Loss of Dact1 disrupts planar cell polarity signaling by altering dishevelled activity and leads to posterior malformation in mice

Inhibition of sphingosine-1-phosphate receptor-2 attenuates idiopathic pulmonary fibrosis by preventing its binding to dapper1 in bronchial epithelial cells

BACKGROUND AND PURPOSE

Activation of the sphingosine-1-phosphate receptor-2 (S1P2 receptor) promotes idiopathic pulmonary fibrosis (IPF). However, the mechanisms associated with IPF development via S1P2 receptor signalling are poorly understood and no S1P2 receptor antagonists have been approved for clinical use.

EXPERIMENTAL APPROACH

Western blotting and immunohistochemical assays analysed inflammatory factors and epithelial-mesenchymal transition (EMT) markers. Co-immunoprecipitation and immunofluorescence analysed the binding of S1P2 receptor to dapper1 (Dpr1) and cyclic AMP response-binding protein 1 (CREB1). X-ray-based computed tomography diagnosed IPF in bleomycin (BLM)-treated mice. Barometric whole-body plethysmography tested pulmonary function of mice. Masson's trichrome and Sirius red staining analysed extracellular matrix deposition. Enzyme-linked immunosorbent assays analysed inflammatory factors and hydroxyproline.

KEY RESULTS

Activation of S1P2 receptors promoted IPF through the binding of S1P2 receptor to Dpr1, decreasing dishevelled (Dvl) degradation to accumulate β-catenin. The β-catenin accumulated in the nucleus, upregulating its target genes by binding to T-cell factor/lymphoid enhancer factor. The binding of S1P2 receptor to Dpr1 also led to S1P2 receptor translocation to the nucleus, where it promoted EMT by activating CREB1. BLM-induced IPF in mice was characterised by activated-S1P2 receptor signalling. Inhibition of S1P2 receptor prevented the binding of S1P2 receptor to Dpr1, resulting in decreased β-catenin accumulation and blocking nuclear translocation of S1P2 receptor. The S1P2 receptor antagonist S118 was more effective than pirfenidone in attenuating IPF through anti-inflammatory, anti-fibrosis, and anti-EMT effects.

CONCLUSIONS AND IMPLICATIONS

Activation of S1P2 receptors promotes IPF through the binding of S1P2 receptor to Dpr1 and the nuclear translocation of S1P2 receptor to activate CREB1. Thus, the S1P2 receptor antagonist S118 has potential clinical application in attenuating IPF.

Dact1 induces Dishevelled oligomerization to facilitate binding partner switch and signalosome formation during convergent extension

Convergent extension (CE) is a universal morphogenetic engine that promotes polarized tissue extension. In vertebrates, CE is regulated by non-canonical Wnt ligands signaling through "core" proteins of the planar cell polarity (PCP) pathway, including the cytoplasmic protein Dishevelled (Dvl), receptor Frizzled (Fz) and tetraspan protein Van gogh-like (Vangl). PCP was discovered in Drosophila to coordinate polarity in the plane of static epithelium, but does not regulate CE in flies. Existing evidence suggests that adopting PCP for CE might be a vertebrate-specific adaptation with incorporation of new regulators. Herein we use Xenopus to investigate Dact1, a chordate-specific protein. Dact1 induces Dvl to form oligomers that dissociate from Vangl, but stay attached with Fz as signalosome-like clusters and co-aggregate with Fz into protein patches upon non-canonical Wnt induction. Functionally, Dact1 antagonizes Vangl, and synergizes with wild-type Dvl but not its oligomerization-defective mutants. We propose that, by promoting Dvl oligomerization, Dact1 couples Dvl binding partner switch with signalosome-like cluster formation to initiate non-canonical Wnt signaling during vertebrate CE.

Heterozygous variants in the teashirt zinc finger homeobox 3 (TSHZ3) gene in human congenital anomalies of the kidney and urinary tract

Around 180 genes have been associated with congenital anomalies of the kidney and urinary tract (CAKUT) in mice, and represent promising novel candidate genes for human CAKUT. In whole-exome sequencing data of two siblings with genetically unresolved multicystic dysplastic kidneys (MCDK), prioritizing variants in murine CAKUT-associated genes yielded a rare variant in the teashirt zinc finger homeobox 3 (TSHZ3) gene. Therefore, the role of TSHZ3 in human CAKUT was assessed. Twelve CAKUT patients from 9/301 (3%) families carried five different rare heterozygous TSHZ3 missense variants predicted to be deleterious. CAKUT patients with versus without TSHZ3 variants were more likely to present with hydronephrosis, hydroureter, ureteropelvic junction obstruction, MCDK, and with genital anomalies, developmental delay, overlapping with the previously described phenotypes in Tshz3-mutant mice and patients with heterozygous 19q12-q13.11 deletions encompassing the TSHZ3 locus. Comparable with Tshz3-mutant mice, the smooth muscle layer was disorganized in the renal pelvis and thinner in the proximal ureter of the nephrectomy specimen of a TSHZ3 variant carrier compared to controls. TSHZ3 was expressed in the human fetal kidney, and strongly at embryonic day 11.5-14.5 in mesenchymal compartments of the murine ureter, kidney, and bladder. TSHZ3 variants in a 5' region were more frequent in CAKUT patients than in gnomAD samples (p < 0.001). Mutant TSHZ3 harboring N-terminal variants showed significantly altered SOX9 and/or myocardin binding, possibly adversely affecting smooth muscle differentiation. Our results provide evidence that heterozygous TSHZ3 variants are associated with human CAKUT, particularly MCDK, hydronephrosis, and hydroureter, and, inconsistently, with specific extrarenal features, including genital anomalies.

Genetic requirement of dact1/2 to regulate noncanonical Wnt signaling and calpain 8 during embryonic convergent extension and craniofacial morphogenesis

Wnt signaling plays crucial roles in embryonic patterning including the regulation of convergent extension (CE) during gastrulation, the establishment of the dorsal axis, and later, craniofacial morphogenesis. Further, Wnt signaling is a crucial regulator of craniofacial morphogenesis. The adapter proteins Dact1 and Dact2 modulate the Wnt signaling pathway through binding to Disheveled. However, the distinct relative functions of Dact1 and Dact2 during embryogenesis remain unclear. We found that dact1 and dact2 genes have dynamic spatiotemporal expression domains that are reciprocal to one another suggesting distinct functions during zebrafish embryogenesis. Both dact1 and dact2 contribute to axis extension, with compound mutants exhibiting a similar CE defect and craniofacial phenotype to the wnt11f2 mutant. Utilizing single-cell RNAseq and an established noncanonical Wnt pathway mutant with a shortened axis (gpc4), we identified dact1/2-specific roles during early development. Comparative whole transcriptome analysis between wildtype and gpc4 and wildtype and dact1/2 compound mutants revealed a novel role for dact1/2 in regulating the mRNA expression of the classical calpain capn8. Overexpression of capn8 phenocopies dact1/2 craniofacial dysmorphology. These results identify a previously unappreciated role of capn8 and calcium-dependent proteolysis during embryogenesis. Taken together, our findings highlight the distinct and overlapping roles of dact1 and dact2 in embryonic craniofacial development, providing new insights into the multifaceted regulation of Wnt signaling.

Genetic requirement of dact1/2 to regulate noncanonical Wnt signaling and calpain 8 during embryonic convergent extension and craniofacial morphogenesis

Wnt signaling plays crucial roles in embryonic patterning including the regulation of convergent extension during gastrulation, the establishment of the dorsal axis, and later, craniofacial morphogenesis. Further, Wnt signaling is a crucial regulator of craniofacial morphogenesis. The adapter proteins Dact1 and Dact2 modulate the Wnt signaling pathway through binding to Disheveled. However, the distinct relative functions of Dact1 and Dact2 during embryogenesis remain unclear. We found that dact1 and dact2 genes have dynamic spatiotemporal expression domains that are reciprocal to one another suggesting distinct functions during zebrafish embryogenesis. Both dact1 and dact2 contribute to axis extension, with compound mutants exhibiting a similar convergent extension defect and craniofacial phenotype to the wnt11f2 mutant. Utilizing single-cell RNAseq and an established noncanonical Wnt pathway mutant with a shortened axis (gpc4), we identified dact1/2 specific roles during early development. Comparative whole transcriptome analysis between wildtype and gpc4 and wildtype and dact1/2 compound mutants revealed a novel role for dact1/2 in regulating the mRNA expression of the classical calpain capn8. Over-expression of capn8 phenocopies dact1/2 craniofacial dysmorphology. These results identify a previously unappreciated role of capn8 and calcium-dependent proteolysis during embryogenesis. Taken together, our findings highlight the distinct and overlapping roles of dact1 and dact2 in embryonic craniofacial development, providing new insights into the multifaceted regulation of Wnt signaling.

Non-canonical Wnt signaling triggered by WNT2B drives adrenal aldosterone production

The steroid hormone aldosterone, produced by the zona glomerulosa (zG) of the adrenal gland, is a master regulator of plasma electrolytes and blood pressure. While aldosterone control by the renin-angiotensin system is well understood, other key regulatory factors have remained elusive. Here, we replicated a prior association between a non-coding variant in WNT2B and an increased risk of primary aldosteronism, a prevalent and debilitating disease caused by excessive aldosterone production. We further show that in both mice and humans, WNT2B is expressed in the mesenchymal capsule surrounding the adrenal cortex, in close proximity to the zG. Global loss of Wnt2b in the mouse results in a dysmorphic and hypocellular zG, with impaired aldosterone production. Similarly, humans harboring WNT2B loss-of-function mutations develop a novel form of Familial Hyperreninemic Hypoaldosteronism, designated here as Type 4. Additionally, we demonstrate that WNT2B signals by activating the non-canonical Wnt/planar cell polarity pathway. Our findings identify WNT2B as a key regulator of zG function and aldosterone production with important clinical implications.

Heterozygous variants in the DVL2 interaction region of DACT1 cause CAKUT and features of Townes-Brocks syndrome 2

Most patients with congenital anomalies of the kidney and urinary tract (CAKUT) remain genetically unexplained. In search of novel genes associated with CAKUT in humans, we applied whole-exome sequencing in a patient with kidney, anorectal, spinal, and brain anomalies, and identified a rare heterozygous missense variant in the DACT1 (dishevelled binding antagonist of beta catenin 1) gene encoding a cytoplasmic WNT signaling mediator. Our patient's features overlapped Townes-Brocks syndrome 2 (TBS2) previously described in a family carrying a DACT1 nonsense variant as well as those of Dact1-deficient mice. Therefore, we assessed the role of DACT1 in CAKUT pathogenesis. Taken together, very rare (minor allele frequency ≤ 0.0005) non-silent DACT1 variants were detected in eight of 209 (3.8%) CAKUT families, significantly more frequently than in controls (1.7%). All seven different DACT1 missense variants, predominantly likely pathogenic and exclusively maternally inherited, were located in the interaction region with DVL2 (dishevelled segment polarity protein 2), and biochemical characterization revealed reduced binding of mutant DACT1 to DVL2. Patients carrying DACT1 variants presented with kidney agenesis, duplex or (multi)cystic (hypo)dysplastic kidneys with hydronephrosis and TBS2 features. During murine development, Dact1 was expressed in organs affected by anomalies in patients with DACT1 variants, including the kidney, anal canal, vertebrae, and brain. In a branching morphogenesis assay, tubule formation was impaired in CRISPR/Cas9-induced Dact1^-/- murine inner medullary collecting duct cells. In summary, we provide evidence that heterozygous hypomorphic DACT1 variants cause CAKUT and other features of TBS2, including anomalies of the skeleton, brain, distal digestive and genital tract.

Wnt/planar cell polarity signaling controls morphogenetic movements of gastrulation and neural tube closure

Gastrulation and neurulation are successive morphogenetic processes that play key roles in shaping the basic embryonic body plan. Importantly, they operate through common cellular and molecular mechanisms to set up the three spatially organized germ layers and to close the neural tube. During gastrulation and neurulation, convergent extension movements driven by cell intercalation and oriented cell division generate major forces to narrow the germ layers along the mediolateral axis and elongate the embryo in the anteroposterior direction. Apical constriction also makes an important contribution to promote the formation of the blastopore and the bending of the neural plate. Planar cell polarity proteins are major regulators of asymmetric cell behaviors and critically involved in a wide variety of developmental processes, from gastrulation and neurulation to organogenesis. Mutations of planar cell polarity genes can lead to general defects in the morphogenesis of different organs and the co-existence of distinct congenital diseases, such as spina bifida, hearing deficits, kidney diseases, and limb elongation defects. This review outlines our current understanding of non-canonical Wnt signaling, commonly known as Wnt/planar cell polarity signaling, in regulating morphogenetic movements of gastrulation and neural tube closure during development and disease. It also attempts to identify unanswered questions that deserve further investigations.

Brachygnathia Inferior in Cloned Dogs Is Possibly Correlated with Variants of Wnt Signaling Pathway Initiators

Abnormalities in animals cloned via somatic cell nuclear transfer (SCNT) have been reported. In this study, to produce bomb-sniffing dogs, we successfully cloned four healthy dogs through SCNT using the same donor genome from the skin of a male German shepherd old dog. Veterinary diagnosis (X-ray/3D-CT imaging) revealed that two cloned dogs showed normal phenotypes, whereas the others showed abnormal shortening of the mandible (brachygnathia inferior) at 1 month after birth, even though they were cloned under the same conditions except for the oocyte source. Therefore, we aimed to determine the genetic cause of brachygnathia inferior in these cloned dogs. To determine the genetic defects related to brachygnathia inferior, we performed karyotyping and whole-genome sequencing (WGS) for identifying small genetic alterations in the genome, such as single-nucleotide variations or frameshifts. There were no chromosomal numerical abnormalities in all cloned dogs. However, WGS analysis revealed variants of Wnt signaling pathway initiators (WNT5B, DVL2, DACT1, ARRB2, FZD 4/8) and cadherin (CDH11, CDH1like) in cloned dogs with brachygnathia inferior. In conclusion, this study proposes that brachygnathia inferior in cloned dogs may be associated with variants in initiators and/or regulators of the Wnt/cadherin signaling pathway.

Glypican 4 regulates planar cell polarity of endoderm cells by controlling the localization of Cadherin 2

Noncanonical Wnt/planar cell polarity (Wnt/PCP) signaling has been implicated in endoderm morphogenesis. However, the underlying cellular and molecular mechanisms of this process are unclear. We found that, during convergence and extension (C&E) in zebrafish, gut endodermal cells are polarized mediolaterally, with GFP-Vangl2 enriched at the anterior edges. Endoderm cell polarity is lost and intercalation is impaired in the absence of glypican 4 (gpc4), a heparan-sulfate proteoglycan that promotes Wnt/PCP signaling, suggesting that this signaling is required for endodermal cell polarity. Live imaging revealed that endoderm C&E is accomplished by polarized cell protrusions and junction remodeling, which are impaired in gpc4-deficient endodermal cells. Furthermore, in the absence of gpc4, Cadherin 2 expression on the endodermal cell surface is increased as a result of impaired Rab5c-mediated endocytosis, which partially accounts for the endodermal defects in these mutants. These findings indicate that Gpc4 regulates endodermal planar cell polarity during endoderm C&E by influencing the localization of Cadherin 2. Thus, our study uncovers a new mechanism by which Gpc4 regulates planar cell polarity and reveals the role of Wnt/PCP signaling in endoderm morphogenesis.

Dact1 is expressed during chicken and mouse skeletal myogenesis and modulated in human muscle diseases

Vertebrate skeletal muscle development and repair relies on the precise control of Wnt signaling. Dact1 (Dapper/Frodo) is an important modulator of Wnt signaling, interacting with key components of the various Wnt transduction pathways. Here, we characterized Dact1 mRNA and protein expression in chicken and mouse fetal muscles in vivo and during the differentiation of chick primary and mouse C2C12 myoblasts in vitro. We also performed in silico analysis to investigate Dact1 gene expression in human myopathies, and evaluated the Dact1 protein structure to seek an explanation for the accumulation of Dact1 protein aggregates in the nuclei of myogenic cells. Our results show for the first time that in both chicken and mouse, Dact1 is expressed during myogenesis, with a strong upregulation as cells engage in terminal differentiation, cell cycle withdrawal and cell fusion. In humans, Dact1 expression was found to be altered in specific muscle pathologies, including muscular dystrophies. Our bioinformatic analyses of Dact1 proteins revealed long intrinsically disordered regions, which may underpin the ability of Dact1 to interact with its many partners in the various Wnt pathways. In addition, we found that Dact1 has strong propensity for liquid-liquid phase separation, a feature that explains its ability to form nuclear aggregates and points to a possible role as a molecular 'on'-'off' switch. Taken together, our data suggest Dact1 as a candidate, multi-faceted regulator of amniote myogenesis with a possible pathophysiological role in human muscular diseases.

Large intestine embryogenesis: Molecular pathways and related disorders (Review)

The large intestine, part of the gastrointestinal tract (GI), is composed of all three germ layers, namely the endoderm, the mesoderm and the ectoderm, forming the epithelium, the smooth muscle layers and the enteric nervous system, respectively. Since gastrulation, these layers develop simultaneously during embryogenesis, signaling to each other continuously until adult age. Two invaginations, the anterior intestinal portal (AIP) and the caudal/posterior intestinal portal (CIP), elongate and fuse, creating the primitive gut tube, which is then patterned along the antero‑posterior (AP) axis and the radial (RAD) axis in the context of left‑right (LR) asymmetry. These events lead to the formation of three distinct regions, the foregut, midgut and hindgut. All the above‑mentioned phenomena are under strict control from various molecular pathways, which are critical for the normal intestinal development and function. Specifically, the intestinal epithelium constitutes a constantly developing tissue, deriving from the progenitor stem cells at the bottom of the intestinal crypt. Epithelial differentiation strongly depends on the crosstalk with the adjacent mesoderm. Major molecular pathways that are implicated in the embryogenesis of the large intestine include the canonical and non‑canonical wingless‑related integration site (Wnt), bone morphogenetic protein (BMP), Notch and hedgehog systems. The aberrant regulation of these pathways inevitably leads to several intestinal malformation syndromes, such as atresia, stenosis, or agangliosis. Novel theories, involving the regulation and homeostasis of intestinal stem cells, suggest an embryological basis for the pathogenesis of colorectal cancer (CRC). Thus, the present review article summarizes the diverse roles of these molecular factors in intestinal embryogenesis and related disorders.

Sestd1 Encodes a Developmentally Dynamic Synapse Protein That Complexes With BCR Rac1-GAP to Regulate Forebrain Dendrite, Spine and Synapse Formation

SEC14 and Spectrin domain-1 (Sestd1) is a synapse protein that exhibits a striking shift from the presynaptic to postsynaptic space as neurons mature postnatally in the mouse hippocampus. Hippocampal pyramidal neurons from mice with global genetic deletion of Sestd1 have reduced dendrite arbors, spines, and excitatory synapses. Electrophysiologically this correlates with cell-autonomous reductions in both AMPA- and NMDA-excitatory postsynaptic currents in individual hippocampal neurons from which Sestd1 has been deleted in vivo. These neurodevelopmental and functional deficits are associated with increased activation of the Rho family GTPases Rac1 and RhoA. Co-immunoprecipitation and mass spectrometry reveal that the Breakpoint Cluster Region protein, a Rho GTPase activating protein (GAP), forms complexes with Sestd1 in brain tissue. This complements earlier findings that Sestd1 can also partner with other Rho family GAPs and guanine nucleotide exchange factors. Our findings demonstrate that Sestd1 is a developmentally dynamic synaptic regulator of Rho GTPases that contributes to dendrite and excitatory synapse formation within differentiating pyramidal neurons of the forebrain.

Wnt5a Signaling in Gastric Cancer

Gastric cancer remains an important health challenge, accounting for a significant number of cancer-related deaths worldwide. Therefore, a deeper understanding of the molecular mechanisms involved in gastric cancer establishment and progression is highly desirable. The Wnt pathway plays a fundamental role in development, homeostasis, and disease, and abnormal Wnt signaling is commonly observed in several cancer types. Wnt5a, a ligand that activates the non-canonical branch of the Wnt pathway, can play a role as a tumor suppressor or by promoting cancer cell invasion and migration, although the molecular mechanisms explaining these roles have not been fully elucidated. Wnt5a is increased in gastric cancer samples; however, most gastric cancer cell lines seem to exhibit little expression of this ligand, thus raising the question about the source of this ligand in vivo. This review summarizes available research about Wnt5a expression and signaling in gastric cancer. In gastric cancer, Wnt5a promotes invasion and migration by modulating integrin adhesion turnover. Disheveled, a scaffolding protein with crucial roles in Wnt signaling, mediates the adhesion-related effects of Wnt5a in gastric cancer cells, and several studies provide growing support for a model whereby Disheveled-interacting proteins mediates Wnt5a signaling to modulate cytoskeleton dynamics. However, Wnt5a might induce other effects in gastric cancer cells, such as cell survival and induction of gene expression. On the other hand, the available evidence suggests that Wnt5a might be expressed by cells residing in the tumor microenvironment, where feedback mechanisms sustaining Wnt5a secretion and signaling might be established. This review analyzes the possible functions of Wnt5a in this pathological context and discusses potential links to mechanosensing and YAP/TAZ signaling.

Cyclin G2 regulates canonical Wnt signalling via interaction with Dapper1 to attenuate tubulointerstitial fibrosis in diabetic nephropathy

Cyclin G2 (CCNG2) is an atypical cyclin that inhibits cell cycle progression and is often dysregulated in human cancers. Cyclin G2 in the occurrence and development of diabetic nephropathy (DN), one of the most severe diabetic complications, has not been fully identified. In this study, we investigated the function and regulatory mechanism of cyclin G2 in DN. In vivo studies revealed that a deficiency of cyclin G2 significantly increased albuminuria and promoted tubulointerstitial fibrosis in established DN. Cyclin G2 regulated the expression of fibrosis‐related proteins via the canonical Wnt signalling pathway in renal tubular epithelial cells. Moreover, the binding of cyclin G2 to Dapper1 (Dpr1/DACT1), a protein involved in Wnt signalling, decreased the phosphorylation of Dpr1 at Ser762 by casein kinase 1 (CK1) and suppressed the Wnt signalling pathway. These findings reveal that cyclin G2 can protect against renal injury and fibrosis associated with DN and, thus, is a new target for the prevention and treatment of diabetic complications.

Analysis of the Cancer Genome Atlas Data Reveals Novel Putative ncRNAs Targets in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the prevalent type of primary liver malignancy. Different noncoding RNAs (ncRNAs) that negatively regulate gene expression, such as the microRNAs and the long ncRNAs (lncRNAs), have been associated with cell invasiveness and cell dissemination, tumor recurrence, and metastasis in HCC. To evaluate which regulatory ncRNAs might be good candidates to disrupt HCC proliferation pathways, we performed both unsupervised and supervised analyses of HCC expression data, comparing samples of solid tumor tissue (TP) and adjacent tissue (NT) of a set of patients, focusing on ncRNAs and searching for common mechanisms that may shed light in future therapeutic options. All analyses were performed using the R software. Differential expression (total RNA and miRNA) and enrichment analyses (Gene Ontology + Pathways) were performed using the package TCGABiolinks. As a result, we improved the set of lncRNAs that could be the target of future studies in HCC, highlighting the potential of FAM170B-AS1 and TTN-AS1.

Leucine repeat adaptor protein 1 interacts with Dishevelled to regulate gastrulation cell movements in zebrafish

Gastrulation is a fundamental morphogenetic event that requires polarised cell behaviours for coordinated asymmetric cell movements. Wnt/PCP signalling plays a critical role in this process. Dishevelled is an important conserved scaffold protein that relays Wnt/PCP signals from membrane receptors to the modulation of cytoskeleton organisation. However, it remains unclear how its activity is regulated for the activation of downstream effectors. Here, we report that Lurap1 is a Dishevelled-interacting protein that regulates Wnt/PCP signalling in convergence and extension movements during vertebrate gastrulation. Its loss-of-function leads to enhanced Dishevelled membrane localisation and increased JNK activity. In maternal-zygotic lurap1 mutant zebrafish embryos, cell polarity and directional movement are disrupted. Time-lapse analyses indicate that Lurap1, Dishevelled, and JNK functionally interact to orchestrate polarised cellular protrusive activity, and Lurap1 is required for coordinated centriole/MTOC positioning in movement cells. These findings demonstrate that Lurap1 functions to regulate cellular polarisation and motile behaviours during gastrulation movements.

Gastrulation is an early morphogenic event driven by coordinated asymmetric/polarised cell movements. Here, the authors show in zebrafish that Lurap1, a protein that interacts with Dishevelled, regulates Wnt and planar cell polarity, coordinating centriole positioning during convergence and extension.

TGF-β signaling regulates DACT1 expression in intestinal epithelial cells

DACT1, was first identified as a Dishevelled-associated antagonist of Wnt signaling pathway. It has been reported that DACT1 functions in embryonic development and tumorigenesis. However, the regulation of DACT1 still remains unclear. We found Wnt signaling has no effect on DACT1, but TGF-β increases expression of DACT1 in intestinal epithelial cells. In addition, the minimal promoter is located in the region of -500bp to +1bp and the region between -3000bp to +1bp enhanced promoter activity. Site-directed mutation analysis was performed and indicated that potential regulatory elements was near -335bp. Our study provided the basic information for the exploration of DACT1 regulation and expression. Moreover, TGF-β inhibits Wnt signaling to enhance the function of DACT1 inhibiting Wnt signaling.

Dact1, a Wnt-Pathway Inhibitor, Mediates Human Mesangial Cell TGF-β1-Induced Apoptosis

Chronic kidney disease (CKD) is a worldwide public health problem that affects millions of men and women of all ages and racial groups. Loss of mesangial cells (MC) represents an early common feature in the pathogenesis of CKD. Transforming growth factor-β1 (TGF-β1) is a key inducer of kidney damage and triggers several pathological changes in renal cells, notably MC apoptosis. However, the mechanism of MC apoptosis induced by TGF-β1 remains elusive. Here, we demonstrate for the first time a novel regulatory pathway in which the disheveled-binding antagonist of β-catenin 1 (Dact1) gene is upregulated by TGF-β1, inducing MC apoptosis. We also show that the inhibitory effect of Dact1 and TGF-β1 on the transcriptional activation of the pro-survival Wnt pathway is the mechanism of death induction. In addition, Dact1 mRNA/protein levels are increased in kidney remnants from 5/6 nephrectomized rats and strongly correlate with TGF-β1 expression. Together, our results point to Dact1 as a novel element controlling MC survival that is causally related to CKD progression. J. Cell. Physiol. 232: 2104-2111, 2017. © 2016 Wiley Periodicals, Inc.

Heterozygous Pathogenic Variant in DACT1 Causes an Autosomal-Dominant Syndrome with Features Overlapping Townes-Brocks Syndrome

A heterozygous nonsense variant was identified in dapper, antagonist of beta-catenin, 1 (DACT1) via whole-exome sequencing in family members with imperforate anus, structural renal abnormalities, genitourinary anomalies, and/or ear anomalies. The DACT1 c.1256G>A;p.Trp419^* variant segregated appropriately in the family consistent with an autosomal dominant mode of inheritance. DACT1 is a member of the Wnt-signaling pathway, and mice homozygous for null alleles display multiple congenital anomalies including absent anus with blind-ending colon and genitourinary malformations. To investigate the DACT1 c.1256G>A variant, HEK293 cells were transfected with mutant DACT1 cDNA plasmid, and immunoblotting revealed stability of the DACT1 p.Trp419^* protein. Overexpression of DACT1 c.1256G>A mRNA in Xenopus embryos revealed a specific gastrointestinal phenotype of enlargement of the proctodeum. Together, these findings suggest that the DACT1 c.1256G>A nonsense variant is causative of a specific genetic syndrome with features overlapping Townes-Brocks syndrome.

Dapper homolog 1 alpha suppresses metastasis ability of gastric cancer through inhibiting planar cell polarity pathway

Dapper homolog 1 alpha (DACT1α) is a member of DACT family and an important regulator in the planar cell polarity pathway. We aim to clarify its functional role in metastasis ability of gastric cancer. DACT1α was silenced in all gastric cancer cell lines (8/8), but expressed in normal gastric tissue. Ectopic expression of DACT1α in silenced gastric cancer cell lines (AGS, BGC823 and MGC803) by stable transfection significantly suppressed cancer cell spreading (P < 0.05), migration (P < 0.01) and invasion (P < 0.01). These effects were associated with downregulation of planar cell polarity pathway related genes involved in cell proliferation (PDGFB, VEGFA), adhesion (ITGA1, ITGA2, ITGA3, ITGB3) and migration/invasion (PLAU, MMP9, MCAM, Dvl-2 and JNK). DACT1α promoter methylation was detected in 205 gastric cancers and 20 normal controls by direct bisulfite genomic sequencing. DACT1α methylation was detected in 29.3% (60/205) of gastric cancer patients, but not in normal tissues. DACT1α methylation was associated with poor survival of gastric cancer patients. In conclusion, DACT1α plays a pivotal role as a potential tumor suppressor in migration and invasion of gastric cancer. DACT1α methylation may serve as a biomarker for the prognosis of gastric cancer.

Association analysis of DACT1 genetic variants and gastric cancer risk in a Chinese Han population: a case-control study

Purpose

Disheveled-binding antagonist of beta-catenin 1 (DACT1) is involved in tumorigenesis through influencing cell apoptosis and proliferation. We aimed to investigate the effect of three tag single-nucleotide polymorphisms (SNPs) in DACT1 (rs863091 C>T, rs17832998 C>T, and rs167481 C>T) on the occurrence of gastric cancer (GC), their association with specific clinical characteristics, and consideration of the functional relevance of GC-related SNPs.

Subjects and methods

In this hospital-based case–control study, the genotypes were acquired using the TaqMan-MGB method consisting of 602 cases and 602 controls. DACT1 messenger RNA level was evaluated in 76 paired tumoral and normal tissues using quantitative reverse transcription–polymerase chain reaction. Logistic regression was used to evaluate the associations among the DACT1 SNPs and GC.

Results

We found a significant association between the variant genotypes of rs863091 and decreased risk of GC (TT vs CC: P=0.009, adjusted odds ratio =0.34, 95% confidence interval =0.15–0.77; CT + TT vs CC: P=0.030, adjusted odds ratio =0.74, 95% confidence interval =0.57–0.97). In further stratified analyses, rs863091 variant genotypes were associated with a reduced risk of GC in younger individuals (<60 years) and males. No overall significant association with GC risk was observed in SNP rs17832998 or rs167481. Additionally, we assessed DACT1 messenger RNA levels in GC and found that DACT1 expressions of individuals carrying CT and TT genotypes were much higher than those with CC genotype.

Conclusion

Our findings suggest that the DACT1 rs863091 C>T polymorphism may be associated with a decreased risk of GC in the Chinese Han population and influence DACT1 expression.

The Genetic Basis of Baculum Size and Shape Variation in Mice

The rapid divergence of male genitalia is a preeminent evolutionary pattern. This rapid divergence is especially striking in the baculum, a bone that occurs in the penis of many mammalian species. Closely related species often display diverse baculum morphology where no other morphological differences can be discerned. While this fundamental pattern of evolution has been appreciated at the level of gross morphology, nearly nothing is known about the genetic basis of size and shape divergence. Quantifying the genetic basis of baculum size and shape variation has been difficult because these structures generally lack obvious landmarks, so comparing them in three dimensions is not straightforward. Here, we develop a novel morphometric approach to quantify size and shape variation from three-dimensional micro-CT scans taken from 369 bacula, representing 75 distinct strains of the BXD family of mice. We identify two quantitative trait loci (QTL) that explain ∼50% of the variance in baculum size, and a third QTL that explains more than 20% of the variance in shape. Together, our study demonstrates that baculum morphology may diverge relatively easily, with mutations at a few loci of large effect that independently modulate size and shape. Based on a combination of bioinformatic investigations and new data on RNA expression, we prioritized these QTL to 16 candidate genes, which have hypothesized roles in bone morphogenesis and may enable future genetic manipulation of baculum morphology.

Delamination of neural crest cells requires transient and reversible Wnt inhibition mediated by Dact1/2

Delamination of neural crest (NC) cells is a bona fide physiological model of epithelial-to-mesenchymal transition (EMT), a process that is influenced by Wnt/β-catenin signalling. Using two in vivo models, we show that Wnt/β-catenin signalling is transiently inhibited at the time of NC delamination. In attempting to define the mechanism underlying this inhibition, we found that the scaffold proteins Dact1 and Dact2, which are expressed in pre-migratory NC cells, are required for NC delamination in Xenopus and chick embryos, whereas they do not affect the motile properties of migratory NC cells. Dact1/2 inhibit Wnt/β-catenin signalling upstream of the transcriptional activity of T cell factor (TCF), which is required for EMT to proceed. Dact1/2 regulate the subcellular distribution of β-catenin, preventing β-catenin from acting as a transcriptional co-activator to TCF, yet without affecting its stability. Together, these data identify a novel yet important regulatory element that inhibits β-catenin signalling, which then affects NC delamination.

Genetic analysis of DACT1 in 100 Chinese Han women with Müllerian duct anomalies

Dapper antagonist of catenin-1 (DACT1) plays an important role in embryogenesis and organogenesis of the female reproductive tract in mouse models. The aim of this study was to investigate the association between DACT1 mutations and human Müllerian duct anomalies (MDA). One hundred clinically well-defined Chinese Han patients with MDA and 200 healthy controls were recruited in this study. All four exons coding for DACT1 were amplified and sequenced. A missense mutation (c.G1084A, p.V362M) was identified in a patient who had a didelphic uterus and was absent from the control group. This variant changed the hydrophilicity of the amino acid residue and was predicted to be deleterious to the structure and function of DACT1 protein. The data indicate that the p.V362M mutation of DACT1 may be an underlying cause of MDA.

The Wnt Signaling Antagonist Dapper1 Accelerates Dishevelled2 Degradation via Promoting Its Ubiquitination and Aggregate-induced Autophagy

Autophagy is a regulated process that sequesters and transports cytoplasmic materials such as protein aggregates via autophagosomes to lysosomes for degradation. Dapper1 (Dpr1), an interacting protein of Dishevelled (Dvl), antagonizes Wnt signaling by promoting Dishevelled degradation via lysosomes. However, the mechanism is unclear. Here, we show that Dpr1 promotes the von Hippel-Lindau tumor suppressor (VHL)-mediated ubiquitination of Dvl2 and its autophagic degradation. Knockdown of Dpr1 decreases the interaction between Dvl2 and pVHL, resulting in reduced ubiquitination of Dvl2. Dpr1-mediated autophagic degradation of Dvl2 depends on Dvl2 aggregation. Moreover, the aggregate-prone proteins Dvl2, p62, and the huntingtin mutant Htt103Q promote autophagy in a Dpr1-dependent manner. These protein aggregates enhance the Beclin1-Vps34 interaction and Atg14L puncta formation, indicating that aggregated proteins stimulate autophagy initiation. Ubiquitination is not essential for the aggregate-induced autophagy initiation as inhibition of the ubiquitin-activation E1 enzyme activity did not block the aggregate-induced Atg14L puncta formation. Our findings suggest that Dpr1 promotes the ubiquitination of Dvl2 by pVHL and mediates the protein aggregate-elicited autophagy initiation.

Myc-interacting zinc-finger protein 1 positively regulates Wnt signalling by protecting Dishevelled from Dapper1-mediated degradation

Wnt signalling regulates embryonic development and tissue homoeostasis by modulating cell proliferation, differentiation and migration. Dapper1 (Dpr1) has been shown to be an important key negative regulator of Wnt signalling by promoting Dishevelled (Dvl) degradation. In the present study, we found that Myc-interacting zinc-finger protein 1 (MIZ1) interacts with Dpr1 and this interaction attenuates the ability of Dpr1 to induce Dvl2 degradation, thus enhancing Wnt signalling. Mechanistically, MIZ1 is translocated from the nucleus to the cytoplasm upon Wnt3a stimulation or overexpression of Dpr1 and Dvl2, disrupting the interaction between Dpr1 and Dvl2. Furthermore, MIZ1 can promote the proliferation of breast cancer MDA-MB-231 and BT-549 cells through Wnt signalling and reverse the anti-proliferative effect of Dpr1 on colorectal cancer Caco-2. Together, our findings establish a novel layer of Wnt signalling regulation via the MIZ1-Dpr1-Dvl axis.

Retinoic acid negatively regulates dact3b expression in the hindbrain of zebrafish embryos

Wnt signaling plays important roles in normal development as well as pathophysiological conditions. The Dapper antagonist of β-catenin (Dact) proteins are modulators of both canonical and non-canonical Wnt signaling via direct interactions with Dishevelled (Dvl) and Van Gogh like-2 (Vangl2). Here, we report the dynamic expression patterns of two zebrafish dact3 paralogs during early embryonic development. Our whole mount in situ hybridization (WISH) analysis indicates that specific dact3a expression starts by the tailbud stage in adaxial cells. Later, it is expressed in the anterior lateral plate mesoderm, somites, migrating cranial neural crest, and hindbrain neurons. By comparison, dact3b expression initiates on the dorsal side at the dome stage and soon after is expressed in the dorsal forerunner cells (DFCs) during gastrulation. At later stages, dact3b expression becomes restricted to the branchial neurons of the hindbrain and to the second pharyngeal arch. To investigate how zebrafish dact3 gene expression is regulated, we manipulated retinoic acid (RA) signaling during development and found that it negatively regulates dact3b in the hindbrain. Our study is the first to document the expression of the paralogous zebrafish dact3 genes during early development and demonstrate dact3b can be regulated by RA signaling. Therefore, our study opens up new avenues to study Dact3 function in the development of multiple tissues and suggests a previously unappreciated cross regulation of Wnt signaling by RA signaling in the developing vertebrate hindbrain.

Dapper1 promotes autophagy by enhancing the Beclin1-Vps34-Atg14L complex formation

Autophagy is an intracellular degradation process to clear up aggregated proteins or aged and damaged organelles. The Beclin1-Vps34-Atg14L complex is essential for autophagosome formation. However, how the complex formation is regulated is unclear. Here, we show that Dapper1 (Dpr1) acts as a critical regulator of the Beclin1-Vps34-Atg14L complex to promote autophagy. Dpr1 ablation in the central nervous system results in motor coordination defect and accumulation of p62 and ubiquitinated proteins. Dpr1 increases autophagosome formation as indicated by elevated puncta formation of LC3, Atg14L and DFCP1 (Double FYVE-containing protein 1). Conversely, loss of Dpr1 impairs LC3 lipidation and causes p62/SQSTM1 accumulation. Dpr1 directly interacts with Beclin1 and Atg14L and enhances the Beclin1-Vps34 interaction and Vps34 activity. Together, our findings suggest that Dpr1 enhances the Atg14L-Beclin1-Vps34 complex formation to drive autophagy.

Dapper-1 is essential for Wnt5a induced cardiomyocyte hypertrophy by regulating the Wnt/PCP pathway

The Wnt signaling pathway was identified as crucial mediator of cardiomyocyte hypertrophy. In this study we found that activation of non-canonical Wnt signaling by Wnt5a stimulates protein synthesis and enlargement of cardiomyocyte surface area. These hypertrophic features were inhibited in Dapper-1 (Dpr1) depleted cells. On the molecular level, we observed inhibition of the non-canonical Wnt/planar-cell-polarity (PCP) pathway denoted by reduction of c-jun-n-terminal-kinase (JNK) phosphorylation. Upstream of JNK, increased protein levels of the Wnt/PCP trans-membrane receptor van-Gogh-like-2 (Vangl2) were observed along with an enrichment of Vangl2 in perinuclear located vesicles. The findings suggest that Dpr1 is essential for execution of the Wnt/PCP pathway and regulation of the Vangl2/JNK axis. Depletion of Dpr1 inhibits non-canonical Wnt signaling induced cardiomyocyte hypertrophy by blocking Wnt/PCP signaling.

NEDD4L regulates convergent extension movements in Xenopus embryos via Disheveled-mediated non-canonical Wnt signaling

During the early vertebrate body plan formation, convergent extension (CE) of dorsal mesoderm and neurectoderm is coordinated by the evolutionarily conserved non-canonical Wnt/PCP signaling. Disheveled (Dvl), a key mediator of Wnt/PCP signaling, is essential for the medial-lateral polarity formation in the cells undergoing convergent extension movements. NEDD4L, a highly conserved HECT type E3 ligase, has been reported to regulate the stability of multiple substrates including Dvl2. Here we demonstrate that NEDD4L is required for the cellular polarity formation and convergent extension in the early Xenopus embryos. Depletion of NEDD4L in early Xenopus embryos results in the loss of mediolateral polarity of the convergent-extending mesoderm cells and the shortened body axis, resembling those defects caused by the disruption of non-canonical Wnt signaling. Depletion of xNEDD4L also blocks the elongation of the animal explants in response to endogenous mesoderm inducing signals and partially compromises the expression of Brachyury. Importantly, reducing Dvl2 expression can largely rescue the cellular polarity and convergent extension defects in NEDD4L-depleted embryos and explants. Together with the data that NEDD4L reduces Dvl2 protein expression in the frog embryos, our findings suggest that regulation of Dvl protein levels by NEDD4L is essential for convergent extension during early Xenopus embryogenesis.

Expression analysis of Dact1 in mice using a LacZ reporter

The Wnt signaling pathway is essential for cell fate decisions during embryonic development as well as for homeostasis after birth. Dapper antagonist of catenin-1 (Dact1) plays an important role during embryogenesis by regulating Wnt signaling pathways. Consequently, targeted disruption of the Dact1 gene in mice leads to perinatal lethality due to severe developmental defects involving the central nervous system, genitourinary system and distal digestive tract. However, the expression and potential function of Dact1 in other tissues during development and postnatal life have not been well studied. Here, we have generated reporter mice in which LacZ expression is driven by the Dact1 gene promoter and characterized Dact1-LacZ expression in embryos and adult tissues. Our data show that while Dact1-LacZ is expressed in multiple mesoderm- and neuroectoderm-derived tissues during development, high expression of Dact1-LacZ is restricted to a small subset of adult tissues, including the brain, eye, heart, and some reproductive organs. These results will serve as a basis for future investigation of Dact1 function in Wnt-mediated organogenesis and tissue homeostasis.

Genetic evidence in planar cell polarity signaling pathway in human neural tube defects

Neural tube defects (NTDs) are a group of birth anomalies having a profound physical, emotional, and financial effects on families and communities. Their etiology is complex, involving environmental and genetic factors that interact to modulate the incidence and severity of the developing phenotype. The planar cell polarity (PCP) pathway controls the process of convergent extension (CE) during gastrulation and neural tube closure and has been implicated in the pathogenesis of NTDs in animal models and human cohorts. This review summarizes the cumulative results of recent studies on PCP signaling pathway and human NTDs. These results demonstrate that PCP gene alterations contribute to the etiology of human NTDs.

SEC14 and Spectrin Domains 1 (Sestd1), Dishevelled 2 (Dvl2) and Dapper Antagonist of Catenin-1 (Dact1) co-regulate the Wnt/Planar Cell Polarity (PCP) pathway during mammalian development

We previously reported that Sestd1 KO phenocopies Dact1 KO in mice, consistent with a model in which Sestd1 and Dact1 act together to form a crucial functional complex that regulates Vangl2 in the Wnt/Planar Cell Polarity (PCP) pathway. Here, we show that Dvl2, a binding partner of Dact1, also forms complexes with Sestd1, and does so independently of both Dact1 and Vangl2. In cell-based assays, whereas Sestd1 does not alter Dvl2 activation of the Wnt/β-catenin signaling pathway, Dvl2 enhances activation of Rho family GTPases by Dact1 and Sestd1, consistent with a role in the PCP pathway. In mice, although Dvl2 KO is recessive in an otherwise wild type background, it leads to dominant embryonic lethality in either the Sestd1 or Dact1 KO background. This genetic synergy stands in contrast to the epistasis we have previously reported between Sestd1 and Dact1 KO, and suggests independent or semi-independent functions for Dvl2 vs. Sestd1/Dact1 in the regulation of the PCP pathway during development. In conclusion, biochemical and genetic interactions between Dvl2, Sestd1, and Dact1, in addition to prior reported interactions between these same molecules and Vangl2, suggest that all these gene products can form complexes together and regulate the PCP pathway during mammalian development. However, Sestd1 and Dact1 have a closely allied function in the post-translational regulation of Vangl2 that is at least partially distinct from the functions of Dvl2 in this pathway.

Gene network analysis of candidate loci for human anorectal malformations

Anorectal malformations (ARMs) are birth defects that require surgery and carry significant chronic morbidity. Our earlier genome-wide copy number variation (CNV) study had provided a wealth of candidate loci. To find out whether these candidate loci are related to important developmental pathways, we have performed an extensive literature search coupled with the currently available bioinformatics tools. This has allowed us to assign both genic and non-genic CNVs to interrelated pathways known to govern the development of the anorectal region. We have linked 11 candidate genes to the WNT signalling pathway and 17 genes to the cytoskeletal network. Interestingly, candidate genes with similar functions are disrupted by the same type of CNV. The gene network we discovered provides evidence that rare mutations in different interrelated genes may lead to similar phenotypes, accounting for genetic heterogeneity in ARMs. Classification of patients according to the affected pathway and lesion type should eventually improve the diagnosis and the identification of common genes/molecules as therapeutic targets.

Planar cell polarity signaling in collective cell movements during morphogenesis and disease

Collective and directed cell movements are crucial for diverse developmental processes in the animal kingdom, but they are also involved in wound repair and disease. During these processes groups of cells are oriented within the tissue plane, which is referred to as planar cell polarity (PCP). This requires a tight regulation that is in part conducted by the PCP pathway. Although this pathway was initially characterized in flies, subsequent studies in vertebrates revealed a set of conserved core factors but also effector molecules and signal modulators, which build the fundamental PCP machinery. The PCP pathway in Drosophila regulates several developmental processes involving collective cell movements such as border cell migration during oogenesis, ommatidial rotation during eye development, and embryonic dorsal closure. During vertebrate embryogenesis, PCP signaling also controls collective and directed cell movements including convergent extension during gastrulation, neural tube closure, neural crest cell migration, or heart morphogenesis. Similarly, PCP signaling is linked to processes such as wound repair, and cancer invasion and metastasis in adults. As a consequence, disruption of PCP signaling leads to pathological conditions. In this review, we will summarize recent findings about the role of PCP signaling in collective cell movements in flies and vertebrates. In addition, we will focus on how studies in Drosophila have been relevant to our understanding of the PCP molecular machinery and will describe several developmental defects and human disorders in which PCP signaling is compromised. Therefore, new discoveries about the contribution of this pathway to collective cell movements could provide new potential diagnostic and therapeutic targets for these disorders.

SEC14 and spectrin domains 1 (Sestd1) and Dapper antagonist of catenin 1 (Dact1) scaffold proteins cooperatively regulate the Van Gogh-like 2 (Vangl2) four-pass transmembrane protein and planar cell polarity (PCP) pathway during embryonic development in mice

The planar cell polarity (PCP) pathway is a conserved non-canonical (β-catenin-independent) branch of Wnt signaling crucial to embryogenesis, during which it regulates cell polarity and polarized cell movements. Disruption of PCP components in mice, including Vangl2 and Dact1, results in defective neural tube closure and other developmental defects. Here, we show that Sestd1 is a novel binding partner of Vangl2 and Dact1. The Sestd1-Dact1 interface is formed by circumscribed regions of Sestd1 (the carboxyl-terminal region) and Dact1 (the amino-terminal region). Remarkably, we show that loss of Sestd1 precisely phenocopies loss of Dact1 during embryogenesis in mice, leading to a spectrum of birth malformations, including neural tube defects, a shortened and/or curly tail, no genital tubercle, blind-ended colons, hydronephrotic kidneys, and no bladder. Moreover, as with Dact1, a knock-out mutation at the Sestd1 locus exhibits reciprocal genetic rescue interactions during development with a semidominant mutation at the Vangl2 locus. Consistent with this, examination of Wnt pathway activities in Sestd1 mutant mouse embryonic tissue reveals disrupted PCP pathway biochemistry similar to that characterized in Dact1 mutant embryos. The Sestd1 protein is a divergent member of the Trio family of GTPase regulatory proteins that lacks a guanine nucleotide exchange factor domain. Nonetheless, in cell-based assays the Sestd1-Dact1 interaction can induce Rho GTPase activation. Together, our data indicate that Sestd1 cooperates with Dact1 in Vangl2 regulation and in the PCP pathway during mammalian embryonic development.

Disruption of the Dapper3 gene aggravates ureteral obstruction-mediated renal fibrosis by amplifying Wnt/β-catenin signaling

Wnt/β-catenin signaling plays key roles in embryonic development and tissue homeostasis. Dapper3/Dact3, one of the three members of the Dapper gene family, is transcriptionally repressed in colorectal cancer and may function as a negative regulator of Wnt/β-catenin signaling. To investigate its physiological functions, we generated a mouse strain harboring conditional null alleles of Dapper3 (Dapper3(flox/flox)), and homozygous Dapper3-deficient (Dapper3(-/-)) mice were produced after crossing with EIIa-cre transgenic mice. We found that Dapper3 is not essential for mouse embryogenesis, postnatal survival, and reproduction. However, adult Dapper3(-/-) mice exhibited a mild reduction in body weight compared with their wild-type littermates, suggesting a functional role of Dapper3 in postnatal growth. To investigate the role of Dapper3 in renal fibrosis, we employed the unilateral ureteral obstruction model. Dapper3 mRNA expression was up-regulated in kidney after unilateral ureteral obstruction. Loss of the Dapper3 gene enhanced myofibroblast activation and extracellular matrix overproduction in the obstructed kidney. Moreover, this aggravated fibrotic phenotype was accompanied with accumulation of Dishevelled2 and β-catenin proteins and activation of Wnt-targeted fibrotic genes. In primary renal tubular cells, Dapper3 inhibits Wnt-induced epithelial-to-mesenchymal transition. Consistently, Dapper3 interacted with and down-regulated Dishevelled2 protein and attenuated the Wnt-responsive Topflash reporter expression. These findings together suggest that Dapper3 antagonizes the fibrotic actions of Wnt signaling in kidney.

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

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

Dapper homolog 1 is a novel tumor suppressor in gastric cancer through inhibiting the nuclear factor-κB signaling pathway

Dapper homolog 1 (DACT1) is a disheveled partner in the planar cell polarity pathway. By using genome-wide promoter methylation screening, dapper homolog 1 (DACT1) was found to be frequently methylated in gastric cancer. We aim to clarify its epigenetic inactivation, biological function and clinical implication in gastric cancer. We demonstrated that DACT1 was silenced in 7 of 10 gastric cancer cell lines and in primary gastric cancers. Transcriptional gene silence of DACT1 was mainly regulated by promoter hypermethylation. Ectopic expression of DACT1 in silenced gastric cancer cell lines (AGS, BGC823 and MGC803) by stable transfection suppressed colony formation (P < 0.001), induced cell apoptosis (P < 0.01) and retarded tumorigenesis in nude mice (P < 0.001). The tumor suppressive effect of DACT1 was further confirmed by loss of DACT1 function experiment. The proapoptotic and antiproliferative effect by DACT1 was associated with inhibition of nuclear factor (NF)-κB activation and its downstream factors, including B-cell CLL/lymphoma-2, Bcl-X, interleukin-8 and tumor necrosis factor-α. Moreover, promoter methylation of DACT1 was detected in 29.3% (60/205) of primary gastric tumors. DACT1 methylation was significantly associated with tumor metastasis (P < 0.05), invasion (P < 0.05) and advanced tumor stage (P < 0.0005). These findings provided insight into the role of DACT1 as a novel functional tumor suppressor in gastric cancer through inhibiting NF-κB signaling pathway. Promoter methylation of DACT1 is associated with tumor aggressiveness.

Genome-wide copy number variation study in anorectal malformations

Anorectal malformations (ARMs, congenital obstruction of the anal opening) are among the most common birth defects requiring surgical treatment (2-5/10 000 live-births) and carry significant chronic morbidity. ARMs present either as isolated or as part of the phenotypic spectrum of some chromosomal abnormalities or monogenic syndromes. The etiology is unknown. To assess the genetic contribution to ARMs, we investigated single-nucleotide polymorphisms and copy number variations (CNVs) at genome-wide scale. A total of 363 Han Chinese sporadic ARM patients and 4006 Han Chinese controls were included. Overall, we detected a 1.3-fold significant excess of rare CNVs in patients. Stratification of patients by presence/absence of other congenital anomalies showed that while syndromic ARM patients carried significantly longer rare duplications than controls (P = 0.049), non-syndromic patients were enriched with both rare deletions and duplications when compared with controls (P = 0.00031). Twelve chromosomal aberrations and 114 rare CNVs were observed in patients but not in 868 controls nor 11 943 healthy individuals from the Database of Genomic Variants. Importantly, these aberrations were observed in isolated ARM patients. Gene-based analysis revealed 79 genes interfered by CNVs in patients only. In particular, we identified a de novo DKK4 duplication. DKK4 is a member of the WNT signaling pathway which is involved in the development of the anorectal region. In mice, Wnt disruption results in ARMs. Our data suggest a role for rare CNVs not only in syndromic but also in isolated ARM patients and provide a list of plausible candidate genes for the disorder.

A consideration of the evidence that genetic defects in planar cell polarity contribute to the etiology of human neural tube defects

A variety of human birth defects originate in failure of closure of the embryonic neural tube. The genetic cause of the most common nonsyndromic defects, spina bifida (SB) or anencephaly, is considered to be combinations of variants at multiple genes. The genes contributing to the etiology of neural tube closure defects (NTDs) are unknown. Mutations in planar cell polarity (PCP) genes in mice cause a variety of defects including the NTD, craniorachischisis, and sometimes SB or exencephaly (EX); they also demonstrate the role of digenic combinations of PCP mutants in NTDs. Recent studies have sought rare predicted-to-be-deleterious alterations (putative mutations) in coding sequence of PCP genes in human cases with various anomalies of the neural tube. This review summarizes the cumulative results of these studies according to a framework based on the embryopathogenesis of NTDs, and considers some of the insights from the approaches used and the limitations. Rare putative mutations in the PCP genes VANGL2, SCRIB, DACT1, and CELSR1 cumulatively contributed to over 20% of cases with craniorachischisis, a rare defect; no contributing variants were found for PRICKLE1 or PTK7. PCP rare putative mutations had a weaker role in myelomeningocele (SB), being found in approximately 6% of cases and cumulated across CELSR1, FUZ, FZD6, PRICKLE1, VANGL1, and VANGL2. These results demonstrate that PCP gene alterations contribute to the etiology of human NTDs. We recommend that future research should explore other types of PCP gene variant such as regulatory mutations and low frequency (1 to 5%) deleterious polymorphisms.

Involvement of the WNT and FGF signaling pathways in non-isolated anorectal malformations: sequencing analysis of WNT3A, WNT5A, WNT11, DACT1, FGF10, FGFR2 and the T gene

Anorectal malformations (ARMs) comprise a broad spectrum of anomalies, including anal atresia, congenital anal fistula and persistence of the cloaca. Research suggests that genetic factors play an important role in ARM development. However, few genetic variants have been identified. Embryogenesis is orchestrated by crosstalk of the wingless-type MMTV integration site family (WNT) and fibroblast growth factor (FGF) signaling pathways in a process that involves several intracellular cascades. Studies in mice have implicated several genes from these pathways in the etiology of ARMs. We performed sequencing analysis of seven of these previously reported genes in 78 patients with ARMs occurring within the context of at least one additional congenital anomaly. No associations were identified with variants in WNT3A, WNT5A, WNT11, DACT1, FGF10 or the T gene. In the FGFR2 gene, three novel heterozygous nucleotide substitutions were identified. Further investigations, including the study of family members, revealed that these variants were not causally related to the phenotype in the present ARM cohort. Mutations in the seven investigated genes may nonetheless be a cause of ARMs in rare cases. However, further studies should consider genes encoding other proteins in the WNT/FGF signaling pathways as possible candidates.

Two types of nanoparticle-based bio-barcode amplification assays to detect HIV-1 p24 antigen

Background

HIV-1 p24 antigen is a major viral component of human immunodeficiency virus type 1 (HIV-1) which can be used to identify persons in the early stage of infection and transmission of HIV-1 from infected mothers to infants. The detection of p24 is usually accomplished by using an enzyme-linked immunosorbent assay (ELISA) with low detection sensitivity. Here we report the use of two bio-barcode amplification (BCA) assays combined with polymerase chain reaction (PCR) and gel electrophoresis to quantify HIV-1 p24 antigen.

Method

A pair of anti-p24 monoclonal antibodies (mAbs) were used in BCA assays to capture HIV-1 p24 antigen in a sandwich format and allowed for the quantitative measurement of captured p24 using PCR and gel electrophoresis. The first 1 G12 mAb was coated on microplate wells or magnetic microparticles (MMPs) to capture free p24 antigens. Captured p24 in turn captured 1D4 mAb coated gold nanoparticle probes (GNPs) containing double-stranded DNA oligonucleotides. One strand of the oligonucleotides was covalently immobilized whereas the unbound complimentary bio-barcode DNA strand could be released upon heating. The released bio-barcode DNA was amplified by PCR, electrophoresed in agarose gel and quantified.

Results

The in-house ELISA assay was found to quantify p24 antigen with a limit of detection (LOD) of 1,000 pg/ml and a linear range between 3,000 and 100,000 pg/ml. In contrast, the BCA-based microplate method yielded an LOD of 1 pg/ml and a linear detection range from 1 to 10,000 pg/ml. The BCA-based MMP method yielded an LOD of 0.1 pg/ml and a linear detection range from 0.1 to 1,000 pg/ml.

Conclusions

When combined with PCR and simple gel electrophoresis, BCA-based microplate and MMPs assays can be used to quantify HIV-1 p24 antigen. These methods are 3–4 orders of magnitude more sensitive than our in-house ELISA-based assay and may provide a useful approach to detect p24 in patients newly infected with HIV.

Planar cell polarity and the developmental control of cell behavior in vertebrate embryos

Planar cell polarity (PCP), the orientation and alignment of cells within a sheet, is a ubiquitous cellular property that is commonly governed by the conserved set of proteins encoded by so-called PCP genes. The PCP proteins coordinate developmental signaling cues with individual cell behaviors in a wildly diverse array of tissues. Consequently, disruptions of PCP protein functions are linked to defects in axis elongation, inner ear patterning, neural tube closure, directed ciliary beating, and left/right patterning, to name only a few. This review attempts to synthesize what is known about PCP and the PCP proteins in vertebrate animals, with a particular focus on the mechanisms by which individual cells respond to PCP cues in order to execute specific cellular behaviors.

PICK1 promotes caveolin-dependent degradation of TGF-β type I receptor

Protein that interacts with C kinase 1 (PICK1) is a critical mediator of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) trafficking in neural synapses. However, its ubiquitous expression suggests that it may have other non-neural functions. Here we show that PICK1 antagonizes transforming growth factor beta (TGF-β) signaling by targeting TGF-β type I receptor (TβRI) for degradation. Biochemical analyses reveal that PICK1 directly interacts with the C-terminus of TβRI via its PDZ domain and acts as a scaffold protein to enhance the interaction between TβRI and caveolin-1, leading to enhanced lipid raft/caveolae localization. Therefore, PICK1 increases caveolin-mediated endocytosis, ubiquitination and degradation of TβRI. Moreover, a negative correlation between PICK1 expression and TβRI or phospho-Smad2 levels is observed in human breast tumors, indicating that PICK1 may participate in breast cancer development through inhibition of TGF-β signaling. Our findings reveal a non-neural function of PICK1 as an important negative regulator of TGF-β signaling.

Identification of novel rare mutations of DACT1 in human neural tube defects

Neural tube defects (NTDs) constitute the second most frequent cause of human congenital abnormalities. Complex multigenetic causes have been suggested to contribute to NTDs. The planar cell polarity (PCP) pathway plays a critical role in neural tube closure in model organisms and in human. Knockout of Dact1 (Dapper, Frodo) leads to deregulated PCP signaling with defective neural tube in mice. Here, we report that five missense heterozygote mutations of the DACT1 gene are specifically identified in 167 stillborn or miscarried Han Chinese fetuses with neural tube defects. Our biochemical analyses revealed that among the five mutations, N356K and R45W show loss-of-function or reduced activities in inducing Dishevelled2 (DVL2) degradation and inhibiting jun-N-terminal kinase (JNK) phosphorylation, implicating mutated DACT1 as a risk factor for human NTDs. Our findings, together with early reports, suggest that rare mutations of the PCP-related genes may constitute a great contribution to human NTDs.

Wnt5a-Ror-Dishevelled signaling constitutes a core developmental pathway that controls tissue morphogenesis

Wnts make up a large family of extracellular signaling molecules that play crucial roles in development and disease. A subset of noncanonical Wnts signal independently of the transcription factor β-catenin by a mechanism that regulates key morphogenetic movements during embryogenesis. The best characterized noncanonical Wnt, Wnt5a, has been suggested to signal via a variety of different receptors, including the Ror family of receptor tyrosine kinases, the Ryk receptor tyrosine kinase, and the Frizzled seven-transmembrane receptors. Whether one or several of these receptors mediates the effects of Wnt5a in vivo is not known. Through loss-of-function experiments in mice, we provide conclusive evidence that Ror receptors mediate Wnt5a-dependent processes in vivo and identify Dishevelled phosphorylation as a physiological target of Wnt5a-Ror signaling. The absence of Ror signaling leads to defects that mirror phenotypes observed in Wnt5a null mutant mice, including decreased branching of sympathetic neuron axons and major defects in aspects of embryonic development that are dependent upon morphogenetic movements, such as severe truncation of the caudal axis, the limbs, and facial structures. These findings suggest that Wnt5a-Ror-Dishevelled signaling constitutes a core noncanonical Wnt pathway that is conserved through evolution and is crucial during embryonic development.

Planar cell polarity in the inner ear

The inner ears of vertebrates represent one of the most striking examples of planar cell polarity (PCP). Populations of directionally sensitive mechanosensory hair cells develop actin-based stereociliary bundles that are uniformly oriented. Analysis of perturbations in bundle polarity in mice with mutations in Vangl2 formed the basis for the initial demonstration of conservation of the PCP signaling pathway in vertebrates. Subsequent studies have demonstrated roles for other "core" PCP genes, such as Frizzled, Disheveled, and Celsr, and for identifying novel PCP molecules such as Scribble and Ptk7. In addition, the demonstration of hearing deficits in humans with mutations in cilia genes combined with analysis of PCP defects in mice with ciliary deletion has implicated the cilia as an important modulator of hair cell polarization. Finally, the presence of shortened cochleae in many PCP mouse mutants has revealed an additional role for the PCP pathway in the development of the auditory system.

All Dact (Dapper/Frodo) scaffold proteins dimerize and exhibit conserved interactions with Vangl, Dvl, and serine/threonine kinases

Background

The Dact family of scaffold proteins was discovered by virtue of binding to Dvl proteins central to Wnt and Planar Cell Polarity (PCP) signaling. Subsequently Dact proteins have been linked to a growing list of potential partners implicated in β-catenin-dependent and β-catenin-independent forms of Wnt and other signaling. To clarify conserved and non-conserved roles for this protein family, we systematically compared molecular interactions of all three murine Dact paralogs by co-immunoprecipitation of proteins recombinantly expressed in cultured human embryonic kidney cells.

Results

Every Dact paralog readily formed complexes with the Vangl, Dvl, and CK1δ/ε proteins of species ranging from fruit flies to humans, as well as with PKA and PKC. Dact proteins also formed complexes with themselves and with each other; their conserved N-terminal leucine-zipper domains, which have no known binding partners, were necessary and sufficient for this interaction, suggesting that it reflects leucine-zipper-mediated homo- and hetero-dimerization. We also found weaker, though conserved, interactions of all three Dact paralogs with the catenin superfamily member p120ctn. Complex formation with other previously proposed partners including most other catenins, GSK3, LEF/TCF, HDAC1, and TGFβ receptors was paralog-specific, comparatively weak, and/or more sensitive to empirical conditions.

Conclusions

Combined with published functional evidence from targeted knock-out mice, these data support a conserved role for Dact proteins in kinase-regulated biochemistry involving Vangl and Dvl. This strongly suggests that a principal role for all Dact family members is in the PCP pathway or a molecularly related signaling cascade in vertebrates.