Planar polarity: A new player in both lung development and disease

Disrupted endosomal trafficking of the Vangl-Celsr polarity complex underlies congenital anomalies in Xenopus trachea-esophageal morphogenesis

Disruptions in foregut morphogenesis can result in life-threatening conditions where the trachea and esophagus fail to separate, such as esophageal atresia (EA) and tracheoesophageal fistulas (TEFs). The developmental basis of these congenital anomalies is poorly understood, but recent genome sequencing reveals that de novo variants in intracellular trafficking genes are enriched in EA/TEF patients. Here, we confirm that mutation of orthologous genes in Xenopus disrupts trachea-esophageal separation similar to EA/TEF patients. The Rab11a recycling endosome pathway is required to localize Vangl-Celsr polarity complexes at the luminal cell surface where opposite sides of the foregut tube fuse. Partial loss of endosomal trafficking or Vangl-Celsr complexes disrupts epithelial polarity and cell division orientation. Mutant cells accumulate at the fusion point, fail to relocalize cadherin, and do not separate into distinct trachea and esophagus. These data provide insights into the mechanisms of congenital anomalies and general paradigms of tissue fusion during organogenesis.

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.

Cigarette smoke-induced injury induces distinct sex-specific transcriptional signatures in mice tracheal epithelial cells

The airway epithelial barrier is crucial for defending against respiratory insults and diseases. Disruption of epithelial integrity contributes to respiratory diseases, and sex-specific differences in susceptibility and severity have been observed. However, sex-specific differences in the context of respiratory diseases are often overlooked, especially in murine models. In this study, we investigated the in vitro transcriptomics of male and female murine tracheal epithelial cells (mTECs) in response to chronic cigarette smoke (CS) exposure using an International Organization for Standardization (ISO) puff regimen. Our findings reveal sex-specific differences in the baseline characteristics of airway epithelial cells. Female mTECs demonstrated stronger barrier function and higher ciliary function compared with males. The barrier function was disrupted in both males and females following chronic CS, but the difference was more significant in females due to their higher baseline. Female mice exhibited transcriptional signatures suggesting dedifferentiation with increased basal cells and markers of cellular senescence. Pathway analysis indicated potential protective roles of planar cell polarity (PCP) in preventing dedifferentiation in male mice exposed to CS. We also observed sex-specific differences in the DNA damage response and antioxidant levels, suggesting distinct mechanisms underlying cellular stress. Understanding these sex-specific mechanisms could facilitate the development of targeted therapeutic strategies for lung diseases associated with environmental insults. Recognizing sex-based differences in disease susceptibility and treatment response can lead to personalized care and improved outcomes. Clinical trials should consider sex as a biological variable to develop effective interventions that address the unique differences between men and women in respiratory diseases.NEW & NOTEWORTHY The study underscores the importance of considering sex-specific differences in the airway epithelium in respiratory diseases such as COPD. Differences in gene expression between males and females at baseline and in response to chronic injury in the airway epithelium could have implications on disease susceptibility, both in COPD and other respiratory diseases. Therefore, understanding these differences is crucial for developing targeted therapies to treat respiratory diseases based on a sex-specific manner.

Eng2, a new player involved in feedback loop regulation of Cdc42 activity in fission yeast

Cell polarity and morphogenesis are regulated by the small GTPase Cdc42. Even though major advances have been done in the field during the last years, the molecular details leading to its activation in particular cellular contexts are not completely understood. In fission yeast, the β(1,3)-glucanase Eng2 is a "moonlighting protein" with a dual function, acting as a hydrolase during spore dehiscence, and as component of the endocytic machinery in vegetative cells. Here, we report that Eng2 plays a role in Cdc42 activation during polarized growth through its interaction with the scaffold protein Scd2, which brings Cdc42 together with its guanine nucleotide exchange factor (GEF) Scd1. eng2Δ mutant cells have defects in activation of the bipolar growth (NETO), remaining monopolar during all the cell cycle. In the absence of Eng2 the accumulation of Scd1 and Scd2 at the poles is reduced, the levels of Cdc42 activation decrease, and the Cdc42 oscillatory behavior, associated with bipolar growth in wild type cells, is altered. Furthermore, overexpression of Eng2 partially rescues the growth and polarity defects of a cdc42-L160S mutant. Altogether, our work unveils a new factor regulating the activity of Cdc42, which could potentially link the polarity and endocytic machineries.

Apical Restriction of the Planar Cell Polarity Component VANGL in Pancreatic Ducts Is Required to Maintain Epithelial Integrity

Cell polarity is essential for the architecture and function of numerous epithelial tissues. Here, we show that apical restriction of planar cell polarity (PCP) components is necessary for the maintenance of epithelial integrity. Using the mammalian pancreas as a model, we find that components of the core PCP pathway, such as the transmembrane protein Van Gogh-like (VANGL), become apically restricted over a period of several days. Expansion of VANGL localization to the basolateral membranes of progenitors leads to their death and disruption of the epithelial integrity. VANGL basolateral expansion does not affect apico-basal polarity but acts in the cells where Vangl is mislocalized by reducing Dishevelled and its downstream target ROCK. This reduction in ROCK activity culminates in progenitor cell egression, death, and eventually pancreatic hypoplasia. Thus, precise spatiotemporal modulation of VANGL-dependent PCP signaling is crucial for proper pancreatic morphogenesis.

Planar cell polarity in organ formation

The planar cell polarity (PCP) pathway controls a variety of morphological events across many species. During embryonic development, the PCP pathway regulates coordinated behaviour of groups of cells to direct morphogenetic processes such as convergent extension and collective cell migration. In this review we discuss the increasingly prominent role of the PCP pathway in organogenesis, focusing on the lungs, kidneys and heart. We also highlight emerging evidence that PCP gene mutations are associated with adult diseases.

WNT receptor signalling in lung physiology and pathology

The WNT signalling cascades have emerged as critical regulators of a wide variety of biological aspects involved in lung development as well as in physiological and pathophysiological processes in the adult lung. WNTs (secreted glycoproteins) interact with various transmembrane receptors and co-receptors to activate signalling pathways that regulate transcriptional as well as non-transcriptional responses within cells. In physiological conditions, the majority of WNT receptors and co-receptors can be detected in the adult lung. However, dysregulation of WNT signalling pathways contributes to the development and progression of chronic lung pathologies, including idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD), asthma and lung cancer. The interaction between a WNT and the (co-)receptor(s) present at the cell surface is the initial step in transducing an extracellular signal into an intracellular response. This proximal event in WNT signal transduction with (cell-specific) ligand-receptor interactions is of great interest as a potential target for pharmacological intervention. In this review we highlight the diverse expression of various WNT receptors and co-receptors in the aforementioned chronic lung diseases and discuss the currently available biologicals and pharmacological tools to modify proximal WNT signalling.

Vangl2 is essential for myocardial remodeling activated by Wnt/JNK signaling

The Wnt/JNK pathway, responsible for tissue polarity in cardiogenesis in vertebrates, has been shown to play numerous roles during differentiation and development of cardiac myocytes. Van Gogh-like-2 (Vangl2) is a core component that regulates the induction of polarized cellular and tissue morphology during animal development. However, little is known about Wnt/JNK signaling pathway in the process of myocardial remodeling. In present study, we found that activation of Wnt/JNK signaling by Wnt5a stimulates enlargement of cardiomyocyte surface area. The hypertrophic features were inhibited in Vangl2 depleted cells. Meanwhile, Wnt/JNK activation induced cytoskeleton rearrangement but failed to activate these effects in cells lacking Vangl2. Moreover, Wnt/JNK activation significantly increased the cell apoptosis by mediating the mitochondrial permeability transition pore (mPTP) dysfunction, whereas knockdown of Vangl2 partly reversed these effects. These results suggest that activation of Wnt/JNK signaling stimulates myocardial remodeling (cell morphological changes, apoptosis and mitochondrial dysfunction), in which Vangl2 may play an essential role.

'WNT-er is coming': WNT signalling in chronic lung diseases

Chronic lung diseases represent a major public health problem with only limited therapeutic options. An important unmet need is to identify compounds and drugs that target key molecular pathways involved in the pathogenesis of chronic lung diseases. Over the last decade, there has been extensive interest in investigating Wingless/integrase-1 (WNT) signalling pathways; and WNT signal alterations have been linked to pulmonary disease pathogenesis and progression. Here, we comprehensively review the cumulative evidence for WNT pathway alterations in chronic lung pathologies, including idiopathic pulmonary fibrosis, pulmonary arterial hypertension, asthma and COPD. While many studies have focused on the canonical WNT/β-catenin signalling pathway, recent reports highlight that non-canonical WNT signalling may also significantly contribute to chronic lung pathologies; these studies will be particularly featured in this review. We further discuss recent advances uncovering the role of WNT signalling early in life, the potential of pharmaceutically modulating WNT signalling pathways and highlight (pre)clinical studies describing promising new therapies for chronic lung diseases.

Patterned cell and matrix dynamics in branching morphogenesis

Many embryonic organs undergo branching morphogenesis to maximize their functional epithelial surface area. Branching morphogenesis requires the coordinated interplay of multiple types of cells with the extracellular matrix (ECM). During branching morphogenesis, new branches form by "budding" or "clefting." Cell migration, proliferation, rearrangement, deformation, and ECM dynamics have varied roles in driving budding versus clefting in different organs. Elongation of the newly formed branch and final maturation of the tip involve cellular mechanisms that include cell elongation, intercalation, convergent extension, proliferation, and differentiation. New methodologies such as high-resolution live imaging, tension sensors, and force-mapping techniques are providing exciting new opportunities for future research into branching morphogenesis.

Temporal dynamics of the developing lung transcriptome in three common inbred strains of laboratory mice reveals multiple stages of postnatal alveolar development

To characterize temporal patterns of transcriptional activity during normal lung development, we generated genome wide gene expression data for 26 pre- and post-natal time points in three common inbred strains of laboratory mice (C57BL/6J, A/J, and C3H/HeJ). Using Principal Component Analysis and least squares regression modeling, we identified both strain-independent and strain-dependent patterns of gene expression. The 4,683 genes contributing to the strain-independent expression patterns were used to define a murine Developing Lung Characteristic Subtranscriptome (mDLCS). Regression modeling of the Principal Components supported the four canonical stages of mammalian embryonic lung development (embryonic, pseudoglandular, canalicular, saccular) defined previously by morphology and histology. For postnatal alveolar development, the regression model was consistent with four stages of alveolarization characterized by episodic transcriptional activity of genes related to pulmonary vascularization. Genes expressed in a strain-dependent manner were enriched for annotations related to neurogenesis, extracellular matrix organization, and Wnt signaling. Finally, a comparison of mouse and human transcriptomics from pre-natal stages of lung development revealed conservation of pathways associated with cell cycle, axon guidance, immune function, and metabolism as well as organism-specific expression of genes associated with extracellular matrix organization and protein modification. The mouse lung development transcriptome data generated for this study serves as a unique reference set to identify genes and pathways essential for normal mammalian lung development and for investigations into the developmental origins of respiratory disease and cancer. The gene expression data are available from the Gene Expression Omnibus (GEO) archive (GSE74243). Temporal expression patterns of mouse genes can be investigated using a study specific web resource (http://lungdevelopment.jax.org).

Association of Forced Vital Capacity with the Developmental Gene NCOR2

Background

Forced Vital Capacity (FVC) is an important predictor of all-cause mortality in the absence of chronic respiratory conditions. Epidemiological evidence highlights the role of early life factors on adult FVC, pointing to environmental exposures and genes affecting lung development as risk factors for low FVC later in life. Although highly heritable, a small number of genes have been found associated with FVC, and we aimed at identifying further genetic variants by focusing on lung development genes.

Methods

Per-allele effects of 24,728 SNPs in 403 genes involved in lung development were tested in 7,749 adults from three studies (NFBC1966, ECRHS, EGEA). The most significant SNP for the top 25 genes was followed-up in 46,103 adults (CHARGE and SpiroMeta consortia) and 5,062 children (ALSPAC). Associations were considered replicated if the replication p-value survived Bonferroni correction (p<0.002; 0.05/25), with a nominal p-value considered as suggestive evidence. For SNPs with evidence of replication, effects on the expression levels of nearby genes in lung tissue were tested in 1,111 lung samples (Lung eQTL consortium), with further functional investigation performed using public epigenomic profiling data (ENCODE).

Results

NCOR2-rs12708369 showed strong replication in children (p = 0.0002), with replication unavailable in adults due to low imputation quality. This intronic variant is in a strong transcriptional enhancer element in lung fibroblasts, but its eQTL effects could not be tested due to low imputation quality in the eQTL dataset. SERPINE2-rs6754561 replicated at nominal level in both adults (p = 0.036) and children (p = 0.045), while WNT16-rs2707469 replicated at nominal level only in adults (p = 0.026). The eQTL analyses showed association of WNT16-rs2707469 with expression levels of the nearby gene CPED1. We found no statistically significant eQTL effects for SERPINE2-rs6754561.

Conclusions

We have identified a new gene, NCOR2, in the retinoic acid signalling pathway pointing to a role of vitamin A metabolism in the regulation of FVC. Our findings also support SERPINE2, a COPD gene with weak previous evidence of association with FVC, and suggest WNT16 as a further promising candidate.

Phosphorylation-dependent inhibition of Cdc42 GEF Gef1 by 14-3-3 protein Rad24 spatially regulates Cdc42 GTPase activity and oscillatory dynamics during cell morphogenesis

The 14-3-3 protein Rad24 modulates the availability of Cdc42 GEF Gef1, spatially regulating Cdc42 activity during cell morphogenesis. Gef1 is sequestered in the cytoplasm upon 14-3-3 interaction, mediated by Orb6 kinase. The resulting competition for Gef1 promotes anticorrelated Cdc42 oscillations at cell tips.

Active Cdc42 GTPase, a key regulator of cell polarity, displays oscillatory dynamics that are anticorrelated at the two cell tips in fission yeast. Anticorrelation suggests competition for active Cdc42 or for its effectors. Here we show how 14-3-3 protein Rad24 associates with Cdc42 guanine exchange factor (GEF) Gef1, limiting Gef1 availability to promote Cdc42 activation. Phosphorylation of Gef1 by conserved NDR kinase Orb6 promotes Gef1 binding to Rad24. Loss of Rad24–Gef1 interaction increases Gef1 protein localization and Cdc42 activation at the cell tips and reduces the anticorrelation of active Cdc42 oscillations. Increased Cdc42 activation promotes precocious bipolar growth activation, bypassing the normal requirement for an intact microtubule cytoskeleton and for microtubule-dependent polarity landmark Tea4-PP1. Further, increased Cdc42 activation by Gef1 widens cell diameter and alters tip curvature, countering the effects of Cdc42 GTPase-activating protein Rga4. The respective levels of Gef1 and Rga4 proteins at the membrane define dynamically the growing area at each cell tip. Our findings show how the 14-3-3 protein Rad24 modulates the availability of Cdc42 GEF Gef1, a homologue of mammalian Cdc42 GEF DNMBP/TUBA, to spatially control Cdc42 GTPase activity and promote cell polarization and cell shape emergence.

Vangl1 and Vangl2: planar cell polarity components with a developing role in cancer

Cancers commonly reactivate embryonic developmental pathways to promote the aggressive behavior of their cells, resulting in metastasis and poor patient outcome. While developmental pathways such as canonical Wnt signaling and epithelial-to-mesenchymal transition have received much attention, our understanding of the role of the planar cell polarity (PCP) pathway in tumor progression remains rudimentary. Protein components of PCP, including a subset that overlaps with the canonical Wnt pathway, partition in polarized epithelial cells along the planar axis and are required for the establishment and maintenance of lateral epithelial polarity. Significant insight into PCP regulation of developmental and cellular processes has come from analysis of the functions of the core PCP scaffolding proteins Vangl1 and Vangl2. In particular, studies on zebrafish and with Looptail (Lp) mice, which harbor point mutations in Vangl2 that alter its trafficking and localization, point to roles for the PCP pathway in maintaining cell polarization along both the apical-basal and planar axes as well as in collective cell motility and invasiveness. Recent findings have suggested that the Vangls can promote similar processes in tumor cells. Initial data-mining efforts suggest that VANGL1 and VANGL2 are dysregulated in human cancers, and estrogen receptor (ER)-positive breast cancer patients whose tumors exhibit elevated VANGL1 expression suffer from shortened overall survival. Overall, evidence is beginning to accumulate that the heightened cellular motility and invasiveness associated with PCP reactivation may contribute to the malignancy of some cancer subtypes.

Breaking barriers. New insights into airway epithelial barrier function in health and disease

Epithelial permeability is a hallmark of mucosal inflammation, but the molecular mechanisms involved remain poorly understood. A key component of the epithelial barrier is the apical junctional complex that forms between neighboring cells. Apical junctional complexes are made of tight junctions and adherens junctions and link to the cellular cytoskeleton via numerous adaptor proteins. Although the existence of tight and adherens junctions between epithelial cells has long been recognized, in recent years there have been significant advances in our understanding of the molecular regulation of junctional complex assembly and disassembly. Here we review the current thinking about the structure and function of the apical junctional complex in airway epithelial cells, emphasizing the translational aspects of relevance to cystic fibrosis and asthma. Most work to date has been conducted using cell culture models, but technical advancements in imaging techniques suggest that we are on the verge of important new breakthroughs in this area in physiological models of airway diseases.

Molecular determinants of lung development

Development of the pulmonary system is essential for terrestrial life. The molecular pathways that regulate this complex process are beginning to be defined, and such knowledge is critical to our understanding of congenital and acquired lung diseases. A recent workshop was convened by the National Heart, Lung, and Blood Institute to discuss the developmental principles that regulate the formation of the pulmonary system. Emerging evidence suggests that key developmental pathways not only regulate proper formation of the pulmonary system but are also reactivated upon postnatal injury and repair and in the pathogenesis of human lung diseases. Molecular understanding of early lung development has also led to new advances in areas such as generation of lung epithelium from pluripotent stem cells. The workshop was organized into four different topics, including early lung cell fate and morphogenesis, mechanisms of lung cell differentiation, tissue interactions in lung development, and environmental impact on early lung development. Critical points were raised, including the importance of epigenetic regulation of lung gene expression, the dearth of knowledge on important mesenchymal lineages within the lung, and the interaction between the developing pulmonary and cardiovascular system. This manuscript describes the summary of the discussion along with general recommendations to overcome the gaps in knowledge in lung developmental biology.

Sox9 plays multiple roles in the lung epithelium during branching morphogenesis

Lung branching morphogenesis is a highly orchestrated process that gives rise to the complex network of gas-exchanging units in the adult lung. Intricate regulation of signaling pathways, transcription factors, and epithelial-mesenchymal cross-talk are critical to ensuring branching morphogenesis occurs properly. Here, we describe a role for the transcription factor Sox9 during lung branching morphogenesis. Sox9 is expressed at the distal tips of the branching epithelium in a highly dynamic manner as branching occurs and is down-regulated starting at embryonic day 16.5, concurrent with the onset of terminal differentiation of type 1 and type 2 alveolar cells. Using epithelial-specific genetic loss- and gain-of-function approaches, our results demonstrate that Sox9 controls multiple aspects of lung branching. Fine regulation of Sox9 levels is required to balance proliferation and differentiation of epithelial tip progenitor cells, and loss of Sox9 leads to direct and indirect cellular defects including extracellular matrix defects, cytoskeletal disorganization, and aberrant epithelial movement. Our evidence shows that unlike other endoderm-derived epithelial tissues, such as the intestine, Wnt/β-catenin signaling does not regulate Sox9 expression in the lung. We conclude that Sox9 collectively promotes proper branching morphogenesis by controlling the balance between proliferation and differentiation and regulating the extracellular matrix.

Testin interacts with vangl2 genetically to regulate inner ear sensory cell orientation and the normal development of the female reproductive tract in mice

BACKGROUND

Planar cell polarity (PCP) signaling regulates the coordinated polarization of cells and is required for the normal development and function of many tissues. Previous studies have identified conserved PCP genes, such as Van Gogh-like 2 (Vangl2) and Prickle (Pk), in the regulation of coordinated orientation of inner ear hair cells and female reproductive tract development. Testin shares a PET-LIM homology with Pk. It is not clear whether Testin acts in PCP processes in mammals.

RESULTS

We identified Testin as a Vangl2-interacting protein through a 2-hybrid screen with a cochlea cDNA library. Testin is enriched to cell-cell boundaries in the presence of Vangl2 in cultured cells. Genetic inactivation of Testin leads to abnormal hair cell orientation in the vestibule and cellular patterning defects in the cochlea. In addition, Testin genetically interacts with Vangl2 to regulate hair cell orientation in the cochlea and the opening of the vaginal tract.

CONCLUSIONS

Our findings suggested Testin as a gene involved in coordinated hair cell orientation in the inner ear and in female reproductive tract development. Furthermore, its genetic interaction with Vangl2 implicated it as a potential molecular link, responsible for mediating the role of Vangl2-containing membranous PCP complexes in directing morphologic polarization.

A unified model for left-right asymmetry? Comparison and synthesis of molecular models of embryonic laterality

Understanding how and when the left-right (LR) axis is first established is a fundamental question in developmental biology. A popular model is that the LR axis is established relatively late in embryogenesis, due to the movement of motile cilia and the resultant directed fluid flow during late gastrulation/early neurulation. Yet, a large body of evidence suggests that biophysical, molecular, and bioelectrical asymmetries exist much earlier in development, some as early as the first cell cleavage after fertilization. Alternative models of LR asymmetry have been proposed that accommodate these data, postulating that asymmetry is established due to a chiral cytoskeleton and/or the asymmetric segregation of chromatids. There are some similarities, and many differences, in how these various models postulate the origin and timing of symmetry breaking and amplification, and these events' linkage to the well-conserved subsequent asymmetric transcriptional cascades. This review examines experimental data that lend strong support to an early origin of LR asymmetry, yet are also consistent with later roles for cilia in the amplification of LR pathways. In this way, we propose that the various models of asymmetry can be unified: early events are needed to initiate LR asymmetry, and later events could be utilized by some species to maintain LR-biases. We also present an alternative hypothesis, which proposes that individual embryos stochastically choose one of several possible pathways with which to establish their LR axis. These two hypotheses are both tractable in appropriate model species; testing them to resolve open questions in the field of LR patterning will reveal interesting new biology of wide relevance to developmental, cell, and evolutionary biology.

Genome-wide analysis of runs of homozygosity identifies new susceptibility regions of lung cancer in Han Chinese

Runs of homozygosity (ROHs) are a class of important but poorly studied genomic variations and may be involved in individual susceptibility to diseases. To better understand ROH and its relationship with lung cancer, we performed a genome-wide ROH analysis of a subset of a previous genome-wide case-control study (1,473 cases and 1,962 controls) in a Han Chinese population. ROHs were classified into two classes, based on lengths, intermediate and long ROHs, to evaluate their association with lung cancer risk using existing genome-wide single nucleotide polymorphism (SNP) data. We found that the overall level of intermediate ROHs was significantly associated with a decreased risk of lung cancer (odds ratio = 0.63; 95% confidence interval: 0.51-0.77; P = 4.78×10⁻⁶ ), while the long ROHs seemed to be a risk factor of lung cancer. We also identified one ROH region at 14q23.1 that was consistently associated with lung cancer risk in the study. These results indicated that ROHs may be a new class of variation which may be associated with lung cancer risk, and genetic variants at 14q23.1 may be involved in the development of lung cancer.

Wnt regulation of planar cell polarity (PCP)

Planar cell polarity (PCP), a process controlling coordinated, uniformly polarized cellular behaviors in a field of cells, has been identified to be critically required for many fundamental developmental processes. However, a global directional cue that establishes PCP in a three-dimensional tissue or organ with respect to the body axes remains elusive. In vertebrate, while Wnt-secreted signaling molecules have been implicated in regulating PCP in a β-catenin-independent manner, whether they function permissively or act as a global cue to convey directional information is not clearly defined. In addition, the underlying molecular mechanism by which Wnt signal is transduced to core PCP proteins is largely unknown. In this chapter, I review the roles of Wnt signaling in regulating PCP during vertebrate development and update our knowledge of its regulatory mechanism.

Scribble is required for normal epithelial cell-cell contacts and lumen morphogenesis in the mammalian lung

During lung development, proper epithelial cell arrangements are critical for the formation of an arborized network of tubes. Each tube requires a lumen, the diameter of which must be tightly regulated to enable optimal lung function. Lung branching and lumen morphogenesis require close epithelial cell–cell contacts that are maintained as a result of adherens junctions, tight junctions and by intact apical–basal (A/B) polarity. However, the molecular mechanisms that maintain epithelial cohesion and lumen diameter in the mammalian lung are unknown. Here we show that Scribble, a protein implicated in planar cell polarity (PCP) signalling, is necessary for normal lung morphogenesis. Lungs of the Scrib mouse mutant Circletail (Crc) are abnormally shaped with fewer airways, and these airways often lack a visible, ‘open’ lumen. Mechanistically we show that Scrib genetically interacts with the core PCP gene Vangl2 in the developing lung and that the distribution of PCP pathway proteins and Rho mediated cytoskeletal modification is perturbed in Scrib^Crc/Crc lungs. However A/B polarity, which is disrupted in Drosophila Scrib mutants, is largely unaffected. Notably, we find that Scrib mediates functions not attributed to other PCP proteins in the lung. Specifically, Scrib localises to both adherens and tight junctions of lung epithelia and knockdown of Scrib in lung explants and organotypic cultures leads to reduced cohesion of lung epithelial cells. Live imaging of Scrib knockdown lungs shows that Scrib does not affect bud bifurcation, as previously shown for the PCP protein Celsr1, but is required to maintain epithelial cohesion. To understand the mechanism leading to reduced cell–cell association, we show that Scrib associates with β-catenin in embryonic lung and the sub-cellular distribution of adherens and tight junction proteins is perturbed in mutant lung epithelia. Our data reveal that Scrib is required for normal lung epithelial organisation and lumen morphogenesis by maintaining cell–cell contacts. Thus we reveal novel and important roles for Scrib in lung development operating via the PCP pathway, and in regulating junctional complexes and cell cohesion.

Gene expression analysis of a murine model with pulmonary vascular remodeling compared to end-stage IPAH lungs

Background

Idiopathic pulmonary arterial hypertension (IPAH) continues to be one of the most serious intractable diseases that might start with activation of several triggers representing the genetic susceptibility of a patient. To elucidate what essentially contributes to the onset and progression of IPAH, we investigated factors playing an important role in IPAH by searching discrepant or controversial expression patterns between our murine model and those previously published for human IPAH. We employed the mouse model, which induced muscularization of pulmonary artery leading to hypertension by repeated intratracheal injection of Stachybotrys chartarum, a member of nonpathogenic and ubiquitous fungus in our envelopment.

Methods

Microarray assays with ontology and pathway analyses were performed with the lungs of mice. A comparison was made of the expression patterns of biological pathways between our model and those published for IPAH.

Results

Some pathways in our model showed the same expression patterns in IPAH, which included bone morphogenetic protein (BMP) signaling with down-regulation of BMP receptor type 2, activin-like kinase type 1, and endoglin. On the other hand, both Wnt/planar cell polarity (PCP) signaling and its downstream Rho/ROCK signaling were found alone to be activated in IPAH and not in our model.

Conclusions

Activation of Wnt/PCP signaling, in upstream positions of the pathway, found alone in lungs from end stage IPAH may play essential roles in the pathogenesis of the disease.