Activity-Regulated N-Cadherin Endocytosis

The role of CSNK1A1 and its de novo mutations in infantile spasms syndrome

Infantile spasms syndrome (ISS) is an early-onset epileptic encephalopathy characterized by uncontrollable seizures, severe electroencephalogram abnormalities, as well as delayed cognitive and behavioral development. Independent studies have shown that a variety of genes are involved in ISS and genetic factors play a critical role in its pathogenesis. Here we report two de novo mutations in the casein kinase 1 isoform alpha (CSNK1A1) gene which underlie severe epilepsy with similar clinical presentation in two patients. The identified variants are one missense mutation c.646G > C (p.Ala216Pro, Mut) in NM_001025105.3 and one deletion c.599_604delACATAC (p.His200_Ile201del, Del). In vitro analyses indicated that the Mut causes significant decreases in both mRNA and protein expression, while the Del demonstrated no significant impact on gene expression level. However, co-immunoprecipitation studies have shown that both mutations lead to reduced interactions between CSNK1A1 and β-catenin, resulting in excessive intracellular β-catenin and aberrant expression of several downstream genes. Compared with the wild type (WT), the EdU positive rates in cells transfected with Mut plasmid or Del plasmid were both elevated. Wnt/β-catenin signaling pathway is crucial to neurogenesis. An abnormal rise in β-catenin level has been utilized to generate genetic models for ISS. Our results not only elucidate the role of a novel candidate gene CSNK1A1 in the pathology of ISS, but also provide further evidence for the findings that mediating Wnt/β-catenin signaling is a potential mechanism causing ISS.

Decoding the Nectin Interactome: Implications for Brain Development, Plasticity, and Neurological Disorders

The nectin family of cell adhesion molecules (CAMs) comprising nectins and nectin-like molecules has emerged as a key regulator of various pivotal neural processes, including neuronal development, migration, synapse formation, and plasticity. Nectins engage in homophilic and heterophilic interactions to mediate cell-cell adhesion, contributing to the establishment and maintenance of neural circuits. Their extracellular domains facilitate trans-synaptic interactions, while intracellular domains participate in signaling cascades influencing cytoskeletal dynamics and synaptic function. The exhibition of distinct localization patterns in neurons, astrocytes, and the blood-brain barrier underscores their diverse roles in the brain. The dysregulation of nectins has been implicated in several neurological disorders, such as neurodevelopmental disorders, depression, schizophrenia, and Alzheimer's disease. This review examines the structural and functional characteristics of nectins and their distribution and molecular mechanisms governing neural connectivity and cognition. It further discusses experimental studies unraveling nectin-mediated pathophysiology and potential therapeutic interventions targeting nectin-related pathways. Collectively, this comprehensive analysis highlights the significance of nectins in brain development, function, and disorders, paving the way for future research directions and clinical implications.

Human transporter de-oligomerization regulates copper uptake into cells

Copper is an essential element involved in various biochemical processes, such as mitochondrial energy production and antioxidant defense, but improper regulation can lead to cellular toxicity and disease. Copper Transporter 1 (CTR1) plays a key role in copper uptake and maintaining cellular copper homeostasis. Although CTR1 endocytosis was previously thought to reduce copper uptake when levels are high, it was unclear how rapid regulation is achieved. Using single-molecule localization microscopy and single-molecule neighbor density assays, we discovered that excess copper induces monomerization of the wild-type trimeric CTR1 prior to endocytosis, a response blocked in the endocytosis-deficient CTR1 (M150L) mutant. This monomerization rapidly halts copper uptake and prevents copper overload. These findings reveal changes in protein oligomerization as a new paradigm of metal transport regulation, linking CTR1's structural changes to its endocytosis and copper homeostasis.

Molecular architecture of synaptic vesicles

Synaptic vesicles (SVs) store and transport neurotransmitters to the presynaptic active zone for release by exocytosis. After release, SV proteins and excess membrane are recycled via endocytosis, and new SVs can be formed in a clathrin-dependent manner. This process maintains complex molecular composition of SVs through multiple recycling rounds. Previous studies explored the molecular composition of SVs through proteomic analysis and fluorescent microscopy, proposing a model for an average SV (1). However, the structural heterogeneity and molecular architecture of individual SVs are not well described. Here, we used cryoelectron tomography to visualize molecular details of SVs isolated from mouse brains and inside cultured neurons. We describe several classes of small proteins on the SV surface and long proteinaceous densities inside SVs. We identified V-ATPases, determined a structure using subtomogram averaging, and showed them forming a complex with the membrane-embedded protein synaptophysin (Syp). Our bioluminescence assay revealed pairwise interactions between vesicle-associated membrane protein 2 and Syp and V-ATPase Voe1 domains. Interestingly, V-ATPases were randomly distributed on the surface of SVs irrespective of vesicle size. A subpopulation of isolated vesicles and vesicles inside neurons contained a partially assembled clathrin coat with an icosahedral symmetry. We observed V-ATPases under clathrin cages in several isolated clathrin-coated vesicles (CCVs). Additionally, from isolated SV preparations and within hippocampal neurons we identified clathrin baskets without vesicles. We determined their and CCVs preferential location in proximity to the cell membrane. Our analysis advances the understanding of individual SVs' diversity and their molecular architecture.

DNA methylation-altered genes in the rat hippocampal neurogenic niche after continuous exposure to amorphous curcumin

Rat offspring who are exposed to an amorphous formula of curcumin (CUR) from the embryonic stage have anti-anxiety-like behaviors, enhanced fear extinction learning, and increased synaptic plasticity in the hippocampal dentate gyrus (DG). In the present study, we investigated the links between genes with altered methylation status in the neurogenic niche and enhanced neural functions after CUR exposure. We conducted methylation and RNA sequencing analyses of the DG of CUR-exposed rat offspring on day 77 after delivery. Methylation status and transcript levels of candidate genes were validated using methylation-sensitive high-resolution melting and real-time reverse-transcription PCR, respectively. In the CUR group, we confirmed the hypermethylation and downregulation of Gpr150, Mmp23, Rprml, and Pcdh8 as well as the hypomethylation and upregulation of Ppm1j, Fam222a, and Opn3. Immunohistochemically, reprimo-like+ hilar cells and protocadherin-8+ granule cells were decreased and opsin-3+ hilar cells were increased by CUR exposure. Both reprimo-like and opsin-3 were partially expressed on subpopulations of glutamic acid decarboxylase 67+ γ-aminobutyric acid-ergic interneurons. Furthermore, the transcript levels of genes involved in protocadherin-8-mediated N-cadherin endocytosis were altered with CUR exposure; this was accompanied by Ctnnb1 and Syp upregulation and Mapk14, Map2k3, and Grip1 downregulation, suggesting that CUR-induced enhanced synaptic plasticity is associated with cell adhesion. Together, our results indicate that functionally different genes have altered methylation and expression in different neuronal populations of the hippocampal neurogenic niche, thus enhancing synaptic plasticity after CUR exposure.

Role of an interdependent Wnt, GSK3-β/β-catenin and HB-EGF/EGFR mechanism in arsenic-induced hippocampal neurotoxicity in adult mice

We previously reported the neurotoxic effects of arsenic in the hippocampus. Here, we explored the involvement of Wnt pathway, which contributes to neuronal functions. Administering environmentally relevant arsenic concentrations to postnatal day-60 (PND60) mice demonstrated a dose-dependent increase in hippocampal Wnt3a and its components, Frizzled, phospho-LRP6, Dishevelled and Axin1 at PND90 and PND120. However, p-GSK3-β(Ser9) and β-catenin levels although elevated at PND90, decreased at PND120. Additionally, treatment with Wnt-inhibitor, rDkk1, reduced p-GSK3-β(Ser9) and β-catenin at PND90, but failed to affect their levels at PND120, indicating a time-dependent link with Wnt. To explore other underlying factors, we assessed epidermal growth factor receptor (EGFR) pathway, which interacts with GSK3-β and appears relevant to neuronal functions. We primarily found that arsenic reduced hippocampal phosphorylated-EGFR and its ligand, Heparin-binding EGF-like growth factor (HB-EGF), at both PND90 and PND120. Moreover, treatment with HB-EGF rescued p-GSK3-β(Ser9) and β-catenin levels at PND120, suggesting their HB-EGF/EGFR-dependent regulation at this time point. Additionally, rDkk1, LiCl (GSK3-β-activity inhibitor), or β-catenin protein treatments induced a time-dependent recovery in HB-EGF, indicating potential inter-dependent mechanism between hippocampal Wnt/β-catenin and HB-EGF/EGFR following arsenic exposure. Fluorescence immunolabeling then validated these findings in hippocampal neurons. Further exploration of hippocampal neuronal survival and apoptosis demonstrated that treatment with rDkk1, LiCl, β-catenin and HB-EGF improved Nissl staining and NeuN levels, and reduced cleaved-caspase-3 levels in arsenic-treated mice. Supportively, we detected improved Y-Maze and Passive Avoidance performances for learning-memory functions in these mice. Overall, our study provides novel insights into Wnt/β-catenin and HB-EGF/EGFR pathway interaction in arsenic-induced hippocampal neurotoxicity.

Exploration of the mechanisms of improving learning and memory in the offspring of aging pregnant mice by supplementation with Paris polyphylla polysaccharide based on the P19-P53-P21 and Wnt/β-catenin signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

First recorded in "Sheng Nong's herbal classic", Paris polyphylla is used to treat diseases, such as convulsions, head shaking and tongue fiddling, and epilepsy. Studies have shown that the ability of three Liliaceae polysaccharides in improving learning and memory may be related to the P19-P53-P21 and Wnt/β-catenin signaling pathways. Moreover, a link between these two signaling pathways and the possible neuroprotective impact of Paris polyphylla polysaccharide has been proposed.

AIM OF THE STUDY

We explored the mechanisms of improving learning and memory in the offspring of pre-pregnant parental mice and D-galactose-induced aging pregnant mice by supplementation with P. polyphylla polysaccharide based on the P19-P53-P21 and Wnt/β-catenin signaling pathways.

STUDY DESIGN AND METHODS

After 3 weeks of supplementation of D-galactose-induced pre-pregnant parental mice with P. polyphylla polysaccharide component 1 (PPPm-1), the male and female parental mice mated in cages. The D-galactose-induced pregnant mice were continued to be supplemented with PPPm-1 for 18 days before delivery of the offspring. Behavioral experiments (Morris water maze and dark avoidance experiments) were conducted on the offspring mice born 48 days later to determine whether PPPm-1 had the effect of improving their learning and memory. Based on the P19/P53/P21 and Wnt/β-catenin signaling pathways, the mechanisms of PPPm-1 in improving learning and memory in offspring mice were further investigated.

RESULTS

Offspring mice administered low- or high-dose PPPm-1 exhibited stronger motor and memory abilities in behavioral experiments than the aging model of offspring mice. Enzyme-linked immunosorbent assay and real-time polymerase chain reaction revealed that the expressions of P19 and P21 mRNA and protein were inhibited in offspring mice administered low- and high-dose PPPm-1. However, P53 expression was inhibited in the low-dose PPPm-1 offspring group but promoted in the high-dose PPPm-1 offspring group. Additionally, PPPm-1 could effectively activate the Wnt/β-catenin signaling pathway, promote the expressions of Wnt/1, β-catenin, CyclinD1, and TCF-4 mRNA and protein, and inhibit GSK-3β mRNA and protein expression to improve the learning and memory abilities of offspring mice.

CONCLUSION

Thus, PPPm-1 improved the learning and memory abilities in the offspring of aging pregnant mice by acting on the P19-P53-P21 and Wnt/β-catenin signaling pathways.

Inhibition of Foxp4 Disrupts Cadherin-based Adhesion of Radial Glial Cells, Leading to Abnormal Differentiation and Migration of Cortical Neurons in Mice

Heterozygous loss-of-function variants of FOXP4 are associated with neurodevelopmental disorders (NDDs) that exhibit delayed speech development, intellectual disability, and congenital abnormalities. The etiology of NDDs is unclear. Here we found that FOXP4 and N-cadherin are expressed in the nuclei and apical end-feet of radial glial cells (RGCs), respectively, in the mouse neocortex during early gestation. Knockdown or dominant-negative inhibition of Foxp4 abolishes the apical condensation of N-cadherin in RGCs and the integrity of neuroepithelium in the ventricular zone (VZ). Inhibition of Foxp4 leads to impeded radial migration of cortical neurons and ectopic neurogenesis from the proliferating VZ. The ectopic differentiation and deficient migration disappear when N-cadherin is over-expressed in RGCs. The data indicate that Foxp4 is essential for N-cadherin-based adherens junctions, the loss of which leads to periventricular heterotopias. We hypothesize that FOXP4 variant-associated NDDs may be caused by disruption of the adherens junctions and malformation of the cerebral cortex.

Turnover of synaptic adhesion molecules

Molecular interactions between pre- and postsynaptic membranes play critical roles during the development, function and maintenance of synapses. Synaptic interactions are mediated by cell surface receptors that may be held in place by trans-synaptic adhesion or intracellular binding to membrane-associated scaffolding and signaling complexes. Despite their role in stabilizing synaptic contacts, synaptic adhesion molecules undergo turnover and degradation during all stages of a neuron's life. Here we review current knowledge about membrane trafficking mechanisms that regulate turnover of synaptic adhesion molecules and the functional significance of turnover for synapse development and function. Based on recent proteomics, genetics and imaging studies, synaptic adhesion molecules exhibit remarkably high turnover rates compared to other synaptic proteins. Degradation occurs predominantly via endolysosomal mechanisms, with little evidence for roles of proteasomal or autophagic degradation. Basal turnover occurs both during synaptic development and maintenance. Neuronal activity typically stabilizes synaptic adhesion molecules while downregulating neurotransmitter receptors based on turnover. In conclusion, constitutive turnover of synaptic adhesion molecules is not a necessarily destabilizing factor, but a basis for the dynamic regulation of trans-synaptic interactions during synapse formation and maintenance.

NMDA Receptor and Its Emerging Role in Cancer

Glutamate is a key player in excitatory neurotransmission in the central nervous system (CNS). The N-methyl-D-aspartate receptor (NMDAR) is a glutamate-gated ion channel which presents several unique features and is involved in various physiological and pathological neuronal processes. Thanks to great efforts in neuroscience, its structure and the molecular mechanisms controlling its localization and functional regulation in neuronal cells are well known. The signaling mediated by NMDAR in neurons is very complex as it depends on its localization, composition, Ca²⁺ influx, and ion flow-independent conformational changes. Moreover, NMDA receptors are highly diffusive in the plasma membrane of neurons, where they form heterocomplexes with other membrane receptors and scaffold proteins which determine the receptor function and activation of downstream signaling. Interestingly, a recent paper demonstrates that NMDAR signaling is involved in epithelial cell competition, an evolutionary conserved cell fitness process influencing cancer initiation and progress. The idea that NMDAR signaling is limited to CNS has been challenged in the past two decades. A large body of evidence suggests that NMDAR is expressed in cancer cells outside the CNS and can respond to the autocrine/paracrine release of glutamate. In this review, we survey research on NMDAR signaling and regulation in neurons that can help illuminate its role in tumor biology. Finally, we will discuss existing data on the role of the glutamine/glutamate metabolism, the anticancer action of NMDAR antagonists in experimental models, NMDAR synaptic signaling in tumors, and clinical evidence in human cancer.

Arvcf Dependent Adherens Junction Stability is Required to Prevent Age-Related Cortical Cataracts

The etiology of age-related cortical cataracts is not well understood but is speculated to be related to alterations in cell adhesion and/or the changing mechanical stresses occurring in the lens with time. The role of cell adhesion in maintaining lens transparency with age is difficult to assess because of the developmental and physiological roles that well-characterized adhesion proteins have in the lens. This report demonstrates that Arvcf, a member of the p120-catenin subfamily of catenins that bind to the juxtamembrane domain of cadherins, is an essential fiber cell protein that preserves lens transparency with age in mice. No major developmental defects are observed in the absence of Arvcf, however, cortical cataracts emerge in all animals examined older than 6-months of age. While opacities are not obvious in young animals, histological anomalies are observed in lenses at 4-weeks that include fiber cell separations, regions of hexagonal lattice disorganization, and absence of immunolabeled membranes. Compression analysis of whole lenses also revealed that Arvcf is required for their normal biomechanical properties. Immunofluorescent labeling of control and Arvcf-deficient lens fiber cells revealed a reduction in membrane localization of N-cadherin, β-catenin, and αN-catenin. Furthermore, super-resolution imaging demonstrated that the reduction in protein membrane localization is correlated with smaller cadherin nanoclusters. Additional characterization of lens fiber cell morphology with electron microscopy and high resolution fluorescent imaging also showed that the cellular protrusions of fiber cells are abnormally elongated with a reduction and disorganization of cadherin complex protein localization. Together, these data demonstrate that Arvcf is required to maintain transparency with age by mediating the stability of the N-cadherin protein complex in adherens junctions.

Fluid markers of synapse degeneration in synucleinopathies

The abnormal accumulation of α-synuclein in the brain is a common feature of Parkinson's disease (PD), PD dementia (PDD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA), and synucleinopathies that present with overlapping but distinct clinical symptoms that include motor and cognitive deficits. Synapse degeneration is the crucial neuropathological event in these synucleinopathies and the neuropathological correlate of connectome dysfunction. The cognitive and motor deficits resulting from the connectome dysfunction are currently measured by scalar systems that are limited in their sensitivity and largely subjective. Ideally, a marker of synapse degeneration would correlate with measures of cognitive or motor impairment, and could therefore be used as a more objective, surrogate biomarker of the core clinical features of these diseases. Furthermore, an objective surrogate biomarker that can detect and monitor the progression of synapse degeneration would improve patient management and clinical trial design, and could provide a measure of therapeutic response. Here, we review the published findings relating to candidate biomarkers of synapse degeneration in PD, PDD, DLB, and MSA patient-derived biofluids and discuss the findings in the context of the mechanisms associated with α-synuclein-mediated synapse degeneration. Understanding these mechanisms is essential not only for discovery of biomarkers, but also to improve our understanding of the earliest changes in disease pathogenesis of synucleinopathies.

N-Cadherin Regulates GluA1-Mediated Depressive-Like Behavior in Adolescent Female Rat Offspring following Prenatal Stress

BACKGROUND

The incidence of depression is twice higher in women than in men, and gender differences in the prevalence rates first emerge around puberty. Prenatal stress (PS) induces gender-dependent depressive-like behavior in adolescent offspring, but the neuro-physiological mechanisms remain unclear. Our study aimed to investigate the possible neuro-physiological mechanisms of gender-dependent depressive-like behavior in PS adolescent offspring and further explored the possibility of treating depression in adolescent female rats.

METHODS

The pregnant rats were exposed to restraint stress in the third trimester for 7 days. The depressive-like behavior and the expression of N-cadherin and AMPARs in the hippocampus of adolescent offspring rats were assessed. 10 mg/kg AMPAR antagonist CNQX and 10 mg/kg N-cadherin antagonist ADH-1 were intraperitoneally injected into female adolescent offspring, respectively; 0.2 µg AMPAR agonist CX546 was administered to the dentate gyrus of male adolescent offspring to determine the role of N-cadherin-AMPARs in depressive-like behavior of the offspring following PS.

RESULTS

We found that PS increased N-cadherin expression, which upregulated GluA1 expression in the dentate gyrus, mediating depressive-like behavior in adolescent female rat offspring by reducing PSD-95. In addition, ADH-1 and CNQX improved depressive-like behavior in adolescent female offspring following PS. Furthermore, injection of the CX546 into the dentate gyrus induced depressive-like behavior in PS male offspring.

CONCLUSION

The gender-dependent expression of N-cadherin-GluA1 pathway in adolescent offspring in the dentate gyrus was the key factor in gender differences of depressive-like behavior following PS.

Sex-dependent expression of N-cadherin-GluA1 pathway-related molecules in the prefrontal cortex mediates anxiety-like behavior in male offspring following prenatal stress

Prenatal stress (PS) affects neurodevelopment and increases the risk for anxiety in adolescence in male offspring, but the mechanism is still unclear. N-Cadherin regulates the expression of AMPA receptors (AMPARs), which mediate anxiety by modulating network excitability in the prefrontal cortex (PFC). Our results revealed that in adolescent male, but not female, offspring rats, PS induced anxiety-like behavior, as assessed by the open field test (OFT). Furthermore, N-cadherin and AMPAR subunit GluA1 were colocalized in the PFC, and the expression of the N-cadherin and the GluA1 decreased following PS exposure in male offspring rats. We also found that the AMPAR agonist CX546 did not alleviate anxiety-like behavior in adolescent male offspring rats; however, it increased the expression of GluA1 in the PFC but did not alter the expression of N-cadherin. In conclusion, our study suggested that the N-cadherin-GluA1 pathway in the PFC mediates anxiety-like behavior in adolescent male offspring rats and that N-cadherin might be required for sex differences in the effect of PS on adolescent offspring.

SLC6A20 transporter: a novel regulator of brain glycine homeostasis and NMDAR function

Glycine transporters (GlyT1 and GlyT2) that regulate levels of brain glycine, an inhibitory neurotransmitter with co-agonist activity for NMDA receptors (NMDARs), have been considered to be important targets for the treatment of brain disorders with suppressed NMDAR function such as schizophrenia. However, it remains unclear whether other amino acid transporters expressed in the brain can also regulate brain glycine levels and NMDAR function. Here, we report that SLC6A20A, an amino acid transporter known to transport proline based on in vitro data but is understudied in the brain, regulates proline and glycine levels and NMDAR function in the mouse brain. SLC6A20A transcript and protein levels were abnormally increased in mice carrying a mutant PTEN protein lacking the C terminus through enhanced β-catenin binding to the Slc6a20a gene. These mice displayed reduced extracellular levels of brain proline and glycine and decreased NMDAR currents. Elevating glycine levels back to normal ranges by antisense oligonucleotide-induced SLC6A20 knockdown, or the competitive GlyT1 antagonist sarcosine, normalized NMDAR currents and repetitive climbing behavior observed in these mice. Conversely, mice lacking SLC6A20A displayed increased extracellular glycine levels and NMDAR currents. Lastly, both mouse and human SLC6A20 proteins mediated proline and glycine transports, and SLC6A20 proteins could be detected in human neurons. These results suggest that SLC6A20 regulates proline and glycine homeostasis in the brain and that SLC6A20 inhibition has therapeutic potential for brain disorders involving NMDAR hypofunction.

Mice with cleavage-resistant N-cadherin exhibit synapse anomaly in the hippocampus and outperformance in spatial learning tasks

N-cadherin is a homophilic cell adhesion molecule that stabilizes excitatory synapses, by connecting pre- and post-synaptic termini. Upon NMDA receptor (NMDAR) activation by glutamate, membrane-proximal domains of N-cadherin are cleaved serially by a-disintegrin-and-metalloprotease 10 (ADAM10) and then presenilin 1(PS1, catalytic subunit of the γ-secretase complex). To assess the physiological significance of the initial N-cadherin cleavage, we engineer the mouse genome to create a knock-in allele with tandem missense mutations in the mouse N-cadherin/Cadherin-2 gene (Cdh2 R714G, I715D, or GD) that confers resistance on proteolysis by ADAM10 (GD mice). GD mice showed a better performance in the radial maze test, with significantly less revisiting errors after intervals of 30 and 300 s than WT, and a tendency for enhanced freezing in fear conditioning. Interestingly, GD mice reveal higher complexity in the tufts of thorny excrescence in the CA3 region of the hippocampus. Fine morphometry with serial section transmission electron microscopy (ssTEM) and three-dimensional (3D) reconstruction reveals significantly higher synaptic density, significantly smaller PSD area, and normal dendritic spine volume in GD mice. This knock-in mouse has provided in vivo evidence that ADAM10-mediated cleavage is a critical step in N-cadherin shedding and degradation and involved in the structure and function of glutamatergic synapses, which affect the memory function.

Neural Markers of Vulnerability to Anxiety Outcomes after Traumatic Brain Injury

Anxiety outcomes after traumatic brain injury (TBI) are complex, and the underlying neural mechanisms are poorly understood. Here, we developed a multi-dimensional behavioral profiling approach to investigate anxiety-like outcomes in mice that takes into account individual variability. Departing from the tradition of comparing outcomes in TBI versus sham groups, we identified a subgroup within the TBI group that is vulnerable to anxiety dysfunction, and present increased exploration of the anxiogenic zone compared to sham controls or resilient injured animals, by applying dimensionality reduction, clustering, and post hoc validation to behavioral data obtained from multiple assays for anxiety at several post-injury time points. These vulnerable animals expressed distinct molecular profiles in the corticolimbic network, with downregulation in gamma-aminobutyric acid and glutamate and upregulation in neuropeptide Y markers. Indeed, among vulnerable animals, not resilient or sham controls, severity of anxiety-related outcomes correlated strongly with expression of molecular markers. Our results establish a foundational approach, with predictive power, for reliably identifying maladaptive anxiety outcomes after TBI and uncovering neural signatures of vulnerability to anxiety.

Molecular Mechanisms of Cadherin Function During Cortical Migration

During development of the cerebral cortex, different types of neurons migrate from distinct origins to create the different cortical layers and settle within them. Along their way, migrating neurons use cell adhesion molecules on their surface to interact with other cells that will play critical roles to ensure that migration is successful. Radially migrating projection neurons interact primarily with radial glia and Cajal-Retzius cells, whereas interneurons originating in the subpallium follow a longer, tangential route and encounter additional cellular substrates before reaching the cortex. Cell-cell adhesion is therefore essential for the correct migration of cortical neurons. Several members of the cadherin superfamily of cell adhesion proteins, which mediate cellular interactions through calcium-dependent, mostly homophilic binding, have been shown to play important roles during neuronal migration of both projection neurons and interneurons. Although several classical cadherins and protocadherins are involved in this process, the most prominent is CDH2. This mini review will explore the cellular and molecular mechanisms underpinning cadherin function during cortical migration, including recent advances in our understanding of the control of adhesive strength through regulation of cadherin surface levels.

Functions of p38 MAP Kinases in the Central Nervous System

Mitogen-activated protein (MAP) kinases are a central component in signaling networks in a multitude of mammalian cell types. This review covers recent advances on specific functions of p38 MAP kinases in cells of the central nervous system. Unique and specific functions of the four mammalian p38 kinases are found in all major cell types in the brain. Mechanisms of p38 activation and downstream phosphorylation substrates in these different contexts are outlined and how they contribute to functions of p38 in physiological and under disease conditions. Results in different model organisms demonstrated that p38 kinases are involved in cognitive functions, including functions related to anxiety, addiction behavior, neurotoxicity, neurodegeneration, and decision making. Finally, the role of p38 kinases in psychiatric and neurological conditions and the current progress on therapeutic inhibitors targeting p38 kinases are covered and implicate p38 kinases in a multitude of CNS-related physiological and disease states.

Trafficking and Activity of Glutamate and GABA Receptors: Regulation by Cell Adhesion Molecules

The efficient targeting of ionotropic receptors to postsynaptic sites is essential for the function of chemical excitatory and inhibitory synapses, constituting the majority of synapses in the brain. A growing body of evidence indicates that cell adhesion molecules (CAMs), which accumulate at synapses at the earliest stages of synaptogenesis, are critical for this process. A diverse variety of CAMs assemble into complexes with glutamate and GABA receptors and regulate the targeting of these receptors to the cell surface and synapses. Presynaptically localized CAMs provide an additional level of regulation, sending a trans-synaptic signal that can regulate synaptic strength at the level of receptor trafficking. Apart from controlling the numbers of receptors present at postsynaptic sites, CAMs can also influence synaptic strength by modulating the conductivity of single receptor channels. CAMs thus act to maintain basal synaptic transmission and are essential for many forms of activity dependent synaptic plasticity. These activities of CAMs may underlie the association between CAM gene mutations and synaptic pathology and represent fundamental mechanisms by which synaptic strength is dynamically tuned at both excitatory and inhibitory synapses.

Integrin linked kinase regulates endosomal recycling of N-cadherin in melanoma cells

Malignant transformation is characterized by a phenotype "switch" from E- to N-cadherin - a major hallmark of epithelial to mesenchymal transition (EMT). The increased expression of N-cadherin is commonly followed by a growing capacity for migration as well as resistance to apoptosis. Integrin Linked Kinase (ILK) is a key molecule involved in EMT and progression of cancer cells. ILK is known as a major signaling mediator involved in cadherin switch, but the specific mechanism through which ILK modulates N-cadherin expression is still not clear. Studies were carried out on human melanoma WM793 and 1205Lu cell lines. Expression of proteins was analyzed using PCR and Western Blot; siRNA transfection was done for ILK. Analysis of cell signaling pathways was monitored with phospho-specific antibodies. Subcellular localization of protein was studied using the ProteoExtract Subcellular Kit and Western blot analysis. Our data show that ILK knockdown by siRNA did suppress N-cadherin expression in melanoma, but only at the protein level. The ILK silencing-induced decrease of N-cadherin membranous expression in melanoma highlights the likely crucial role of ILK in the coordination of membrane trafficking through alteration of Rab expression. It is essential to understand the molecular mechanism of increased N-cadherin expression in cancer to possibly use it in the search of new therapeutic targets.

Adjustable viscoelasticity allows for efficient collective cell migration

Cell migration is essential for a wide range of biological processes such as embryo morphogenesis, wound healing, regeneration, and also in pathological conditions, such as cancer. In such contexts, cells are required to migrate as individual entities or as highly coordinated collectives, both of which requiring cells to respond to molecular and mechanical cues from their environment. However, whilst the function of chemical cues in cell migration is comparatively well understood, the role of tissue mechanics on cell migration is just starting to be studied. Recent studies suggest that the dynamic tuning of the viscoelasticity within a migratory cluster of cells, and the adequate elastic properties of its surrounding tissues, are essential to allow efficient collective cell migration in vivo. In this review we focus on the role of viscoelasticity in the control of collective cell migration in various cellular systems, mentioning briefly some aspects of single cell migration. We aim to provide details on how viscoelasticity of collectively migrating groups of cells and their surroundings is adjusted to ensure correct morphogenesis, wound healing, and metastasis. Finally, we attempt to show that environmental viscoelasticity triggers molecular changes within migrating clusters and that these new molecular setups modify clusters' viscoelasticity, ultimately allowing them to migrate across the challenging geometries of their microenvironment.

β-Catenin in the Adult Visual Cortex Regulates NMDA-Receptor Function and Visual Responses

The formation, plasticity and maintenance of synaptic connections is regulated by molecular and electrical signals. β-Catenin is an important protein in these events and regulates cadherin-mediated cell adhesion and the recruitment of pre- and postsynaptic proteins in an activity-dependent fashion. Mutations in the β-catenin gene can cause cognitive disability and autism, with life-long consequences. Understanding its synaptic function may thus be relevant for the treatment of these disorders. So far, β-catenin's function has been studied predominantly in cell culture and during development but knowledge on its function in adulthood is limited. Here, we show that ablating β-catenin in excitatory neurons of the adult visual cortex does not cause the same synaptic deficits previously observed during development. Instead, it reduces NMDA-receptor currents and impairs visual processing. We conclude that β-catenin remains important for adult cortical function but through different mechanisms than during development.

Rab18 Collaborates with Rab7 to Modulate Lysosomal and Autophagy Activities in the Nervous System: an Overlapping Mechanism for Warburg Micro Syndrome and Charcot-Marie-Tooth Neuropathy Type 2B

Mutations in RAB18, a member of small G protein, cause Warburg micro syndrome (WARBM), whose clinical features include vision impairment, postnatal microcephaly, and lower limb spasticity. Previously, our Rab18^-/- mice exhibited hind limb weakness and spasticity as well as signs of axonal degeneration in the spinal cord and lumbar spinal nerves. However, the cellular and molecular function of RAB18 and its roles in the pathogenesis of WARBM are still not fully understood. Using immunofluorescence staining and expression of Rab18 and organelle markers, we find that Rab18 associates with lysosomes and actively traffics along neurites in cultured neurons. Interestingly, Rab18^-/- neurons exhibit impaired lysosomal transport. Using autophagosome marker LC3-II, we show that Rab18 dysfunction leads to aberrant autophagy activities in neurons. Electron microscopy further reveals accumulation of lipofuscin-like granules in the dorsal root ganglion of Rab18^-/- mice. Surprisingly, Rab18 colocalizes, cofractionates, and coprecipitates with the lysosomal regulator Rab7, mutations of which cause Charcot-Marie-Tooth (CMT) neuropathy type 2B. Moreover, Rab7 is upregulated in Rab18-deficient neurons, suggesting a compensatory effect. Together, our results suggest that the functions of RAB18 and RAB7 in lysosomal and autophagic activities may constitute an overlapping mechanism underlying WARBM and CMT pathogenesis in the nervous system.

Long-Term Effects of Traumatic Brain Injury on Anxiety-Like Behaviors in Mice: Behavioral and Neural Correlates

Traumatic brain injury (TBI) has been frequently linked to affective disorders such as anxiety and depression. However, much remains to be understood about the underlying molecular and signaling mechanisms that mediate affective dysfunctions following injury. A lack of consensus in animal studies regarding what the affective sequelae of TBI are has been a major hurdle that has slowed progress, with studies reporting the full range of effects: increase, decrease, and no change in anxiety following injury. Here, we addressed this issue directly by investigating long-term anxiety outcomes in mice following a moderate to severe controlled cortical impact (CCI) injury using a battery of standard behavioral tests-the open field (OF), elevated zero maze (EZM), and elevated plus maze (EPM). Mice were tested on weeks 1, 3, 5 and 7 post-injury. Our results show that the effect of injury is time- and task-dependent. Early on-up to 3 weeks post-injury, there is an increase in anxiety-like behaviors in the elevated plus and zero mazes. However, after 5 weeks post-injury, anxiety-like behavior decreases, as measured in the OF and EZM. Immunostaining in the basolateral amygdala (BLA) for GAD, a marker for GABA, at the end of the behavioral testing showed the late decrease in anxiety behavior was correlated with upregulation of inhibition. The approach adopted in this study reveals a complex trajectory of affective outcomes following injury, and highlights the importance of comparing outcomes in different assays and time-points, to ensure that the affective consequences of injury are adequately assessed.

Shank and Zinc Mediate an AMPA Receptor Subunit Switch in Developing Neurons

During development, pyramidal neurons undergo dynamic regulation of AMPA receptor (AMPAR) subunit composition and density to help drive synaptic plasticity and maturation. These normal developmental changes in AMPARs are particularly vulnerable to risk factors for Autism Spectrum Disorders (ASDs), which include loss or mutations of synaptic proteins and environmental insults, such as dietary zinc deficiency. Here, we show how Shank2 and Shank3 mediate a zinc-dependent regulation of AMPAR function and subunit switch from GluA2-lacking to GluA2-containing AMPARs. Over development, we found a concomitant increase in Shank2 and Shank3 with GluA2 at synapses, implicating these molecules as potential players in AMPAR maturation. Since Shank activation and function require zinc, we next studied whether neuronal activity regulated postsynaptic zinc at glutamatergic synapses. Zinc was found to increase transiently and reversibly with neuronal depolarization at synapses, which could affect Shank and AMPAR localization and activity. Elevated zinc induced multiple functional changes in AMPAR, indicative of a subunit switch. Specifically, zinc lengthened the decay time of AMPAR-mediated synaptic currents and reduced their inward rectification in young hippocampal neurons. Mechanistically, both Shank2 and Shank3 were necessary for the zinc-sensitive enhancement of AMPAR-mediated synaptic transmission and act in concert to promote removal of GluA1 while enhancing recruitment of GluA2 at pre-existing Shank puncta. These findings highlight a cooperative local dynamic regulation of AMPAR subunit switch controlled by zinc signaling through Shank2 and Shank3 to shape the biophysical properties of developing glutamatergic synapses. Given the zinc sensitivity of young neurons and its dependence on Shank2 and Shank3, genetic mutations and/or environmental insults during early development could impair synaptic maturation and circuit formation that underlie ASD etiology.

Social Stimulus Causes Aberrant Activation of the Medial Prefrontal Cortex in a Mouse Model With Autism-Like Behaviors

Autism spectrum disorder (ASD) is a highly prevalent and genetically heterogeneous brain disorder. Developing effective therapeutic interventions requires knowledge of the brain regions that malfunction and how they malfunction during ASD-relevant behaviors. Our study provides insights into brain regions activated by a novel social stimulus and how the activation pattern differs between mice that display autism-like disabilities and control littermates. Adenomatous polyposis coli (APC) conditional knockout (cKO) mice display reduced social interest, increased repetitive behaviors and dysfunction of the β-catenin pathway, a convergent target of numerous ASD-linked human genes. Here, we exposed the mice to a novel social vs. non-social stimulus and measured neuronal activation by immunostaining for the protein c-Fos. We analyzed three brain regions known to play a role in social behavior. Compared with control littermates, APC cKOs display excessive activation, as evidenced by an increased number of excitatory pyramidal neurons stained for c-Fos in the medial prefrontal cortex (mPFC), selectively in the infralimbic sub-region. In contrast, two other social brain regions, the medial amygdala and piriform cortex show normal levels of neuron activation. Additionally, APC cKOs exhibit increased frequency of miniature excitatory postsynaptic currents (mEPSCs) in layer 5 pyramidal neurons of the infralimbic sub-region. Further, immunostaining is reduced for the inhibitory interneuron markers parvalbumin (PV) and somatostatin (SST) in the APC cKO mPFC. Our findings suggest aberrant excitatory-inhibitory balance and activation patterns. As β-catenin is a core pathway in ASD, we identify the infralimbic sub-region of the mPFC as a critical brain region for autism-relevant social behavior.

Transcriptional Regulation Involved in Fear Memory Reconsolidation

Memory reconsolidation has been demonstrated to offer a potential target period during which the fear memories underlying fear disorders can be disrupted. Reconsolidation is a labile stage that consolidated memories re-enter after memories are reactivated. Reactivated memories, induced by cues related to traumatic events, are susceptible to strengthening and weakening. Gene transcription regulation and protein synthesis have been suggested to be required for fear memory reconsolidation. Investigating the transcriptional regulation mechanisms underlying reconsolidation may provide a therapeutic method for the treatment of fear disorders such as post-traumatic stress disorder (PTSD). However, the therapeutic effect of treating a fear disorder through interfering with reconsolidation is still contradictory. In this review, we summarize several transcription factors that have been linked to fear memory reconsolidation and propose that transcription factors, as well as related signaling pathways can serve as targets for fear memory interventions. Then, we discuss the application of pharmacological and behavioral interventions during reconsolidation that may or not efficiently treat fear disorders.

PRRT2 mutations lead to neuronal dysfunction and neurodevelopmental defects

Mutations in the proline-rich transmembrane protein 2 (PRRT2) gene cause a wide spectrum of neurological diseases, ranging from paroxysmal kinesigenic dyskinesia (PKD) to mental retardation and epilepsy. Previously, seven PKD-related PRRT2 heterozygous mutations were identified in the Taiwanese population: P91QfsX, E199X, S202HfsX, R217PfsX, R217EfsX, R240X and R308C. This study aimed to investigate the disease-causing mechanisms of these PRRT2 mutations. We first documented that Prrt2 was localized at the pre- and post-synaptic membranes with a close spatial association with SNAP25 by synaptic membrane fractionation and immunostaining of the rat neurons. Our results then revealed that the six truncating Prrt2 mutants were accumulated in the cytoplasm and thus failed to target to the cell membrane; the R308C missense mutant had significantly reduced protein expression, suggesting loss-of function effects generated by these mutations. Using in utero electroporation of shRNA into cortical neurons, we further found that knocking down Prrt2 expression in vivo resulted in a delay in neuronal migration during embryonic development and a marked decrease in synaptic density after birth. These pathologic effects and novel disease-causing mechanisms may contribute to the severe clinical symptoms in PRRT2–related diseases.

Chondroitin sulfate-mediated N-cadherin/β-catenin signaling is associated with basal-like breast cancer cell invasion

Tumor metastasis involves cancer cell invasion across basement membranes and interstitial tissues. The initial invasion step consists of adherence of the tumor cell to the extracellular matrix (ECM), and this binding transduces a variety of signals from the ECM to the tumor cell. Accordingly, it is critical to establish the mechanisms by which extracellular cues influence the intracellular activities that regulate tumor cell invasion. Here, we found that invasion of the basal-like breast cancer cell line BT-549 is enhanced by the ECM component chondroitin sulfates (CSs). CSs interacted with and induced proteolytic cleavage of N-cadherin in the BT-549 cells, yielding a C-terminal intracellular N-cadherin fragment that formed a complex with β-catenin. Of note, the cleavage of N-cadherin increased cytoplasmic and nuclear β-catenin levels; induced the matrix metalloproteinase 9 (MMP9) gene, a target of β-catenin nuclear signaling; and augmented the invasion potential of the cells. We also found that CS-induced N-cadherin proteolysis requires caveolae-mediated endocytosis. An inhibitor of that process, nystatin, blocked both the endocytosis and proteolytic cleavage of N-cadherin induced by CS and also suppressed BT-549 cell invasion. Knock-out of chondroitin 4-O-sulfotransferase-1 (C4ST-1), a key CS biosynthetic enzyme, suppressed activation of the N-cadherin/β-catenin pathway through N-cadherin endocytosis and significantly decreased BT-549 cell invasion. These results suggest that CSs produced by C4ST-1 might be useful therapeutic targets in the management of basal-like breast cancers.

A Critical Role of Presynaptic Cadherin/Catenin/p140Cap Complexes in Stabilizing Spines and Functional Synapses in the Neocortex

The formation of functional synapses requires coordinated assembly of presynaptic transmitter release machinery and postsynaptic trafficking of functional receptors and scaffolds. Here, we demonstrate a critical role of presynaptic cadherin/catenin cell adhesion complexes in stabilizing functional synapses and spines in the developing neocortex. Importantly, presynaptic expression of stabilized β-catenin in either layer (L) 4 excitatory neurons or L2/3 pyramidal neurons significantly upregulated excitatory synaptic transmission and dendritic spine density in L2/3 pyramidal neurons, while its sparse postsynaptic expression in L2/3 neurons had no such effects. In addition, presynaptic β-catenin expression enhanced release probability of glutamatergic synapses. Newly identified β-catenin-interacting protein p140Cap is required in the presynaptic locus for mediating these effects. Together, our results demonstrate that cadherin/catenin complexes stabilize functional synapses and spines through anterograde signaling in the neocortex and provide important molecular evidence for a driving role of presynaptic components in spinogenesis in the neocortex.

Cadherins mediate cocaine-induced synaptic plasticity and behavioral conditioning

Drugs of abuse alter synaptic connections in the ‘reward circuit’ of the brain, which leads to long-lasting behavioral changes that underlie addiction. Here we show that cadherin adhesion molecules play a critical role in mediating synaptic plasticity and behavioral changes driven by cocaine. We demonstrate that cadherin is essential for long-term potentiation (LTP) in the ventral tegmental area (VTA), and is recruited to the synaptic membrane of excitatory inputs onto dopaminergic neurons following cocaine-mediated behavioral conditioning. Furthermore, we show that stabilization of cadherin at the membrane of these synapses blocks cocaine-induced synaptic plasticity, leading to a significant reduction in conditioned place preference induced by cocaine. Our findings identify cadherins and associated molecules as targets of interest for understanding pathological plasticity associated with addiction.

Dynamic Control of Synaptic Adhesion and Organizing Molecules in Synaptic Plasticity

Synapses play a critical role in establishing and maintaining neural circuits, permitting targeted information transfer throughout the brain. A large portfolio of synaptic adhesion/organizing molecules (SAMs) exists in the mammalian brain involved in synapse development and maintenance. SAMs bind protein partners, forming trans-complexes spanning the synaptic cleft or cis-complexes attached to the same synaptic membrane. SAMs play key roles in cell adhesion and in organizing protein interaction networks; they can also provide mechanisms of recognition, generate scaffolds onto which partners can dock, and likely take part in signaling processes as well. SAMs are regulated through a portfolio of different mechanisms that affect their protein levels, precise localization, stability, and the availability of their partners at synapses. Interaction of SAMs with their partners can further be strengthened or weakened through alternative splicing, competing protein partners, ectodomain shedding, or astrocytically secreted factors. Given that numerous SAMs appear altered by synaptic activity, in vivo, these molecules may be used to dynamically scale up or scale down synaptic communication. Many SAMs, including neurexins, neuroligins, cadherins, and contactins, are now implicated in neuropsychiatric and neurodevelopmental diseases, such as autism spectrum disorder, schizophrenia, and bipolar disorder and studying their molecular mechanisms holds promise for developing novel therapeutics.

APC conditional knock-out mouse is a model of infantile spasms with elevated neuronal β-catenin levels, neonatal spasms, and chronic seizures

Infantile spasms (IS) are a catastrophic childhood epilepsy syndrome characterized by flexion-extension spasms during infancy that progress to chronic seizures and cognitive deficits in later life. The molecular causes of IS are poorly defined. Genetic screens of individuals with IS have identified multiple risk genes, several of which are predicted to alter β-catenin pathways. However, evidence linking malfunction of β-catenin pathways and IS is lacking. Here, we show that conditional deletion in mice of the adenomatous polyposis coli gene (APC cKO), the major negative regulator of β-catenin, leads to excessive β-catenin levels and multiple salient features of human IS. Compared with wild-type littermates, neonatal APC cKO mice exhibit flexion-extension motor spasms and abnormal high-amplitude electroencephalographic discharges. Additionally, the frequency of excitatory postsynaptic currents is increased in layer V pyramidal cells, the major output neurons of the cerebral cortex. At adult ages, APC cKOs display spontaneous electroclinical seizures. These data provide the first evidence that malfunctions of APC/β-catenin pathways cause pathophysiological changes consistent with IS. Our findings demonstrate that the APC cKO is a new genetic model of IS, provide novel insights into molecular and functional alterations that can lead to IS, and suggest novel targets for therapeutic intervention.

Cadherin tales: Regulation of cadherin function by endocytic membrane trafficking

Cadherins are the primary adhesion molecules in adherens junctions and desmosomes and play essential roles in embryonic development. Although significant progress has been made in understanding cadherin structure and function, we lack a clear vision of how cells confer plasticity upon adhesive junctions to allow for cellular rearrangements during development, wound healing and metastasis. Endocytic membrane trafficking has emerged as a fundamental mechanism by which cells confer a dynamic state to adhesive junctions. Recent studies indicate that the juxtamembrane domain of classical cadherins contains multiple endocytic motifs, or "switches," that can be used by cellular membrane trafficking machinery to regulate adhesion. The cadherin-binding protein p120-catenin (p120) appears to be the master regulator of access to these switches, thereby controlling cadherin endocytosis and turnover. This review focuses on p120 and other cadherin-binding proteins, ubiquitin ligases, and growth factors as key modulators of cadherin membrane trafficking.

N-cadherin regulates beta-catenin signal and its misexpression perturbs commissural axon projection in the developing chicken spinal cord

N-cadherin is a calcium-sensitive cell adhesion molecule that plays an important role in the formation of the neural circuit and the development of the nervous system. In the present study, we investigated the function of N-cadherin in cell-cell connection in vitro with HEK293T cells, and in commissural axon projections in the developing chicken spinal cord using in ovo electroporation. Cell-cell connections increased with N-cadherin overexpression in HEK293T cells, while cell contacts disappeared after co-transfection with an N-cadherin-shRNA plasmid. The knockdown of N-cadherin caused the accumulation of β-catenin in the nucleus, supporting the notion that N-cadherin regulates β-catenin signaling in vitro. Furthermore, N-cadherin misexpression perturbed commissural axon projections in the spinal cord. The overexpression of N-cadherin reduced the number of axons that projected alongside the contralateral margin of the floor plate, and formed intermediate longitudinal commissural axons. In contrast, the knockdown of N-cadherin perturbed commissural axon projections significantly, affecting the projections alongside the contralateral margin of the floor plate, but did not affect intermediate longitudinal commissural axons. Taken together, these findings suggest that N-cadherin regulates commissural axon projections in the developing chicken spinal cord.

Hepatocyte Growth Factor Modulates MET Receptor Tyrosine Kinase and β-Catenin Functional Interactions to Enhance Synapse Formation

MET, a pleiotropic receptor tyrosine kinase implicated in autism risk, influences multiple neurodevelopmental processes. There is a knowledge gap, however, in the molecular mechanism through which MET mediates developmental events related to disorder risk. In the neocortex, MET is expressed transiently during periods of peak dendritic outgrowth and synaptogenesis, with expression enriched at developing synapses, consistent with demonstrated roles in dendritic morphogenesis, modulation of spine volume, and excitatory synapse development. In a recent coimmunoprecipitation/mass spectrometry screen, β-catenin was identified as part of the MET interactome in developing neocortical synaptosomes. Here, we investigated the influence of the MET/β-catenin complex in mouse neocortical synaptogenesis. Western blot analysis confirms that MET and β-catenin coimmunoprecipitate, but N-cadherin is not associated with the MET complex. Following stimulation with hepatocyte growth factor (HGF), β-catenin is phosphorylated at tyrosine¹⁴² (Y142) and dissociates from MET, accompanied by an increase in β-catenin/N-cadherin and MET/synapsin 1 protein complexes. In neocortical neurons in vitro, proximity ligation assays confirmed the close proximity of these proteins. Moreover, in neurons transfected with synaptophysin-GFP, HGF stimulation increases the density of synaptophysin/bassoon (a presynaptic marker) and synaptophysin/PSD-95 (a postsynaptic marker) clusters. Mutation of β-catenin at Y142 disrupts the dissociation of the MET/β-catenin complex and prevents the increase in clusters in response to HGF. The data demonstrate a new mechanism for the modulation of synapse formation, whereby MET activation induces an alignment of presynaptic and postsynaptic elements that are necessary for assembly and formation of functional synapses by subsets of neocortical neurons that express MET/β-catenin complex.

ADP Ribosylation Factor 6 Regulates Neuronal Migration in the Developing Cerebral Cortex through FIP3/Arfophilin-1-dependent Endosomal Trafficking of N-cadherin

During neural development, endosomal trafficking controls cell shape and motility through the polarized transport of membrane proteins related to cell–cell and cell–extracellular matrix interactions. ADP ribosylation factor 6 (Arf6) is a critical small GTPase that regulates membrane trafficking between the plasma membrane and endosomes. We herein demonstrated that the knockdown of endogenous Arf6 in mouse cerebral cortices led to impaired neuronal migration in the intermediate zone and cytoplasmic retention of N-cadherin and syntaxin12 in migrating neurons. Rescue experiments with separation-of-function Arf6 mutants identified Rab11 family-interacting protein 3 (FIP3)/Arfophilin-1, a dual effector for Arf6 and Rab11, as a downstream effector of Arf6 in migrating neurons. The knockdown of FIP3 led to impaired neuronal migration in the intermediate zone and cytoplasmic retention of N-cadherin in migrating neurons, similar to that of Arf6, which could be rescued by the coexpression of wild-type FIP3 but not FIP3 mutants lacking the binding site for Arf6 or Rab11. These results suggest that Arf6 regulates cortical neuronal migration in the intermediate zone through the FIP3-dependent endosomal trafficking.

Organization and dynamics of the actin cytoskeleton during dendritic spine morphological remodeling

In the central nervous system, most excitatory post-synapses are small subcellular structures called dendritic spines. Their structure and morphological remodeling are tightly coupled to changes in synaptic transmission. The F-actin cytoskeleton is the main driving force of dendritic spine remodeling and sustains synaptic plasticity. It is therefore essential to understand how changes in synaptic transmission can regulate the organization and dynamics of actin binding proteins (ABPs). In this review, we will provide a detailed description of the organization and dynamics of F-actin and ABPs in dendritic spines and will discuss the current models explaining how the actin cytoskeleton sustains both structural and functional synaptic plasticity.

Postsynaptic Y654 dephosphorylation of β-catenin modulates presynaptic vesicle turnover through increased n-cadherin-mediated transsynaptic signaling

Synaptic adhesion molecules, which coordinately control structural and functional changes at both sides of synapses, are important for synaptogenesis and synaptic plasticity. Because they physically form homophilic or heterophilic adhesions across synaptic junctions, these molecules can initiate transsynaptic communication in both anterograde and retrograde directions. Using optical imaging approaches, we investigated whether an increase in postsynaptic N-cadherin could correspondingly alter the function of connected presynaptic terminals. Postsynaptic expression of β-catenin Y654F, a phosphorylation-defective form with enhanced binding to N-cadherin, is sufficient to increase postsynaptic surface levels of N-cadherin and consequently promote presynaptic reorganizations. Such reorganizations include increases in the densities of the synaptic vesicle protein, Synaptotagmin 1 and the active zone scaffold protein, Bassoon, the number of active boutons and the size of the total recycling vesicle pool. In contrast, synaptic vesicle turnover is significantly impaired, preventing the exchange of synaptic vesicles with adjacent boutons. Together, N-cadherin-mediated retrograde signaling, governed by phosphoregulation of postsynaptic β-catenin Y654, coordinately modulates presynaptic vesicle dynamics to enhance synaptic communication in mature neurons. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 61-74, 2017.

Deletion of CTNNB1 in inhibitory circuitry contributes to autism-associated behavioral defects

Mutations in β-catenin (CTNNB1) have been implicated in cancer and mental disorders. Recently, loss-of-function mutations of CTNNB1 were linked to intellectual disability (ID), and rare mutations were identified in patients with autism spectrum disorder (ASD). As a key regulator of the canonical Wnt pathway, CTNNB1 plays an essential role in neurodevelopment. However, the function of CTNNB1 in specific neuronal subtypes is unclear. To understand how CTNNB1 deficiency contributes to ASD, we generated CTNNB1 conditional knockout (cKO) mice in parvalbumin interneurons. The cKO mice had increased anxiety, but had no overall change in motor function. Interestingly, CTNNB1 cKO in PV-interneurons significantly impaired object recognition and social interactions and elevated repetitive behaviors, which mimic the core symptoms of patients with ASD. Surprisingly, deleting CTNNB1 in parvalbumin-interneurons enhanced spatial memory. To determine the effect of CTNNB1 KO in overall neuronal activity, we found that c-Fos was significantly reduced in the cortex, but not in the dentate gyrus and the amygdala. Our findings revealed a cell type-specific role of CTNNB1 gene in regulation of cognitive and autistic-like behaviors. Thus, this study has important implications for development of therapies for ASDs carrying the CTNNB1 mutation or other ASDs that are associated with mutations in the Wnt pathway. In addition, our study contributes to a broader understanding of the regulation of the inhibitory circuitry.

Cadherins and catenins in dendrite and synapse morphogenesis

Neurons are highly polarized specialized cells. Neuronal integrity and functional roles are critically dependent on dendritic architecture and synaptic structure, function and plasticity. The cadherins are glycosylated transmembrane proteins that form cell adhesion complexes in various tissues. They are associated with a group of cytosolic proteins, the catenins. While the functional roles of the complex have been extensively investigates in non-neuronal cells, it is becoming increasingly clear that components of the complex have critical roles in regulating dendritic and synaptic architecture, function and plasticity in neurons. Consistent with these functional roles, aberrations in components of the complex have been implicated in a variety of neurodevelopmental disorders. In this review, we discuss the roles of the classical cadherins and catenins in various aspects of dendrite and synapse architecture and function and their relevance to human neurological disorders. Cadherins are glycosylated transmembrane proteins that were initially identified as Ca(2+)-dependent cell adhesion molecules. They are present on plasma membrane of a variety of cell types from primitive metazoans to humans. In the past several years, it has become clear that in addition to providing mechanical adhesion between cells, cadherins play integral roles in tissue morphogenesis and homeostasis. The cadherin family is composed of more than 100 members and classified into several subfamilies, including classical cadherins and protocadherins. Several of these cadherin family members have been implicated in various aspects of neuronal development and function. (1-3) The classical cadherins are associated with a group of cytosolic proteins, collectively called the catenins. While the functional roles of the cadherin-catenin cell adhesion complex have been extensively investigated in epithelial cells, it is now clear that components of the complex are well expressed in central neurons at different stages during development. (4,5) Recent exciting studies have shed some light on the functional roles of cadherins and catenins in central neurons. In this review, we will provide a brief overview of the cadherin superfamily, describe cadherin family members expressed in central neurons, cadherin-catenin complexes in central neurons and then focus on role of the cadherin-catenin complex in dendrite morphogenesis and synapse morphogenesis, function and plasticity. The final section is dedicated to discussion of the emerging list of neural disorders linked to cadherins and catenins. While the roles of cadherins and catenins have been examined in several different types of neurons, the focus of this review is their role in mammalian central neurons, particularly those of the cortex and hippocampus. Accompanying this review is a series of excellent reviews targeting the roles of cadherins and protocadherins in other aspects of neural development.

Lateral assembly of N-cadherin drives tissue integrity by stabilizing adherens junctions

Cadherin interactions ensure the correct registry and anchorage of cells during tissue formation. Along the plasma membrane, cadherins form inter-junctional lattices via cis- and trans-dimerization. While structural studies have provided models for cadherin interactions, the molecular nature of cadherin binding in vivo remains unexplored. We undertook a multi-disciplinary approach combining live cell imaging of three-dimensional cell assemblies (spheroids) with a computational model to study the dynamics of N-cadherin interactions. Using a loss-of-function strategy, we demonstrate that each N-cadherin interface plays a distinct role in spheroid formation. We found that cis-dimerization is not a prerequisite for trans-interactions, but rather modulates trans-interfaces to ensure tissue stability. Using a model of N-cadherin junction dynamics, we show that the absence of cis-interactions results in low junction stability and loss of tissue integrity. By quantifying the binding and unbinding dynamics of the N-cadherin binding interfaces, we determined that mutating either interface results in a 10-fold increase in the dissociation constant. These findings provide new quantitative information on the steps driving cadherin intercellular adhesion and demonstrate the role of cis-interactions in junction stability.

Acid-sensing ion channels: trafficking and pathophysiology

Acid-sensing ion channels (ASICs) are proton-gated cation channels that are widely expressed in both the peripheral and central nervous systems. ASICs contribute to a variety of pathophysiological conditions that involve tissue acidosis, such as ischemic stroke, epileptic seizures and multiple sclerosis. Although much progress has been made in researching the structure-function relationship and pharmacology of ASICs, little is known about the trafficking of ASICs and its contribution to ASIC function. The recent identification of the mechanism of membrane insertion and endocytosis of ASIC1a highlights the emerging role of ASIC trafficking in regulating its pathophysiological functions. In this review, we summarize the recent advances and discuss future directions on this topic.