion and facilitate cleft formation. Second, PAPC controls formation of a distinct type of adhesive contact between mesoderm and ectoderm cells that shows properties of a cleft-like boundary at the single-cell level. It consists of short stretches of adherens junction–like contacts inserted between intermediate-sized contacts and large intercellular gaps. These roles of PAPC constitute a self/non–self-recognition mechanism that determines the site of boundary formation at the interface between PAPC-expressing and -nonexpressing cells.

Dishevelled promotes Wnt receptor degradation through recruitment of ZNRF3/RNF43 E3 ubiquitin ligases

Tumor suppressors ZNRF3 and RNF43 inhibit Wnt signaling through promoting degradation of Wnt coreceptors Frizzled (FZD) and LRP6, and this activity is counteracted by stem cell growth factor R-spondin. The mechanism by which ZNRF3 and RNF43 recognize Wnt receptors remains unclear. Here we uncover an unexpected role of Dishevelled (DVL), a positive Wnt regulator, in promoting Wnt receptor degradation. DVL knockout cells have significantly increased cell surface levels of FZD and LRP6. DVL is required for ZNRF3/RNF43-mediated ubiquitination and degradation of FZD. Physical interaction with DVL is essential for the Wnt inhibitory activity of ZNRF3/RNF43. Binding of FZD through the DEP domain of DVL is required for DVL-mediated downregulation of FZD. Fusion of the DEP domain to ZNRF3/RNF43 overcomes their DVL dependency to downregulate FZD. Our study reveals DVL as a dual function adaptor to recruit negative regulators ZNRF3/RNF43 to Wnt receptors to ensure proper control of pathway activity.

Sulf1 has ligand-dependent effects on canonical and non-canonical Wnt signalling

Wnt signalling plays essential roles during embryonic development and is known to be mis-regulated in human disease. There are many molecular mechanisms that ensure tight regulation of Wnt activity. One such regulator is the heparan-sulfate-specific 6-O-endosulfatase Sulf1. Sulf1 acts extracellularly to modify the structure of heparan sulfate chains to affect the bio-availability of Wnt ligands. Sulf1 could, therefore, influence the formation of Wnt signalling complexes to modulate the activation of both canonical and non-canonical pathways. In this study, we use well-established assays in Xenopus to investigate the ability of Sulf1 to modify canonical and non-canonical Wnt signalling. In addition, we model the ability of Sulf1 to influence morphogen gradients using fluorescently tagged Wnt ligands in ectodermal explants. We show that Sulf1 overexpression has ligand-specific effects on Wnt signalling: it affects membrane accumulation and extracellular levels of tagged Wnt8a and Wnt11b ligands differently, and inhibits the activity of canonical Wnt8a but enhances the activity of non-canonical Wnt11b.

Ras-activated Dsor1 promotes Wnt signaling in Drosophila development

Wnt/Wingless (Wg) and Ras/MAPK signaling both play fundamental roles in growth, cell-fate determination, and when dysregulated, can lead to tumorigenesis. Several conflicting modes of interaction between Ras/MAPK and Wnt signaling have been identified in specific cellular contexts, causing synergistic or antagonistic effects on target genes. We find novel evidence that the dual specificity kinase MEK, Downstream of Raf1 (Dsor1), is required for Wnt signaling. Knockdown of Dsor1 results in loss of Wg target gene expression, as well as reductions in stabilized Armadillo (Arm; Drosophila β-catenin). We have identified a close physical interaction between Dsor1 and Arm, and find that catalytically inactive Dsor1 causes a reduction inactive Arm. These results suggest that Dsor1 normally counteracts the Axin-mediated destruction of Arm. We find that Ras-Dsor1 activity is independent of upstream activation by EGFR, rather it appears to be activated by the insulin-like growth factor receptor to promote Wg signaling. Together our results suggest novel crosstalk between Insulin and Wg signaling via Dsor1.

Targeting the Wnt pathway in human cancers: therapeutic targeting with a focus on OMP-54F28

The Wnt signaling pathways are a group of signal transduction pathways that play an important role in cell fate specification, cell proliferation and cell migration. Aberrant signaling in these pathways has been implicated in the development and progression of multiple cancers by allowing increased proliferation, angiogenesis, survival and metastasis. Activation of the Wnt pathway also contributes to the tumorigenicity of cancer stem cells (CSCs). Therefore, inhibiting this pathway has been a recent focus of cancer research with multiple targetable candidates in development. OMP-54F28 is a fusion protein that combines the cysteine-rich domain of frizzled family receptor 8 (Fzd8) with the immunoglobulin Fc domain that competes with the native Fzd8 receptor for its ligands and antagonizes Wnt signaling. Preclinical models with OMP-54F28 have shown reduced tumor growth and decreased CSC frequency as a single agent and in combination with other chemotherapeutic agents. Due to these findings, a phase 1a study is nearing completion with OMP-54F28 in advanced solid tumors and 3 phase 1b studies have been opened with OMP-54F28 in combination with standard-of-care chemotherapy backbones in ovarian, pancreatic and hepatocellular cancers. This article will review the Wnt signaling pathway, preclinical data on OMP-54F28 and other Wnt pathway inhibitors and ongoing clinical trials.

Wnt5a uses CD146 as a receptor to regulate cell motility and convergent extension

Dysregulation of Wnt signalling leads to developmental defects and diseases. Non-canonical Wnt signalling via planar cell polarity proteins regulates cell migration and convergent extension; however, the underlying mechanisms are poorly understood. Here we report that Wnt5a uses CD146 as a receptor to regulate cell migration and zebrafish embryonic convergent extension. CD146 binds to Wnt5a with the high affinity required for Wnt5a-induced activation of Dishevelled (Dvl) and c-jun amino-terminal kinase (JNK). The interaction between CD146 and Dvl2 is enhanced on Wnt5a treatment. Mutation of the Dvl2-binding region impairs its ability to activate JNK, promote cell migration and facilitate the formation of cell protrusions. Knockdown of Dvls impairs CD146-induced cell migration. Interestingly, CD146 inhibits canonical Wnt signalling by promoting β-catenin degradation. Our results suggest a model in which CD146 acts as a functional Wnt5a receptor in regulating cell migration and convergent extension, turning off the canonical Wnt signalling branch.

Avian facial morphogenesis is regulated by c-Jun N-terminal kinase/planar cell polarity (JNK/PCP) wingless-related (WNT) signaling

Wingless-related proteins (WNTs) regulate extension of the central axis of the vertebrate embryo (convergent extension) as well as morphogenesis of organs such as limbs and kidneys. Here, we asked whether WNT signaling directs facial morphogenesis using a targeted approach in chicken embryos. WNT11 is thought to mainly act via β-catenin-independent pathways, and little is known about its role in craniofacial development. RCAS::WNT11 retrovirus was injected into the maxillary prominence, and the majority of embryos developed notches in the upper beak or the equivalent of cleft lip. Three-dimensional morphometric analysis revealed that WNT11 prevented lengthening of the maxillary prominence, which was due in part to decreased proliferation. We next determined, using a series of luciferase reporters, that WNT11 strongly induced JNK/planar cell polarity signaling while repressing the β-catenin-mediated pathway. The activation of the JNK-ATF2 reporter was mediated by the DEP domain of Dishevelled. The impacts of altered signaling on the mesenchyme were assessed by implanted Wnt11- or Wnt3a-expressing cells (activates β-catenin pathway) into the maxillary prominence or by knocking down endogenous WNT11 with RNAi. Host cells were attracted to Wnt11 donor cells. In contrast, cells exposed to Wnt3a or the control cells did not migrate. Cells in which endogenous WNT11 was knocked down were more oriented and shorter than those exposed to exogenous WNT11. The data suggest that JNK/planar cell polarity WNT signaling operates in the face to regulate several morphogenetic events leading to lip fusion.

Migrating cells mediate long-range WNT signaling

In amniotes, it is widely accepted that WNTs secreted by the dorsal neural tube form a concentration gradient that regulates early somite patterning and myotome organization. Here we demonstrate in the chicken embryo that WNT protein is not secreted to act at a distance, but rather loaded onto migrating neural crest cells that deliver it to somites. Inhibiting neural crest migration or ablating their population has a profound impact on the WNT response in somites. Furthermore, we show that a central player in the efficient delivery of WNT to somites is the heparan sulfate proteoglycan GPC4, expressed by neural crest. Together, our data describe a novel mode of signaling whereby WNT proteins hitch a ride on migratory neural crest cells to pattern the somites at a distance from its source.

The E3 ligase RNF185 negatively regulates osteogenic differentiation by targeting Dvl2 for degradation

Osteoblast plays a pivotal role in bone metabolism and bone remodeling by mediating bone formation and regulating the activity of osteoclast. Clarifying the regulators and regulation mechanisms of osteogenic differentiation of mesenchymal stem cells (MSCs) and pre-osteoblasts will provide tremendous promise for bone repair and bone regeneration. RNF185 was identified as a candidate of endogenous suppressors of osteogenic specification in human mesenchymal stem cells (hMSCs). Here we show that RNF185 down regulates osteogenic differentiation of mouse calvaria-derived MC3T3-E1 cells, confirmed by quantitative real-time-PCR (qRT-PCR) and alkaline phosphatase (ALP) activity. Further we confirm that RNF185 interacts with dishevelled2 (Dvl2), a key mediator of Wnt signaling pathway. Overexpression of RNF185 decreases the exogenous and endogenous level of Dvl2, promotes the ubiquitination and degradation of Dvl2 and inhibits Wnt signaling, which is evident from the down-regulation of β-catenin mediated transcriptional activity. And Dvl2 reverses the effect of RNF185 on osteogenic differentiation of MC3T3-E1 cells. Taken together, our results indicate that RNF185 negatively regulates osteogenesis through the degradation of Dvl2 and down-regulation of canonical Wnt signaling pathway and suggest a possible therapeutic target in osteoporosis.