The planar cell polarity effector gene Fuz regulates ciliogenesis and Fuz loss of function studies reveal an array of embryonic phenotypes. However, cilia defects can affect many signaling pathways and, in humans, cilia defects underlie several craniofacial anomalies. To address this, we analyzed the craniofacial phenotype and signaling responses of the Fuz−/− mice. We demonstrate a unique role for Fuz in regulating both Hedgehog (Hh) and Wnt/β-catenin signaling during craniofacial development. Fuz expression first appears in the dorsal tissues and later in ventral tissues and craniofacial regions during embryonic development coincident with cilia development. The Fuz−/− mice exhibit severe craniofacial deformities including anophthalmia, agenesis of the tongue and incisors, a hypoplastic mandible, cleft palate, ossification/skeletal defects and hyperplastic malformed Meckel's cartilage. Hh signaling is down-regulated in the Fuz null mice, while canonical Wnt signaling is up-regulated revealing the antagonistic relationship of these two pathways. Meckel's cartilage is expanded in the Fuz−/− mice due to increased cell proliferation associated with the up-regulation of Wnt canonical target genes and decreased non-canonical pathway genes. Interestingly, cilia development was decreased in the mandible mesenchyme of Fuz null mice, suggesting that cilia may antagonize Wnt signaling in this tissue. Furthermore, expression of Fuz decreased expression of Wnt pathway genes as well as a Wnt-dependent reporter. Finally, chromatin IP experiments demonstrate that β-catenin/TCF-binding directly regulates Fuz expression. These data demonstrate a new model for coordination of Hh and Wnt signaling and reveal a Fuz-dependent negative feedback loop controlling Wnt/β-catenin signaling.
The planar cell polarity effector Fuz is required for normal particle dynamics of the intraflagellar transport system, specifically in the retrograde transport of proteins.
Cilia play key roles in development and homeostasis, and defects in cilia structure or function lead to an array of human diseases. Ciliogenesis is accomplished by the intraflagellar transport (IFT) system, a set of proteins governing bidirectional transport of cargoes within ciliary axonemes. In this paper, we present a novel platform for in vivo analysis of vertebrate IFT dynamics. Using this platform, we show that the planar cell polarity (PCP) effector Fuz was required for normal IFT dynamics in vertebrate cilia, the first evidence directly linking PCP to the core machinery of ciliogenesis. Further, we show that Fuz played a specific role in trafficking of retrograde, but not anterograde, IFT proteins. These data place Fuz in the small group of known IFT effectors outside the core machinery and, additionally, identify Fuz as a novel cytoplasmic effector that differentiates between the retrograde and anterograde IFT complexes.
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.
The planar cell polarity (PCP) signaling system governs many aspects of polarized cell behavior. Here, we use an in vivo model of vertebrate mucociliary epithelial development to show that Dishevelled (Dvl) is essential for the apical positioning of basal bodies. We find that Dvl and Inturned mediate the activation of the Rho GTPase specifically at basal bodies, and that these three proteins together mediate the docking of basal bodies to the apical plasma membrane. Moreover, we find that the docking involves a Dvl-dependent association of basal bodies with membrane-bound vesicles and with the vesicle-trafficking protein, Sec8. Once docked, Dvl and Rho are once again required for the planar polarization of basal bodies that underlies directional beating of cilia. These results demonstrate novel functions for PCP signaling components and suggest that a common signaling appratus governs both apical docking and planar polarization of basal bodies.
In the phytopathogenic fungus Ustilago maydis, pheromone-mediated cell fusion is a prerequisite for the generation of the infectious dikaryon. The pheromone signal elevates transcription of the pheromone genes and elicits formation of conjugation hyphae. Cyclic AMP and mitogen-activated protein kinase (MAPK) signaling are involved in this process. The MAPK cascade is presumed to be composed of Ubc4 (MAPK kinase kinase), Fuz7 (MAPK kinase), and Ubc3/Kpp2 (MAPK). We isolated the kpp4 gene and found it to be allelic to ubc4. Epistasis analyses with constitutively active alleles of kpp4 and fuz7 substantiate that Kpp4, Fuz7, and Kpp2/Ubc3 are components of the same module. Moreover, we demonstrate that Fuz7 activates Kpp2 and shows interactions in vitro. Signaling via this cascade regulates expression of pheromone-responsive genes, presumably through acting on the transcription factor Prf1. Interestingly, the same cascade is needed for conjugation tube formation, and this process does not involve Prf1. In addition, fuz7 as well as kpp4 deletion strains are nonpathogenic, while kpp2 deletion mutants are only attenuated in pathogenesis. Here we show that strains expressing the unphosphorylatable allele kpp2T182A/Y184F are severely affected in tumor induction and display defects in early infection-related differentiation.
Ustilago maydis is a Basidiomycete fungus that exhibits a yeast-like nonpathogenic form and a dikaryotic filamentous pathogenic form. Generation of these two forms is controlled by two mating type loci, a and b. The fungus undergoes additional morphological transitions in the plant that result in formation of a third cell type, the teliospore. The fuz1 gene is necessary for this developmental program. Here we report cloning and sequencing of fuz1 and show that it contains an open reading frame with coding capacity for a protein of 1421 amino acids. The Fuz1 protein belongs to the family of MYND Zn finger domain proteins. We generate a null mutation in strains of opposite mating type and show that fuz1 is necessary for conjugation tube formation, a morphological transition that occurs in response to pheromones. We generate fuz1− diploid strains heterozygous at a and b and show that fuz1 is also necessary for postfusion events (maintenance of filamentous growth). We also demonstrate that fuz1 is necessary for cell morphogenesis of the yeast-like cell: normal cell length, location and number of septa, cell separation and constriction of the neck region. Fuz1 is also required for cell wall integrity and to prevent secretion of a dark pigment. We propose that the MYND domain may interact with different proteins to regulate cell morphogenesis.
cell separation; conjugation tube; filamentous growth; pigment production; septum location
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.
Planar Cell Polarity (PCP) signaling is a key regulator of epithelial morphogenesis, including neural tube closure and the orientation of inner ear sensory hair cells, and is mediated by a conserved noncanonical Wnt pathway. Ptk7 is a novel vertebrate-specific regulator of PCP, yet the mechanisms by which Ptk7 regulates mammalian epithelial PCP remain poorly understood.
Here we show that, in the mammalian auditory epithelium, Ptk7 is not required for membrane recruitment of Dishevelled 2; Ptk7 and Frizzled3/Frizzled6 receptors act in parallel and have opposing effects on hair cell PCP. Mosaic analysis identified a requirement of Ptk7 in neighboring supporting cells for hair cell PCP. Ptk7 and the noncanonical Wnt pathway differentially regulate a contractile myosin II network near the apical surface of supporting cells. We provide evidence that this apical myosin II network exerts polarized contractile tension on hair cells to align their PCP, as revealed by asymmetric junctional recruitment of vinculin, a tension-sensitive actin binding protein. In Ptk7 mutants, compromised myosin II activity resulted in loss of planar asymmetry and reduced junctional localization of vinculin. By contrast, vinculin planar asymmetry and stereociliary bundle orientation were restored in Fz3−/−; Ptk7−/− double mutants.
These findings suggest that PTK7 acts in conjunction with the noncanonical Wnt pathway to orient epithelial PCP through modulation of myosin-II based contractile tension between supporting cells and hair cells.
PTK7; Frizzled3; non-muscle myosin II; vinculin; planar cell polarity; sensory hair cells; supporting cells; contractile tension
CK1-γ/gilgamesh spatially limits the planar cell polarity–regulated process of trichome formation in Drosophila through its effect on polarized vesicle recycling.
Cellular morphogenesis, including polarized outgrowth, promotes tissue shape and function. Polarized vesicle trafficking has emerged as a fundamental mechanism by which protein and membrane can be targeted to discrete subcellular domains to promote localized protrusions. Frizzled (Fz)/planar cell polarity (PCP) signaling orchestrates cytoskeletal polarization and drives morphogenetic changes in such contexts as the vertebrate body axis and external Drosophila melanogaster tissues. Although regulation of Fz/PCP signaling via vesicle trafficking has been identified, the interplay between the vesicle trafficking machinery and downstream terminal PCP-directed processes is less established. In this paper, we show that Drosophila CK1-γ/gilgamesh (gish) regulates the PCP-associated process of trichome formation through effects on Rab11-mediated vesicle recycling. Although the core Fz/PCP proteins dictate prehair formation broadly, CK1-γ/gish restricts nucleation to a single site. Moreover, CK1-γ/gish works in parallel with the Fz/PCP effector multiple wing hairs, which restricts prehair formation along the perpendicular axis to Gish. Our findings suggest that polarized Rab11-mediated vesicle trafficking regulated by CK1-γ is required for PCP-directed processes.
Dishevelled (Dsh) is a cytoplasmic multidomain protein that is required for all known branches of the Wnt signalling pathway1–3. The Frizzled/planar cell polarity (Fz/PCP) signalling branch requires an asymmetric cortical localization of Dsh, but this process remains poorly understood. Using a genome-wide RNA interference (RNAi) screen in Drosophila melanogaster cells, we show that Dsh membrane localization is dependent on the Na+/H+ exchange activity of the plasma membrane exchanger Nhe2. Manipulating Nhe2 expression levels in the eye causes PCP defects, and Nhe2 interacts genetically with Fz. Our data show that the binding and surface recruitment of Dsh by Fz is pH- and charge-dependent. We identify a polybasic stretch within the Dsh DEP domain that binds to negatively charged phospholipids and appears to be mechanistically important. Dsh recruitment by Fz can be abolished by converting these basic amino-acid residues into acidic ones, as in the mutant, DshKR/E. In vivo, the DshKR/E(2×) mutant with two substituted residues fails to associate with the membrane during active PCP signalling but rescues canonical Wnt signalling defects in a dsh-background. These results suggest that direct interaction between Fz and Dsh is stabilized by a pH and charge-dependent interaction of the DEP domain with phospholipids. This stabilization is particularly important for the PCP signalling branch and, thus, promotes specific pathway selection in Wnt signalling.
Although growing body of evidence supports that Wnt-Frizzled signaling controls axon guidance from vertebrates to worms, whether and how this is mediated by planar cell polarity (PCP) signaling remains elusive. We show here that the core PCP components are required for Wnt5a-stimulated outgrowth and anterior-posterior guidance of commissural axons. Dishevelled1 can inhibit PCP signaling by increasing hyperphosphorylation of Frizzled3 and preventing its internalization. Vangl2 antagonizes that by reducing Frizzled3 phosphorylation and promotes internalization. In commissural axon growth cones, Vangl2 is predominantly localized on the plasma membrane and is highly enriched on the tips of the filopodia as well as in patches of membrane where new filopodia emerge. Taken together, we propose that the antagonistic functions of Vangl2 and Dvl1 (over Frizzled3 hyperphosphorylation and endocytosis) allows sharpening of PCP signaling locally on the tips of the filopodia for sensing directional cues, Wnts, eventually causing turning of growth cones.
The regular array of distally pointing hairs on the mature Drosophila wing is evidence for the fine control of Planar Cell Polarity (PCP) during wing development. Normal wing PCP requires both the Frizzled (Fz) PCP pathway and the Fat/Dachsous (Ft/Ds) pathway, although the functional relationship between these pathways remains under debate. There is strong evidence that the Fz PCP pathway signals twice during wing development, and we have previously presented a Bidirectional-Biphasic Fz PCP signaling model which proposes that the Early and Late Fz PCP signals are in different directions and employ different isoforms of the Prickle protein. The goal of this study was to investigate the role of the Ft/Ds pathway in the context of our Fz PCP signaling model. Our results allow us to draw the following conclusions: (1) The Early Fz PCP signals are in opposing directions in the anterior and posterior wing and converge precisely at the site of the L3 wing vein. (2) Increased or decreased expression of Ft/Ds pathway genes can alter the direction of the Early Fz PCP signal without affecting the Late Fz PCP signal. (3) Lowfat, a Ft/Ds pathway regulator, is required for the normal orientation of the Early Fz PCP signal but not the Late Fz PCP signal. (4) At the time of the Early Fz PCP signal there are symmetric gradients of dachsous (ds) expression centered on the L3 wing vein, suggesting Ds activity gradients may orient the Fz signal. (5) Localized knockdown or over-expression of Ft/Ds pathway genes shows that boundaries/gradients of Ft/Ds pathway gene expression can redirect the Early Fz PCP signal specifically. (6) Altering the timing of ds knockdown during wing development can separate the role of the Ft/Ds pathway in wing morphogenesis from its role in Early Fz PCP signaling.
Planar Cell Polarity (PCP) describes the orientation of a cell within the plane of a cell layer. The precise control of PCP has been shown to be vital for normal development in both vertebrates and invertebrates, and failures of PCP have been implicated in human disease. Studies in the fruit fly Drosophila have identified two genetic pathways, the Frizzled and Fat/Dachsous pathways, that are required to organize PCP, although the functional relationship between the two pathways remains unresolved. We have previously proposed a model of Frizzled pathway activity in the Drosophila wing that invokes two consecutive Frizzled signaling events oriented in different directions. The Early and Late Fz PCP signals use different isoforms of the Prickle protein. The goal of this study was to define the activity of the Fat/Dachsous pathway in the context of our Frizzled signaling model. Our results suggest that the Fat/Dachsous pathway has a different functional relationship with each of the Frizzled signaling events. Specifically, we find that by altering Fat/Dachsous pathway activity, we can reorient the Early Frizzled signal without affecting the Late Frizzled signal. This suggests that the functional relationship between the Fat/Dachsous pathway and the Frizzled pathway can vary, even between consecutive Frizzled signaling events within the same set of cells.
The planar cell polarity (PCP) signaling pathway governs collective cell movements duringvertebrate embryogenesis, and certain PCP proteins are also implicated in the assembly ofcilia. The septins are cytoskeletal proteins controlling behaviors such as cell division and migration. Here, we identified control of septin localization by the PCP protein Fritz as a crucial control point for both collective cell movement and ciliogenesis in Xenopus embryos. We also linked mutations in human Fritz to Bardet-Biedl and Meckel-Gruber syndromes, a notable link given that other genes mutated in these syndromes also influence collective cell movement and ciliogenesis. These findings shed light on the mechanisms by which fundamental cellular machinery, such as the cytoskeleton, is regulated during embryonic development and human disease.
Members of the Frizzled (Fz) family of seven-pass transmembrane receptors are required for the transduction of both Wnt-Fz/β-catenin and Fz/Planar Cell Polarity (PCP) signals. Although both pathways transduce signals via interactions between Fz and the cytoplasmic protein Dishevelled (Dsh), each pathway has specific and distinct effectors. One explanation for the pathway specificity is that signal-induced conformational changes result in unique Fz-Dsh interactions. Our mutational analyses of Fz-Dsh activities in vivo do however not support this model, since both pathways are affected by all mutations tested. Alternatively, the interaction of Fz or Dsh with other proteins could modulate the signaling outcome. We examined the role of a Dsh-binding PCP molecule, Diego (Dgo), in both Wnt-Fz/β-catenin and Fz/PCP signaling. Both loss-of-function and gain-of-function results suggest that Dgo promotes Fz-Dsh/PCP signaling at the expense of Wnt-Fz/β-catenin signaling. Our data suggest that Dgo sequesters Dsh to a functionally distinct Fz/PCP signaling compartment within the cell.
Wnt ligands and Frizzled (Fz) receptors have been shown to activate multiple intracellular signaling pathways. Activation of the Wnt–β-catenin pathway has been described in greatest detail, but it has been reported that Wnts and Fzs also activate vertebrate planar cell polarity (PCP) and Wnt–Ca2+ pathways. Although the intracellular protein Dishevelled (Dsh) plays a dual role in both the Wnt–β-catenin and the PCP pathways, its potential involvement in the Wnt–Ca2+ pathway has not been investigated. Here we show that a Dsh deletion construct, XDshΔDIX, which is sufficient for activation of the PCP pathway, is also sufficient for activation of three effectors of the Wnt–Ca2+ pathway: Ca2+ flux, PKC, and calcium/calmodulin-dependent protein kinase II (CamKII). Furthermore, we find that interfering with endogenous Dsh function reduces the activation of PKC by Xfz7 and interferes with normal heart development. These data suggest that the Wnt–Ca2+ pathway utilizes Dsh, thereby implicating Dsh as a component of all reported Fz signaling pathways.
Dishevelled; PKC; Wnt; calcium; signal transduction
Upon activation by Wnt, the Frizzled receptor is internalized in a process that requires the recruitment of Dishevelled. We describe a novel interaction between Dishevelled2 (Dvl2) and μ2-adaptin, a subunit of the clathrin adaptor AP-2; this interaction is required to engage activated Frizzled4 with the endocytic machinery and for its internalization. The interaction of Dvl2 with AP-2 requires simultaneous association of the DEP domain and a peptide YHEL motif within Dvl2 with the C terminus of μ2. Dvl2 mutants in the YHEL motif fail to associate with μ2 and AP-2, and prevent Frizzled4 internalization. Corresponding Xenopus Dishevelled mutants show compromised ability to interfere with gastrulation mediated by the planar cell polarity (PCP) pathway. Conversely, a Dvl2 mutant in its DEP domain impaired in PCP signaling exhibits defective AP-2 interaction and prevents the internalization of Frizzled4. We suggest that the direct interaction of Dvl2 with AP-2 is important for Frizzled internalization and Frizzled/PCP signaling.
During vertebrate gastrulation, the body axis is established by coordinated and directional movements of cells that include epiboly, involution, and convergence and extension (C&E). Recent work implicates a non-canonical Wnt/planar cell polarity (PCP) pathway in the regulation of C&E. The Drosophila atypical cadherin Flamingo (Fmi) and its vertebrate homologue Celsr, a 7-pass transmembrane protein with extracellular cadherin repeats, regulate several biological processes, including C&E, cochlear cell orientation, axonal pathfinding and neuronal migration. Fmi/Celsr can function together with molecules involved in PCP, such as Frizzled (Fz) and Dishevelled (Dsh), but there is also some evidence that it may act as a cell adhesion molecule in a PCP-pathway-independent manner. We show that abrogation of Celsr activity in zebrafish embryos results in epiboly defects that appear to be independent of the requirement for Celsr in PCP signalling during C&E. Using a C-terminal truncated form of Celsr that inhibits membrane presentation of wild-type Celsr through its putative pro-region, a hanging drop assay reveals that cells from embryos with compromised Celsr activity have different cohesive properties from wild-type cells. It is disruption of this ability of Celsr to affect cell cohesion that primarily leads to the in vivo epiboly defects. In addition, Lyn-Celsr, in which the intracellular domain of Celsr is fused to a membrane localisation signal (Lyn), inhibits Fz-Dsh complex formation during Wnt/PCP signalling without affecting epiboly. Fmi/Celsr therefore has a dual role in mediating two separate morphogenetic movements through its roles in mediating cell cohesion and Wnt/PCP signalling during zebrafish gastrulation.
Epiboly; Convergent extension; Planar cell polarity; Celsr; Flamingo; Drosophila; Zebrafish
Dishevelled/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 - DshY473F behaves like a PCP-specific allele; and (3) defects associated with the PCP specific dsh1 allele, DshK417M, 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.
Phospho-protein; Dishevelled; Wingless; Wnt-signaling; Signaling specificity; PCP
In mammals, the skin can form complex global and local patterns to meet diverse functional requirements in different parts of the body. To date, the fundamental principles that underlie skin patterning remain poorly understood due to the involvement of multiple interacting processes. Genes involved in the planar cell polarity (PCP) signalling pathway, which is capable of polarizing cells within the planar plane of an epithelium, can control the orientation and differentiation of hair follicles, underlining their involvement in skin pattern formation. Here, we summarize recent progress that has been made to understand the PCP signalling pathway and its function in mammalian skin, including its role in hair follicle morphogenesis, ciliogenesis, and wound healing. We argue that dissecting PCP signalling in the context of hair follicle formation might reveal many as-yet-undiscovered functions for PCP in the development, homeostasis, and regeneration of skin.
Planar cell polarity; PCP; Skin; Hair follicle; Pattern
Planar cell polarity (PCP) describes the orientation of a cell within the plane of an epithelial cell layer. During tissue development, epithelial cells normally align their PCP so that they face in the same direction. This alignment allows cells to move in a common direction, or to generate structures with a common orientation. A classic system for studying the coordination of epithelial PCP is the developing Drosophila wing. The alignment of epithelial PCP during pupal wing development allows the production of an array of cell hairs that point towards the wing tip. Multiple studies have established that the Frizzled (Fz) PCP signaling pathway coordinates wing PCP. Recently, we have found that the same pathway also controls the formation of ridges on the Drosophila wing membrane. However, in contrast to hair polarity, ridge orientation differs between the anterior and posterior wing. How can the Fz PCP pathway generate a different relationship between hair and ridge orientation in different parts of the wing? In this Extra View article, we discuss membrane ridge development drawing upon our recent PLoS Genetics paper and other, published and unpublished, data. We also speculate upon how our findings impact the ongoing debate concerning the interaction of the Fz PCP and Fat/Dachsous pathways in the control of PCP.
Drosophila; frizzled; prickle; Dachsous; wing; membrane
Planar cell polarity (PCP) signaling polarises cells along tissue axes. Although pathways involved are becoming better understood, outstanding issues include; (i) existence/identity of cues that orchestrate global polarisation in tissues, and (ii) the generality of the link between polarisation of primary cilia and asymmetric localisation of PCP proteins. Mammalian lenses are mainly comprised of epithelial-derived fiber cells. Concentrically arranged fibers are precisely aligned as they elongate along the anterior-posterior axis and orientate towards lens poles where they meet fibers from other segments to form characteristic sutures. We show that lens exhibits PCP, with each fiber cell having a apically situated cilium and in most cases this is polarised towards the anterior pole. Frizzled and other PCP proteins are also asymmetrically localised along the equatorial-anterior axis. Mutations in core PCP genes Van Gogh-like 2 and Celsr1 perturb oriented fiber alignment and suture formation. Suppression of the PCP pathway by overexpressing Sfrp2, shows that whilst local groups of fibers are often similarly oriented, they lack global orientation; consequently when local groups of fibers with different orientations meet they form multiple, small, ectopic suture-like configurations. This indicates that this extracellular inhibitor disrupts a global polarising signal that utilises a PCP-mediated mechanism to coordinate the global alignment and orientation of fibers to lens poles.
Growth factors; Lens development; Planar cell polarity; Frizzled; Primary cilia; Secreted frizzled-related protein; Wnt; Loop-tail
Understanding how planar cell polarity (PCP) is established, maintained, and coordinated in migrating cell populations is an important area of research with implications for both embryonic morphogenesis and tumor cell invasion. We recently reported that the PCP protein Vang-like 2 (VANGL2) regulates the endocytosis and cell surface level of membrane type-1 matrix metalloproteinase (MMP14 or MT1-MMP). Here, we further discuss these findings in terms of extracellular matrix (ECM) remodeling, cell migration, and zebrafish gastrulation. We also demonstrate that VANGL2 function impacts the focal degradation of ECM by human cancer cells including the formation or stability of invadopodia. Together, our findings implicate MMP14 as a downstream effector of VANGL2 signaling and suggest a model whereby the regulation of pericellular proteolysis is a fundamental aspect of PCP in migrating cells.
extracellular matrix; fibronectin; gastrulation; invadopodia; migration; MMP14/MT1-MMP; planar cell polarity; VANGL2; zebrafish
The Frizzled receptor and Dishevelled effector regulate mitotic spindle orientation in both vertebrates and invertebrates, but how Dishevelled orients the mitotic spindle is unknown. Using the Drosophila S2 cell "induced polarity" system, we find that Dishevelled cortical polarity is sufficient to orient the spindle, and that Dishevelled's DEP domain mediates this function. This domain binds a C-terminal domain of Mud (the Drosophila NuMA ortholog), and Mud is required for Dishevelled-mediated spindle orientation. In Drosophila, Frizzled-Dishevelled planar cell polarity (PCP) orients the sensory organ precursor (pI) spindle along the anterior-posterior axis. We show that Dishevelled and Mud colocalize at the posterior cortex of pI, Mud localization at the posterior cortex requires Dsh, and Mud loss-of-function randomizes spindle orientation. During zebrafish gastrulation, the Wnt11-Frizzled-Dishevelled PCP pathway orients spindles along the animal-vegetal axis, and reducing NuMA levels disrupts spindle orientation. Overall, we describe a Frizzled-Dishevelled-NuMA pathway that orients division from Drosophila to vertebrates.
Vangl2 was identified as the gene defective in the Looptail mouse model for neural tube defects (NTDs). This gene forms part of the planar cell polarity pathway, also called the non-canonical Frizzled/Dishevelled pathway, which mediates the morphogenetic process of convergent extension essential for proper gastrulation and neural tube formation in vertebrates. Genetic defects in PCP signaling have strongly been associated with NTDs in mouse models. To assess the role of VANGL2 in the complex etiology of NTDs in humans, we resequenced this gene in a large multi-ethnic cohort of 673 familial and sporadic NTD patients, including 453 open spina bifida and 202 closed spinal NTD cases. Six novel rare missense mutations were identified in 7 patients, five of which were affected with closed spinal NTDs. This suggests that VANGL2 mutations may predispose to NTDs in approximately 2.5% of closed spinal NTDs (5 in 202), at a frequency that is significantly different from that of 0.4% (2 in 453) detected in open spina bifida patients (P=0.027). Our findings strongly implicate VANGL2 in the genetic causation of spinal NTDs in a subset of patients and provide additional evidence for a pathogenic role of PCP signaling in these malformations.
VANGL2; neural tube defects; planar cell polarity
Inversin is a ciliary protein that critically regulates developmental processes and tissue homeostasis in vertebrates, partly through the degradation of Dishevelled (Dvl) proteins to coordinate Wnt signaling in planar cell polarity (PCP). Here, we investigated the role of Inversin in coordinating cell migration, which highly depends on polarity processes at the single-cell level, including the spatial and temporal organization of the cytoskeleton as well as expression and cellular localization of proteins in leading edge formation of migrating cells. Using cultures of mouse embryonic fibroblasts (MEFs) derived from inv−/− and inv+/+ animals, we confirmed that both inv−/− and inv+/+ MEFs form primary cilia, and that Inversin localizes to the primary cilium in inv+/+ MEFs. In wound healing assays, inv−/− MEFs were severely compromised in their migratory ability and exhibited cytoskeletal rearrangements, including distorted lamellipodia formation and cilia orientation. Transcriptome analysis revealed dysregulation of Wnt signaling and of pathways regulating actin organization and focal adhesions in inv−/− MEFs as compared to inv+/+ MEFs. Further, Dvl-1 and Dvl-3 localized to MEF primary cilia, and β-catenin/Wnt signaling was elevated in inv−/− MEFs, which moreover showed reduced ciliary localization of Dvl-3. Finally, inv−/− MEFs displayed dramatically altered activity and localization of RhoA, Rac1, and Cdc42 GTPases, and aberrant expression and targeting of the Na+/H+ exchanger NHE1 and ezrin/radixin/moesin (ERM) proteins to the edge of cells facing the wound. Phosphorylation of β-catenin at the ciliary base and formation of well-defined lamellipodia with localization and activation of ERM to the leading edge of migrating cells were restored in inv−/− MEFs expressing Inv-GFP. Collectively, our findings point to the significance of Inversin in controlling cell migration processes, at least in part through transcriptional regulation of genes involved in Wnt signaling and pathways that control cytoskeletal organization and ion transport.