Dishevelled controls cell polarity during Xenopus gastrulation

The dual nature of KLHL proteins: From cellular regulators to disease drivers

The Kelch-like (KLHL) protein family, characterized by its conserved BTB, BACK, and Kelch domains, serves as substrate adaptors for Cullin 3-RING ligases (CRL3), facilitating the ubiquitination and degradation of specific target proteins. Through this mechanism, KLHL proteins regulate numerous physiological processes, including cytoskeletal organization, oxidative stress response, and cell cycle progression. Dysregulation of KLHL proteins-via mutations or abnormal expression-has been implicated in various pathological conditions, including neurodegenerative disorders, cancer, cardiovascular diseases, and hereditary syndromes. This review provides a comprehensive overview of the physiological and pathological roles of KLHL proteins, emphasizing their specific substrates and mechanisms of action. By integrating structural and mechanistic insights with translational research, this review underscores the potential of KLHL proteins as promising therapeutic targets, offering new opportunities to combat a wide spectrum of complex diseases.

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.

Marcks and Marcks-like 1 proteins promote spinal cord development and regeneration in Xenopus

Marcks and Marcksl1 are abundant proteins that shuttle between the cytoplasm and membrane to modulate multiple cellular processes, including cytoskeletal dynamics, proliferation, and secretion. Here, we performed loss- and gain-of-function experiments in Xenopus laevis to reveal the novel roles of these proteins in spinal cord development and regeneration. We show that Marcks and Marcksl1 have partly redundant functions and are required for normal neurite formation and proliferation of neuro-glial progenitors during embryonic spinal cord development and for its regeneration during tadpole stages. Rescue experiments in Marcks and Marcksl1 loss-of-function animals further suggested that some of the functions of Marcks and Marcksl1 in the spinal cord are mediated by phospholipid signaling. Taken together, these findings identify Marcks and Marcksl1 as critical new players in spinal cord development and regeneration and suggest new pathways to be targeted for therapeutic stimulation of spinal cord regeneration in human patients.

Twisted cell flow facilitates three-dimensional somite morphogenesis in zebrafish

Tissue elongation is a fundamental morphogenetic process to construct complex embryonic structures. In zebrafish, somites rapidly elongate in both dorsal and ventral directions, transforming from a cuboidal to a V-shape within a few hours of development. Despite its significance, the cellular behaviors that directly lead to somite elongation have not been examined at single-cell resolution. Here, we describe the motion and shapes of all cells composing the dorsal half of the somite in three-dimensional space using lightsheet microscopy. We identified two types of cell movements-in horizontal and dorsal directions-that occur simultaneously within individual cells, creating a complex, twisted flow of cells during somite elongation. Chemical inhibition of Sdf1 signaling disrupted the collective movement in both directions and inhibited somite elongation, suggesting that Sdf1 signaling is crucial for this cell flow. Furthermore, three-dimensional computational modeling suggested that horizontal cell rotation accelerates the perpendicular elongation of the somite along the dorsoventral axis. Together, our study offers novel insights into the role of collective cell migration in tissue morphogenesis, which proceeds dynamically in the three-dimensional space of the embryo.

Formin Binding Protein 1 (FNBP1) regulates non-canonical Wnt signaling and vertebrate gastrulation

The Formin protein Daam1 is required for Wnt-induced cytoskeletal changes during gastrulation, though how it accomplishes this remains unresolved. Here we report the characterization of Formin Binding Protein 1 (FNBP1) as a binding partner of Daam1. The interaction of Daam1 with FNBP1 and its domains required for this interaction were delineated. Immunofluorescence studies showed FNBP1 co-localizes with Daam1, and is an integral component of the actin cytoskeletal complex that is responsive to Wnt stimulation. Specifically, FNBP1 can induce intracellular tubule-like structures and localize to focal adhesions suggesting a role for FNBP1 in cell migration. Functional FNBP1 studies in Xenopus embryos uncover a critical role for FNBP1 in regulating vertebrate gastrulation. Additionally, suboptimal doses of Daam1 and FNBP1 synergize to produce severe gastrulation defects, indicating FNBP1 and Daam1 may function within the same signaling pathway. These results together show FNBP1 is an integral component of Daam1-regulated non-canonical Wnt signaling required for vertebrate gastrulation.

Carboxy-terminal polyglutamylation regulates signaling and phase separation of the Dishevelled protein

Polyglutamylation is a reversible posttranslational modification that is catalyzed by enzymes of the tubulin tyrosine ligase-like (TTLL) family. Here, we found that TTLL11 generates a previously unknown type of polyglutamylation that is initiated by the addition of a glutamate residue to the free C-terminal carboxyl group of a substrate protein. TTLL11 efficiently polyglutamylates the Wnt signaling protein Dishevelled 3 (DVL3), thereby changing the interactome of DVL3. Polyglutamylation increases the capacity of DVL3 to get phosphorylated, to undergo phase separation, and to act in the noncanonical Wnt pathway. Both carboxy-terminal polyglutamylation and the resulting reduction in phase separation capacity of DVL3 can be reverted by the deglutamylating enzyme CCP6, demonstrating a causal relationship between TTLL11-mediated polyglutamylation and phase separation. Thus, C-terminal polyglutamylation represents a new type of posttranslational modification, broadening the range of proteins that can be modified by polyglutamylation and providing the first evidence that polyglutamylation can modulate protein phase separation.

From polarity to pathology: Decoding the role of cell orientation in osteoarthritis

Cell polarity refers to the orientation of tissue and organelles within a cell and the direction of its function. It is one of the most critical characteristics of metazoans. The development, growth, and functional tissue distribution are closely related to holistic tissue or organ homeostasis. However, the connection between cell polarity and osteoarthritis (OA) is less well-known. In OA, multiple chondrocyte clusters and tissue disorganisation can be observed in the degraded cartilage tissue. The excessive upregulation of the planar cell polarity (PCP) signalling pathway leads to the loss of cell polarity and organisation in OA progression and aetiology. Recent research has become increasingly aware of the importance of cell polarity and its correlation with OA. Several cell polarity-related treatments have shed light on OA. A thorough understanding of cell polarity and OA would provide more insights for future investigations to treat this worldwide disease.

The translational potential of this article

Understanding cell polarity, associated signalling pathways, organelle changes, and cell movement in the development of OA could lead to advances in precision medicine and enhanced treatment strategies for OA patients.

Differential Sensitivity of Midline Patterning to Mitosis during and after Primitive Streak Extension

Background

Midline establishment is a fundamental process during early embryogenesis for Bilaterians . Midline patterning in nonamniotes can occur without mitosis, through Planar Cell Polarity (PCP) signaling. By contrast, amniotes utilize both cell proliferation and PCP signaling for patterning early midline landmark, the primitive streak (PS). This study examined their roles for midline patterning at post PS-extension.

Results

In contrast to PS extension stages, embryos under mitotic arrest during the post PS-extension preserved notochord (NC) extension and Hensen's node (HN)/PS regression judged by both morphology and marker genes, although they became shorter, and laterality was lost. Remarkably, no or background level of expression was detected for the majority of PCP core components in the NC-HN-PS area at post PS-extension stages, except for robustly detected prickle-1 . Morpholino knockdown of Prickle-1 showed little influence on midline patterning, except for suppressed embryonic growth. Lastly, associated with mitotic arrest-induced size reduction, midline tissue cells displayed hypertrophy.

Conclusion

Thus, the study has identified at least two distinct mitosis sensitivity phases during early midline pattering: One is PS extension that requires both mitosis and PCP, and the other is mitotic arrest-resistant midline patterning with little influence by PCP at post PS-extension stages.

Mesenchymal Vangl1 and Vangl2 facilitate airway elongation and widening independently of the planar cell polarity complex

Adult mammalian lungs exhibit a fractal pattern, as each successive generation of airways is a fraction of the size of the parental branch. Achieving this structure likely requires precise control of airway length and diameter, as the embryonic airways initially lack the fractal scaling observed in the adult. In monolayers and tubes, directional growth can be regulated by the planar cell polarity (PCP) complex. Here, we characterized the roles of PCP complex components in airway initiation, elongation and widening during branching morphogenesis of the lung. Using tissue-specific knockout mice, we surprisingly found that branching morphogenesis proceeds independently of PCP complex function in the lung epithelium. Instead, we found a previously unreported Celsr1-independent role for the PCP complex components Vangl1 and Vangl2 in the pulmonary mesenchyme, where they are required for branch initiation, elongation and widening. Our data thus reveal an explicit function for Vangl1 and Vangl2 that is independent of the core PCP complex, suggesting a functional diversification of PCP complex components in vertebrate development. These data also reveal an essential role for the embryonic mesenchyme in generating the fractal structure of airways in the mature lung.

Canonical and Non-Canonical Wnt Signaling Generates Molecular and Cellular Asymmetries to Establish Embryonic Axes

The formation of embryonic axes is a critical step during animal development, which contributes to establishing the basic body plan in each particular organism. Wnt signaling pathways play pivotal roles in this fundamental process. Canonical Wnt signaling that is dependent on β-catenin regulates the patterning of dorsoventral, anteroposterior, and left-right axes. Non-canonical Wnt signaling that is independent of β-catenin modulates cytoskeletal organization to coordinate cell polarity changes and asymmetric cell movements. It is now well documented that components of these Wnt pathways biochemically and functionally interact to mediate cell-cell communications and instruct cellular polarization in breaking the embryonic symmetry. The dysfunction of Wnt signaling disrupts embryonic axis specification and proper tissue morphogenesis, and mutations of Wnt pathway genes are associated with birth defects in humans. This review discusses the regulatory roles of Wnt pathway components in embryonic axis formation by focusing on vertebrate models. It highlights current progress in decoding conserved mechanisms underlying the establishment of asymmetry along the three primary body axes. By providing an in-depth analysis of canonical and non-canonical pathways in regulating cell fates and cellular behaviors, this work offers insights into the intricate processes that contribute to setting up the basic body plan in vertebrate embryos.

Vangl-dependent mesenchymal thinning shapes the distal lung during murine sacculation

The planar cell polarity (PCP) complex is speculated to function in murine lung development, where branching morphogenesis generates an epithelial tree whose distal tips expand dramatically during sacculation. Here, we show that PCP is dispensable in the airway epithelium for sacculation. Rather, we find a Celsr1-independent role for the PCP component Vangl in the pulmonary mesenchyme: loss of Vangl1/2 inhibits mesenchymal thinning and expansion of the saccular epithelium. Further, loss of mesenchymal Wnt5a mimics sacculation defects observed in Vangl2-mutant lungs, implicating mesenchymal Wnt5a/Vangl signaling as a key regulator of late lung morphogenesis. A computational model predicts that sacculation requires a fluid mesenchymal compartment. Lineage-tracing and cell-shape analyses are consistent with the mesenchyme acting as a fluid tissue, suggesting that loss of Vangl1/2 impacts the ability of mesenchymal cells to exchange neighbors. Our data thus identify an explicit function for Vangl and the pulmonary mesenchyme in actively shaping the saccular epithelium.

Conserved physical mechanisms of cell and tissue elongation

Living organisms have the ability to self-shape into complex structures appropriate for their function. The genetic and molecular mechanisms that enable cells to do this have been extensively studied in several model and non-model organisms. In contrast, the physical mechanisms that shape cells and tissues have only recently started to emerge, in part thanks to new quantitative in vivo measurements of the physical quantities guiding morphogenesis. These data, combined with indirect inferences of physical characteristics, are starting to reveal similarities in the physical mechanisms underlying morphogenesis across different organisms. Here, we review how physics contributes to shape cells and tissues in a simple, yet ubiquitous, morphogenetic transformation: elongation. Drawing from observed similarities across species, we propose the existence of conserved physical mechanisms of morphogenesis.

Planar Cell Polarity Signaling: Coordinated Crosstalk for Cell Orientation

The planar cell polarity (PCP) system is essential for positioning cells in 3D networks to establish the proper morphogenesis, structure, and function of organs during embryonic development. The PCP system uses inter- and intracellular feedback interactions between components of the core PCP, characterized by coordinated planar polarization and asymmetric distribution of cell populations inside the cells. PCP signaling connects the anterior-posterior to left-right embryonic plane polarity through the polarization of cilia in the Kupffer's vesicle/node in vertebrates. Experimental investigations on various genetic ablation-based models demonstrated the functions of PCP in planar polarization and associated genetic disorders. This review paper aims to provide a comprehensive overview of PCP signaling history, core components of the PCP signaling pathway, molecular mechanisms underlying PCP signaling, interactions with other signaling pathways, and the role of PCP in organ and embryonic development. Moreover, we will delve into the negative feedback regulation of PCP to maintain polarity, human genetic disorders associated with PCP defects, as well as challenges associated with PCP.

PCP and Septins govern the polarized organization of the actin cytoskeleton during convergent extension

Convergent extension (CE) requires the coordinated action of the planar cell polarity (PCP) proteins1,2 and the actin cytoskeleton,3,4,5,6 but this relationship remains incompletely understood. For example, PCP signaling orients actomyosin contractions, yet actomyosin is also required for the polarized localization of PCP proteins.7,8 Moreover, the actin-regulating Septins play key roles in actin organization9 and are implicated in PCP and CE in frogs, mice, and fish5,6,10,11,12 but execute only a subset of PCP-dependent cell behaviors. Septin loss recapitulates the severe tissue-level CE defects seen after core PCP disruption yet leaves overt cell polarity intact.5 Together, these results highlight the general fact that cell movement requires coordinated action by distinct but integrated actin populations, such as lamella and lamellipodia in migrating cells13 or medial and junctional actin populations in cells engaged in apical constriction.14,15 In the context of Xenopus mesoderm CE, three such actin populations are important, a superficial meshwork known as the "node-and-cable" system,4,16,17,18 a contractile network at deep cell-cell junctions,6,19 and mediolaterally oriented actin-rich protrusions, which are present both superficially and deeply.4,19,20,21 Here, we exploited the amenability of the uniquely "two-dimensional" node and cable system to probe the relationship between PCP proteins, Septins, and the polarization of this actin network. We find that the PCP proteins Vangl2 and Prickle2 and Septins co-localize at nodes, and that the node and cable system displays a cryptic, PCP- and Septin-dependent anteroposterior (AP) polarity in its organization and dynamics.

Cyclic stretching combined with cell-cell adhesion is sufficient for inducing cell intercalation

Although the important role of cell intercalation within a collective has long been recognized particularly for morphogenesis, the underlying mechanism remains poorly understood. Here we investigate the possibility that cellular responses to cyclic stretching play a major role in this process. By applying synchronized imaging and cyclic stretching to epithelial cells cultured on micropatterned polyacrylamide (PAA) substrates, we discovered that uniaxial cyclic stretching induces cell intercalation along with cell shape change and cell-cell interfacial remodeling. The process involved intermediate steps as previously reported for cell intercalation during embryonic morphogenesis, including the appearance of cell vertices, anisotropic vertex resolution, and directional expansion of cell-cell interface. Using mathematical modeling, we further found that cell shape change in conjunction with dynamic cell-cell adhesions was sufficient to account for the observations. Further investigation with small-molecule inhibitors indicated that disruption of myosin II activities suppressed cyclic stretching-induced intercalation while inhibiting the appearance of oriented vertices. Inhibition of Wnt signaling did not suppress stretch-induced cell shape change but disrupted cell intercalation and vertex resolution. Our results suggest that cyclic stretching, by inducing cell shape change and reorientation in the presence of dynamic cell-cell adhesions, can induce at least some aspects of cell intercalation and that this process is dependent in distinct ways on myosin II activities and Wnt signaling.

Force propagation between epithelial cells depends on active coupling and mechano-structural polarization

Cell-generated forces play a major role in coordinating the large-scale behavior of cell assemblies, in particular during development, wound healing, and cancer. Mechanical signals propagate faster than biochemical signals, but can have similar effects, especially in epithelial tissues with strong cell-cell adhesion. However, a quantitative description of the transmission chain from force generation in a sender cell, force propagation across cell-cell boundaries, and the concomitant response of receiver cells is missing. For a quantitative analysis of this important situation, here we propose a minimal model system of two epithelial cells on an H-pattern ('cell doublet'). After optogenetically activating RhoA, a major regulator of cell contractility, in the sender cell, we measure the mechanical response of the receiver cell by traction force and monolayer stress microscopies. In general, we find that the receiver cells show an active response so that the cell doublet forms a coherent unit. However, force propagation and response of the receiver cell also strongly depend on the mechano-structural polarization in the cell assembly, which is controlled by cell-matrix adhesion to the adhesive micropattern. We find that the response of the receiver cell is stronger when the mechano-structural polarization axis is oriented perpendicular to the direction of force propagation, reminiscent of the Poisson effect in passive materials. We finally show that the same effects are at work in small tissues. Our work demonstrates that cellular organization and active mechanical response of a tissue are key to maintain signal strength and lead to the emergence of elasticity, which means that signals are not dissipated like in a viscous system, but can propagate over large distances.

Mesenchymal Vangl facilitates airway elongation and widening independently of the planar cell polarity complex

A hallmark of mammalian lungs is the fractal nature of the bronchial tree. In the adult, each successive generation of airways is a fraction of the size of the parental branch. This fractal structure is physiologically beneficial, as it minimizes the energy needed for breathing. Achieving this pattern likely requires precise control of airway length and diameter, as the branches of the embryonic airways initially lack the fractal scaling observed in those of the adult lung. In epithelial monolayers and tubes, directional growth can be regulated by the planar cell polarity (PCP) complex. Here, we comprehensively characterized the roles of PCP-complex components in airway initiation, elongation, and widening during branching morphogenesis of the murine lung. Using tissue-specific knockout mice, we surprisingly found that branching morphogenesis proceeds independently of PCP-component expression in the developing airway epithelium. Instead, we found a novel, Celsr1-independent role for the PCP component Vangl in the pulmonary mesenchyme. Specifically, mesenchymal loss of Vangl1/2 leads to defects in branch initiation, elongation, and widening. At the cellular level, we observe changes in the shape of smooth muscle cells that indicate a potential defect in collective mesenchymal rearrangements, which we hypothesize are necessary for lung morphogenesis. Our data thus reveal an explicit function for Vangl that is independent of the core PCP complex, suggesting a functional diversification of PCP components in vertebrate development. These data also reveal an essential role for the embryonic mesenchyme in generating the fractal structure of airways of the mature lung.

A quest for genetic causes underlying signaling pathways associated with neural tube defects

Neural tube defects (NTDs) are serious congenital deformities of the nervous system that occur owing to the failure of normal neural tube closures. Genetic and non-genetic factors contribute to the etiology of neural tube defects in humans, indicating the role of gene-gene and gene-environment interaction in the occurrence and recurrence risk of neural tube defects. Several lines of genetic studies on humans and animals demonstrated the role of aberrant genes in the developmental risk of neural tube defects and also provided an understanding of the cellular and morphological programs that occur during embryonic development. Other studies observed the effects of folate and supplementation of folic acid on neural tube defects. Hence, here we review what is known to date regarding altered genes associated with specific signaling pathways resulting in NTDs, as well as highlight the role of various genetic, and non-genetic factors and their interactions that contribute to NTDs. Additionally, we also shine a light on the role of folate and cell adhesion molecules (CAMs) in neural tube defects.

Blastopore gating mechanism to regulate extracellular fluid excretion

Fluid uptake and efflux play roles in early embryogenesis as well as in adult homeostasis. Multicellular organisms have two main pathways for fluid movement: cellular-level, such as transcellular and paracellular pathways, and tissue-level, involving muscle contraction. Interestingly, early Xenopus embryos with immature functional muscles excrete archenteron fluid via a tissue-level mechanism that opens the blastopore through a gating mechanism that is unclear. Using microelectrodes, we show that the archenteron has a constant fluid pressure and as development progress the blastopore pressure resistance decreases. Combining physical perturbations and imaging analyses, we found that the pushing force exerted by the circumblastoporal collars (CBCs) at the slit periphery regulates pressure resistance. We show that apical constriction at the blastopore dorsoventral ends contributes to this pushing force, and relaxation of ventral constriction causes fluid excretion. These results indicate that actomyosin contraction mediates temporal control of tissue-level blastopore opening and fluid excretion in early Xenopus embryos.

A Yap-dependent mechanoregulatory program sustains cell migration for embryo axis assembly

The assembly of the embryo's primary axis is a fundamental landmark for the establishment of the vertebrate body plan. Although the morphogenetic movements directing cell convergence towards the midline have been described extensively, little is known on how gastrulating cells interpret mechanical cues. Yap proteins are well-known transcriptional mechanotransducers, yet their role in gastrulation remains elusive. Here we show that the double knockout of yap and its paralog yap1b in medaka results in an axis assembly failure, due to reduced displacement and migratory persistence in mutant cells. Accordingly, we identified genes involved in cytoskeletal organization and cell-ECM adhesion as potentially direct Yap targets. Dynamic analysis of live sensors and downstream targets reveal that Yap is acting in migratory cells, promoting cortical actin and focal adhesions recruitment. Our results indicate that Yap coordinates a mechanoregulatory program to sustain intracellular tension and maintain the directed cell migration for embryo axis development.

Dorsal lip maturation and initial archenteron extension depend on Wnt11 family ligands

Wnt11 family proteins are ligands that activate a type of Dishevelled-mediated, non-canonical Wnt signaling pathway. Loss of function causes defects in gastrulation and/or anterior-posterior axis extension in all vertebrates. Non-mammalian vertebrate genomes encode two Wnt11 family proteins whose distinct functions have been unclear. We knocked down Wnt11b and Wnt11, separately and together, in Xenopus laevis. Single morphants exhibited very similar phenotypes of delayed blastopore closure, but they had different phenotypes during the tailbud period. In response to their very similar gastrulation phenotypes, we chose to characterize dual morphants. Using dark field illuminated time-lapse imaging and kymograph analysis, we identified a failure of dorsal blastopore lip maturation that correlated with slower blastopore closure and failure to internalize the endoderm at the dorsal blastopore lip. We connected these externally visible phenotypes to cellular events in the internal tissues by imaging intact fixed embryos stained for anillin and microtubules. We found that the initial extension of the archenteron is correlated with blastopore lip maturation, and archenteron extension is dramatically disrupted by decreased Wnt11 family signaling. We were aided in our interpretation of the immunofluorescence by the novel, membrane proximal location of the cleavage furrow protein anillin in the epithelium of the blastopore lip and early archenteron.

Dishevelled controls bulk cadherin dynamics and the stability of individual cadherin clusters during convergent extension

Animals are shaped through the movement of large cellular collectives. Such morphogenetic processes require cadherin-based cell adhesion to maintain tissue cohesion and planar cell polarity to coordinate movement. Despite a vast literature surrounding cadherin-based adhesion and planar cell polarity, it is unclear how these molecular networks interface. Here we investigate the relationship between cadherins and planar cell polarity during gastrulation cell movements in Xenopus laevis. We first assessed bulk cadherin localization and found that cadherins were enriched at a specific subset of morphogenetically active cell-cell junctions. We then found that cadherin and actin had coupled temporal dynamics and that disruption of planar cell polarity uncoupled these dynamics. Next, using superresolution time-lapse microscopy and quantitative image analysis, we were able to measure the lifespan and size of individual cadherin clusters. Finally, we show that planar cell polarity not only controls the size of cadherin clusters but, more interestingly, regulates cluster stability. These results reveal an intriguing link between two essential cellular properties, adhesion and planar polarity, and provide insight into the molecular control of morphogenetic cell movements.

Single nucleotide polymorphisms of PCP pathway related genes participate in the occurrence and development of neural tube defect

BACKGROUND

To screen the single nucleotide polymorphisms (SNPs) in the coding regions of VANGL and FZD family members related to the plane cell polarity (PCP) signaling pathway in neural tube defects (NTDs) patients, so as to provide theoretical and experimental basis for the prevention and treatment of NTDs by intervening PCP signal transduction.

METHODS

112 NTDs patients were collected as the case group and 112 craniocerebral trauma patients as control. Afterwards, blood genomic DNA was extracted and sequenced. The distribution of SNP alleles and genotypes between case and control groups was analyzed. Finally, the NTD rat model was constructed, and the effect of SNPs on the expression level of VANGL and FZD genes was verified by qRT-PCR.

RESULTS

GC genotype was newly found at VANGL1 c.346G>A, as well as AT genotype in FZD6 c.97A>G. The distribution of VANGL1 c.346g>A allele and genotype was statistically different between the case and control groups (p < 0.05). The newly found genotype GC increased the risk of NTDs (OR = 9.918, 95% CI: 1.234%-79.709%). The results of qRT-PCR showed that the expression level of FZD6 in E11 NTD fetuses were significantly increased (p < 0.05), but there was no obvious difference in the expression of VANGL1.

CONCLUSION

We found a new variant of VANGL1 c.346G>A, whose GC genotype might play an important role in the pathogenesis of NTDs. The SNPs of VANGL1 had no significant effect on its expression level, indicating that it may induce NTDs through other ways. FZD6 was significantly overexpressed in NTDs fetuses.

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.

Nuclear Dishevelled: An enigmatic role in governing cell fate and Wnt signaling

The Dishevelled gene was first identified in Drosophila mutants with disoriented hair and bristle polarity and subsequent work has now demonstrated its importance in critical and diverse aspects of biology. Since those early discoveries, Dishevelled has been shown to coordinate a plethora of developmental and cellular processes that range from controlling cell polarity during gastrulation to partnering with chromatin modifying enzymes to regulate histone methylation at genomic loci. While the role of DVL in development is well-respected and the cytosolic function of DVL has been studied more extensively, its nuclear role continues to remain murky. In this review we highlight some of the seminal discoveries that have contributed to the field, but the primary focus is to discuss recent advances with respect to the nuclear role of Dishevelled. This nuclear function of Dishevelled is a dimension which is proving to be increasingly important yet remains enigmatic.

Cell cortex regulation by the planar cell polarity protein Prickle1

The planar cell polarity pathway regulates cell polarity, adhesion, and rearrangement. Its cytoplasmic core components Prickle (Pk) and Dishevelled (Dvl) often localize as dense puncta at cell membranes to form antagonizing complexes and establish cell asymmetry. In vertebrates, Pk and Dvl have been implicated in actomyosin cortex regulation, but the mechanism of how these proteins control cell mechanics is unclear. Here we demonstrate that in Xenopus prechordal mesoderm cells, diffusely distributed, cytoplasmic Pk1 up-regulates the F-actin content of the cortex. This counteracts cortex down-regulation by Dvl2. Both factors act upstream of casein kinase II to increase or decrease cortical tension. Thus, cortex modulation by Pk1 and Dvl2 is translated into mechanical force and affects cell migration and rearrangement during radial intercalation in the prechordal mesoderm. Pk1 also forms puncta and plaques, which are associated with localized depletion of cortical F-actin, suggesting opposite roles for diffuse and punctate Pk1.

Imaging Methods in Xenopus Cells, Embryos, and Tadpoles

Xenopus is an excellent vertebrate model system ideally suited for a wide range of imaging methods designed to investigate cell and developmental biology processes. The individual cells of Xenopus are much larger than those in many other vertebrate model systems, such that both cell behavior and subcellular processes can more easily be observed and resolved. Gene function in Xenopus can be manipulated and visualized using a variety of approaches, and the embryonic fate map is stereotypical, such that microinjections can target specific tissues and cell types during development. Tissues, organotypic explants, and individual cells can also be mounted in stable chambers and cultured easily in simple salt solutions without cumbersome environmental controls. Furthermore, Xenopus embryonic tissues can be microsurgically isolated and shaped to expose cell behaviors and protein dynamics in any regions of the embryo to high-resolution live-cell imaging. The combination of these attributes makes Xenopus a powerful system for understanding cell and developmental processes as well as disease mechanisms, through quantitative analysis of protein dynamics, cell movements, tissue morphogenesis, and regeneration. Here, we introduce various methods, of both fixed and living tissues, for visualizing Xenopus cells, embryos, and tadpoles. Specifically, we highlight protocol updates for whole-mount in situ hybridization and immunofluorescence, as well as robust live imaging approaches including methods for optimizing the time-lapse imaging of whole embryos and explants.

Putting in the Erk: Growth factor signaling and mesoderm morphogenesis

It has long been known that FGF signaling contributes to mesoderm formation, a germ layer found in triploblasts that is composed of highly migratory cells that give rise to muscles and to the skeletal structures of vertebrates. FGF signaling activates several pathways in the developing mesoderm, including transient activation of the Erk pathway, which triggers mesodermal fate specification through the induction of the gene brachyury and activates morphogenetic programs that allow mesodermal cells to position themselves in the embryo. In this review, we discuss what is known about the generation and interpretation of transient Erk signaling in mesodermal tissues across species. We focus specifically on mechanisms that translate the level and duration of Erk signaling into cell fate and cell movement instructions and discuss strategies for further interrogating the role that Erk signaling dynamics play in mesodermal gastrulation and morphogenesis.

ARVCF catenin controls force production during vertebrate convergent extension

The design of an animal's body plan is encoded in the genome, and the execution of this program is a mechanical progression involving coordinated movement of proteins, cells, and whole tissues. Thus, a challenge to understanding morphogenesis is connecting events that occur across various length scales. Here, we describe how a poorly characterized adhesion effector, Arvcf catenin, controls Xenopus head-to-tail axis extension. We find that Arvcf is required for axis extension within the intact organism but not within isolated tissues. We show that the organism-scale phenotype results from a defect in tissue-scale force production. Finally, we determine that the force defect results from the dampening of the pulsatile recruitment of cell adhesion and cytoskeletal proteins to membranes. These results provide a comprehensive understanding of Arvcf function during axis extension and produce an insight into how a cellular-scale defect in adhesion results in an organism-scale failure of development.

USP39 is essential for mammalian epithelial morphogenesis through upregulation of planar cell polarity components

Previously, we have shown that the translocation of Grainyhead-like 3 (GRHL3) transcription factor from the nucleus to the cytoplasm triggers the switch from canonical Wnt signaling for epidermal differentiation to non-canonical Wnt signaling for epithelial morphogenesis. However, the molecular mechanism that underlies the cytoplasmic localization of GRHL3 protein and that activates non-canonical Wnt signaling is not known. Here, we show that ubiquitin-specific protease 39 (USP39), a deubiquitinating enzyme, is involved in the subcellular localization of GRHL3 as a potential GRHL3-interacting protein and is necessary for epithelial morphogenesis to up-regulate expression of planar cell polarity (PCP) components. Notably, mouse Usp39-deficient embryos display early embryonic lethality due to a failure in primitive streak formation and apico-basal polarity in epiblast cells, resembling those of mutant embryos of the Prickle1 gene, a crucial PCP component. Current findings provide unique insights into how differentiation and morphogenesis are coordinated to construct three-dimensional complex structures via USP39.

The ubiquitin specific protease 39 (USP39) interacts with the transcription factor and cytoplasmic regulator of planar cell polarity (PCP), Grainyheadlike 3 (Grhl3). USP39-dependent PCP gene upregulation contributes to epithelial morphogenesis.

Characterization of convergent thickening, a major convergence force producing morphogenic movement in amphibians

The morphogenic process of convergent thickening (CT) was originally described as the mediolateral convergence and radial thickening of the explanted ventral involuting marginal zone (IMZ) of Xenopus gastrulae (Keller and Danilchik, 1988). Here, we show that CT is expressed in all sectors of the pre-involution IMZ, which transitions to expressing convergent extension (CE) after involution. CT occurs without CE and drives symmetric blastopore closure in ventralized embryos. Assays of tissue affinity and tissue surface tension measurements suggest CT is driven by increased interfacial tension between the deep IMZ and the overlying epithelium. The resulting minimization of deep IMZ surface area drives a tendency to shorten the mediolateral (circumblastoporal) aspect of the IMZ, thereby generating tensile force contributing to blastopore closure (Shook et al., 2018). These results establish CT as an independent force-generating process of evolutionary significance and provide the first clear example of an oriented, tensile force generated by an isotropic, Holtfreterian/Steinbergian tissue affinity change.

Mechanical regulation of early vertebrate embryogenesis

Embryonic cells grow in environments that provide a plethora of physical cues, including mechanical forces that shape the development of the entire embryo. Despite their prevalence, the role of these forces in embryonic development and their integration with chemical signals have been mostly neglected, and scrutiny in modern molecular embryology tilted, instead, towards the dissection of molecular pathways involved in cell fate determination and patterning. It is now possible to investigate how mechanical signals induce downstream genetic regulatory networks to regulate key developmental processes in the embryo. Here, we review the insights into mechanical control of early vertebrate development, including the role of forces in tissue patterning and embryonic axis formation. We also highlight recent in vitro approaches using individual embryonic stem cells and self-organizing multicellular models of human embryos, which have been instrumental in expanding our understanding of how mechanics tune cell fate and cellular rearrangements during human embryonic development.

Generation, Transmission, and Regulation of Mechanical Forces in Embryonic Morphogenesis

Embryonic morphogenesis is a biological process which depicts shape forming of tissues and organs during development. Unveiling the roles of mechanical forces generated, transmitted, and regulated in cells and tissues through these processes is key to understanding the biophysical mechanisms governing morphogenesis. To this end, it is imperative to measure, simulate, and predict the regulation and control of these mechanical forces during morphogenesis. This article aims to provide a comprehensive review of the recent advances on mechanical properties of cells and tissues, generation of mechanical forces in cells and tissues, the transmission processes of these generated forces during cells and tissues, the tools and methods used to measure and predict these mechanical forces in vivo, in vitro, or in silico, and to better understand the corresponding regulation and control of generated forces. Understanding the biomechanics and mechanobiology of morphogenesis will not only shed light on the fundamental physical mechanisms underlying these concerted biological processes during normal development, but also uncover new information that will benefit biomedical research in preventing and treating congenital defects or tissue engineering and regeneration.

Wnt-frizzled planar cell polarity signaling in the regulation of cell motility

The molecular complexes underlying planar cell polarity (PCP) were first identified in Drosophila through analysis of mutant phenotypes in the adult cuticle and the orientation of associated polarized protrusions such as wing hairs and sensory bristles. The same molecules are conserved in vertebrates and are required for the localization of polarized protrusions such as primary or sensory cilia and the orientation of hair follicles. Not only is PCP signaling required to align cellular structures across a tissue, it is also required to coordinate movement during embryonic development and adult homeostasis. PCP signaling allows cells to interpret positional cues within a tissue to move in the appropriate direction and to coordinate this movement with their neighbors. In this review we outline the molecular basis of the core Wnt-Frizzled/PCP pathway, and describe how this signaling orchestrates collective motility in Drosophila and vertebrates. Here we cover the paradigms of ommatidial rotation and border cell migration in Drosophila, and convergent extension in vertebrates. The downstream cell biological processes that underlie polarized motility include cytoskeletal reorganization, and adherens junctional and extracellular matrix remodeling. We discuss the contributions of these processes in the respective cell motility contexts. Finally, we address examples of individual cell motility guided by PCP factors during nervous system development and in cancer disease contexts.

BAC Recombineering and Transgenesis to Study Cell Polarity and Polarized Tissue Morphogenesis in Mice

Planar cell polarity (PCP) signaling plays a critical role in coordinating cell polarity during various organogenesis processes in mammals, and its disruption is causal to numerous congenital disorders in humans. To elucidate its actions in mammals, mouse genetics is an indispensable approach. Given that both gain- and loss-of-function of many PCP genes often cause similar defects, the standard mouse transgenic approach may not always be ideal for studying PCP genes in their wild-type and mutant forms. Here we describe using BAC (bacterial artificial chromosomes) transgenes as a versatile and effective alternative. Transgenes made from BACs, which are genomic clones 100-200 kb in size, can more faithful recapitulate endogenous gene expression levels and patterns. Bacterial based recombination system can be used to efficiently introduce mutations, fluorescent protein tags, and LoxP sites for conditional expressions. Cre can also be inserted into BACs to map the contribution of cells expressing any PCP gene of interest, and study PCP mediated tissue morphogenesis.

Bmp Signal Gradient Modulates Convergent Cell Movement via Xarhgef3.2 during Gastrulation of Xenopus Embryos

Gastrulation is a critical step in the establishment of a basic body plan during development. Convergence and extension (CE) cell movements organize germ layers during gastrulation. Noncanonical Wnt signaling has been known as major signaling that regulates CE cell movement by activating Rho and Rac. In addition, Bmp molecules are expressed in the ventral side of a developing embryo, and the ventral mesoderm region undergoes minimal CE cell movement while the dorsal mesoderm undergoes dynamic cell movements. This suggests that Bmp signal gradient may affect CE cell movement. To investigate whether Bmp signaling negatively regulates CE cell movements, we performed microarray-based screening and found that the transcription of Xenopus Arhgef3.2 (Rho guanine nucleotide exchange factor) was negatively regulated by Bmp signaling. We also showed that overexpression or knockdown of Xarhgef3.2 caused gastrulation defects. Interestingly, Xarhgef3.2 controlled gastrulation cell movements through interacting with Disheveled (Dsh2) and Dsh2-associated activator of morphogenesis 1 (Daam1). Our results suggest that Bmp gradient affects gastrulation cell movement (CE) via negative regulation of Xarhgef3.2 expression.

In search of conserved principles of planar cell polarization

The making of an embryo and its internal organs entails the spatial coordination of cellular activities. This manifests during tissue morphogenesis as cells change shape, rearrange and divide along preferential axis and during cell differentiation. Cells live in a polarized field and respond to it by polarizing their cellular activities in the plane of the tissue by a phenomenon called planar cell polarization. This phenomenon is ubiquitous in animals and depends on a few conserved planar cell polarity (PCP) pathways. All PCP pathways share two essential characteristics: the existence of local interactions between protein complexes present at the cell surface leading to their asymmetric distribution within cells; a supracellular graded cue that aligns these cellular asymmetries at the tissue level. Here, we discuss the potential common principles of planar cell polarization by comparing the local and global mechanisms employed by the different PCP pathways identified so far. The focus of the review is on the logic of the system rather than the molecules per se.

Distinct Frizzled receptors independently mediate endomesoderm specification and primary archenteron invagination during gastrulation in Nematostella

Endomesodermal cell fate specification and archenteron formation during gastrulation are tightly linked developmental processes in most metazoans. However, studies have shown that in the anthozoan cnidarian Nematostella vectensis, Wnt/β-catenin (cWnt) signalling-mediated endomesodermal cell fate specification can be experimentally uncoupled from Wnt/Planar Cell Polarity (PCP) signalling-mediated primary archenteron invagination. The upstream signalling mechanisms regulating cWnt signalling-dependent endomesoderm cell fate specification and Wnt/PCP signalling-mediated primary archenteron invagination in Nematostella embryos are not well understood. By screening for potential upstream mediators of cWnt and Wnt/PCP signalling, we identified two Nematostella Frizzled homologs that are expressed early in development. NvFzd1 is expressed maternally and in a broad pattern during early development while NvFzd10 is zygotically expressed at the animal pole in blastula stage embryos and is restricted to the invaginating cells of the presumptive endomesoderm. Molecular and morphological characterization of NvFzd1 and NvFzd10 knock-down phenotypes provide evidence for distinct regulatory roles for the two receptors in endomesoderm cell fate specification and primary archenteron invagination. These results provide further experimental evidence for the independent regulation of endomesodermal cell fate specification and primary archenteron invagination during gastrulation in Nematostella. Moreover, these results provide additional support for the previously proposed two-step model for the independent evolution of cWnt-mediated cell fate specification and Wnt/PCP-mediated primary archenteron invagination.

Imaging of dynamic actin remodeling reveals distinct behaviors of head and trunk mesoderm in gastrulating Xenopus laevis

Gastrulation involves coordinated movements of cells, facilitating mesoderm and endoderm internalization and proper patterning of tissues across the germ layers. In Xenopus laevis, head mesoderm migrates collectively along the blastocoel roof fibronectin network towards the animal pole. Meanwhile, the trunk mesodermal cells migrate over each other in convergent thickening and convergent extension movements elongating the body axis. The behaviors of cells in these regions are investigated mainly in tissue explants taken from the respective head or trunk mesodermal regions. How cells behave at the transitional zone between these territories is not described in detail. To learn about cell behaviors around this junction, we imaged cell movements in an explant that encompassed the head and trunk mesoderm. We observed that head mesoderm migration on fibronectin employed lamellipodial protrusions at the leading edge and dynamic actin remodeling in the trailing cells. Trunk mesodermal cells underwent mediolateral cell elongation and intercalation to form the notochord. Lateral edges of the notochord were defined before the anterior edge. Our movie reveals distinct mesodermal cell behaviors occurring simultaneously in different regions of gastrulating embryos. This study highlights the power of applying modern microscopy tools to revisit classical experiments, permitting a greater understanding of the cellular dynamics that shape the embryo.

Core pathway proteins and the molecular basis of planar polarity in the zebrafish gastrula

The planar polarization of cells and subcellular structures is critical for embryonic development. Coordination of this polarity can provide cells a sense of direction in relation to the anterior-posterior and dorsal-ventral body axes. Fly epithelia use a core pathway comprised of transmembrane (Van Gogh/Strabismus, Frizzled, and Flamingo/Starry night) and cytoplasmic (Prickle or Spiny-legs, Dishevelled, and Diego) proteins to communicate directional information between cells and thereby promote the uniform orientation of structures such as hairs. In the zebrafish gastrula, planar polarity underlies complex cellular processes, including directed migration and intercalation, that are required to shape the embryo body. Like other vertebrates, the zebrafish genome encodes homologs of each core protein, and it is well-established that polarized gastrula cell behaviors are regulated by some of them. However, it is unknown whether a conserved six-member core protein pathway regulates planar polarity during zebrafish gastrulation. Here, we review our current understanding of core protein function as it relates to two specific examples of planar polarity, the dorsal convergence of lateral gastrula cells and the mediolateral intercalation of midline cells. We consider the hallmarks of fly planar polarity and discuss data regarding asymmetric protein localization and function, and the intercellular communication of polarity information.

Otic Neurogenesis in Xenopus laevis: Proliferation, Differentiation, and the Role of Eya1

Using immunostaining and confocal microscopy, we here provide the first detailed description of otic neurogenesis in Xenopus laevis. We show that the otic vesicle comprises a pseudostratified epithelium with apicobasal polarity (apical enrichment of Par3, aPKC, phosphorylated Myosin light chain, N-cadherin) and interkinetic nuclear migration (apical localization of mitotic, pH3-positive cells). A Sox3-immunopositive neurosensory area in the ventromedial otic vesicle gives rise to neuroblasts, which delaminate through breaches in the basal lamina between stages 26/27 and 39. Delaminated cells congregate to form the vestibulocochlear ganglion, whose peripheral cells continue to proliferate (as judged by EdU incorporation), while central cells differentiate into Islet1/2-immunopositive neurons from stage 29 on and send out neurites at stage 31. The central part of the neurosensory area retains Sox3 but stops proliferating from stage 33, forming the first sensory areas (utricular/saccular maculae). The phosphatase and transcriptional coactivator Eya1 has previously been shown to play a central role for otic neurogenesis but the underlying mechanism is poorly understood. Using an antibody specifically raised against Xenopus Eya1, we characterize the subcellular localization of Eya1 proteins, their levels of expression as well as their distribution in relation to progenitor and neuronal differentiation markers during otic neurogenesis. We show that Eya1 protein localizes to both nuclei and cytoplasm in the otic epithelium, with levels of nuclear Eya1 declining in differentiating (Islet1/2+) vestibulocochlear ganglion neurons and in the developing sensory areas. Morpholino-based knockdown of Eya1 leads to reduction of proliferating, Sox3- and Islet1/2-immunopositive cells, redistribution of cell polarity proteins and loss of N-cadherin suggesting that Eya1 is required for maintenance of epithelial cells with apicobasal polarity, progenitor proliferation and neuronal differentiation during otic neurogenesis.

Tril dampens Nodal signaling through Pellino2- and Traf6-mediated activation of Nedd4l

Toll-like receptor 4 (Tlr) interactor with leucine-rich repeats (Tril) functions as a Tlr coreceptor to mediate innate immunity in adults. In Xenopus embryos, Tril triggers degradation of the transforming growth factor β (Tgf-ß) family inhibitor, Smad7. This enhances bone morphogenetic protein (Bmp) signaling to enable ventral mesoderm to commit to a blood fate. Here, we show that Tril simultaneously dampens Nodal signaling by catalytically activating the ubiquitin ligase NEDD4 Like (Nedd4l). Nedd4l then targets Nodal receptors for degradation. How Tril signals are transduced in a nonimmune context is unknown. We identify the ubiquitin ligase Pellino2 as a protein that binds to the cytoplasmic tail of Tril and subsequently forms a complex with Nedd4l and another E3 ligase, TNF-receptor associated factor 6 (Traf6). Pellino2 and Traf6 are essential for catalytic activation of Nedd4l, both in Xenopus and in mammalian cells. Traf6 ubiquitinates Nedd4l, which is then recruited to membrane compartments where activation occurs. Collectively, our findings reveal that Tril initiates a noncanonical Tlr-like signaling cascade to activate Nedd4l, thereby coordinately regulating the Bmp and Nodal arms of the Tgf-ß superfamily during vertebrate development.

Frizzled7 Activates β-Catenin-Dependent and β-Catenin-Independent Wnt Signalling Pathways During Developmental Morphogenesis: Implications for Therapeutic Targeting in Colorectal Cancer

Frizzled₇ activates β-catenin-dependent and β-catenin-independent Wnt signalling pathways, is highly conserved through evolution from the ancient phylum hydra to man, plays essential roles in stem cells, tissue homeostasis and regeneration in the adult, and is upregulated in diverse cancers. Much of what is known about the core components of the Wnt signalling pathways was derived from studying the function of Frizzled₇ orthologues in the development of lower organism. As we interrogate Frizzled₇ signalling and function for therapeutic targeting in cancer, it is timely to revisit lower organisms to gain insight into the context dependent and dynamic nature of Wnt signalling for effective drug design.

The Ascidia Ciona robusta Provides Novel Insights on the Evolution of the AP-1 Transcriptional Complex

The Activator Protein-1 transcription factor family (AP-1) transcriptional complex is historically defined as an early response group of transcription factors formed by dimeric complexes of the Jun, Fos, Atf, and Maf bZIP proteins that control cell proliferation and differentiation by regulating gene expression. It has been greatly investigated in many model organisms across metazoan evolution. Nevertheless, its complexity and variability of action made its multiple functions difficult to be defined. Here, we place the foundations for understanding the complexity of AP-1 transcriptional members in tunicates. We investigated the gene members of this family in the ascidian Ciona robusta and identified single copies of Jun, Fos, Atf3, Atf2/7, and Maf bZIP-related factors that could have a role in the formation of the AP-1 complex. We highlight that mesenchyme is a common cellular population where all these factors are expressed during embryonic development, and that, moreover, Fos shows a wider pattern of expression including also notochord and neural cells. By ectopic expression in transgenic embryos of Jun and Fos genes alone or in combination, we investigated the phenotypic alterations induced by these factors and highlighted a degree of functional conservation of the AP-1 complex between Ciona and vertebrates. The lack of gene redundancy and the first pieces of evidence of conserved functions in the control of cell movements and structural organization exerted by these factors open the way for using Ciona as a helpful model system to uncover the multiple potentialities of this highly complex family of bZIP transcription factors.

Twinfilin1 controls lamellipodial protrusive activity and actin turnover during vertebrate gastrulation

The dynamic control of the actin cytoskeleton is a key aspect of essentially all animal cell movements. Experiments in single migrating cells and in vitro systems have provided an exceptionally deep understanding of actin dynamics. However, we still know relatively little of how these systems are tuned in cell-type-specific ways, for example in the context of collective cell movements that sculpt the early embryo. Here, we provide an analysis of the actin-severing and depolymerization machinery during vertebrate gastrulation, with a focus on Twinfilin1 (Twf1) in Xenopus. We find that Twf1 is essential for convergent extension, and loss of Twf1 results in a disruption of lamellipodial dynamics and polarity. Moreover, Twf1 loss results in a failure to assemble polarized cytoplasmic actin cables, which are essential for convergent extension. These data provide an in vivo complement to our more-extensive understanding of Twf1 action in vitro and provide new links between the core machinery of actin regulation and the specialized cell behaviors of embryonic morphogenesis.

Ciliary Signalling and Mechanotransduction in the Pathophysiology of Craniosynostosis

Craniosynostosis (CS) is the second most prevalent inborn craniofacial malformation; it results from the premature fusion of cranial sutures and leads to dimorphisms of variable severity. CS is clinically heterogeneous, as it can be either a sporadic isolated defect, more frequently, or part of a syndromic phenotype with mendelian inheritance. The genetic basis of CS is also extremely heterogeneous, with nearly a hundred genes associated so far, mostly mutated in syndromic forms. Several genes can be categorised within partially overlapping pathways, including those causing defects of the primary cilium. The primary cilium is a cellular antenna serving as a signalling hub implicated in mechanotransduction, housing key molecular signals expressed on the ciliary membrane and in the cilioplasm. This mechanical property mediated by the primary cilium may also represent a cue to understand the pathophysiology of non-syndromic CS. In this review, we aimed to highlight the implication of the primary cilium components and active signalling in CS pathophysiology, dissecting their biological functions in craniofacial development and in suture biomechanics. Through an in-depth revision of the literature and computational annotation of disease-associated genes we categorised 18 ciliary genes involved in CS aetiology. Interestingly, a prevalent implication of midline sutures is observed in CS ciliopathies, possibly explained by the specific neural crest origin of the frontal bone.

Planar cell polarity pathway in kidney development, function and disease

Planar cell polarity (PCP) refers to the coordinated orientation of cells in the tissue plane. Originally discovered and studied in Drosophila melanogaster, PCP is now widely recognized in vertebrates, where it is implicated in organogenesis. Specific sets of PCP genes have been identified. The proteins encoded by these genes become asymmetrically distributed to opposite sides of cells within a tissue plane and guide many processes that include changes in cell shape and polarity, collective cell movements or the uniform distribution of cell appendages. A unifying characteristic of these processes is that they often involve rearrangement of actomyosin. Mutations in PCP genes can cause malformations in organs of many animals, including humans. In the past decade, strong evidence has accumulated for a role of the PCP pathway in kidney development including outgrowth and branching morphogenesis of ureteric bud and podocyte development. Defective PCP signalling has been implicated in the pathogenesis of developmental kidney disorders of the congenital anomalies of the kidney and urinary tract spectrum. Understanding the origins, molecular constituents and cellular targets of PCP provides insights into the involvement of PCP molecules in normal kidney development and how dysfunction of PCP components may lead to kidney disease.

Mechanical heterogeneity along single cell-cell junctions is driven by lateral clustering of cadherins during vertebrate axis elongation

Morphogenesis is governed by the interplay of molecular signals and mechanical forces across multiple length scales. The last decade has seen tremendous advances in our understanding of the dynamics of protein localization and turnover at subcellular length scales, and at the other end of the spectrum, of mechanics at tissue-level length scales. Integrating the two remains a challenge, however, because we lack a detailed understanding of the subcellular patterns of mechanical properties of cells within tissues. Here, in the context of the elongating body axis of Xenopus embryos, we combine tools from cell biology and physics to demonstrate that individual cell-cell junctions display finely-patterned local mechanical heterogeneity along their length. We show that such local mechanical patterning is essential for the cell movements of convergent extension and is imparted by locally patterned clustering of a classical cadherin. Finally, the patterning of cadherins and thus local mechanics along cell-cell junctions are controlled by Planar Cell Polarity signaling, a key genetic module for CE that is mutated in diverse human birth defects.

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.