The carbonic anhydrase domain of receptor tyrosine phosphatase beta is a functional ligand for the axonal cell recognition molecule contactin

Repulsive interactions instruct synaptic partner matching in an olfactory circuit

Neurons exhibit extraordinary precision in selecting synaptic partners. Whereas cell-surface proteins (CSPs) mediating attractive interactions between developing axons and dendrites have been shown to instruct synaptic partner matching1,2, it is less clear the degree to which repulsive interactions play a role. Here, using a genetic screen guided by single cell transcriptomes3,4, we identified three CSP pairs-Toll2-Ptp10D, Fili-Kek1, and Hbs/Sns-Kirre-in mediating repulsive interactions between non-partner olfactory receptor neuron (ORN) axons and projection neuron (PN) dendrites in the developing Drosophila olfactory circuit. Each CSP pair exhibits inverse expression patterns in the select PN-ORN partners. Loss of each CSP in ORNs led to similar synaptic partner matching deficits as the loss of its partner CSP in PNs, and mistargeting phenotypes caused by overexpressing one CSP could be suppressed by loss of its partner CSP. Each CSP pair is also differentially expressed in other brain regions. Together, our data reveal that multiple repulsive CSP pairs work together to ensure precise synaptic partner matching during development by preventing neurons from forming connections with non-cognate partners.

Novel RPTPγ and RPTPζ splice variants from mixed neuron-astrocyte hippocampal cultures as well as from the hippocampi of newborn and adult mice

Receptor protein tyrosine phosphatases γ and ζ (RPTPγ and RPTPζ) are transmembrane signaling proteins with extracellular carbonic anhydrase-like domains that play vital roles in the development and functioning of the central nervous system (CNS) and are implicated in tumor suppression, neurodegeneration, and sensing of extracellular [CO2] and [HCO3 -]. RPTPγ expresses throughout the body, whereas RPTPζ preferentially expresses in the CNS. Here, we investigate differential RPTPγ-RPTPζ expression in three sources derived from a wild-type laboratory strain of C57BL/6 mice: (a) mixed neuron-astrocyte hippocampal (HC) cultures 14 days post isolation from P0-P2 pups; (b) P0-P2 pup hippocampi; and (c) 9- to 12-week-old adult hippocampi. Regarding RPTPγ, we detect the Ptprg variant-1 (V1) transcript, representing canonical exons 1-30. Moreover, we newly validate the hypothetical assembly [XM_006517956] (propose name, Ptprg-V3), which lacks exon 14. Both transcripts are in all three HC sources. Regarding RPTPζ, we confirm the expression of Ptprz1-V1, detecting it in pups and adults but not in cultures, and Ptprz1-V3 through Ptprz1-V7 in all three preparations. We newly validate hypothetical assemblies Ptprz1-X1 (in cultures and pups), Ptprz1-X2 (in all three), and Ptprz1-X5 (in pups and adults) and propose to re-designate them as Ptprz1-V0, Ptprz1-V2, and Ptprz1-V8, respectively. The diversity of RPTPγ and RPTPζ splice variants likely corresponds to distinct signaling functions, in different cellular compartments, during development vs later life. In contrast to previous studies that report divergent RPTPγ and RPTPζ protein expressions in neurons and sometimes in the glia, we observe that RPTPγ and RPTPζ co-express in the somata and processes of almost all HC neurons but not in astrocytes, in all three HC preparations.

Antibody-directed extracellular proximity biotinylation reveals that Contactin-1 regulates axo-axonic innervation of axon initial segments

Axon initial segment (AIS) cell surface proteins mediate key biological processes in neurons including action potential initiation and axo-axonic synapse formation. However, few AIS cell surface proteins have been identified. Here, we use antibody-directed proximity biotinylation to define the cell surface proteins in close proximity to the AIS cell adhesion molecule Neurofascin. To determine the distributions of the identified proteins, we use CRISPR-mediated genome editing for insertion of epitope tags in the endogenous proteins. We identify Contactin-1 (Cntn1) as an AIS cell surface protein. Cntn1 is enriched at the AIS through interactions with Neurofascin and NrCAM. We further show that Cntn1 contributes to assembly of the AIS extracellular matrix, and regulates AIS axo-axonic innervation by inhibitory basket cells in the cerebellum and inhibitory chandelier cells in the cortex.

Protein-protein interactions between tenascin-R and RPTPζ/phosphacan are critical to maintain the architecture of perineuronal nets

Neural plasticity, the ability to alter the structure and function of neural circuits, varies throughout the age of an individual. The end of the hyperplastic period in the central nervous system coincides with the appearance of honeycomb-like structures called perineuronal nets (PNNs) that surround a subset of neurons. PNNs are a condensed form of neural extracellular matrix that include the glycosaminoglycan hyaluronan and extracellular matrix proteins such as aggrecan and tenascin-R (TNR). PNNs are key regulators of developmental neural plasticity and cognitive functions, yet our current understanding of the molecular interactions that help assemble them remains limited. Disruption of Ptprz1, the gene encoding the receptor protein tyrosine phosphatase RPTPζ, altered the appearance of nets from a reticulated structure to puncta on the surface of cortical neuron bodies in adult mice. The structural alterations mirror those found in Tnr-/- mice, and TNR is absent from the net structures that form in dissociated cultures of Ptprz1-/- cortical neurons. These findings raised the possibility that TNR and RPTPζ cooperate to promote the assembly of PNNs. Here, we show that TNR associates with the RPTPζ ectodomain and provide a structural basis for these interactions. Furthermore, we show that RPTPζ forms an identical complex with tenascin-C, a homolog of TNR that also regulates neural plasticity. Finally, we demonstrate that mutating residues at the RPTPζ-TNR interface impairs the formation of PNNs in dissociated neuronal cultures. Overall, this work sets the stage for analyzing the roles of protein-protein interactions that underpin the formation of nets.

Protein Tyrosine Phosphatase Receptor Zeta 1 as a Potential Target in Cancer Therapy and Diagnosis

Protein tyrosine phosphatase receptor zeta 1 (PTPRZ1) is a type V transmembrane tyrosine phosphatase that is highly expressed during embryonic development, while its expression during adulthood is limited. PTPRZ1 is highly detected in the central nervous system, affecting oligodendrocytes' survival and maturation. In gliomas, PTPRZ1 expression is significantly upregulated and is being studied as a potential cancer driver and as a target for therapy. PTPRZ1 expression is also increased in other cancer types, but there are no data on the potential functional significance of this finding. On the other hand, low PTPRZ1 expression seems to be related to a worse prognosis in some cancer types, suggesting that in some cases, it may act as a tumor-suppressor gene. These discrepancies may be due to our limited understanding of PTPRZ1 signaling and tumor microenvironments. In this review, we present evidence on the role of PTPRZ1 in angiogenesis and cancer and discuss the phenomenal differences among the different types of cancer, depending on the regulation of its tyrosine phosphatase activity or ligand binding. Clarifying the involved signaling pathways will lead to its efficient exploitation as a novel therapeutic target or as a biomarker, and the development of proper therapeutic approaches.

Antibody-directed extracellular proximity biotinylation reveals Contactin-1 regulates axo-axonic innervation of axon initial segments

Axon initial segment (AIS) cell surface proteins mediate key biological processes in neurons including action potential initiation and axo-axonic synapse formation. However, few AIS cell surface proteins have been identified. Here, we used antibody-directed proximity biotinylation to define the cell surface proteins in close proximity to the AIS cell adhesion molecule Neurofascin. To determine the distributions of the identified proteins, we used CRISPR-mediated genome editing for insertion of epitope tags in the endogenous proteins. We found Contactin-1 (Cntn1) among the previously unknown AIS proteins we identified. Cntn1 is enriched at the AIS through interactions with Neurofascin and NrCAM. We further show that Cntn1 contributes to assembly of the AIS-extracellular matrix, and is required for AIS axo-axonic innervation by inhibitory basket cells in the cerebellum and inhibitory chandelier cells in the cortex.

Hereditable variants of classical protein tyrosine phosphatase genes: Will they prove innocent or guilty?

Protein tyrosine phosphatases, together with protein tyrosine kinases, control many molecular signaling steps that control life at cellular and organismal levels. Impairing alterations in the genes encoding the involved proteins is expected to profoundly affect the quality of life-if compatible with life at all. Here, we review the current knowledge on the effects of germline variants that have been reported for genes encoding a subset of the protein tyrosine phosphatase superfamily; that of the thirty seven classical members. The conclusion must be that the newest genome research tools produced an avalanche of data that suggest 'guilt by association' for individual genes to specific disorders. Future research should face the challenge to investigate these accusations thoroughly and convincingly, to reach a mature genotype-phenotype map for this intriguing protein family.

CA10 is associated with HBV-related hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the main threat for the patients infected with hepatitis B virus (HBV), but the oncogenic mechanism of HBV-related HCC is still controversial. Previously, we have found that several HBV surface gene (HBS) non-sense mutations are oncogenic. Among these mutations, sW182* was found to have the most potent oncogenicity. In this study, we found that Carbonic Anhydrase X (CA10) level was specifically increased in sW182* mutant-expressing cells. CA10 overexpression was also associated with HBS nonsense mutation in HBV-related HCC tumor tissues. Transformation and tumorigenesis assays revealed that CA10 had significant oncogenic activity. In addition, CA10 overexpression resulted in dysregulation of apoptosis-related proteins, including Mcl-1, Bcl-2, Bcl-xL and Bad. While searching for the regulatory mechanism of CA10, miR-27b was found to downregulate CA10 expression by regulating its mRNA degradation and its expression was decreased in sW182* mutant cells. Moreover, CA10 overexpression was associated with down-regulation of miR-27b in human HBV-related HCC tumor tissues with sW182* mutation. Therefore, induction of the expression of CA10 through repression of miR-27b by sW182* might be one mechanism involved in HBS mutation-related hepatocarcinogenesis.

The Role of the Tumor Suppressor Gene Protein Tyrosine Phosphatase Gamma in Cancer

Members of the Protein Tyrosine Phosphatase (PTPs) family are associated with growth regulation and cancer development. Acting as natural counterpart of tyrosine kinases (TKs), mainly involved in crucial signaling pathways such as regulation of cell cycle, proliferation, invasion and angiogenesis, they represent key parts of complex physiological homeostatic mechanisms. Protein tyrosine phosphatase gamma (PTPRG) is classified as a R5 of the receptor type (RPTPs) subfamily and is broadly expressed in various isoforms in different tissues. PTPRG is considered a tumor-suppressor gene (TSG) mapped on chromosome 3p14-21, a region frequently subject to loss of heterozygosity in various tumors. However, reported mechanisms of PTPRG downregulation include missense mutations, ncRNA gene regulation and epigenetic silencing by hypermethylation of CpG sites on promoter region causing loss of function of the gene product. Inactive forms or total loss of PTPRG protein have been described in sporadic and Lynch syndrome colorectal cancer, nasopharyngeal carcinoma, ovarian, breast, and lung cancers, gastric cancer or diseases affecting the hematopoietic compartment as Lymphoma and Leukemia. Noteworthy, in Central Nervous System (CNS) PTPRZ/PTPRG appears to be crucial in maintaining glioblastoma cell-related neuronal stemness, carving out a pathological functional role also in this tissue. In this review, we will summarize the current knowledge on the role of PTPRG in various human cancers.

A Comprehensive Review of Receptor-Type Tyrosine-Protein Phosphatase Gamma (PTPRG) Role in Health and Non-Neoplastic Disease

Protein tyrosine phosphatase receptor gamma (PTPRG) is known to interact with and regulate several tyrosine kinases, exerting a tumor suppressor role in several type of cancers. Its wide expression in human tissues compared to the other component of group 5 of receptor phosphatases, PTPRZ expressed as a chondroitin sulfate proteoglycan in the central nervous system, has raised interest in its role as a possible regulatory switch of cell signaling processes. Indeed, a carbonic anhydrase-like domain (CAH) and a fibronectin type III domain are present in the N-terminal portion and were found to be associated with its role as [HCO3-] sensor in vascular and renal tissues and a possible interaction domain for cell adhesion, respectively. Studies on PTPRG ligands revealed the contactins family (CNTN) as possible interactors. Furthermore, the correlation of PTPRG phosphatase with inflammatory processes in different normal tissues, including cancer, and the increasing amount of its soluble form (sPTPRG) in plasma, suggest a possible role as inflammatory marker. PTPRG has important roles in human diseases; for example, neuropsychiatric and behavioral disorders and various types of cancer such as colon, ovary, lung, breast, central nervous system, and inflammatory disorders. In this review, we sum up our knowledge regarding the latest discoveries in order to appreciate PTPRG function in the various tissues and diseases, along with an interactome map of its relationship with a group of validated molecular interactors.

Neuronal Cell Adhesion Molecules May Mediate Neuroinflammation in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by restrictive and repetitive behaviors, alongside deficits in social interaction and communication. The etiology of ASD is largely unknown but is strongly linked to genetic variants in neuronal cell adhesion molecules (CAMs), cell-surface proteins that have important roles in neurodevelopment. A combination of environmental and genetic factors are believed to contribute to ASD pathogenesis. Inflammation in ASD has been identified as one of these factors, demonstrated through the presence of proinflammatory cytokines, maternal immune activation, and activation of glial cells in ASD brains. Glial cells are the main source of cytokines within the brain and, therefore, their activity is vital in mediating inflammation in the central nervous system. However, it is unclear whether the aforementioned neuronal CAMs are involved in modulating neuroimmune signaling or glial behavior. This review aims to address the largely unexplored role that neuronal CAMs may play in mediating inflammatory cascades that underpin neuroinflammation in ASD, primarily focusing on the Notch, nuclear factor-κB (NF-κB), and mitogen-activated protein kinase (MAPK) cascades. We will also evaluate the available evidence on how neuronal CAMs may influence glial activity associated with inflammation. This is important when considering the impact of environmental factors and inflammatory responses on ASD development. In particular, neural CAM1 (NCAM1) can regulate NF-κB transcription in neurons, directly altering proinflammatory signaling. Additionally, NCAM1 and contactin-1 appear to mediate astrocyte and oligodendrocyte precursor proliferation which can alter the neuroimmune response. Importantly, although this review highlights the limited information available, there is evidence of a neuronal CAM regulatory role in inflammatory signaling. This warrants further investigation into the role other neuronal CAM family members may have in mediating inflammatory cascades and would advance our understanding of how neuroinflammation can contribute to ASD pathology.

Contactin 1: An Important and Emerging Oncogenic Protein Promoting Cancer Progression and Metastasis

Even with recent progress, cancer remains the second leading cause of death, outlining a need to widen the current understanding on oncogenic factors. Accumulating evidence from recent years suggest Contactin 1 (CNTN1)'s possession of multiple oncogenic activities in a variety of cancer types. CNTN1 is a cell adhesion molecule that is dysregulated in many human carcinomas and plays important roles in cancer progression and metastases. Abnormalities in CNTN1 expression associate with cancer progression and poor prognosis. Mechanistically, CNTN1 functions in various signaling pathways frequently altered in cancer, such as the vascular endothelial growth factor C (VEGFC)-VEGF receptor 3 (VEFGR3)/fms-related tyrosine kinase 4 (Flt4) axis, phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT), Notch signaling pathway and epithelial-mesenchymal transition (EMT) process. These oncogenic events are resulted via interactions between tumor and stroma, which can be contributed by CNTN1, an adhesion protein. CNTN1 expression in breast cancer correlates with the expression of genes functioning in cancer-stroma interactions and skeletal system development. Evidence supports that CNTN1 promotes cancer-stromal interaction, resulting in activation of a complex network required for cancer progression and metastasis (bone metastasis for breast cancer). CNTN1 inhibitions has been proven to be effective in experimental models to reduce oncogenesis. In this paper, we will review CNTN1's alterations in cancer, its main biochemical mechanisms and interactions with its relevant cancer pathways.

Pleiotrophin: Activity and mechanism

Pleiotrophin (PTN) is a potent mitogenic cytokine with a high affinity for the polysaccharide glycosaminoglycan (GAG). Although it is most strongly associated with neural development during embryogenesis and the neonatal period, its expression has also been linked to a plethora of other physiological events including cancer metastasis, angiogenesis, bone development, and inflammation. A considerable amount of research has been carried out to understand the mechanisms by which PTN regulates these events. In particular, PTN has now been shown to bind a diverse collection of receptors including many GAG-containing proteoglycans. These interactions lead to the activation of many intracellular kinases and, ultimately, activation and transformation of cells. Structural studies of PTN in complex with both GAG and domains from its non-proteoglycan receptors reveal a binding mechanism that relies on electrostatic interactions and points to PTN-induced receptor oligomerization as one of the possible ways PTN uses to control cellular functions.

Role of a Contactin multi-molecular complex secreted by oligodendrocytes in nodal protein clustering in the CNS

The fast and reliable propagation of action potentials along myelinated fibers relies on the clustering of voltage‐gated sodium channels at nodes of Ranvier. Axo‐glial communication is required for assembly of nodal proteins in the central nervous system, yet the underlying mechanisms remain poorly understood. Oligodendrocytes are known to support node of Ranvier assembly through paranodal junction formation. In addition, the formation of early nodal protein clusters (or prenodes) along axons prior to myelination has been reported, and can be induced by oligodendrocyte conditioned medium (OCM). Our recent work on cultured hippocampal neurons showed that OCM‐induced prenodes are associated with an increased conduction velocity (Freeman et al., 2015). We here unravel the nature of the oligodendroglial secreted factors. Mass spectrometry analysis of OCM identified several candidate proteins (i.e., Contactin‐1, ChL1, NrCAM, Noelin2, RPTP/Phosphacan, and Tenascin‐R). We show that Contactin‐1 combined with RPTP/Phosphacan or Tenascin‐R induces clusters of nodal proteins along hippocampal GABAergic axons. Furthermore, Contactin‐1‐immunodepleted OCM or OCM from Cntn1‐null mice display significantly reduced clustering activity, that is restored by addition of soluble Contactin‐1. Altogether, our results identify Contactin‐1 secreted by oligodendrocytes as a novel factor that may influence early steps of nodal sodium channel cluster formation along specific axon populations.

VE-PTP inhibition stabilizes endothelial junctions by activating FGD5

Inhibition of VE-PTP, an endothelial receptor-type tyrosine phosphatase, triggers phosphorylation of the tyrosine kinase receptor Tie-2, which leads to the suppression of inflammation-induced vascular permeability. Analyzing the underlying mechanism, we show here that inhibition of VE-PTP and activation of Tie-2 induce tyrosine phosphorylation of FGD5, a GTPase exchange factor (GEF) for Cdc42, and stimulate its translocation to cell contacts. Interfering with the expression of FGD5 blocks the junction-stabilizing effect of VE-PTP inhibition in vitro and in vivo. Likewise, FGD5 is required for strengthening cortical actin bundles and inhibiting radial stress fiber formation, which are each stimulated by VE-PTP inhibition. We identify Y820 of FGD5 as the direct substrate for VE-PTP. The phosphorylation of FGD5-Y820 is required for the stabilization of endothelial junctions and for the activation of Cdc42 by VE-PTP inhibition but is dispensable for the recruitment of FGD5 to endothelial cell contacts. Thus, activation of FGD5 is a two-step process that comprises membrane recruitment and phosphorylation of Y820. These steps are necessary for the junction-stabilizing effect stimulated by VE-PTP inhibition and Tie-2 activation.

Behavioral and neurological analyses of adult mice carrying null and distinct loss-of-receptor function mutations in protein tyrosine phosphatase receptor type Z (PTPRZ)

Protein tyrosine phosphatase receptor type Z (PTPRZ) is preferentially expressed in the central nervous system as two transmembrane receptor isoforms PTPRZ-A/B and one secretory isoform PTPRZ-S. Ptprz-knockout mice lacking the expression of all three isoforms show behavioral, learning, and neurological abnormalities, including increased exploratory activities to novelty, deficits in spatial and contextual learning, and reduced responses to methamphetamine, relative to wild-type mice. To investigate whether PTPRZ isoforms play distinct physiological roles, we herein performed behavioral studies on two knock-in mouse lines: One expresses the catalytically inactive Cys-1930 to Ser (CS) mutants of PTPRZ-A/B, while the other generated in the present study expresses catalytically active mutants of PTPRZ-A/B lacking the negative regulatory PTP-D2 domain and C-terminal PDZ-binding motif (ΔD2) instead of wild-type PTPRZ-A/-B. In contrast to Ptprz-knockout mice, neither increased responses to novelty in the open field nor memory impairments in the inhibitory-avoidance task were observed in Ptprz-CS or Ptprz-ΔD2 mice. However, the effects of methamphetamine on locomotor activity were significantly weaker in Ptprz-KO mice and CS mutant mice than in wild-type mice, but were normal in ΔD2 mutant mice. Furthermore, microdialysis experiments revealed that methamphetamine-evoked dopamine release in the nucleus accumbens was reduced in Ptprz-KO mice and CS mutant mice. These results suggest that the extracellular region of PTPRZ, including the secretory isoform, is crucial for behavioral responses to novelty and the formation of aversive memories, whereas the PTPase activities of PTPRZ receptor isoforms are involved in regulating the dopaminergic system.

GlcNAc6ST3 is a keratan sulfate sulfotransferase for the protein-tyrosine phosphatase PTPRZ in the adult brain

Keratan sulfate (KS) is a carbohydrate side chain covalently attached to extracellular proteoglycans. KS is composed of disaccharide units of 6-sulfated N-acetylglucosamine (GlcNAc) and galactose. We have previously shown that GlcNAc-6-O-sulfotransferase (GlcNAc6ST) 1 encoded by Chst2 is an enzyme necessary for the synthesis of GlcNAc-6-sulfated KS chains that are required for neuronal plasticity in the visual cortex of the mouse brain during the critical period, but not in adulthood. Here, we show that GlcNAc-6-sulfated KS recognized by the R-10G anti-KS antibody, of which the minimum epitope structure is Galß1-4GlcNAc(6S)ß1-3Galß1-4GlcNAc(6S), distributes diffusely in neuropils and presents densely in close proximity to the perineuronal region of the perineuronal net (PNN)-positive neurons in the adult visual cortex. Surprisingly, GlcNAc6ST3, which was discovered as an intestinal GlcNAc6ST encoded by Chst5, is a major brain KS sulfotransferase expressed in oligodendrocytes in adulthood. Moreover, we identified an isoform of the protein-tyrosine phosphatase PTPRZ as a R-10G-reactive KS proteoglycan. These results indicate that GlcNAc6ST3 may play a role in synthesis of a component of PNN in the adult brain, and that the KS-modified isoform of PTPRZ encoded by Ptprz1 could be an extracellular molecule associated with PNNs.

IL-34-Dependent Intrarenal and Systemic Mechanisms Promote Lupus Nephritis in MRL-Faslpr Mice

BACKGROUND

In people with SLE and in the MRL-Fas^lpr lupus mouse model, macrophages and autoantibodies are central to lupus nephritis. IL-34 mediates macrophage survival and proliferation, is expressed by tubular epithelial cells (TECs), and binds to the cFMS receptor on macrophages and to a newly identified second receptor, PTPRZ.

METHODS

To investigate whether IL-34-dependent intrarenal and systemic mechanisms promote lupus nephritis, we compared lupus nephritis and systemic illness in MRL-Fas^lpr mice expressing IL-34 and IL-34 knockout (KO) MRL-Fas^lpr mice. We also assessed expression of IL-34 and the cFMS and PTPRZ receptors in patients with lupus nephritis.

RESULTS

Intrarenal IL-34 and its two receptors increase during lupus nephritis in MRL-Fas^lpr mice. In knockout mice lacking IL-34, nephritis and systemic illness are suppressed. IL-34 fosters intrarenal macrophage accumulation via monocyte proliferation in bone marrow (which increases circulating monocytes that are recruited by chemokines into the kidney) and via intrarenal macrophage proliferation. This accumulation leads to macrophage-mediated TEC apoptosis. We also found suppression of circulating autoantibodies and glomerular antibody deposits in the knockout mice. This is consistent with fewer activated and proliferating intrarenal and splenic B cells in mice lacking IL-34, and with our novel discovery that PTPRZ is expressed by macrophages, B and T cells. These findings appear translatable to human patients with lupus nephritis, whose expression of IL-34, cFMS, and PTPRZ is similar to that seen in the MRL-Fas^lpr lupus mouse model. Moreover, expression of IL-34 in TECs correlates with disease activity.

CONCLUSIONS

IL-34 is a promising novel therapeutic target for patients with lupus nephritis.

Contactin-1/F3 Regulates Neuronal Migration and Morphogenesis Through Modulating RhoA Activity

During neocortical development, newborn neurons migrate along radial fibers from the germinal ventricular zone (VZ) toward the cortical plate (CP) to populate the cerebral cortex. This radial migration requires adhesion activities between neurons and radial fibers; however, past research has identified only a limited number of adhesion molecules involved in this process. Contactin-1/F3 (Cntn1), a cell adhesion molecule expressed in the developing nervous system is essential for many key developmental events including neural cell adhesion, neurite outgrowth, axon guidance and myelination. However, the potential role of Cntn1 in neuronal migration during cortical development has not been investigated. Here we used in utero electroporation to introduce short hairpin RNA (shRNA) to knock down (KD) Cntn1 in neural stem cells in vivo. We found that Cntn1 KD led to a delay in neuronal migration. The arrested cells presented abnormal morphology in their leading process and more multipolar cells were observed in the deep layers of the brain, suggestive of dysregulation in process formation. Intriguingly, Cntn1 KD also resulted in upregulation of RhoA, a negative regulator for neuronal migration. Interference of RhoA by expression of the dominant-negative RhoA^N19 partially rescued the neuronal migration defects caused by Cntn1 KD. Our results showed that Cntn1 is a novel adhesion protein that is essential for neuronal migration and regulates process formation of newborn cortical neurons through modulating RhoA signaling pathway.

Cell adhesion and matricellular support by astrocytes of the tripartite synapse

Astrocytes contribute to the formation, function, and plasticity of synapses. Their processes enwrap the neuronal components of the tripartite synapse, and due to this close interaction they are perfectly positioned to modulate neuronal communication. The interaction between astrocytes and synapses is facilitated by cell adhesion molecules and matricellular proteins, which have been implicated in the formation and functioning of tripartite synapses. The importance of such neuron-astrocyte integration at the synapse is underscored by the emerging role of astrocyte dysfunction in synaptic pathologies such as autism and schizophrenia. Here we review astrocyte-expressed cell adhesion molecules and matricellular molecules that play a role in integration of neurons and astrocytes within the tripartite synapse.

Glycosylphosphatidylinositol-Anchored Immunoglobulin Superfamily Cell Adhesion Molecules and Their Role in Neuronal Development and Synapse Regulation

Immunoglobulin superfamily (IgSF) cell adhesion molecules (CAMs) are cell surface glycoproteins that not only mediate interactions between neurons but also between neurons and other cells in the nervous system. While typical IgSF CAMs are transmembrane molecules, this superfamily also includes CAMs, which do not possess transmembrane and intracellular domains and are instead attached to the plasma membrane via a glycosylphosphatidylinositol (GPI) anchor. In this review, we focus on the role GPI-anchored IgSF CAMs have as signal transducers and ligands in neurons, and discuss their functions in regulation of neuronal development, synapse formation, synaptic plasticity, learning, and behavior. We also review the links between GPI-anchored IgSF CAMs and brain disorders.

Stepping out of the shadows: Oncogenic and tumor-promoting protein tyrosine phosphatases

Protein tyrosine phosphorylation is critical for proper function of cells and organisms. Phosphorylation is regulated by the concerted but generically opposing activities of tyrosine kinases (PTKs) and tyrosine phosphatases (PTPs), which ensure its proper regulation, reversibility, and ability to respond to changing physiological situations. Historically, PTKs have been associated mainly with oncogenic and pro-tumorigenic activities, leading to the generalization that protein dephosphorylation is anti-oncogenic and hence that PTPs are tumor-suppressors. In many cases PTPs do suppress tumorigenesis. However, a growing body of evidence indicates that PTPs act as dominant oncogenes and drive cell transformation in a number of contexts, while in others PTPs support transformation that is driven by other oncogenes. This review summarizes the known transforming and tumor-promoting activities of the classical, tyrosine specific PTPs and highlights their potential as drug targets for cancer therapy.

Immunoregulatory properties of the cytokine IL-34

Interleukin-34 is a cytokine with only partially understood functions, described for the first time in 2008. Although IL-34 shares very little homology with CSF-1 (CSF1, M-CSF), they share a common receptor CSF-1R (CSF-1R) and IL-34 has also two distinct receptors (PTP-ζ) and CD138 (syndecan-1). To make the situation more complex, IL-34 has also been shown as pairing with CSF-1 to form a heterodimer. Until now, studies have demonstrated that this cytokine is released by some tissues that differ to those where CSF-1 is expressed and is involved in the differentiation and survival of macrophages, monocytes, and dendritic cells in response to inflammation. The involvement of IL-34 has been shown in areas as diverse as neuronal protection, autoimmune diseases, infection, cancer, and transplantation. Our recent work has demonstrated a new and possible therapeutic role for IL-34 as a Foxp3+ Treg-secreted cytokine mediator of transplant tolerance. In this review, we recapitulate most recent findings on IL-34 and its controversial effects on immune responses and address its immunoregulatory properties and the potential of targeting this cytokine in human.

Investigating the effect of different transducer stiffness values on the contactin complex detachment by steered molecular dynamics

This study investigated the adhesion behavior of Contactin4 (CNTN4), a member of Immunoglobulin Super Family (Ig-SF) of cell adhesion molecules. Contactin4 plays a crucial role in the formation, maintenance, and plasticity of neuronal networks. Contactin in its complex configuration with protein tyrosine phosphatase gamma (PTPRG) was selected for simulation. By utilizing Steered Molecular Dynamics (SMD), the uniaxial force was applied to induce unbinding of the complex, and the force-induced detachment of complex components was probed. Three sets of simulations with three values of transducer stiffness and five pulling speeds were designed. Our results showed the dependence of unbinding force on both accessible parameters of pulling speed and spring stiffness. By increasing the stiffness value and pulling speed the rupture force increased. Accordingly, the dissociation rates due to the Bell's theory based on rupture forces and loading rates were calculated.

A Glycosylphosphatidylinositol-Anchored Carbonic Anhydrase-Related Protein of Toxoplasma gondii Is Important for Rhoptry Biogenesis and Virulence

Carbonic anhydrase-related proteins (CARPs) have previously been described as catalytically inactive proteins closely related to α-carbonic anhydrases (α-CAs). These CARPs are found in animals (both vertebrates and invertebrates) and viruses as either independent proteins or domains of other proteins. We report here the identification of a new CARP (TgCA_RP) in the unicellular organism Toxoplasma gondii that is related to the recently described η-class CA found in Plasmodium falciparum. TgCA_RP is posttranslationally modified at its C terminus with a glycosylphosphatidylinositol anchor that is important for its localization in intracellular tachyzoites. The protein localizes throughout the rhoptry bulbs of mature tachyzoites and to the outer membrane of nascent rhoptries in dividing tachyzoites, as demonstrated by immunofluorescence and immunoelectron microscopy using specific antibodies. T. gondii mutant tachyzoites lacking TgCA_RP display a growth and invasion phenotype in vitro and have atypical rhoptry morphology. The mutants also exhibit reduced virulence in a mouse model. Our results show that TgCA_RP plays an important role in the biogenesis of rhoptries. IMPORTANCEToxoplasma gondii is an intracellular pathogen that infects humans and animals. The pathogenesis of T. gondii is linked to its lytic cycle, which starts when tachyzoites invade host cells and secrete proteins from specialized organelles. Once inside the host cell, the parasite creates a parasitophorous vacuole (PV) where it divides. Rhoptries are specialized secretory organelles that contain proteins, many of which are secreted during invasion. These proteins have important roles not only during the initial interaction between parasite and host but also in the formation of the PV and in the modification of the host cell. We report here the identification of a new T. gondii carbonic anhydrase-related protein (TgCA_RP), which localizes to rhoptries of mature tachyzoites. TgCA_RP is important for the morphology of rhoptries and for invasion and growth of parasites. TgCA_RP is also critical for parasite virulence. We propose that TgCA_RP plays a role in the biogenesis of rhoptries.

Carbonic anhydrase-related protein CA10 is an evolutionarily conserved pan-neurexin ligand

Establishment, specification, and validation of synaptic connections are thought to be mediated by interactions between pre- and postsynaptic cell-adhesion molecules. Arguably, the best-characterized transsynaptic interactions are formed by presynaptic neurexins, which bind to diverse postsynaptic ligands. In a proteomic screen of neurexin-1 (Nrxn1) complexes immunoisolated from mouse brain, we identified carbonic anhydrase-related proteins CA10 and CA11, two homologous, secreted glycoproteins of unknown function that are predominantly expressed in brain. We found that CA10 directly binds in a cis configuration to a conserved membrane-proximal, extracellular sequence of α- and β-neurexins. The CA10-neurexin complex is stable and stoichiometric, and results in formation of intermolecular disulfide bonds between conserved cysteine residues in neurexins and CA10. CA10 promotes surface expression of α- and β-neurexins, suggesting that CA10 may form a complex with neurexins in the secretory pathway that facilitates surface transport of neurexins. Moreover, we observed that the Nrxn1 gene expresses from an internal 3' promoter a third isoform, Nrxn1γ, that lacks all Nrxn1 extracellular domains except for the membrane-proximal sequences and that also tightly binds to CA10. Our data expand the understanding of neurexin-based transsynaptic interaction networks by providing further insight into the interactions nucleated by neurexins at the synapse.

A current view on contactin-4, -5, and -6: Implications in neurodevelopmental disorders

Contactins (Cntns) are a six-member subgroup of the immunoglobulin cell adhesion molecule superfamily (IgCAMs) with pronounced brain expression and function. Recent genetic studies of neuropsychiatric disorders have pinpointed contactin-4 (CNTN4), contactin-5 (CNTN5) and contactin-6 (CNTN6) as candidate genes in neurodevelopmental disorders, particularly in autism spectrum disorders (ASDs), but also in intellectual disability, schizophrenia (SCZ), attention-deficit hyperactivity disorder (ADHD), bipolar disorder (BD), alcohol use disorder (AUD) and anorexia nervosa (AN). This suggests that they have important functions during neurodevelopment. This suggestion is supported by data showing that neurite outgrowth, cell survival and neural circuit formation can be affected by disruption of these genes. Here, we review the current genetic data about their involvement in neuropsychiatric disorders and explore studies on how null mutations affect mouse behavior. Finally, we highlight to role of protein-protein interactions in the potential mechanism of action of Cntn4, -5 and -6 and emphasize that complexes with other membrane proteins may play a role in neuronal developmental functions.

Human odontogenic epithelial cells derived from epithelial rests of Malassez possess stem cell properties

Epithelial cell rests of Malassez (ERM) are quiescent epithelial remnants of the Hertwig's epithelial root sheath (HERS) that are involved in the formation of tooth roots. ERM cells are unique epithelial cells that remain in periodontal tissues throughout adult life. They have a functional role in the repair/regeneration of cement or enamel. Here, we isolated odontogenic epithelial cells from ERM in the periodontal ligament, and the cells were spontaneously immortalized. Immortalized odontogenic epithelial (iOdE) cells had the ability to form spheroids and expressed stem cell-related genes. Interestingly, iOdE cells underwent osteogenic differentiation, as demonstrated by the mineralization activity in vitro in mineralization-inducing media and formation of calcification foci in iOdE cells transplanted into immunocompromised mice. These findings suggest that a cell population with features similar to stem cells exists in ERM and that this cell population has a differentiation capacity for producing calcifications in a particular microenvironment. In summary, iOdE cells will provide a convenient cell source for tissue engineering and experimental models to investigate tooth growth, differentiation, and tumorigenesis.

Developmental and Regulatory Functions of Na(+) Channel Non-pore-forming β Subunits

Voltage-gated Na(+) channels (VGSCs) isolated from mammalian neurons are heterotrimeric complexes containing one pore-forming α subunit and two non-pore-forming β subunits. In excitable cells, VGSCs are responsible for the initiation of action potentials. VGSC β subunits are type I topology glycoproteins, containing an extracellular amino-terminal immunoglobulin (Ig) domain with homology to many neural cell adhesion molecules (CAMs), a single transmembrane segment, and an intracellular carboxyl-terminal domain. VGSC β subunits are encoded by a gene family that is distinct from the α subunits. While α subunits are expressed in prokaryotes, β subunit orthologs did not arise until after the emergence of vertebrates. β subunits regulate the cell surface expression, subcellular localization, and gating properties of their associated α subunits. In addition, like many other Ig-CAMs, β subunits are involved in cell migration, neurite outgrowth, and axon pathfinding and may function in these roles in the absence of associated α subunits. In sum, these multifunctional proteins are critical for both channel regulation and central nervous system development.

Auto-antibodies to contactin-associated protein 1 (Caspr) in two patients with painful inflammatory neuropathy

Auto-antibodies against the paranodal proteins neurofascin-155 and contactin-1 have recently been described in patients with chronic inflammatory demyelinating polyradiculoneuropathy and are associated with a distinct clinical phenotype and response to treatment. Contactin-associated protein 1 (Caspr, encoded by CNTNAP1) is a paranodal protein that is attached to neurofascin-155 and contactin-1 (CNTN1) but has not yet been identified as a sole antigen in patients with inflammatory neuropathies. In the present study, we screened a cohort of 35 patients with chronic inflammatory demyelinating polyradiculoneuropathy (age range 20-80, 10 female, 25 male) and 22 patients with Guillain-Barré syndrome (age range 17-86, eight female, 14 male) for autoantibodies against paranodal antigens. We identified two patients, one with chronic inflammatory demyelinating polyradiculoneuropathy and one with Guillain-Barré syndrome, with autoantibodies against Caspr by binding assays using Caspr transfected human embryonic kidney cells and murine teased fibres. IgG3 was the predominant autoantibody subclass in the patient with Guillain-Barré syndrome, IgG4 was predominant in the patient with chronic inflammatory demyelinating polyradiculoneuropathy. Accordingly, complement deposition after binding to HEK293 cells was detectable in the patient with IgG3 autoantibodies only, not in the patient with IgG4. Severe disruption of the paranodal and nodal architecture was detectable in teased fibres of the sural nerve biopsy and in dermal myelinated fibres, supporting the notion of the paranodes being the site of pathology. Deposition of IgG at the paranodes was detected in teased fibre preparations of the sural nerve, further supporting the pathogenicity of anti-Caspr autoantibodies. Pain was one of the predominant findings in both patients, possibly reflected by binding of patients' IgG to TRPV1 immunoreactive dorsal root ganglia neurons. Our results demonstrate that the paranodal protein Caspr constitutes a new antigen that leads to autoantibody generation as part of the novel entity of neuropathies associated with autoantibodies against paranodal proteins.

Regulation of GABAergic synapse development by postsynaptic membrane proteins

In the adult mammalian brain, GABAergic neurotransmission provides the majority of synaptic inhibition that balances glutamatergic excitatory drive and thereby controls neuronal output. It is generally accepted that synaptogenesis is initiated through highly specific protein-protein interactions mediated by membrane proteins expressed in developing presynaptic terminals and postsynaptic membranes. Accumulating studies have uncovered a number of membrane proteins that regulate different aspects of GABAergic synapse development. In this review, we summarize recent advances in understanding of GABAergic synapse development with a focus on postsynaptic membrane molecules, including receptors, synaptogenic cell adhesion molecules and immunoglobulin superfamily proteins.

Detection and Identification of Ligands for Mammalian RPTP Extracellular Domains

Receptor protein tyrosine phosphatases (RPTPs) form a group of over 20 enzymes in vertebrates, each with unique ectodomains subject to potential extracellular interactions with ligands. It has recently become clear that a remarkably diverse range of ligands exist, including homophilic binders, adhesion molecules, neurotrophin receptors, and proteoglycans. Individual RPTPs can bind several ligands, and vice versa, suggesting that complex cell signaling networks exist. The identification of RPTP ligands and where they are located in tissues remains a challenge for a large number of these enzymes. Here we describe some powerful methods that have proved successful for several research groups, leading to our improved understanding of RPTP-ligand interactions and functional regulation.

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.

IL-34 mediates acute kidney injury and worsens subsequent chronic kidney disease

Macrophages (Mø) are integral in ischemia/reperfusion injury-incited (I/R-incited) acute kidney injury (AKI) that leads to fibrosis and chronic kidney disease (CKD). IL-34 and CSF-1 share a receptor (c-FMS), and both cytokines mediate Mø survival and proliferation but also have distinct features. CSF-1 is central to kidney repair and destruction. We tested the hypothesis that IL-34-dependent, Mø-mediated mechanisms promote persistent ischemia-incited AKI that worsens subsequent CKD. In renal I/R, the time-related magnitude of Mø-mediated AKI and subsequent CKD were markedly reduced in IL-34-deficient mice compared with controls. IL-34, c-FMS, and a second IL-34 receptor, protein-tyrosine phosphatase ζ (PTP-ζ) were upregulated in the kidney after I/R. IL-34 was generated by tubular epithelial cells (TECs) and promoted Mø-mediated TEC destruction during AKI that worsened subsequent CKD via 2 distinct mechanisms: enhanced intrarenal Mø proliferation and elevated BM myeloid cell proliferation, which increases circulating monocytes that are drawn into the kidney by chemokines. CSF-1 expression in TECs did not compensate for IL-34 deficiency. In patients, kidney transplants subject to I/R expressed IL-34, c-FMS, and PTP-ζ in TECs during AKI that increased with advancing injury. Moreover, IL-34 expression increased, along with more enduring ischemia in donor kidneys. In conclusion, IL-34-dependent, Mø-mediated, CSF-1 nonredundant mechanisms promote persistent ischemia-incited AKI that worsens subsequent CKD.

Intracellular and extracellular domains of protein tyrosine phosphatase PTPRZ-B differentially regulate glioma cell growth and motility

Gliomas are primary brain tumors for which surgical resection and radiotherapy is difficult because of the diffuse infiltrative growth of the tumor into the brain parenchyma. For development of alternative, drug-based, therapies more insight in the molecular processes that steer this typical growth and morphodynamic behavior of glioma cells is needed. Protein tyrosine phosphatase PTPRZ-B is a transmembrane signaling molecule that is found to be strongly up-regulated in glioma specimens. We assessed the contribution of PTPRZ-B protein domains to tumor cell growth and migration, via lentiviral knock-down and over-expression using clinically relevant glioma xenografts and their derived cell models. PTPRZ-B knock-down resulted in reduced migration and proliferation of glioma cells in vitro and also inhibited tumor growth in vivo. Interestingly, expression of only the PTPRZ-B extracellular segment was sufficient to rescue the in vitro migratory phenotype that resulted from PTPRZ-B knock-down. In contrast, PTPRZ-B knock-down effects on proliferation could be reverted only after re-expression of PTPRZ-B variants that contained its C-terminal PDZ binding domain. Thus, distinct domains of PTPRZ-B are differentially required for migration and proliferation of glioma cells, respectively. PTPRZ-B signaling pathways therefore represent attractive therapeutic entry points to combat these tumors.

Extracellular regulation of type IIa receptor protein tyrosine phosphatases: mechanistic insights from structural analyses

The receptor protein tyrosine phosphatases (RPTPs) exhibit a wide repertoire of cellular signalling functions. In particular, type IIa RPTP family members have recently been highlighted as hubs for extracellular interactions in neurons, regulating neuronal extension and guidance, as well as synaptic organisation. In this review, we will discuss the recent progress of structural biology investigations into the architecture of type IIa RPTP ectodomains and their interactions with extracellular ligands. Structural insights, in combination with biophysical and cellular studies, allow us to begin to piece together molecular mechanisms for the transduction and integration of type IIa RPTP signals and to propose hypotheses for future experimental validation.

RPTPs in axons, synapses and neurology

Receptor-like protein tyrosine phosphatases represent a large protein family related to cell adhesion molecules, with diverse roles throughout neural development in vertebrates and invertebrates. This review focuses on their roles in axon growth, guidance and repair, as well as more recent findings demonstrating their key roles in pre-synaptic and post-synaptic maturation and function. These enzymes have been linked to memory and neuropsychiatric defects in loss-of-function rodent models, highlighting their potential as future drug targets.

The node of Ranvier in CNS pathology

Healthy nodes of Ranvier are crucial for action potential propagation along myelinated axons, both in the central and in the peripheral nervous system. Surprisingly, the node of Ranvier has often been neglected when describing CNS disorders, with most pathologies classified simply as being due to neuronal defects in the grey matter or due to oligodendrocyte damage in the white matter. However, recent studies have highlighted changes that occur in pathological conditions at the node of Ranvier, and at the associated paranodal and juxtaparanodal regions where neurons and myelinating glial cells interact. Lengthening of the node of Ranvier, failure of the electrically resistive seal between the myelin and the axon at the paranode, and retraction of myelin to expose voltage-gated K⁺ channels in the juxtaparanode, may contribute to altering the function of myelinated axons in a wide range of diseases, including stroke, spinal cord injury and multiple sclerosis. Here, we review the principles by which the node of Ranvier operates and its molecular structure, and thus explain how defects at the node and paranode contribute to neurological disorders.

Actions and interactions of alcohol and transforming growth factor β1 on prepubertal hypothalamic gonadotropin-releasing hormone

BACKGROUND

Alcohol (ALC) diminishes gonadotropin-releasing hormone (GnRH) secretion and delays puberty. Glial transforming growth factor β1 (TGFβ1) plays a role in glial-neuronal communications facilitating prepubertal GnRH secretion. We assessed the effects of acute ALC administration on TGFβ1-induced GnRH gene expression in the brain preoptic area (POA) and release of the peptide from the medial basal hypothalamus (MBH). Furthermore, we assessed actions and interactions of TGFβ1 and ALC on an adhesion/signaling gene family involved in glial-neuronal communications.

METHODS

Prepubertal female rats were administered ALC or water via gastric gavage at 7:30 am. At 9:00 am, saline or TGFβ1 (100 ng/3 μl) was administered into the third ventricle. At 3:00 pm, the POA was removed and frozen for gene expression analysis and repeated for protein assessments. In another experiment, the MBH was removed from ALC-free rats. After equilibration, tissues were incubated in Locke's medium only or medium containing TGFβ1 with or without 50 mM ALC for measurement of GnRH peptide released in vitro.

RESULTS

TGFβ1 induced GnRH gene expression in the POA, and this effect was blocked by ALC. We also described the presence and responsiveness of the TGFβ1 receptor in the POA and showed that acute ALC exposure not only altered the TGFβ1-induced increase in TGFβ-R1 protein expression but also the activation of receptor-associated proteins, Smad2 and Smad3, key downstream components of the TGFβ1 signaling pathway. Assessment of an adhesion/signaling family consisting of glial receptor protein tyrosine phosphatase beta and neuronal contactin-associated protein-1 (Caspr1) and contactin showed that the neuronal components were induced by TGFβ1 and that ALC blocked these effects. Finally, TGFβ1 was shown to induce release of the GnRH peptide in vitro, an action that was blocked by ALC.

CONCLUSIONS

We have demonstrated glial-derived TGFβ1 induces GnRH gene expression in the POA and stimulates release of the peptide from the MBH, actions necessary for driving the pubertal process. Importantly, ALC acted at both brain regions to block stimulatory effects of TGFβ1. Furthermore, ALC altered neuronal components of an adhesion/signaling family previously shown to be expressed on GnRH neurons and implicated in glial-GnRH neuronal communications. These results further demonstrate detrimental effects of ALC at puberty.

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

Myelin, a multilayered membrane sheath formed by oligodendrocytes around axons in the CNS, enables rapid nerve impulse conduction and sustains neuronal health. The signals exchanged between axons and oligodendrocytes in myelin remain to be fully elucidated. Here we provide genetic evidence for multiple and critical functions of Contactin-1 in central myelin. We document dynamic Contactin-1 expression on oligodendrocytes in vivo, and progressive accumulation at nodes of Ranvier and paranodes during postnatal mouse development. Nodal and paranodal expression stabilized in mature myelin, but overall membranous expression diminished. Contactin-1-deficiency disrupted paranodal junction formation as evidenced by loss of Caspr, mislocalized potassium Kv1.2 channels, and abnormal myelin terminal loops. Reduced numbers and impaired maturation of sodium channel clusters accompanied this phenotype. Histological, electron microscopic, and biochemical analyses uncovered significant hypomyelination in Contactin-1-deficient central nerves, with up to 60% myelin loss. Oligodendrocytes were present in normal numbers, albeit a minor population of neuronal/glial antigen 2-positive (NG2(+)) progenitors lagged in maturation by postnatal day 18, when the mouse null mutation was lethal. Major contributing factors to hypomyelination were defects in the generation and organization of myelin membranes, as judged by electron microscopy and quantitative analysis of oligodendrocyte processes labeled by GFP transgenically expressed from the proteolipid protein promoter. These data reveal that Contactin-1 regulates both myelin formation and organization of nodal and paranodal domains in the CNS. These multiple roles distinguish central Contactin-1 functions from its specific role at paranodes in the periphery, and emphasize mechanistic differences in central and peripheral myelination.

Carbonic anhydrase related proteins: molecular biology and evolution

The catalytically inactive isoforms of α-carbonic anhydrases are known as carbonic anhydrase related proteins (CARPs). The CARPs occur independently or as domains of other proteins in animals (both vertebrates and invertebrates) and viruses. The catalytic inactivity of CARPs is due to the lack of histidine residues required for the coordination of the zinc atom. The phylogenetic analysis shows that these proteins are highly conserved across the species. The three CARPs in vertebrates are known as CARP VIII, X and XI. CARPs orthologous to CARP VIII are found in deuterostome invertebrates, whereas protostomes only possess orthologs of CARP X. The CA-like domains of receptor-type protein tyrosine phosphatases (PTPR) are found only in PTPRG and PTPRZ. Most of these CARPs are predominantly expressed in central nervous system. Among the three vertebrate CA isoforms, CARP VIII is functionally associated with motor coordination in human, mouse and zebrafish and certain types of cancers in humans. Vertebrate expression studies show that CARP X is exclusively expressed in the brain. CARP XI is only found in tetrapods and is highly expressed in the central nervous system (CNS) of humans and mice and is also associated with several cancers. CARP VIII, PTPRZ and PTPRG have been shown to coordinate the function of other proteins by protein-protein interaction, and viral CARPs participate in attachment to host cells, but the precise biological function of CARPs X and XI is still unknown. The findings so far suggest many novel functions for the CARP subfamily, most likely related to binding to other proteins.

New insights into the roles of the contactin cell adhesion molecules in neural development

In vertebrates, the contactin (CNTN) family of neural cell recognition molecules includes six related cell adhesion molecules that play non-overlapping roles in the formation and maintenance of the nervous system. CNTN1 and CNTN2 are the prototypical members of the family and have been involved, through cis- and trans-interactions with distinct cell adhesion molecules, in neural cell migration, axon guidance, and the organization of myelin subdomains. In contrast, the roles of CNTN3-6 are less well characterized although the generation of null mice and the recent identification of a common extracellular binding partner have considerably advanced our grasp of their physiological roles in particular as they relate to the wiring of sensory tissues. In this review, we aim to present a summary of our current understanding of CNTN functions and give an overview of the challenges that lie ahead in understanding the roles these proteins play in nervous system development and maintenance.

Neuro-glial interactions at the nodes of Ranvier: implication in health and diseases

Specific cell adhesion molecules (CAMs) are dedicated to the formation of axo-glial contacts at the nodes of Ranvier of myelinated axons. They play a central role in the organization and maintenance of the axonal domains: the node, paranode, and juxtaparanode. In particular, CAMs are essential for the accumulation of voltage-gated sodium channels at the nodal gap that ensures the rapid and saltatory propagation of the action potentials (APs). The mechanisms regulating node formation are distinct in the central and peripheral nervous systems, and recent studies have highlighted the relative contribution of paranodal junctions and nodal extracellular matrix. In addition, CAMs at the juxtaparanodal domains mediate the clustering of voltage-gated potassium channels which regulate the axonal excitability. In several human pathologies, the axo-glial contacts are altered leading to disruption of the nodes of Ranvier or mis-localization of the ion channels along the axons. Node alterations and the failure of APs to propagate correctly from nodes to nodes along the axons both contribute to the disabilities in demyelinating diseases. This article reviews the mechanisms regulating the association of the axo-glial complexes and the role of CAMs in inherited and acquired neurological diseases.

Contactins in the neurobiology of autism

Autism is a disease of brain plasticity. Inspiring work of Willem Hendrik Gispen on neuronal plasticity has stimulated us to investigate gene defects in autism and the consequences for brain development. The central process in the pathogenesis of autism is local dendritic mRNA translation which is dependent on axodendritic communication. Hence, most autism-related gene products (i) are part of the protein synthesis machinery itself, (ii) are components of the mTOR signal transduction pathway, or (iii) shape synaptic activity and plasticity. Accordingly, prototype drugs have been recognized that interfere with these pathways. The contactin (CNTN) family of Ig cell adhesion molecules (IgCAMs) harbours at least three members that have genetically been implicated in autism: CNTN4, CNTN5, and CNTN6. In this chapter we review the genetic and neurobiological data underpinning their role in normal and abnormal development of brain systems, and the consequences for behavior. Although data on each of these CNTNs are far from complete, we tentatively conclude that these three contactins play roles in brain development in a critical phase of establishing brain systems and their plasticity. They modulate neuronal activities, such as neurite outgrowth, synaptogenesis, survival, guidance of projections and terminal branching of axons in forming neural circuits. Current research on these CNTNs concentrate on the neurobiological mechanism of their developmental functions. A future task will be to establish if proposed pharmacological strategies to counteract ASD-related symptomes can also be applied to reversal of phenotypes caused by genetic defects in these CNTN genes.

Receptor-type protein-tyrosine phosphatase ζ is a functional receptor for interleukin-34

Interleukin-34 (IL-34) is highly expressed in brain. IL-34 signaling via its cognate receptor, colony-stimulating factor-1 receptor (CSF-1R), is required for the development of microglia. However, the differential expression of IL-34 and the CSF-1R in brain suggests that IL-34 may signal via an alternate receptor. By IL-34 affinity chromatography of solubilized mouse brain membrane followed by mass spectrometric analysis, we identified receptor-type protein-tyrosine phosphatase ζ (PTP-ζ), a cell surface chondroitin sulfate (CS) proteoglycan, as a novel IL-34 receptor. PTP-ζ is primarily expressed on neural progenitors and glial cells and is highly expressed in human glioblastomas. IL-34 selectively bound PTP-ζ in CSF-1R-deficient U251 human glioblastoma cell lysates and inhibited the proliferation, clonogenicity, and motility of U251 cells in a PTP-ζ-dependent manner. These effects were correlated with an increase in tyrosine phosphorylation of the previously identified PTP-ζ downstream effectors focal adhesion kinase and paxillin. IL-34 binding to U251 cells was abrogated by chondroitinase ABC treatment, and CS competed with IL-34 for binding to the extracellular domain of PTP-ζ and to the cells, indicating a dependence of binding on PTP-ζ CS moieties. This study identifies an alternate receptor for IL-34 that may mediate its action on novel cellular targets.