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

Genetic Markers of Spina Bifida: Enrichment of Pathogenic Variants and Variants of Uncertain Significance

Introduction

The genetic diversity of the population in India, shaped by its unique history of migrations and varied ethnic landscape, suggests the possibility of genetic profiles distinct from the western populations.

Objective

The objective is to investigate the genetic basis of spina bifida in the Indian cohort through whole-exome sequencing and pathway enrichment.

Methods

The variants of uncertain significance (VUS) of spina bifida were identified through whole-exome sequencing in the study cohort (n = 3). The pathogenic, likely pathogenic, and VUS were analyzed for protein-protein interactions and functional associations with genes implicated in spina bifida using tools such as STRING and KEGG pathways, which were validated through a literature review. The study was focused on the Wnt/planar cell polarity signaling pathway, which is crucial for neural tube closure.

Results

The study-cohort was collectively represented through 40 common VUS, including eight deleterious SNPs related to genes AP3D1, NLRP9, PCDHGA11, PRSS3, MTSS2, ENDOV, C9, and NSD3. These genes were functionally linked to neural development, immune response, and cellular processes critical for neural tube closure. Notably, interactions were observed between four genes (NLGN2, PKD1, PRSS3, and PLK1) and CTNNB1 (Wnt signaling pathway) crucial for embryonic neural tube formation.

Conclusions

This study has identified novel genetic variants and pathways potentially contributing to the etiopathogenesis of spina bifida in the Indian population. Future research with larger cohorts and functional studies is necessary to validate these findings and explore their potential for clinical applications in spina bifida.

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.

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.

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.

Expression of DACT1 in children with asthma and its regulation mechanism

The aim of the present study was to detect DACT1 expression levels in the lungs of children with asthma, and to investigate its role and molecular mechanisms in regulating the expression of inflammatory factors in RAW264.7 cells. DACT1, DACT2 and DACT3 expression was analyzed in biopsy specimens from 10 cases of newly diagnosed children with asthma and 10 healthy controls by reverse transcription-quantitative polymerase chain reaction, and their expression was confirmed in RAW264.7 cells. DACT1 expression was silenced by small interfering RNA or enhanced by transfection of pcDNA-3.1-DACT1 in RAW264.7 cells, and expression of β-catenin and inflammatory factors, interleukin (IL) 5, IL6 and IL13, was analyzed. Nuclear translocation of β-catenin was detected by western blot analysis, and the effect of DACT1 on β-catenin was investigated with rescue experiments. Regulation of the Wnt signaling pathway by DACT1 and β-catenin was analyzed in RAW264.7 cells after recombinant Wnt5A stimulation. DACT1, DACT2 and DACT3 were significantly upregulated in specimens from children with asthma compared with controls (P<0.05) and the expression of DACT1 was significantly more increased compared with DACT2 and DACT3 (P<0.05). Inhibition of DACT1 expression significantly suppressed IL5, IL6 and IL13 mRNA expression levels compared with the control (P<0.05), while upregulated DACT1 expression significantly increased IL5, IL6 and IL13 mRNA expression (P<0.05). DACT1 inhibited the expression and nuclear translocation of β-catenin, while overexpression of β-catenin significantly inhibited the biological function of DACT1 (P<0.05). Overexpression of β-catenin also significantly suppressed the upregulation of IL5, IL6 and IL13 mRNA induced by pcDNA3.1-DACT1 transfection (P<0.05). Following the addition of Wnt5A, overexpression of DACT1 inhibited the expression and nuclear translocation of β-catenin, and upregulated IL5, IL6 and IL13 mRNA expression. In conclusion, DACT1 was indicated to be upregulated in lung tissues from children with asthma, which could induce higher pro-inflammatory factor expression. DACT1 may act via inhibiting the expression and nuclear translocation of β-catenin, a factor in the Wnt signaling pathway. The present results suggested that DACT1 may be a potential target for the treatment of asthma.

Overexpression of dishevelled 2 is involved in tumor metastasis and is associated with poor prognosis in hepatocellular carcinoma

PURPOSE

Although hepatocellular carcinoma (HCC) is one of the most common malignant tumors, its molecular mechanism is still unknown. Dishevelled 2 (Dvl2) is one of the downstream targets of non-canonical Wnt signaling, which has been demonstrated to be of great importance in the progression of cancers. Nevertheless, the expression mechanisms and physiological significance of Dvl2 in HCC remain unclear.

METHODS

Western blotting and immunohistochemistry were used to measure Dvl2 protein expression in HCC and adjacent normal tissues of 101 patients. Wound healing and transwell assays were used to determine cell migration and invasion.

RESULTS

Dvl2 expression was upregulated in HCC tissues compared to the adjacent normal tissues. Moreover, its expression level was significantly correlated with histological grade (P = 0.042), metastasis (P = 0.005) and vein invasion (P = 0.009) in patients with HCC. Wound healing and transwell assays showed that knockdown of Dvl2 reduced cell migration and invasion in HepG2 cells. Finally, we confirmed that Dvl2 could regulate the migration and invasion of HCC cells by interacting with P62 in non-canonical Wnt signaling.

CONCLUSIONS

Our data showed that Dvl2 was overexpressed in HCC tissues and was also correlated with poor prognosis, suggesting that Dvl2 is a novel therapeutic target for HCC.

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.

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.