Planar Cell Polarity Proteins Research Articles

Planar Cell Polarity in the Multiciliated Epithelial Lining of the Mouse Eustachian Tube.

Planar cell polarity (PCP) signaling, essential for uniform alignment and directional beating of motile cilia, has been investigated in multiciliated epithelia. As a complex structure connecting the middle ear to the nasopharynx, the eustachian tube (ET) is important in the onset of ear-nose-throat diseases. However, PCP signaling, including the orientation that is important for ciliary motility and clearance function in the ET, has not been studied. We evaluated PCP in the ET epithelium. Morphometric examination of the mouse ET. We performed electron microscopy to assess ciliary polarity in the mouse ET, along with immunohistochemical analysis of PCP protein localization in the ET epithelium. We discovered PCP in the ET epithelium. Motile cilia were aligned in the same direction in individual and neighboring cells; this alignment manifested as ciliary polarity in multiciliated cells. Additionally, PCP proteins were asymmetrically localized between adjacent cells in the plane of the ET. The multiciliated ET epithelium exhibits polarization, suggesting novel structural features that may be critical for ET function. NA Laryngoscope, 2024.

The Planar Cell Polarity Protein Fat1 in Sertoli Cell Function.

Fat (FAT atypical cadherin) and Dchs (Dachsous cadherin-related protein) in adjacent Sertoli:Sertoli, Sertoli:spermatid, and spermatid:spermatid interfaces create an important intercellular bridge whose adhesive function is in turn supported by Fjx1, a nonreceptor Ser/Thr protein kinase. This concept is derived from earlier studies of Drosophila, which has been confirmed in this and earlier reports as well. Herein, we use the approach of knockdown of Fat1 by RNAi using primary cultures of Sertoli cells that mimicked the blood-testis barrier (BTB) in vivo, and a series of coherent experiments including functional assays to monitor the Sertoli cell tight junction (TJ) permeability barrier and a functional in vitro TJ integrity assay to assess the role of Fat1 in the testis. It was shown that planar cell polarity (PCP) protein Fat1 affected Sertoli cell function through its modulation of actin and microtubule cytoskeletal function, altering their polymerization activity through the Fat1/Fjx1 complex. Furthermore, Fat1 is intimately associated with β-catenin and α-N-catenin, as well as with Prickle 1 of the Vangl1/Prickle 1 complex, another PCP core protein to support intercellular interactions to confer PCP. In summary, these findings support the notion that the Fat:Dchs and the Vangl2:Fzd PCP intercellular bridges are tightly associated with basal ES/TJ structural proteins to stabilize PCP function at the Sertoli:Sertoli, Sertoli:spermatid, and spermatid:spermatid interface to sustain spermatogenesis.

Van Gogh-like 2 is essential for the architectural patterning of the mammalian biliary tree

In the developing liver, bipotent epithelial progenitor cells known as hepatoblasts undergo lineage segregation to form the two major epithelial cell types, hepatocytes that constitute the bulk of the liver parenchyma and biliary epithelial cells (cholangiocytes) which comprise the bile duct, a complex tubular network which is critical for normal liver function. Notch and TGFβ signalling promote the formation of a sheet of biliary epithelial cells, the ductal plate that organises into discontinuous tubular structures. How these structures elongate and connect to form a continuous duct remains undefined. We aimed to define the mechanisms by which the ductal plate transitions from simple sheet of epithelial cells to a complex and connected bile duct. By combining single cell RNA sequencing from embryonic mouse livers with genetic tools and organoid models we functionally dissected the role of planar cell polarity in duct patterning. We show that the planar cell polarity protein, VANGL2 is expressed late in intrahepatic bile duct development and patterns the formation of cell-cell contacts between biliary cells. The patterning of these cell contacts regulates the normal polarisation of the actin cytoskeleton within biliary cells and loss of Vangl2-function results in the abnormal distribution of cortical actin remodelling resulting in the failure of bile duct formation. Planar cell polarity is a critical step in the post-specification sculpture of the bile duct and is essential for establishing normal tissue architecture. Human disease and mouse models have allowed us to define how the mammalian biliary lineage is specified during liver development. Once this relatively simple epithelium has formed though, how it undergoes morphogenesis to form a complex and branched structure is not clear. Similar to other branched tissues such as the liver and kidney the bile ducts use planar cell polarity signalling to coordinate cell movements; however how these biochemical signals are linked to ductular patterning remains unclear. Here we show that the core planar cell polarity protein, VANGL2 patterns how cell-cell contacts form in the mammalian bile duct and how ductular cells transmit confluent mechanical changes along the length of a duct. This work sheds light on how biological tubes are pattered across mammalian tissues (including within the liver) and will be important in how we promote ductular growth in patients where the duct is mis-patterned or poorly formed.

Bi-allelic variants in CELSR3 are implicated in central nervous system and urinary tract anomalies

CELSR3 codes for a planar cell polarity protein. We describe twelve affected individuals from eleven independent families with bi-allelic variants in CELSR3. Affected individuals presented with an overlapping phenotypic spectrum comprising central nervous system (CNS) anomalies (7/12), combined CNS anomalies and congenital anomalies of the kidneys and urinary tract (CAKUT) (3/12) and CAKUT only (2/12). Computational simulation of the 3D protein structure suggests the position of the identified variants to be implicated in penetrance and phenotype expression. CELSR3 immunolocalization in human embryonic urinary tract and transient suppression and rescue experiments of Celsr3 in fluorescent zebrafish reporter lines further support an embryonic role of CELSR3 in CNS and urinary tract formation.

Astrocyte-induced mGluR1 activates human lung cancer brain metastasis via glutamate-dependent stabilization of EGFR

There are limited methods to stably analyze the interactions between cancer cells and glial cells invitro, which hinders our molecular understanding. Here, we develop a simple and stable culture method of mouse glial cells, termed mixed-glial culture on/in soft substrate (MGS), which serves well as a platform to study cancer-glia interactions. Using this method, we find that human lung cancer cells become overly dependent on metabotropic glutamate receptor 1 (mGluR1) signaling in the brain microenvironment. Mechanistically, interactions with astrocytes induce mGluR1 in cancer cells through the Wnt-5a/prickle planar cell polarity protein 1 (PRICKLE1)/RE1 silencing transcription factor (REST) axis. Induced mGluR1 directly interacts with and stabilizes the epidermal growth factor receptor (EGFR) in a glutamate-dependent manner, and these cells then become responsive to mGluR1 inhibition. Our results highlight increased dependence on mGluR1 signaling as an adaptive strategy and vulnerability of human lung cancer brain metastasis.

CELSR1, a core planar cell polarity protein, features a weakly adhesive and flexible cadherin ectodomain

Planar cell polarity (PCP), essential to multicellular developmental processes, arises when cells polarize and align across tissues. Central to PCP is CELSR1, an atypical cadherin featuring a long ectodomain with nine extracellular cadherin (EC) repeats, a membrane adjacent domain (MAD10), and several characteristic adhesion GPCR domains. Cell-based aggregation assays have demonstrated CELSR1's homophilic adhesive nature, but mechanistic details are missing. Here, we investigate the possible adhesive properties and structures of CELSR1 EC repeats. Our bead aggregation assays do not support strong adhesion by EC repeats alone. Consistently, EC1-4 only dimerizes at high concentration in solution. Crystal structures of human CELSR1 EC1-4 and EC4-7 reveal typical folds and a non-canonical linker between EC5 and EC6. Simulations and experiments using EC4-7 indicate flexibility at EC5-6, and solution experiments show EC7-MAD10-mediated dimerization. Our results suggest weak homophilic adhesion by CELSR1 cadherin repeats and provide mechanistic insights into the structural determinants of CELSR1 function.

Nuclear VANGL2 Inhibits Lactogenic Differentiation.

Planar cell polarity (PCP) proteins coordinate tissue morphogenesis by governing cell patterning and polarity. Asymmetrically localized on the plasma membrane of cells, transmembrane PCP proteins are trafficked by endocytosis, suggesting they may have intracellular functions that are dependent or independent of their extracellular role, but whether these functions extend to transcriptional control remains unknown. Here, we show the nuclear localization of transmembrane, PCP protein, VANGL2, in the HCC1569 breast cancer cell line, and in undifferentiated, but not differentiated, HC11 cells that serve as a model for mammary lactogenic differentiation. The loss of Vangl2 function results in upregulation of pathways related to STAT5 signaling. We identify DNA binding sites and a nuclear localization signal in VANGL2, and use CUT&RUN to demonstrate recruitment of VANGL2 to specific DNA binding motifs, including one in the Stat5a promoter. Knockdown (KD) of Vangl2 in HC11 cells and primary mammary organoids results in upregulation of Stat5a, Ccnd1 and Csn2, larger acini and organoids, and precocious differentiation; phenotypes are rescued by overexpression of Vangl2, but not Vangl2ΔNLS. Together, these results advance a paradigm whereby PCP proteins coordinate tissue morphogenesis by keeping transcriptional programs governing differentiation in check.

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.

Nasal polyps show decreased mucociliary transport despite vigorous ciliary beating

ObjectiveMucociliary transport function in the airway mucosa is essential for maintaining a clean mucosal surface. This function is impaired in upper and lower airway diseases. Nasal polyps are a noticeable pathological feature that develop in some of the patients with chronic rhinosinusitis. Like ordinary nasal mucosae, nasal polyps have a ciliated pseudostratified epithelium with vigorous ciliary beating. We measured ex vivo Mucociliary Transport Velocity (MCTV) and Ciliary Beat Frequency (CBF) and explored the expressions of Planar Cell Polarity (PCP) proteins in nasal polyps in comparison with turbinate mucosae. MethodsInferior turbinates and nasal polyps were surgically collected from patients with chronic rhinosinusitis. Ex vivo MCTV and CBF were measured using a high-speed digital imaging system. Expressions of PCP proteins were explored by fluorescence immunohistochemistry and quantitative RT-PCR. ResultsThe MCTV of nasal polyps was significantly lower than that of the turbinates (7.43 ± 2.01 vs. 14.56 ± 2.09 μm/s; p = 0.0361), whereas CBF did not differ between the two tissues. The MCTV vector was pointed to the posteroinferior direction in all turbinates with an average inclination angle of 41.0 degrees. Immunohistochemical expressions of Dishevelled-1, Dishevelled-3, Frizzled3, Frizzled6, Prickle2 and Vangl2 were lower in the nasal polyps than in the turbinates. Confocal laser scanning microscopy showed that Frizzled3 was localized along the cell junction on the apical surface. The expression levels of mRNAs for Dishevelled-1, Dishevelled-3 and Frizzled3 in the nasal polyps were also decreased in comparison with the turbinates. ConclusionThese results indicate that muco ciliary transport in nasal polyps is impaired although vigorous ciliary beating is maintained, and that the impairment may be caused by a decrease in Dishevelled/Frizzled proteins and resultant PCP disarrangement. Level of evidenceLevel 3.

Upregulation of CELSR1 expression promotes ovarian cancer cell proliferation, migration, and invasion.

Cadherin epidermal growth factor and laminin-G seven-pass G-type receptor 1 (CELSR1) is a planar cell polarity protein involved in the transmission of directional cues to align either individual cells within an epithelial sheet or multicellular clusters. CELSR1 has been suggested to play a role in glioma, breast cancer, and chronic lymphocytic leukemia development; however, whether it has a role in the pathogenesis of ovarian cancer remains unknown. The aim of this study was to determine the role of CELSR1 in ovarian cancer and elucidate its underlying molecular mechanisms. By analyzing gene expression data downloaded from the Cancer Genome Atlas database,we found that CELSR1 expression was upregulated in ovarian cancer tissues compared to that in normal ovarian tissues. High CELSR1 expression levels were associated with poor prognosis in patients with ovarian cancer. Cell proliferation, scratch, and transwell assays revealed that CELSR1 promoted the proliferation, migration, and invasion of ovarian cancer cells in vitro. In addition, transcriptome sequencing analysis revealed that CELSR1 knockdown in T29H cells resulted in the dysregulation of the expression of 1320 genes. Further analysis revealed that genes involved in proliferation- and migration-associated signaling pathways were regulated by CELSR1. Our study demonstrates that CELSR1 is highly expressed in ovarian cancer cells and regulates their proliferation and migration, suggesting its potential as a diagnostic marker and therapeutic target.

The Fuzzy planar cell polarity protein (FUZ), necessary for primary cilium formation, is essential for pituitary development.

The primary cilium is an essential organelle that is important for normal cell signalling during development and homeostasis but its role in pituitary development has not been reported. The primary cilium facilitates signal transduction for multiple pathways, the best-characterised being the SHH pathway, which is known to be necessary for correct pituitary gland development. FUZ is a planar cell polarity (PCP) effector that is essential for normal ciliogenesis, where the primary cilia of Fuz-/- mutants are shorter or non-functional. FUZ is part of a group of proteins required for recruiting retrograde intraflagellar transport proteins to the base of the organelle. Previous work has reported ciliopathy phenotypes in Fuz-/- homozygous null mouse mutants, including neural tube defects, craniofacial abnormalities, and polydactyly, alongside PCP defects including kinked/curly tails and heart defects. Interestingly, the pituitary gland was reported to be missing in Fuz-/- mutants at 14.5 dpc but the mechanisms underlying this phenotype were not investigated. Here, we have analysed the pituitary development of Fuz-/- mutants. Histological analyses reveal that Rathke's pouch (RP) is initially induced normally but is not specified and fails to express LHX3, resulting in hypoplasia and apoptosis. Characterisation of SHH signalling reveals reduced pathway activation in Fuz-/- mutant relative to control embryos, leading to deficient specification of anterior pituitary fate. Analyses of the key developmental signals FGF8 and BMP4, which are influenced by SHH, reveal abnormal patterning in the ventral diencephalon, contributing further to abnormal RP development. Taken together, our analyses suggest that primary cilia are required for normal pituitary specification through SHH signalling.

Region-specific reversal of epidermal planar polarity in the rosette fancy mouse.

The planar cell polarity (PCP) pathway collectively orients cells with respect to a body axis. Hair follicles of the murine epidermis provide a striking readout of PCP activity in their uniform alignment across the skin. Here, we characterize, from the molecular to tissue-scale, PCP establishment in the rosette fancy mouse, a natural variant with posterior-specific whorls in its fur, to understand how epidermal polarity is coordinated across the tissue. We find that rosette hair follicles emerge with reversed orientations specifically in the posterior region, creating a mirror image of epidermal polarity. The rosette trait is associated with a missense mutation in the core PCP gene Fzd6, which alters a consensus site for N-linked glycosylation, inhibiting its membrane localization. Unexpectedly, the Fzd6 trafficking defect does not block asymmetric localization of the other PCP proteins. Rather, the normally uniform axis of PCP asymmetry rotates where the PCP-directed cell movements that orient follicles are reversed, suggesting the PCP axis rotates 180°. Collectively, our multiscale analysis of epidermal polarity reveals PCP patterning can be regionally decoupled to produce posterior whorls in the rosette fancy mouse.

[Prickle planar cell polarity protein 1 involved in the pathogenesis of skeletal class Ⅲ malocclusion].

Objective: To explore the mechanisms of prickle planar cell polarity protein 1 (PRICKLE1) involved in the occurrence of skeletal Class Ⅲ malocclusion. Methods: After extracting the genomic DNA of all family members of the skeletal Class Ⅲ malocclusion pedigree with maxillary hypoplasia collected in the Department of Orthodontics at the Affiliated Stomatological Hospital of Nanjing Medical University in October 2021, whole exome sequencing and Sanger sequencing were performed to screen pathogenic genes/mutation sites and validate the mutations. Jaw tissue was collected during the operation of orthognathic patients who were treated in the Department of Oral and Maxillofacial Surgery at the same hospital from October 2021 to December 2022. Following the extraction of human jaw bone marrow mesenchymal stem cells and transfection with overexpressing lentivirus (lentiviruses overexpressing the gene of interest served as the wild group, lentiviruses overexpressing mutation site served as the mutant group) and knockdown lentivirus (divided into knockdown group 1 and 2, with transfection interference negative lentiviruses as the control group). Various assays including real-time fluorescence quantitative PCR (RT-qPCR), Western blotting, proliferation and Transwell assays, alkaline phosphatase staining and alizarin red staining were performed. Construction of zebrafish animal model, antisense morpholino oligonucleotide (MO) were injected to knock down the expression of prickle1a and prickle1b in zebrafish (co-knocking group), and the control group was injected with standardized MO as a reference. Transcriptome sequencing, enrichment analysis and co-expression analysis were performed on the zebrafish craniofacial tissues of the two groups. Results: Two patients of this family carried this mutation PRICKLE1 c.113C>T. The transfection experiments showed that compared with the wild group (relative expression of PRICKLE1 was 21.97±0.60), the relative expression of mutant group (5.05±0.05) was significantly reduced (P<0.05), and cell proliferation and migration ability significantly enhanced (P<0.05), and osteogenic differentiation ability was significantly reduced (P<0.05). Compared with the control group, the proliferation and migration ability of cells in the two knockdown groups were significantly enhanced (P<0.05), and the osteogenic differentiation ability was significantly reduced (P<0.05). Zebrafish model experiments showed the width of the ethmoid plate was significantly reduced in the co-knocking group (282.50±61.77, t=5.29, P<0.001) compared with the control group (338.80±24.92). Transcriptome data and enrichment analysis showed that the differentially expressed genes were significantly enriched in the mitogen-activated protein kinase (MAPK) signaling pathway after the simultaneous knockdown of prickle1a and prickle1b in zebrafish. Conclusions: PRICKLE1 c.113C>T mutation might suppress the osteoblastic differentiation ability of jaw bone marrow mesenchymal stem cells by downregulating the MAPK signaling pathway, thereby involving the development of skeletal Class Ⅲ malocclusion.

TRAF7 is an essential regulator of blood vessel integrity during mouse embryonic and neonatal development

Targeted deletion of TRAF7 revealed that it is a crucial part of shear stress-responsive MEKK3-MEK5-ERK5 signaling pathway induced in endothelial cells by blood flow. Similar to Mekk3-, Mek5- or Erk5-deficient mice, Traf7-deficient embryos died in utero around midgestation due to impaired endothelium integrity. They displayed significantly lower expression of transcription factor Klf2, an essential regulator of vascular hemodynamic forces downstream of the MEKK3-MEK-ERK5 signaling pathway. In addition, deletion of Traf7 in endothelial cells of postnatal mice was associated with severe cerebral hemorrhage. Here, we show that besides MEKK3 and MEK5, TRAF7 associates with a planar cell polarity protein SCRIB. SCRIB binds with an N-terminal region of TRAF7, while MEKK3 associates with the C-terminal WD40 domain. Downregulation of TRAF7 as well as SCRIB inhibited fluid shear stress-induced phosphorylation of ERK5 in cultured endothelial cells. These findings suggest that TRAF7 and SCRIB may comprise an upstream part of the MEKK3-MEK5-ERK5 signaling pathway.

Construction of T cell exhaustion model for predicting survival and immunotherapy effect of bladder cancer based on WGCNA.

The prognosis of bladder cancer (BLCA) and response to immune checkpoint inhibitors (ICIs) are determined by multiple factors. Existed biomarkers for predicting the effect of immunotherapy cannot accurately predict the response of BLCA patients to ICIs. To further accurately stratify patients' response to ICIs and identify potential novel predictive biomarkers, we used the known T cell exhaustion (TEX)-related specific pathways, including tumor necrosis factor (TNF), interleukin (IL)-2, interferon (IFN)-g, and T- cell cytotoxicpathways, combined with weighted correlation network analysis (WGCNA) to analyze the characteristics of TEX in BLCA in detail, constructed a TEX model. This model including 28 genes can robustly predict the survival of BLCA and immunotherapeutic efficacy. This model could divide BLCA into two groups, TEXhigh and TEXlow, with significantly different prognoses, clinical features, and reactivity to ICIs. The critical characteristic genes, such as potential biomarkers Charged Multivesicular Body Protein 4C (CHMP4C), SH2 Domain Containing 2A (SH2D2A), Prickle Planar Cell Polarity Protein 3 (PRICKLE3) and Zinc Finger Protein 165 (ZNF165) were verified in BLCA clinical samples by real-time quantitative chain reaction (qPCR) and immunohistochemistry (IHC). Our findings show that the TEX model can serve as biological markers for predicting the response to ICIs, and the involving molecules in the TEX model might provide new potential targets for immunotherapy in BLCA.

The dark kinase STK32A regulates hair cell planar polarity opposite of EMX2 in the developing mouse inner ear.

The vestibular maculae of the inner ear contain sensory receptor hair cells that detect linear acceleration and contribute to equilibrioception to coordinate posture and ambulatory movements. These hair cells are divided between two groups, separated by a line of polarity reversal (LPR), with oppositely oriented planar-polarized stereociliary bundles that detect motion in opposite directions. The transcription factor EMX2 is known to establish this planar polarized organization in mouse by regulating the distribution of the transmembrane receptor GPR156 at hair cell boundaries in one group of cells. However, the genes regulated by EMX2 in this context were previously not known. Using mouse as a model, we have identified the serine threonine kinase STK32A as a downstream effector negatively regulated by EMX2. Stk32a is expressed in hair cells on one side of the LPR in a pattern complementary to Emx2 expression in hair cells on the opposite side. Stk32a is necessary to align the intrinsic polarity of the bundle with the core planar cell polarity (PCP) proteins in EMX2-negative regions, and is sufficient to reorient bundles when ectopically expressed in neighboring EMX2-positive regions. We demonstrate that STK32A reinforces LPR formation by regulating the apical localization of GPR156. These observations support a model in which bundle orientation is determined through separate mechanisms in hair cells on opposite sides of the maculae, with EMX2-mediated repression of Stk32a determining the final position of the LPR.

Regulation of Sertoli cell function by planar cell polarity (PCP) protein Fjx1

Four-jointed box kinase 1 (Fjx1) is a planar cell polarity (PCP) protein and a member of the Fat (FAT atypical cadherin 1)/Dchs (Dachsous cadherin-related protein)/Fjx1 PCP complex. Fjx1 is also a non-receptor Ser/Thr protein kinase capable of phosphorylating Fat1 at is extracellular cadherin domains when it is being transported across the Golgi system. As such, Fjx1 is a Golgi-based regulator of Fat1 function by determining its extracellular deposition. Herein, Fjx1 was found to localize across the Sertoli cell cytoplasm, partially co-localized with the microtubules (MTs) across the seminiferous epithelium. It was most notable at the apical ES (ectoplasmic specialization) and basal ES, displaying distinctive stage-specific expression. The apical ES and basal ES are the corresponding testis-specific cell adhesion ultrastructures at the Sertoli-elongated spermatid interface and the Sertoli cell-cell interface, respectively, consistent with the role of Fjx1 as a Golgi-associated Ser/Thr kinase that modulates the Fat (and/or Dchs) integral membrane proteins. Its knockdown (KD) by RNAi using specific Fjx1 siRNA duplexes versus non-targeting negative control siRNA duplexes was found to perturb the Sertoli cell tight junction function, as well as perturbing the function and organization of MT and actin. While Fjx1 KD did not affect the steady-state levels of almost two dozens of BTB-associated Sertoli cell proteins, including structural and regulatory proteins, its KD was found to down-regulate Fat1 (but not Fat2, 3, and 4) and to up-regulate Dchs1 (but not Dchs2) expression. Based on results of biochemical analysis, Fjx1 KD was found to be capable of abolishing phosphorylation of its putative substrate Fat1 at its Ser/Thr sites, but not at its Tyr site, illustrating an intimate functional relationship of Fjx1 and Fat1 in Sertoli cells.

Emerging roles of planar cell polarity proteins in glutamatergic synapse formation, maintenance and function in health and disease.

The local signaling mechanism which directly assembles and maintains glutamatergic synapses has not been well understood. Glutamatergic synapses are made of presynaptic and postsynaptic compartments with distinct sets of proteins. Theplanar cell polarity (PCP) pathwayis highly conserved and responsible for establishing and maintaining the cell and tissue polarity along the tissue plane. The six core PCP proteins form antagonizing complexes within the cells and asymmetric intercellular complexes across neighboring cells which regulate cell-cell interactions during planar polarity signaling. Accumulating evidence suggests that the PCP proteins play essential roles in glutamatergic synapse assembly, maintenance and function in the brain. This review summarizes the key evidence that PCP proteins may be responsible for the formation and stability of the vast majority of the glutamatergic synapses in hippocampus and medial prefrontal cortex, the progress in understanding the mechanisms of how PCP proteins assemble and maintain glutamatergic synapses and initial insights on how disruption of the function of the PCP proteins can lead to neurodegenerative, neurodevelopmental and neuropsychiatric disorders. The PCP proteins may be the missing pieces of a long-standing puzzle and filling this gap of knowledge may provide the basis for understanding many unsolved questions in synapse biology.

LRP2 contributes to planar cell polarity-dependent coordination of motile cilia function

Motile cilia are protruding organelles on specialized epithelia that beat in a synchronous fashion to propel extracellular fluids. Coordination and orientation of cilia beating on individual cells and across tissues is a complex process dependent on planar cell polarity (PCP) signaling. Asymmetric sorting of PCP pathway components, essential to establish planar polarity, involves trafficking along the endocytic path, but the underlying regulatory processes remain incompletely understood. Here, we identified the endocytic receptor LRP2 as regulator of PCP component trafficking in ependyma, a multi-ciliated cell type that is involved in facilitating flow of the cerebrospinal fluid in the brain ventricular system. Lack of receptor expression in gene-targeted mice results in a failure to sort PCP core proteins to the anterior or posterior cell side and, consequently, in the inability to coordinate cilia arrangement and to aligned beating (loss of rotational and translational polarity). LRP2 deficiency coincides with a failure to sort NHERF1, a cytoplasmic LRP2 adaptor to the anterior cell side. As NHERF1 is essential to translocate PCP core protein Vangl2 to the plasma membrane, these data suggest a molecular mechanism whereby LRP2 interacts with PCP components through NHERF1 to control their asymmetric sorting along the endocytic path. Taken together, our findings identified the endocytic receptor LRP2 as a novel regulator of endosomal trafficking of PCP proteins, ensuring their asymmetric partition and establishment of translational and rotational planar cell polarity in the ependyma.

Molecular mechanism of core planar cell polarity complex function elucidated with single-molecule methods.

The planar cell polarity (PCP) signaling pathway polarizes epithelial cells along an axis parallel to the epithelial sheet in order to generate front-back asymmetry at the tissue level. Failures in PCP signaling underlie developmental defects and diseases such as neural tube and heart defects, deafness and contribute to cancer. Six core PCP proteins assemble into large, asymmetric complexes at cell-cell junctions, with Vang and Prickle recruited to one side of the cell-cell junction while Frizzled and Dishevelled are recruited to the other. How this asymmetric assembly process occurs is not known. Genetic evidence suggests that the process of symmetry breaking at PCP clusters is coupled to cluster formation. To test how this occurs, we developed a method to count the number of each of the six core proteins in individual PCP complexes. Specifically, by analyzing bleaching traces obtained with a high frame rate in live Drosophila wing cells imaged using total internal reflection microscopy, we quantify the intensity of single fluorophores in each complex and thereby calculate the molecular number in the corresponding PCP complex. Using this approach, we find that the molecular size distribution of PCP complexes follows an exponential function, indicating a single underlying growth mechanism. We report that specifically, the number of Vang molecules in PCP complexes increases from 15 hours after puparium formation until reaching a steady state around 28 hours. Besides, we measure the asymmetry as a function of cluster size and test the dependence of the observed relationship by introducing gain and loss of function mutations that perturb cluster assembly. In conclusion, our findings provide a detailed understanding of how the PCP mechanism generates stable polarization during embryonic development.