Molecular and cellular mechanisms underlying neural tube defects in the loop-tail mutant mouse

A vertebrate Vangl2 translational variant required for planar cell polarity

First described in the milkweed bug Oncopeltus fasciatus, planar cell polarity (PCP) is a developmental process essential for embryogenesis and development of polarized structures in Metazoans. This signaling pathway involves a set of evolutionarily conserved genes encoding transmembrane (Vangl, Frizzled, Celsr) and cytoplasmic (Prickle, Dishevelled) molecules. Vangl2 is of major importance in embryonic development as illustrated by its pivotal role during neural tube closure in human, mouse, Xenopus, and zebrafish embryos. Here, we report on the molecular and functional characterization of a Vangl2 isoform, Vangl2-Long, containing an N-terminal extension of about 50 aa, which arises from an alternative near-cognate AUA translation initiation site, lying upstream of the conventional start codon. While missing in Vangl1 paralogs and in all invertebrates, including Drosophila, this N-terminal extension is conserved in all vertebrate Vangl2 sequences. We show that Vangl2-Long belongs to a multimeric complex with Vangl1 and Vangl2. Using morpholino oligonucleotides to specifically knockdown Vangl2-Long in Xenopus, we found that this isoform is functional and required for embryo extension and neural tube closure. Furthermore, both Vangl2 and Vangl2-Long must be correctly expressed for the polarized distribution of the PCP molecules Pk2 and Dvl1 and for centriole rotational polarity in ciliated epidermal cells. Altogether, our study suggests that Vangl2-Long significantly contributes to the pool of Vangl2 molecules present at the plasma membrane to maintain PCP in vertebrate tissues.

An interaction between OTULIN and SCRIB uncovers roles for linear ubiquitination in planar cell polarity

Planar cell polarity (PCP) plays critical roles in developmental and homeostatic processes. Membrane presentation of PCP complexes containing Van Gogh-like (VANGL) transmembrane proteins is central to PCP and can be directed by the scaffold protein scribble (SCRIB). The role atypical linear ubiquitin (Met1-Ub) chains might play in PCP is unknown. Here, HEK293 cell-based interactomic analyses of the Met1-Ub deubiquitinase OTULIN revealed that OTULIN can interact with SCRIB. Moreover, Met1-Ub chains associated with VANGL2 and PRICKLE1, but not SCRIB, can direct VANGL2 surface presentation. Mouse embryos lacking Otulin showed variable neural tube malformations, including rare open neural tubes, a deficit associated with PCP disruption in mice. In Madin-Darby canine kidney cells, in which the enrichment of VANGL2-GFP proteins at cell-cell contacts represents activated PCP complexes, endogenous OTULIN was recruited to these sites. In the human MDA-MB-231 breast cancer cell model, OTULIN loss caused deficits in Wnt5a-induced filopodia extension and trafficking of transfected HA-VANGL2. Taken together, these findings support a role for linear (de)ubiquitination in PCP signaling. The association of Met1-Ub chains with PCP complex components offers new opportunities for integrating PCP signaling with OTULIN-dependent immune and inflammatory pathways.

The Helicobacter pylori CagA oncoprotein disrupts Wnt/PCP signaling and promotes hyperproliferation of pyloric gland base cells

Helicobacter pylori strains that deliver the oncoprotein CagA into gastric epithelial cells are the major etiologic agents of upper gastric diseases including gastric cancer. CagA promotes gastric carcinogenesis through interactions with multiple host proteins. Here, we show that CagA also disrupts Wnt-dependent planar cell polarity (Wnt/PCP), which orients cells within the plane of an epithelium and coordinates collective cell behaviors such as convergent extension to enable epithelial elongation during development. Ectopic expression of CagA in Xenopus laevis embryos impaired gastrulation, neural tube formation, and axis elongation, processes driven by convergent extension movements that depend on the Wnt/PCP pathway. Mice specifically expressing CagA in the stomach epithelium had longer pyloric glands and mislocalization of the tetraspanin proteins VANGL1 and VANGL2 (VANGL1/2), which are critical components of Wnt/PCP signaling. The increased pyloric gland length was due to hyperproliferation of cells at the gland base, where Lgr5⁺ stem and progenitor cells reside, and was associated with fewer differentiated enteroendocrine cells. In cultured human gastric epithelial cells, the N terminus of CagA interacted with the C-terminal cytoplasmic tails of VANGL1/2, which impaired Wnt/PCP signaling by inducing the mislocalization of VANGL1/2 from the plasma membrane to the cytoplasm. Thus, CagA may contribute to the development of gastric cancer by subverting a Wnt/PCP-dependent mechanism that restrains pyloric gland stem cell proliferation and promotes enteroendocrine differentiation.

Scribble mutation disrupts convergent extension and apical constriction during mammalian neural tube closure

Morphogenesis of the vertebrate neural tube occurs by elongation and bending of the neural plate, tissue shape changes that are driven at the cellular level by polarized cell intercalation and cell shape changes, notably apical constriction and cell wedging. Coordinated cell intercalation, apical constriction, and wedging undoubtedly require complex underlying cytoskeletal dynamics and remodeling of adhesions. Mutations of the gene encoding Scribble result in neural tube defects in mice, however the cellular and molecular mechanisms by which Scrib regulates neural cell behavior remain unknown. Analysis of Scribble mutants revealed defects in neural tissue shape changes, and live cell imaging of mouse embryos showed that the Scrib mutation results in defects in polarized cell intercalation, particularly in rosette resolution, and failure of both cell apical constriction and cell wedging. Scrib mutant embryos displayed aberrant expression of the junctional proteins ZO-1, Par3, Par6, E- and N-cadherins, and the cytoskeletal proteins actin and myosin. These findings show that Scribble has a central role in organizing the molecular complexes regulating the morphomechanical neural cell behaviors underlying vertebrate neurulation, and they advance our understanding of the molecular mechanisms involved in mammalian neural tube closure.

Mutations associated with human neural tube defects display disrupted planar cell polarity in Drosophila

Planar cell polarity (PCP) and neural tube defects (NTDs) are linked, with a subset of NTD patients found to harbor mutations in PCP genes, but there is limited data on whether these mutations disrupt PCP signaling in vivo. The core PCP gene Van Gogh (Vang), Vangl1/2 in mammals, is the most specific for PCP. We thus addressed potential causality of NTD-associated Vangl1/2 mutations, from either mouse or human patients, in Drosophila allowing intricate analysis of the PCP pathway. Introducing the respective mammalian mutations into Drosophila Vang revealed defective phenotypic and functional behaviors, with changes to Vang localization, post-translational modification, and mechanistic function, such as its ability to interact with PCP effectors. Our findings provide mechanistic insight into how different mammalian mutations contribute to developmental disorders and strengthen the link between PCP and NTD. Importantly, analyses of the human mutations revealed that each is a causative factor for the associated NTD.

Vangl2 interaction plays a role in the proteasomal degradation of Prickle2

The PET and LIM domain-containing protein, Prickle, plays a key role in planar cell polarity (PCP) in Drosophila. It has been reported that mutations in the PRICKLE2 gene, which encodes one of the human orthologues of Prickle, are associated with human diseases such as epilepsy and autism spectrum disorder. To develop preventive and therapeutic strategies for these intractable diseases, we studied the regulation of Prickle2 protein levels in transfected HEK293T cells. Prickle2 levels were negatively regulated by a physical interaction with another PCP protein, Van Gogh-like 2 (Vangl2). The Vangl2-mediated reduction in Prickle2 levels was, at least in part, relieved by proteasome inhibitors or by functional inhibition of the Cullin-1 E3 ubiquitin ligase. Furthermore, the expression of Vangl2 enhanced the polyubiquitination of Prickle2. This ubiquitination was partially blocked by co-expression of a ubiquitin mutant, which cannot be polymerised through their Lys48 residue to induce target proteins toward proteasomal degradation. Together, these results suggest that Prickle2 is polyubiquitinated by the Vangl2 interaction in a Cullin-1-dependent manner to limit its expression levels. This regulation may play a role in the local and temporal fine-tuning of Prickle protein levels during PCP signal-dependent cellular behaviours.

Identification and characterization of a novel chemically induced allele at the planar cell polarity gene Vangl2

Planar cell polarity (PCP) signaling controls a number of morphogenetic processes including convergent extension during gastrulation and neural tube formation. Defects in this pathway cause neural tube defects (NTD), the most common malformations of the central nervous system. The Looptail (Lp) mutant mouse was the first mammalian mutant implicating a PCP gene (Vangl2) in the pathogenesis of NTD. We report on a novel chemically induced mutant allele at Vangl2 called Curly Bob that causes a missense mutation p.Ile268Asn (I268N) in the Vangl2 protein. This mutant segregates in a semi-dominant fashion with heterozygote mice displaying a looped tail appearance, bobbing head, and a circling behavior. Homozygote mutant embryos suffer from a severe form of NTD called craniorachischisis, severe PCP defects in the inner hair cells of the cochlea and posterior cristae, and display a distinct defect in retinal axon guidance. This mutant genetically interacts with the Lp allele (Vangl2 ^S464N ) in neural tube development and inner ear hair cell polarity. The Vangl2^I268N protein variant is expressed at very low levels in affected neural and retinal tissues of mutant homozygote embryos. Biochemical studies show that Vangl2^I268N exhibits impaired targeting to the plasma membrane and accumulates in the endoplasmic reticulum. The Vangl2^I268N variant no longer physically interacts with its PCP partner DVL3 and has a reduced protein half-life. This mutant provides an important model for dissecting the role of Vangl2 in the development of the neural tube, establishment of polarity of sensory cells of the auditory and vestibular systems, and retinal axon guidance.

Wnt-induced Vangl2 phosphorylation is dose-dependently required for planar cell polarity in mammalian development

Planar cell polarity (PCP) is an evolutionarily conserved essential mechanism that provides directional information to control and coordinate polarized cellular and tissue behavior during embryonic development. Disruption of PCP leads to severe morphological defects in vertebrates and its dysregulation results in a variety of human diseases such as neural tube defects and skeletal dysplasia. PCP is governed by a set of highly conserved core proteins that are asymmetrically localized at the cell surface throughout the polarized tissues. The uniform directionality of PCP is established by global cues, such as Wg/Wnt signaling gradients that break the original symmetrical localization of core PCP proteins including Vang/Vangl and Fz/Fzd. However, the exact mechanism remains elusive. In this study, we found that Vangl2 phosphorylation, which was previously identified to be induced by Wnt5a signaling, is required for Vangl2 functions in mammalian PCP in multiple tissues. The in vivo activities of Vangl2 are determined by its phosphorylation level. Phospho-mutant Vangl2 exhibits dominant negative effects, whereas Vangl2 with reduced phosphorylation is hypomorphic. We show that Vangl2 phosphorylation is essential for its uniform polarization pattern. Moreover, serine/threonine kinases CK1ɛ and CK1δ are redundantly required for Wnt5a-induced Vangl2 phosphorylation. Dvl family members are also required for Wnt5a-induced Vangl2 phosphorylation by enhancing the interaction of CK1 and Vangl2. These findings demonstrate that induction of Vangl protein phosphorylation plays an essential role in transducing Wnt5a signaling to establish PCP in mammalian development, suggesting a phosphorylation-regulated "Vangl activity gradient" model in addition to the well-documented "Fz activity gradient" model in Wnt/PCP signaling.

The Planar Cell Polarity Transmembrane Protein Vangl2 Promotes Dendrite, Spine and Glutamatergic Synapse Formation in the Mammalian Forebrain

The transmembrane protein Vangl2, a key regulator of the Wnt/planar cell polarity (PCP) pathway, is involved in dendrite arbor elaboration, dendritic spine formation and glutamatergic synapse formation in mammalian central nervous system neurons. Cultured forebrain neurons from Vangl2 knockout mice have simpler dendrite arbors, fewer total spines, less mature spines and fewer glutamatergic synapse inputs on their dendrites than control neurons. Neurons from mice heterozygous for a semidominant Vangl2 mutation have similar but not identical phenotypes, and these phenotypes are also observed in Golgi-stained brain tissue from adult mutant mice. Given increasing evidence linking psychiatric pathophysiology to these subneuronal sites and structures, our findings underscore the relevance of core PCP proteins including Vangl2 to the underlying biology of major mental illnesses and their treatment.

Identification of p62/SQSTM1 as a component of non-canonical Wnt VANGL2-JNK signalling in breast cancer

The non-canonical Wnt/planar cell polarity (Wnt/PCP) pathway plays a crucial role in embryonic development. Recent work has linked defects of this pathway to breast cancer aggressiveness and proposed Wnt/PCP signalling as a therapeutic target. Here we show that the archetypal Wnt/PCP protein VANGL2 is overexpressed in basal breast cancers, associated with poor prognosis and implicated in tumour growth. We identify the scaffold p62/SQSTM1 protein as a novel VANGL2-binding partner and show its key role in an evolutionarily conserved VANGL2–p62/SQSTM1–JNK pathway. This proliferative signalling cascade is upregulated in breast cancer patients with shorter survival and can be inactivated in patient-derived xenograft cells by inhibition of the JNK pathway or by disruption of the VANGL2–p62/SQSTM1 interaction. VANGL2–JNK signalling is thus a potential target for breast cancer therapy.

Defects in non-canonical Wnt/planar cell polarity signalling have recently been linked to breast cancer aggressiveness. Puvirajesinghe et al. identify VANGL2, p62/SQSTM1 and JNK as important players in this pathway which may be amenable to therapeutic intervention in breast cancer.

A novel electrochemical immunosensor based on the rGO-TEPA-PTC-NH₂ and AuPt modified C₆₀ bimetallic nanoclusters for the detection of Vangl1, a potential biomarker for dysontogenesis

The aberrant expression of Vangl1 is highly correlated with dysontogenesis, especially for neural tube defects. Therefore, the ultrasensitive detection of Vangl1 would provide a new approach for the specific early diagnostics in dysembryoplasia. However, no quantitative detection method is currently available. Herein, we describe the development of a new approach to fill this assay gap. We utilized C60-templated AuPt bimetallic nanoclusters for signal amplification because the promising C60 nanomaterial provides a large surface area for the in site reduction of bimetallic nanocomposites as well as excellent conductivity. To further amplify the electrochemical signal, reduced graphene oxide-tetraethylene pentamine (rGO-TEPA) and a derivative of 3,4,9,10-perylenetetracarboxylicdianhydride (PTC-NH2) were selected for modification of the electrode to provide more amino groups for the immobilization of antibodies and to enhance the conductivity. The electrochemical signal was primarily derived from the catalysis of H2O2 by C60-AuPt. Chronoamperometry was applied to record the electrochemical signals. Under optimal conditions, the prepared immunosensor exhibited a wide linear range from 0.1 pg mL(-1) to 450 pg mL(-1) and a low detection limit of 0.03 pg mL(-1). Moreover, the proposed method exhibited good stability and recovery, suggesting its potential for use in clinical research.

Vangl2 regulates E-cadherin in epithelial cells

E-cadherin belongs to the classic cadherin subfamily of calcium-dependent cell adhesion molecules and is crucial for the formation and function of epithelial adherens junctions. In this study, we demonstrate that Vangl2, a vertebrate regulator of planar cell polarity (PCP), controls E-cadherin in epithelial cells. E-cadherin co-immunoprecipitates with Vangl2 from embryonic kidney extracts, and this association is also observed in transfected fibroblasts. Vangl2 enhances the internalization of E-cadherin when overexpressed. Conversely, the quantitative ratio of E-cadherin exposed to the cell surface is increased in cultured renal epithelial cells derived from Vangl2(Lpt/+) mutant mice. Interestingly, Vangl2 is also internalized through protein traffic involving Rab5- and Dynamin-dependent endocytosis. Taken together with recent reports regarding the transport of Frizzled3, MMP14 and nephrin, these results suggest that one of the molecular functions of Vangl2 is to enhance the internalization of specific plasma membrane proteins with broad selectivity. This function may be involved in the control of intercellular PCP signalling or in the PCP-related rearrangement of cell adhesions.

Independent mutations at Arg181 and Arg274 of Vangl proteins that are associated with neural tube defects in humans decrease protein stability and impair membrane targeting

In vertebrates, Vangl proteins play important roles during embryogenesis, including establishing planar polarity and coordinating convergent extension movements. In mice, homozygosity for mutations in the Vangl1 and Vangl2 genes or combined heterozygosity for Vangl1/Vangl2 mutations causes the very severe neural tube defect (NTD) craniorachischisis. Recently, a number of patient-specific VANGL1 and VANGL2 protein mutations have been identified in familial and sporadic cases of mild and severe forms of NTDs. The biochemical nature of pathological effects in these mutations remains unknown. Of interest are two arginine residues, R181 and R274, that are highly conserved in Vangl protein homologues and found to be independently mutated in VANGL1 (R181Q and R274Q) and VANGL2 (R177H and R270H) in human cases of NTDs. The cellular and biochemical properties of R181Q and R274Q were established in transfected MDCK kidney epithelial cells and compared to those of wild-type (WT) Vangl1. Compared to that of WT, these mutations displayed impaired targeting to the plasma membrane and were instead detected in an intracellular endomembrane compartment that was positive for the endoplasmic reticulum. R181Q and R274Q showed impaired stability with significant reductions in measured half-lives from >20 h for WT protein to 9 and 5 h, respectively. These mutations have a cellular and biochemical phenotype that is indistinguishable from that of Vangl mutations known to cause craniorachichisis in mice (Lp). These results strongly suggest that R181 and R274 play critical roles in Vangl protein function and that their mutations cause neural tube defects in humans.

The intracellular carboxyl terminal domain of Vangl proteins contains plasma membrane targeting signals

Vangl1 and Vangl2 are integral membrane proteins that play a critical role in establishing planar cell polarity (PCP) in epithelial cells and are required for convergent extension (CE) movements during embryogenesis. Their proper targeting to the plasma membrane (PM) is required for function. We created discrete deletions at the amino and carboxy termini of Vangl1 and monitored the effect of the mutations on PM targeting in Madin-Darby canine kidney cells. Our results show that the Vangl1 amino terminus lacks PM targeting determinants, and these are restricted to the carboxy terminus, including the predicted PDZBM motif at the C-terminus.

Recurrent anencephaly: a case report and examination of the VANGL1 and FOXN1 genes

We report a new and rare case of recurrent anencephaly in a family with no other apparent abnormalities. The karyotypes of the family and all affected subjects were normal. Thorough mutational analyses of VANGL1 of chromosome 1p13.1 and FOXN1 of chromosome 17q11-q12, genes that are associated with phenotypes of the anencephaly spectrum, unfortunately did not disclose any DNA variations in an affected fetus of this family. The etiology of recurrent anencephaly in this family is therefore due to mutations in genes yet to be discovered, perhaps of the planar cell polarity pathway, or to possible environmental gestational factors during development.

Syndecan 4 interacts genetically with Vangl2 to regulate neural tube closure and planar cell polarity

Syndecan 4 (Sdc4) is a cell-surface heparan sulfate proteoglycan (HSPG) that regulates gastrulation, neural tube closure and directed neural crest migration in Xenopus development. To determine whether Sdc4 participates in Wnt/PCP signaling during mouse development, we evaluated a possible interaction between a null mutation of Sdc4 and the loop-tail allele of Vangl2. Sdc4 is expressed in multiple tissues, but particularly in the non-neural ectoderm, hindgut and otic vesicles. Sdc4;Vangl2^Lp compound mutant mice have defective spinal neural tube closure, disrupted orientation of the stereocilia bundles in the cochlea and delayed wound healing, demonstrating a strong genetic interaction. In Xenopus, co-injection of suboptimal amounts of Sdc4 and Vangl2 morpholinos resulted in a significantly greater proportion of embryos with defective neural tube closure than each individual morpholino alone. To probe the mechanism of this interaction, we overexpressed or knocked down Vangl2 function in HEK293 cells. The Sdc4 and Vangl2 proteins colocalize, and Vangl2, particularly the Vangl2^Lp mutant form, diminishes Sdc4 protein levels. Conversely, Vangl2 knockdown enhances Sdc4 protein levels. Overall HSPG steady-state levels were regulated by Vangl2, suggesting a molecular mechanism for the genetic interaction in which Vangl2^Lp/+ enhances the Sdc4-null phenotype. This could be mediated via heparan sulfate residues, as Vangl2^Lp/+ embryos fail to initiate neural tube closure and develop craniorachischisis (usually seen only in Vangl2^Lp/Lp) when cultured in the presence of chlorate, a sulfation inhibitor. These results demonstrate that Sdc4 can participate in the Wnt/PCP pathway, unveiling its importance during neural tube closure in mammalian embryos.

Molecular characterisation of endogenous Vangl2/Vangl1 heteromeric protein complexes

BACKGROUND

Mutations in the Planar Cell Polarity (PCP) core gene Vangl2 cause the most severe neural tube defects (NTD) in mice and humans. Genetic studies show that the Vangl2 gene genetically interacts with a close homologue Vangl1. How precisely Vangl2 and Vangl1 proteins interact and crosstalk has remained a difficult issue to address, with the main obstacle being the accurate discrimination of the two proteins, which share close sequence homology. Experimental evidence previously presented has been sparse and addressed with ectopically expressed proteins or with antibodies unable to biochemically discriminate Vangl1 from Vangl2, therefore giving rise to unclear results.

METHODOLOGY AND MAIN FINDINGS

A highly specific monoclonal anti-Vangl2 antibody was generated and rigorously tested on both recombinant and extracted Vangl2 using surface plasmon resonance (SPR) analysis, western blot, and immunoprecipitation experiments. This antibody efficiently affinity-purified Vangl2 from cell lysates and allowed the unambiguous identification of endogenous Vangl2 by proteomic analysis. Vangl1 was also present in Vangl2 immunoprecipitates, establishing the first biochemical evidence for the existence of Vangl2/Vangl1 heterodimers at an endogenous level. Epitope-tagged Vangl2 and Vangl1 confirmed that both proteins interact and colocalize at the plasma membrane. The Vangl2 antibody is able to acutely assess differential expression levels of Vangl2 protein in culture cell lines, as corroborated with gene expression analysis. We characterised Vangl2 expression in the cochlea of homozygous and heterozygous Lp mutant mice bearing a point mutation within the C-terminal Vangl2 region that leads to profound PCP defects. Our antibody could detect much lower levels of Vangl2(Lp) protein in mutant mice compared to the wild type mice.

CONCLUSION

Our results provide an in-depth biochemical characterisation of the interaction observed between Vangl paralogues.

Novel VANGL1 Gene Mutations in 144 Slovakian, Romanian and German Patients with Neural Tube Defects

Neural tube defects (NTDs) are a group of congenital malformations of the central nervous system occurring at an average rate of 1 per 1,000 human pregnancies worldwide. Numerous genetic and environmental factors are discussed to be relevant in their etiology. In mice, mutants in >200 genes including the planar cell polarity (PCP) pathway are known to cause NTDs, and recently, heterozygous mutations in the human VANGL1 gene have been described in a small subset of patients with NTDs. We performed a VANGL1 mutation analysis in 144 unrelated individuals with NTDs from Slovakia, Romania and Germany and identified 3 heterozygous missense mutations: c.613G>A (p.Gly205Arg) with an open spina bifida (lumbosacral meningomyelocele), c.557G>A (p.Arg186His) with a closed spina bifida (tethered cord and spinal lipoma) and c.518G>A (p.Arg173His) with an unknown NTD. The c.613G>A mutation was also found in a healthy sibling. None of the mutations were described previously. Findings support that heterozygous VANGL1 mutations represent hypomorphs or conditional mutants predisposing to NTDs and occur at a frequency of approximately 2.1% of open and closed spinal NTDs. The mutations (p.Arg173His, p.Arg186His, p.Gly205Arg) modified conserved regions of the VANGL1 protein and shared similarities with previously described mutants, providing further evidence for the presence of mutational hot spots in these patients.

An expanding role of Vangl proteins in embryonic development

The mammalian Vangl1 and Vangl2 genes were discovered a decade ago through their association with neural tube defects, in particular the presence of Vangl2 mutations in independent alleles of the mouse mutant Loop-tail (Lp), a mouse model of the severe neural tube defect craniorachischisis. Vangl1 and Vangl2 variants have also been detected in familial and sporadic cases of spina bifida. Vangl proteins are highly conserved in evolution with relatives in flies, and distant invertebrates and vertebrates. In these organisms, they play a central role in planar cell polarity (PCP) and convergent extension (CE) movements. Over the past decade, these functional characteristics have also been established for mammalian Vangl genes. The careful analysis of mouse Vangl genes mutants has showed that these genes and the associated PCP pathway and CE movements are involved in many unexpected developmental processes, from morphogenesis of different tissues, left-right asymmetry, asymmetric cell division, and organization of many epithelial structures, as well as positioning and function of cellular appendages. Genetic studies in double mutants and biochemical studies of interacting proteins have started to elucidate the molecular pathways in which Vangl proteins participate and that regulate these complex events.

Mutations in the planar cell polarity genes CELSR1 and SCRIB are associated with the severe neural tube defect craniorachischisis

Craniorachischisis (CRN) is a severe neural tube defect (NTD) resulting from failure to initiate closure, leaving the hindbrain and spinal neural tube entirely open. Clues to the genetic basis of this condition come from several mouse models, which harbor mutations in core members of the planar cell polarity (PCP) signaling pathway. Previous studies of humans with CRN failed to identify mutations in the core PCP genes, VANGL1 and VANGL2. Here, we analyzed other key PCP genes: CELSR1, PRICKLE1, PTK7, and SCRIB, with the finding of eight potentially causative mutations in both CELSR1 and SCRIB. Functional effects of these unique or rare human variants were evaluated using known protein-protein interactions as well as subcellular protein localization. While protein interactions were not affected, variants from five of the 36 patients exhibited a profound alteration in subcellular protein localization, with diminution or abolition of trafficking to the plasma membrane. Comparable effects were seen in the crash and spin cycle mouse Celsr1 mutants, and the line-90 mouse Scrib mutant. We conclude that missense variants in CELSR1 and SCRIB may represent a cause of CRN in humans, as in mice, with defective PCP protein trafficking to the plasma membrane a likely pathogenic mechanism.

Extracorporeal shock wave therapy promotes cell proliferation and collagen synthesis of primary cultured human tenocytes

PURPOSE

The aim of this study was to investigate whether the effects of extracorporeal shock wave therapy (ESWT) could affect the behavior of primary cultured human tenocytes over a 12-day period.

METHODS

In this controlled laboratory study, primary human tenocytes were established from semitendinosus tendons collected from 3 patients undergoing arthroscopic anterior cruciate ligament (ACL) reconstruction. Cell viability, overall cell morphology, cell proliferation, and collagen synthesis following ESWT have been evaluated.

RESULTS

ESWT significantly interferes with the overall cell morphology, by impairing dedifferentiation of the cells. Furthermore, a shock wave-mediated growth-promoting effect was measured by the MTT (tetrazolium) colorimetric assay and by the proliferation marker Ki67. Lastly, a significant increase in collagen (mainly type I) synthesis by ESWT-tenocytes compared with control cells was found.

CONCLUSIONS

Shock wave treatment promoted cell growth and collagen synthesis of primary cultured human tenocytes. The clinical benefits of ESWT may be ascribed to an increased efficiency of tendon repair after injury.

A novel hypomorphic Looptail allele at the planar cell polarity Vangl2 gene

Vangl2 forms part of the planar cell polarity signalling pathway and is the gene defective in the Looptail (Lp) mouse mutant. Two previously described alleles, Lp and Lp(m1Jus) , segregate in a semi-dominant fashion, with heterozygotes displaying the looped-tail appearance, while homozygotes show the neural tube defect called craniorachischisis. Here, we report a novel experimentally induced allele, Lp(m2Jus) , that carries a missense mutation, R259L, in Vangl2. This mutation was specific to the Lp phenotype and absent from both parental strains and 28 other inbred strains. Notably, this mutation segregates in a recessive manner with all heterozygotes appearing normal and 47% of homozygotes showing a looped-tail. Homozygous Lp(m2Jus) embryos showed spina bifida in 12%. Lp(m2Jus) genetically interacts with Lp with 77% of compound heterozygotes displaying craniorachischisis. Vangl2(R259L) behaved like the wild-type allele in overexpression and morpholino knockdown/rescue assays in zebrafish embryos. These data suggest that Lp(m2Jus) represents a new hypomorphic allele of Lp.

A single GATA factor plays discrete, lineage specific roles in ascidian heart development

GATA family transcription factors are core components of the vertebrate heart gene network. GATA factors also contribute to heart formation indirectly through regulation of endoderm morphogenesis. However, the precise impact of GATA factors on vertebrate cardiogenesis is masked by functional redundancy within multiple lineages. Early heart specification in the invertebrate chordate Ciona intestinalis is similar to that of vertebrates but only one GATA factor, Ci-GATAa, is expressed in the heart progenitor cells and adjacent endoderm. Here we delineate precise, tissue specific contributions of GATAa to heart formation. Targeted repression of GATAa activity in the heart progenitors perturbs their transcriptional identity. Targeted repression of endodermal GATAa function disrupts endoderm morphogenesis. Subsequently, the bilateral heart progenitors fail to fuse at the ventral midline. The resulting phenotype is strikingly similar to cardia bifida, as observed in vertebrate embryos when endoderm morphogenesis is disturbed. These findings indicate that GATAa recapitulates cell-autonomous and non-cell-autonomous roles performed by multiple, redundant GATA factors in vertebrate cardiogenesis.

Loss of membrane targeting of Vangl proteins causes neural tube defects

In the mouse, the loop-tail mutation (Lp) causes a very severe neural tube defect, which is caused by mutations in the Vangl2 gene. In mammals, Vangl1 and Vangl2 code for integral membrane proteins that assemble into asymmetrically distributed membrane complexes that establish planar cell polarity in epithelial cells and that regulate convergent extension movements during embryogenesis. To date, VANGL are the only genes in which mutations cause neural tube defects in humans. Three independently arising Lp alleles have been described for Vangl2: D255E, S464N, and R259L. Here we report a common mechanism for both the naturally occurring Lp (S464N) and a novel ENU-induced mutation Lp(m2Jus)(R259L). We show that the S464N and R259L variants stably expressed in polarized MDCK kidney cells fail to reach the plasma membrane, their site for biological function. The mutant variants are retained intracellularly in the endoplasmic reticulum, colocalizing with ER chaperone calreticulin. Furthermore, the mutants also show a dramatically reduced half-life of ∼3 h, compared to ∼22 h for the wild-type protein, and are rapidly degraded in a proteasome-dependent and MG132-sensitive fashion. Coexpressing individually the three known allelic Lp variants with the wild-type protein does not influence the localization of the WT at the plasma membrane, suggesting that the codominant nature of the Lp trait in vivo is due to haploid insufficiency caused by a partial loss of function in a gene dosage-dependent pathway, as opposed to a dominant negative phenotype. Our study provides a biochemical framework for the study of recently identified mutations in hVANGL1 and hVANGL2 in sporadic or familial cases of neural tube defects.

The planar cell polarity gene Vangl2 is required for mammalian kidney-branching morphogenesis and glomerular maturation

The planar cell polarity (PCP) pathway, incorporating non-canonical Wnt signalling, controls embryonic convergent (CE) extension, polarized cell division and ciliary orientation. It also limits diameters of differentiating renal tubules, with mutation of certain components of the pathway causing cystic kidneys. Mutations in mouse Vangl genes encoding core PCP proteins cause neural tube defects (NTDs) and Vangl2 mutations also impair branching of embryonic mouse lung airways. Embryonic metanephric kidneys also undergo branching morphogenesis and Vangl2 is known to be expressed in ureteric bud/collecting duct and metanephric mesenchymal/nephron lineages. These observations led us to investigate metanephroi in Vangl2 mutant mice, Loop-tail (Lp). Although ureteric bud formation is normal in Vangl2^Lp/Lp embryos, subsequent in vivo and in vitro branching morphogenesis is impaired. Null mutant kidneys are short, consistent with a CE defect. Differentiating glomerular epithelia express several PCP genes (Vangl1/2, Celsr1, Scrib, Mpk1/2 and Fat4) and glomeruli in Vangl2^Lp/Lp fetuses are smaller and contain less prominent capillary loops than wild-type littermates. Furthermore, Vangl2^Lp/+ kidneys had modest reduction in glomerular numbers postnatally. Vangl2^Lp/Lp metanephroi contained occasional dilated tubules but no overt cystic phenotype. These data show for the first time that a PCP gene is required for normal morphogenesis of both the ureteric bud and metanephric mesenchyme-derived structures. It has long been recognized that certain individuals with NTDs are born with malformed kidneys, and recent studies have discovered VANGL mutations in some NTD patients. On the basis of our mutant mouse study, we suggest that PCP pathway mutations should be sought when NTD and renal malformation co-exist.