Contactin-1 regulates myelination and nodal/paranodal domain organization in the central nervous system

Microglial Lectins in Health and Neurological Diseases

Microglia are the innate sentinels of the central nervous system (CNS) and are responsible for the homeostasis and immune defense of the CNS. Under the influence of the local environment and cell-cell interaction, microglia exhibit a multidimensional and context-dependent phenotypes that can be cytotoxic and neuroprotective. Recent studies suggest that microglia express multitudinous types of lectins, including galectins, Siglecs, mannose-binding lectins (MBLs) and other glycan binding proteins. Because most studies that examine lectins focus on the peripheral system, the functions of lectins have not been critically investigated in the CNS. In addition, the types of brain cells that contribute to the altered levels of lectins present in diseases are often unclear. In this review, we will discuss how galectins, Siglecs, selectins and MBLs contribute to the dynamic functions of microglia. The interacting ligands of these lectins are complex glycoconjugates, which consist of glycoproteins and glycolipids that are expressed on microglia or surrounding cells. The current understanding of the heterogeneity and functions of glycans in the brain is limited. Galectins are a group of pleotropic proteins that recognize both β-galactoside-containing glycans and non- β-galactoside-containing proteins. The function and regulation of galectins have been implicated in immunomodulation, neuroinflammation, apoptosis, phagocytosis and oxidative bursts. Most Siglecs are expressed at a low level on the plasma membrane and bind to sialic acid residues for immunosurveillance and cell-cell communication. Siglecs are classified based on their inhibitory and activatory downstream signaling properties. Inhibitory Siglecs negatively regulate microglia activation upon recognizing the intact sialic acid patterns and vice versa. MBLs are expressed upon infection in cytoplasm and can be secreted in order to recognize molecules containing terminal mannose as an innate immune defense machinery. Most importantly, multiple studies have reported dysregulation of lectins in neurological disorders. Here, we reviewed recent studies on microglial lectins and their functions in CNS health and disease, and suggest that these lectin families are novel, potent therapeutic targets for neurological diseases.

Overexpression of Contactin 1 promotes growth, migration and invasion in Hs578T breast cancer cells

Background

Contactin1 (CNTN1) has been shown to play an important role in the invasion and metastasis of several tumors; however, the role of CNTN1 in breast cancer has not been fully studied. The purpose of this study is to investigate the role of CNTN1 in regulating tumor growth, migration and invasion in breast cancer.

Results

To investigate its function, CNTN1 was expressed in Hs578T cells. CNTN1 expression was confirmed by western blot, immunohistochemistry and real-time RT-PCR. The effect of CNTN1 overexpression on proliferation, migration and invasion of Hs578T breast cancer cells was assessed in vitro and in vivo. Our results showed that CNTN1 overexpression promoted Hs578T cell proliferation, cell cycle progression, colony formation, invasion and migration. Notably, overexpression of CNTN1 in Hs578T cells enhanced the growth of mouse xenograft tumors.

Conclusions

CNTN1 promotes growth, metastasis and invasion of Hs578T breast cancer cell line. Thus, therapies targeting CNTN1 may prove efficacious for breast cancer. However, further investigation is required to understand the mechanism by which CNTN1 influences proliferation, metastasis and invasion in breast cancer.

Electronic supplementary material

The online version of this article (10.1186/s12860-018-0154-3) contains supplementary material, which is available to authorized users.

The function of contactin-2/TAG-1 in oligodendrocytes in health and demyelinating pathology

The oligodendrocyte maturation process and the transition from the pre-myelinating to the myelinating state are extremely important during development and in pathology. In the present study, we have investigated the role of the cell adhesion molecule CNTN2/TAG-1 on oligodendrocyte proliferation, differentiation, myelination, and function during development and under pathological conditions. With the combination of in vivo, in vitro, ultrastructural, and electrophysiological methods, we have mapped the expression of CNTN2 protein in the oligodendrocyte lineage during the different stages of myelination and its involvement on oligodendrocyte maturation, branching, myelin-gene expression, myelination, and axonal function. The cuprizone model of central nervous system demyelination was further used to assess CNTN2 in pathology. During development, CNTN2 can transiently affect the expression levels of myelin and myelin-regulating genes, while its absence results in reduced oligodendrocyte branching, hypomyelination of fiber tracts and impaired axonal conduction. In pathology, CNTN2 absence does not affect the extent of de- and remyelination. However during remyelination, a novel, CNTN2-independent mechanism is revealed that is able to recluster voltage gated potassium channels (VGKCs) resulting in the improvement of fiber conduction.

Synaptosomal Proteome of the Orbitofrontal Cortex from Schizophrenia Patients Using Quantitative Label-Free and iTRAQ-Based Shotgun Proteomics

Schizophrenia is a chronic and incurable neuropsychiatric disorder that affects about one percent of the world population. The proteomic characterization of the synaptosome fraction of the orbitofrontal cortex is useful for providing valuable information about the molecular mechanisms of synaptic functions in these patients. Quantitative analyses of synaptic proteins were made with eight paranoid schizophrenia patients and a pool of eight healthy controls free of mental diseases. Label-free and iTRAQ labeling identified a total of 2018 protein groups. Statistical analyses revealed 12 and 55 significantly dysregulated proteins by iTRAQ and label-free, respectively. Quantitative proteome analyses showed an imbalance in the calcium signaling pathway and proteins such as reticulon-1 and cytochrome c, related to endoplasmic reticulum stress and programmed cell death. Also, it was found that there is a significant increase in limbic-system-associated membrane protein and α-calcium/calmodulin-dependent protein kinase II, associated with the regulation of human behavior. Our data contribute to a better understanding about apoptosis as a possible pathophysiological mechanism of this disease as well as neural systems supporting social behavior in schizophrenia. This study also is a joint effort of the Chr 15 C-HPP team and the Human Brain Proteome Project of B/D-HPP. All MS proteomics data are deposited in the ProteomeXchange Repository under PXD006798.

Gene Network Construction from Microarray Data Identifies a Key Network Module and Several Candidate Hub Genes in Age-Associated Spatial Learning Impairment

As humans age many suffer from a decrease in normal brain functions including spatial learning impairments. This study aimed to better understand the molecular mechanisms in age-associated spatial learning impairment (ASLI). We used a mathematical modeling approach implemented in Weighted Gene Co-expression Network Analysis (WGCNA) to create and compare gene network models of young (learning unimpaired) and aged (predominantly learning impaired) brains from a set of exploratory datasets in rats in the context of ASLI. The major goal was to overcome some of the limitations previously observed in the traditional meta- and pathway analysis using these data, and identify novel ASLI related genes and their networks based on co-expression relationship of genes. This analysis identified a set of network modules in the young, each of which is highly enriched with genes functioning in broad but distinct GO functional categories or biological pathways. Interestingly, the analysis pointed to a single module that was highly enriched with genes functioning in “learning and memory” related functions and pathways. Subsequent differential network analysis of this “learning and memory” module in the aged (predominantly learning impaired) rats compared to the young learning unimpaired rats allowed us to identify a set of novel ASLI candidate hub genes. Some of these genes show significant repeatability in networks generated from independent young and aged validation datasets. These hub genes are highly co-expressed with other genes in the network, which not only show differential expression but also differential co-expression and differential connectivity across age and learning impairment. The known function of these hub genes indicate that they play key roles in critical pathways, including kinase and phosphatase signaling, in functions related to various ion channels, and in maintaining neuronal integrity relating to synaptic plasticity and memory formation. Taken together, they provide a new insight and generate new hypotheses into the molecular mechanisms responsible for age associated learning impairment, including spatial learning.

Nanomechanics of multidomain neuronal cell adhesion protein contactin revealed by single molecule AFM and SMD

Contactin-4 (CNTN4) is a complex cell adhesion molecule (CAM) localized at neuronal membranes, playing a key role in maintaining the mechanical integrity and signaling properties of the synapse. CNTN4 consists of six immunoglobulin C2 type (IgC2) domains and four fibronectin type III (FnIII) domains that are shared with many other CAMs. Mutations in CNTN4 gene have been linked to various psychiatric disorders. Toward elucidating the response of this modular protein to mechanical stress, we studied its force-induced unfolding using single molecule atomic force microscopy (smAFM) and steered molecular dynamics (SMD) simulations. Extensive smAFM and SMD data both indicate the distinctive mechanical behavior of the two types of modules distinguished by unique force-extension signatures. The data also reveal the heterogeneity of the response of the individual FNIII and IgC2 modules, which presumably plays a role in the adaptability of CNTN4 to maintaining cell-cell communication and adhesion properties under different conditions. Results show that extensive sampling of force spectra, facilitated by robot-enhanced AFM, can help reveal the existence of weak stabilizing interactions between the domains of multidomain proteins, and provide insights into the nanomechanics of such multidomain or heteromeric proteins.

Contactin-Associated Protein 1 (CNTNAP1) Mutations Induce Characteristic Lesions of the Paranodal Region

Congenital hypomyelinating neuropathy is a rare neonatal syndrome responsible for hypotonia and weakness. Nerve microscopic examination shows amyelination or hypomyelination. Recently, mutations in CNTNAP1 have been described in a few patients. CNTNAP1 encodes contactin-associated protein 1 (caspr-1), which is an essential component of the paranodal junctions of the peripheral and central nervous systems, and is necessary for the establishment of transverse bands that stabilize paranodal axo-glial junctions. We present the results of nerve biopsy studies of three patients from two unrelated, non-consanguineous families with compound heterozygous CNTNAP1 mutations. The lesions were identical, characterized by a hypomyelinating process; on electron microscopy, we detected, in all nodes of Ranvier, subtle lesions that have never been previously described in human nerves. Transverse bands of the myelin loops were absent, with a loss of attachment between myelin and the axolemma; elongated Schwann cell processes sometimes dissociated the Schwann cell and axon membranes that bound the space between them. These lesions were observed in the area where caspr-1 is located and are reminiscent of the lesions reported in sciatic nerves of caspr-1 null mice. CNTNAP1 mutations appear to induce characteristic ultrastructural lesions of the paranodal region.

A hypomorphic PIGA gene mutation causes severe defects in neuron development and susceptibility to complement-mediated toxicity in a human iPSC model

Mutations in genes involved in glycosylphosphatidylinositol (GPI) anchor biosynthesis underlie a group of congenital syndromes characterized by severe neurodevelopmental defects. GPI anchored proteins have diverse roles in cell adhesion, signaling, metabolism and complement regulation. Over 30 enzymes are required for GPI anchor biosynthesis and PIGA is involved in the first step of this process. A hypomorphic mutation in the X-linked PIGA gene (c.1234C>T) causes multiple congenital anomalies hypotonia seizure syndrome 2 (MCAHS2), indicating that even partial reduction of GPI anchored proteins dramatically impairs central nervous system development, but the mechanism is unclear. Here, we established a human induced pluripotent stem cell (hiPSC) model containing the PIGAc.1234C>T mutation to study the effects of a hypomorphic allele of PIGA on neuronal development. Neuronal differentiation from neural progenitor cells generated by EB formation in PIGAc.1234C>T is significantly impaired with decreased proliferation, aberrant synapse formation and abnormal membrane depolarization. The results provide direct evidence for a critical role of GPI anchor proteins in early neurodevelopment. Furthermore, neural progenitors derived from PIGAc.1234C>T hiPSCs demonstrate increased susceptibility to complement-mediated cytotoxicity, suggesting that defective complement regulation may contribute to neurodevelopmental disorders.

Identification of serum protein biomarkers for utrophin based DMD therapy

Despite promising therapeutic avenues, there is currently no effective treatment for Duchenne muscular dystrophy (DMD), a lethal monogenic disorder caused by the loss of the large cytoskeletal protein, dystrophin. A highly promising approach to therapy, applicable to all DMD patients irrespective to their genetic defect, is to modulate utrophin, a functional paralogue of dystrophin, able to compensate for the primary defects of DMD restoring sarcolemmal stability. One of the major difficulties in assessing the effectiveness of therapeutic strategies is to define appropriate outcome measures. In the present study, we utilised an aptamer based proteomics approach to profile 1,310 proteins in plasma of wild-type, mdx and Fiona (mdx overexpressing utrophin) mice. Comparison of the C57 and mdx sera revealed 83 proteins with statistically significant >2 fold changes in dystrophic serum abundance. A large majority of previously described biomarkers (ANP32B, THBS4, CAMK2A/B/D, CYCS, CAPNI) were normalised towards wild-type levels in Fiona animals. This work also identified potential mdx markers specific to increased utrophin (DUS3, TPI1) and highlights novel mdx biomarkers (GITR, MYBPC1, HSP60, SIRT2, SMAD3, CNTN1). We define a panel of putative protein mdx biomarkers to evaluate utrophin based strategies which may help to accelerate their translation to the clinic.

Sodium Channel Trafficking

Voltage-gated sodium channels (VGSC) are critical determinants of cellular electrical activity through the control of initiation and propagation of action potential. To ensure this role, these proteins are not consistently delivered to the plasma membrane but undergo drastic quality controls throughout various adaptive processes such as biosynthesis, anterograde and retrograde trafficking, and membrane targeting. In pathological conditions, this quality control could lead to the retention of functional VGSC and is therefore the target of different pharmacological approaches. The present chapter gives an overview of the current understanding of the facets of VGSC life cycle in the context of both cardiac and neuronal cell types.

Structure and function of the contactin-associated protein family in myelinated axons and their relationship with nerve diseases

The contactin-associated protein (Caspr) family participates in nerve excitation and conduction, and neurotransmitter release in myelinated axons. We analyzed the structures and functions of the Caspr family–CNTNAP1 (Caspr1), CNTNAP2 (Caspr2), CNTNAP3 (Caspr3), CNTNAP4 (Caspr4) and CNTNAP5 (Caspr5), Caspr1–5 is not only involved in the formation of myelinated axons, but also participates in maintaining the stability of adjacent connections. Caspr1 participates in the formation, differentiation, and proliferation of neurons and astrocytes, and in motor control and cognitive function. We also analyzed the relationship between the Caspr family and neurodegenerative diseases, multiple sclerosis, and autoimmune encephalitis. However, the effects of Caspr on disease course and prognosis remain poorly understood. The effects of Caspr on disease diagnosis and treatment need further investigation.

The role of Gpi-anchored axonal glycoproteins in neural development and neurological disorders

This review article focuses on the Contactin (CNTN) subset of the Immunoglobulin supergene family (IgC2/FNIII molecules), whose components share structural properties (the association of Immunoglobulin type C2 with Fibronectin type III domains), as well as a general role in cell contact formation and axonal growth control. IgC2/FNIII molecules include 6 highly related components (CNTN 1-6), associated with the cell membrane via a Glycosyl Phosphatidyl Inositol (GPI)-containing lipid tail. Contactin 1 and Contactin 2 share ~50 (49.38)% identity at the aminoacid level. They are components of the cell surface, from which they may be released in soluble forms. They bind heterophilically to multiple partners in cis and in trans, including members of the related L1CAM family and of the Neurexin family Contactin-associated proteins (CNTNAPs or Casprs). Such interactions are important for organising the neuronal membrane, as well as for modulating the growth and pathfinding of axon tracts. In addition, they also mediate the functional maturation of axons by promoting their interactions with myelinating cells at the nodal, paranodal and juxtaparanodal regions. Such interactions also mediate differential ionic channels (both Na⁺ and K⁺) distribution, which is of critical relevance in the generation of the peak-shaped action potential. Indeed, thanks to their interactions with Ankyrin G, Na⁺ channels map within the nodal regions, where they drive axonal depolarization. However, no ionic channels are found in the flanking Contactin1-containing paranodal regions, where CNTN1 interactions with Caspr1 and with the Ig superfamily component Neurofascin 155 in cis and in trans, respectively, build a molecular barrier between the node and the juxtaparanode. In this region K⁺ channels are clustered, depending upon molecular interactions with Contactin 2 and with Caspr2. In addition to these functions, the Contactins appear to have also a role in degenerative and inflammatory disorders: indeed Contactin 2 is involved in neurodegenerative disorders with a special reference to the Alzheimer disease, given its ability to work as a ligand of the Alzheimer Precursor Protein (APP), which results in increased Alzheimer Intracellular Domain (AICD) release in a γ-secretase-dependent manner. On the other hand Contactin 1 drives Notch signalling activation via the Hes pathway, which could be consistent with its ability to modulate neuroinflammation events, and with the possibility that Contactin 1-dependent interactions may participate to the pathogenesis of the Multiple Sclerosis and of other inflammatory disorders.

Two novel variants in CNTNAP1 in two siblings presenting with congenital hypotonia and hypomyelinating neuropathy

Homozygous frameshift variants in CNTNAP1 have recently been reported in patients with arthrogryposis and abnormal axon myelination. In two brothers with severe congenital hypotonia and foot deformities, we identified compound heterozygous variants in CNTNAP1, reporting the first causative missense variant, p.(Cys323Arg). Motor nerve conductions were markedly decreased. Nerve microscopical lesions confirmed a severe hypomyelinating process and showed loss of attachment sites of the myelin loops on the axons, which could be a characteristic of Caspr loss-of-function. We discuss the pathophysiology of the myelination process and we propose to consider this disorder as a congenital hypomyelinating neuropathy.

Pathway-related molecules of VEGFC/D-VEGFR3/NRP2 axis in tumor lymphangiogenesis and lymphatic metastasis

Precondition for tumor lymphatic metastasis is that tumor cells induce formation of original and newborn lymphatic vessels and invade surrounding lymphatic vessels in tumor stroma, while some pathway-related molecules play an important role in mechanisms associated with proliferation and migration of lymphatic endothelial cells (LECs) and tumor cells. In lymphangiogenesis and lymphatic metastasis, the pathway-related molecules of VEGFC/D-VEGFR3/NRP2 axis, such as Furin-like enzyme, CNTN1, Prox1, LYVE-1, Podoplanin, SOX18, SDF1 and CXCR4, are direct constitutors as a portion of VEGFC/D-VEGFR3/NRP2 axis, and their biological activities rely on this ligand-receptor system. These axis-related signal molecules could gradually produce waterfall-like cascading effects, mediate differentiation and maturation of LECs, remodel original and neonatal lymphatic vessels, as well as ultimately promote tumor cell chemotaxis, migration, invasion and metastasis to lymphoid tracts. This review summarizes the structure and function features of pathway-related molecules of VEGFC/D-VEGFR3/NRP2 axis, the expression changes of these molecules in different anatomic organs or histopathologic types or development stages of various tumors, the characteristics of transduction, implementation, integration of signal networks, the interactive effects on biological behaviors between tumor cells and lymphatic endothelial cells, and their molecular mechanisms and significances in tumor lymphangiogenesis and lymphatic metastasis.

Regulating Axonal Responses to Injury: The Intersection between Signaling Pathways Involved in Axon Myelination and The Inhibition of Axon Regeneration

Following spinal cord injury (SCI), a multitude of intrinsic and extrinsic factors adversely affect the gene programs that govern the expression of regeneration-associated genes (RAGs) and the production of a diversity of extracellular matrix molecules (ECM). Insufficient RAG expression in the injured neuron and the presence of inhibitory ECM at the lesion, leads to structural alterations in the axon that perturb the growth machinery, or form an extraneous barrier to axonal regeneration, respectively. Here, the role of myelin, both intact and debris, in antagonizing axon regeneration has been the focus of numerous investigations. These studies have employed antagonizing antibodies and knockout animals to examine how the growth cone of the re-growing axon responds to the presence of myelin and myelin-associated inhibitors (MAIs) within the lesion environment and caudal spinal cord. However, less attention has been placed on how the myelination of the axon after SCI, whether by endogenous glia or exogenously implanted glia, may alter axon regeneration. Here, we examine the intersection between intracellular signaling pathways in neurons and glia that are involved in axon myelination and axon growth, to provide greater insight into how interrogating this complex network of molecular interactions may lead to new therapeutics targeting SCI.

Individual Neuronal Subtypes Exhibit Diversity in CNS Myelination Mediated by Synaptic Vesicle Release

Regulation of myelination by oligodendrocytes in the CNS has important consequences for higher-order nervous system function (e.g., [1, 2, 3, 4]), and there is growing consensus that neuronal activity regulates CNS myelination (e.g., [5, 6, 7, 8, 9]) through local axon-oligodendrocyte synaptic-vesicle-release-mediated signaling [10, 11, 12]. Recent analyses have indicated that myelination along axons of distinct neuronal subtypes can differ [13, 14], but it is not known whether regulation of myelination by activity is common to all neuronal subtypes or only some. This limits insight into how specific neurons regulate their own conduction. Here, we use a novel fluorescent fusion protein reporter to study myelination along the axons of distinct neuronal subtypes over time in zebrafish. We find that the axons of reticulospinal and commissural primary ascending (CoPA) neurons are among the first myelinated in the zebrafish CNS. To investigate how activity regulates myelination by different neuronal subtypes, we express tetanus toxin (TeNT) in individual reticulospinal or CoPA neurons to prevent synaptic vesicle release. We find that the axons of individual tetanus toxin expressing reticulospinal neurons have fewer myelin sheaths than controls and that their myelin sheaths are 50% shorter than controls. In stark contrast, myelination along tetanus-toxin-expressing CoPA neuron axons is entirely normal. These results indicate that while some neuronal subtypes modulate myelination by synaptic vesicle release to a striking degree in vivo, others do not. These data have implications for our understanding of how different neurons regulate myelination and thus their own function within specific neuronal circuits.

•

Live imaging of myelin sheath dynamics along single axons over time in zebrafish

•

Vesicular release from reticulospinal axons required for normal myelination

•

Vesicular release from CoPA axons not required for myelination

•

Evidence of neuronal subtype diversity of activity-regulated myelination

Structural Characterization of the Extracellular Domain of CASPR2 and Insights into Its Association with the Novel Ligand Contactin1

Contactin-associated protein-like 2 (CNTNAP2) encodes for CASPR2, a multidomain single transmembrane protein belonging to the neurexin superfamily that has been implicated in a broad range of human phenotypes including autism and language impairment. Using a combination of biophysical techniques, including small angle x-ray scattering, single particle electron microscopy, analytical ultracentrifugation, and bio-layer interferometry, we present novel structural and functional data that relate the architecture of the extracellular domain of CASPR2 to a previously unknown ligand, Contactin1 (CNTN1). Structurally, CASPR2 is highly glycosylated and has an overall compact architecture. Functionally, we show that CASPR2 associates with micromolar affinity with CNTN1 but, under the same conditions, it does not interact with any of the other members of the contactin family. Moreover, by using dissociated hippocampal neurons we show that microbeads loaded with CASPR2, but not with a deletion mutant, co-localize with transfected CNTN1, suggesting that CNTN1 is an endogenous ligand for CASPR2. These data provide novel insights into the structure and function of CASPR2, suggesting a complex role of CASPR2 in the nervous system.

Mechanisms of sodium channel clustering and its influence on axonal impulse conduction

The efficient propagation of action potentials along nervous fibers is necessary for animals to interact with the environment with timeliness and precision. Myelination of axons is an essential step to ensure fast action potential propagation by saltatory conduction, a process that requires highly concentrated voltage-gated sodium channels at the nodes of Ranvier. Recent studies suggest that the clustering of sodium channels can influence axonal impulse conduction in both myelinated and unmyelinated fibers, which could have major implications in disease, particularly demyelinating pathology. This comprehensive review summarizes the mechanisms governing the clustering of sodium channels at the peripheral and central nervous system nodes and the specific roles of their clustering in influencing action potential conduction. We further highlight the classical biophysical parameters implicated in conduction timing, followed by a detailed discussion on how sodium channel clustering along unmyelinated axons can impact axonal impulse conduction in both physiological and pathological contexts.

Roles of contactin-1 in solid tumors

The neural cell adhesion molecule contactin-1 (CNTN1), first identified as a member of the contactin subpopulation of the immunoglobulin superfamily, is associated with many other cell surface proteins expressed on a variety of neurocytes, contributing to their functions and maturation. It has been recently found that the abnormal expression of CNTN1 has a close correlation with tumor initiation, development, invasiveness, metastasis and prognosis. The acquired metastatic ability of malignant tumors is caused by a population of cancer cells with the capacities of invasiveness, metastasis, adherence and proliferation, in which abnormal gene expression may play an important role. This review focuses on the current advances in research of CNTN1 in the nerve system, and mainly in the malignant tumors, with an aim to provide new clues to clinical prevention, diagnosis and treatment of these malignancies.

Contactin 1: A potential therapeutic target and biomarker in gastric cancer

Despite advances in diagnosis and treatment, gastric cancer remains one of the most common malignant tumors worldwide, and early diagnosis remains a challenge. The lack of effective methods to detect these tumors early is a major factor contributing to the high mortality in patients with gastric cancer, who are typically diagnosed at an advanced stage. Additionally, the early detection of metastases and the curative treatment of gastric cancer are difficult to achieve, and the detailed mechanisms remain to be fully elucidated. Thus, the identification of valuable predictive biomarkers and therapeutic targets to improve the prognosis of patients with gastric cancer is becoming increasingly important. Contactin 1 (CNTN1), a cell adhesion molecule, is a glycosylphosphatidylinositol-anchored neuronal membrane protein that plays an important role in cancer progression. The expression of CNTN1 is upregulated in primary lesions, and its expression level correlates with tumor metastasis in cancer patients. The current evidence reveals that the functions of CNTN1 in the development and progression of cancer likely promote the invasion and metastasis of cancer cells via the VEGFC/FLT4 axis, the RHOA-dependent pathway, the Notch signaling pathway and the epithelial-mesenchymal transition progression. Therefore, CNTN1 may be a novel biomarker and a possible therapeutic target in cancer treatment in the near future.

Myelination at a glance

The myelin sheath is a plasma membrane extension that is laid down in regularly spaced segments along axons of the nervous system. This process involves extensive changes in oligodendrocyte cell shape and membrane architecture. In this Cell Science at a Glance article and accompanying poster, we provide a model of how myelin of the central nervous system is wrapped around axons to form a tightly compacted, multilayered membrane structure. This model may not only explain how myelin is generated during brain development, but could also help us to understand myelin remodeling in adult life, which might serve as a form of plasticity for the fine-tuning of neuronal networks.

Role of F3/contactin expression profile in synaptic plasticity and memory in aged mice

We have recently shown that overexpression of the F3/contactin adhesive glycoprotein (also known as Contactin-1) promotes neurogenesis in adult hippocampus, which correlates with improved synaptic plasticity and memory. Because F3/contactin levels physiologically decrease with age, here, we aim at investigating whether its overexpression might counteract the cognitive decline in aged animals. For this we use 20- to 24-month-old TAG/F3 transgenic mice in which F3/contactin overexpression is driven by regulatory sequences from the gene encoding the transient axonal glycoprotein TAG-1 throughout development. We show that aged TAG/F3 mice display improved hippocampal long-term potentiation and memory compared with wild-type littermates. The same mice undergo a decrease of neuronal apoptosis at the hippocampal level, which correlated to a decrease of active caspase-3; by contrast, procaspase-3 and Bax as well as the anti-apoptotic and plasticity-related pathway BDNF/CREB/Bcl-2 were rather increased. Interestingly, amyloid-precursor protein processing was shifted toward sAPPα generation, with a decrease of sAPPβ and amyloid-beta levels. Our data confirm that F3/contactin plays a role in hippocampal synaptic plasticity and memory also in aged mice, suggesting that it acts on molecular pathways related to apoptosis and amyloid-beta production.

[New insights on the organization of the nodes of Ranvier]

Myelin plays a crucial role in the rapid and saltatory conduction of the nerve impulse along myelinated axons. In addition, myelin closely regulates the organization of the axonal compartments. This organization involves several complex mechanisms including axo-glial contact, diffusion barriers, the cytoskeletal network, and the extracellular matrix. In peripheral nerves, the axo-glial contact dictates the formation of the nodes and the clustering of the voltage-gated sodium channels (Nav). The axo-glial contact at nodes implicates adhesion molecules expressed by the Schwann cell (gliomedin and NrCAM), which binds a partner, neurofascin-186, on the axonal side. This complex is essential for the recruitment of ankyrin-G, a cytoskeletal scaffolding protein, which binds and concentrates Nav channels at nodes. The paranodal junctions flanking the nodes also play a complementary function in node formation. These junctions are formed by the association of contactin-1/caspr-1/neurofascin-155 and create a diffusion barrier, which traps proteins at the nodes and dampens their diffusion along the internode. In the central nervous system, the mechanisms of node formation are different and the formation of the paranodal junctions precedes the aggregation of Nav channels at nodes. However, node formation can still happen in absence of paranodal junctions in the CNS. One explanation is that NF186 interacts with components of the extracellular matrix around the node and thereby stabilizes the aggregation of nodal proteins. It is likely that many other proteins are also implicated in the signaling pathways that regulate the differentiation of the axonal compartments. The nature and function of these proteins are yet to be identified.