Glial and neuronal isoforms of Neurofascin have distinct roles in the assembly of nodes of Ranvier in the central nervous system

Rapid nerve impulse conduction in myelinated axons requires the concentration of voltage-gated sodium channels at nodes of Ranvier. Myelin-forming oligodendrocytes in the central nervous system (CNS) induce the clustering of sodium channels into nodal complexes flanked by paranodal axoglial junctions. However, the molecular mechanisms for nodal complex assembly in the CNS are unknown. Two isoforms of Neurofascin, neuronal Nfasc186 and glial Nfasc155, are components of the nodal and paranodal complexes, respectively. Neurofascin-null mice have disrupted nodal and paranodal complexes. We show that transgenic Nfasc186 can rescue the nodal complex when expressed in Nfasc−/− mice in the absence of the Nfasc155–Caspr–Contactin adhesion complex. Reconstitution of the axoglial adhesion complex by expressing transgenic Nfasc155 in oligodendrocytes also rescues the nodal complex independently of Nfasc186. Furthermore, the Nfasc155 adhesion complex has an additional function in promoting the migration of myelinating processes along CNS axons. We propose that glial and neuronal Neurofascins have distinct functions in the assembly of the CNS node of Ranvier

Protein 4.1B Contributes to the Organization of Peripheral Myelinated Axons

Neurons are characterized by extremely long axons. This exceptional cell shape is likely to depend on multiple factors including interactions between the cytoskeleton and membrane proteins. In many cell types, members of the protein 4.1 family play an important role in tethering the cortical actin-spectrin cytoskeleton to the plasma membrane. Protein 4.1B is localized in myelinated axons, enriched in paranodal and juxtaparanodal regions, and also all along the internodes, but not at nodes of Ranvier where are localized the voltage-dependent sodium channels responsible for action potential propagation. To shed light on the role of protein 4.1B in the general organization of myelinated peripheral axons, we studied 4.1B knockout mice. These mice displayed a mildly impaired gait and motility. Whereas nodes were unaffected, the distribution of Caspr/paranodin, which anchors 4.1B to the membrane, was disorganized in paranodal regions and its levels were decreased. In juxtaparanodes, the enrichment of Caspr2, which also interacts with 4.1B, and of the associated TAG-1 and Kv1.1, was absent in mutant mice, whereas their levels were unaltered. Ultrastructural abnormalities were observed both at paranodes and juxtaparanodes. Axon calibers were slightly diminished in phrenic nerves and preterminal motor axons were dysmorphic in skeletal muscle. βII spectrin enrichment was decreased along the axolemma. Electrophysiological recordings at 3 post-natal weeks showed the occurrence of spontaneous and evoked repetitive activity indicating neuronal hyperexcitability, without change in conduction velocity. Thus, our results show that in myelinated axons 4.1B contributes to the stabilization of membrane proteins at paranodes, to the clustering of juxtaparanodal proteins, and to the regulation of the internodal axon caliber

Le rôle de phosphacan, la forme soluble de RPTP , dans le développement oligodendrocytaire

La sclérose en plaques est une maladie neurologique caractérisée par des lésions démyélinisantes affectant l intégrité de la membrane myélinique, essentielle à une conduction rapide du signal nerveux. Le processus de remyélinisation joue un rôle crucial dans cette pathologie, puisqu il permet de réparer les lésions, de protéger à nouveau les axones et de rétablir une vélocité de conduction normale de l influx nerveux.Les biopsies de cerveaux de patients atteints de sclérose en plaques ont mis en évidence que l homologue humain de l ARN messager de RPTP est exprimé de façon spécifique dans les oligodendrocytes remyélinisants, suggérant l implication de cette molécule dans la réparation des maladies démyélinisantes (Harroch et al., 2002). De plus, il a été démontré l implication du gène Ptprz1 (codant pour RPTP ) dans les processus physiologiques de formation de la myéline (Harroch et al., 2000) et le rôle de phosphacan, la forme soluble de RPTP , dans la prolifération des oligodendrocytes (Lamprianou et al., en préparation). En particulier, il a été mis en évidence que les oligodendrocytes précurseurs des souris déficientes pour Ptprz1 sont caractérisés par une prolifération accrue, qui est normalement inhibée chez les souris sauvages par la présence de phosphacan. Afin de comprendre le mécanisme d action de phosphacan au cours de l inhibition de la prolifération oligodendrocytaire, de même que les voies de signalisation impliquées dans ce processus, nous avons utilisé la protéine de fusion CFS-Fc, comme substitut de la molécule de novo. Nous avons ainsi démontré que la forme soluble de RPTP se lie spécifiquement aux membranes des oligodendrocytes au sein de cultures primaires mixtes et plus particulièrement des oligodendrocytes précurseurs. De manière intéressante, nous avons identifié contactine-1 comme étant le récepteur de phosphacan sur ce type cellulaire. De plus, en utilisant des protéines de fusion qui présentent les différents domaines de phosphacan, nous avons démontré que le domaine CAH est suffisant à l interaction de phosphacan avec contactine-1. Enfin, nous avons montré que phosphacan module l expression dans les oligodendrocytes des protéines Tnc et de Tnr, molécules impliquées dans le développement oligodendrocytaire. Ces données suggèrent un rôle crucial de ces molécules dans les voies de signalisation du complexe contactine-1/phosphacan.Ces résultats constituent le point de départ pour une analyse plus détaillée sur la fonctionnalité des protéines de fusion, qui vise à tester et valider l activité biologique in vitro et in vivo de ces molécules, afin de pouvoir envisager à long terme leur utilisation médicale dans le traitement de la sclérose en plaques.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Receptor Protein Tyrosine Phosphatase γ Is a Marker for Pyramidal Cells and Sensory Neurons in the Nervous System and Is Not Necessary for Normal Development

In order to gain insight into the biological role of receptor protein tyrosine phosphatase γ (RPTPγ), we have generated RPTPγ-null mice. RPTPγ was disrupted by insertion of the β-galactosidase gene under the control of the RPTPγ promoter. As the RPTPγ-null mice did not exhibit any obvious phenotype, we made use of these mice to study RPTPγ expression and thus shed light on potential biological functions of this phosphatase. Inspection of mouse embryos shows that RPTPγ is expressed in a variety of tissues during embryogenesis. RPTPγ is expressed in both embryonic and adult brains. Specifically, we detected RPTPγ expression in cortical layers II and V and in the stratum pyramidale of the hippocampus, indicating that RPTPγ is a marker for pyramidal neurons. Mixed primary culture of glial cells showed a lack of expression of RPTPγ in astrocytes and a low expression of RPTPγ in oligodendrocytes and in microglia. Interestingly, RPTPγ expression was detected in all sensory organs, including the ear, nose, tongue, eye, and vibrissa follicles, suggesting a potential role of RPTPγ in sensory neurons. An initial behavioral analysis showed minor changes in the RPTPγ-null mice

Structural Basis for Interactions Between Contactin Family Members and Protein-tyrosine Phosphatase Receptor Type G in Neural Tissues.

Protein-tyrosine phosphatase receptor type G (RPTPγ/PTPRG) interacts in vitro with contactin-3-6 (CNTN3-6), a group of glycophosphatidylinositol-anchored cell adhesion molecules involved in the wiring of the nervous system. In addition to PTPRG, CNTNs associate with multiple transmembrane proteins and signal inside the cell via cis-binding partners to alleviate the absence of an intracellular region. Here, we use comprehensive biochemical and structural analyses to demonstrate that PTPRG·CNTN3-6 complexes share similar binding affinities and a conserved arrangement. Furthermore, as a first step to identifying PTPRG·CNTN complexes in vivo, we found that PTPRG and CNTN3 associate in the outer segments of mouse rod photoreceptor cells. In particular, PTPRG and CNTN3 form cis-complexes at the surface of photoreceptors yet interact in trans when expressed on the surfaces of apposing cells. Further structural analyses suggest that all CNTN ectodomains adopt a bent conformation and might lie parallel to the cell surface to accommodate these cis and trans binding modes. Taken together, these studies identify a PTPRG·CNTN complex in vivo and provide novel insights into PTPRG- and CNTN-mediated signaling

Loss-of-function of PTPR γ and ζ, observed in sporadic schizophrenia, causes brain region-specific deregulation of monoamine levels and altered behavior in mice.

International audienceThe receptor protein tyrosine phosphatase PTPRG has been genetically associated with psychiatric disorders and is a ligand for members of the contactin family, which are themselves linked to autism spectrum disorders.OBJECTIVE:Based on our finding of a phosphatase-null de novo mutation in PTPRG associated with a case of sporadic schizophrenia, we used PTPRG knockout (KO) mice to model the effect of a loss-of-function mutation. We compared the results with loss-of-function in its close paralogue PTPRZ, previously associated with schizophrenia. We tested PTPRG -/- , PTPRZ -/- , and wild-type male mice for effects on social behavior, forced swim test, and anxiety, as well as on regional brain neurochemistry.RESULTS:The most notable behavioral consequences of PTPRG gene inactivation were reduced immobilization in the forced swim test, suggestive of some negative symptoms of schizophrenia. By contrast, PTPRZ -/- mice demonstrated marked social alteration with increased aggressivity, reminiscent of some positive symptoms of schizophrenia. Both knockouts showed elevated dopamine levels in prefrontal cortex, hippocampus, and most particularly amygdala, but not striatum, accompanied by reduced dopamine beta hydroxylase activity only in amygdala. In addition, PTPRG KO elicited a distinct increase in hippocampal serotonin level not observed in PTPRZ KO.CONCLUSION:PTPRG and PTPRZ gene loss therefore induces distinct patterns of behavioral change and region-specific alterations in neurotransmitters, highlighting their usefulness as models for neuropsychiatric disorder mechanisms and making these receptors attractive targets for therapy

Structural Basis for Interactions Between Contactin Family Members and Protein-tyrosine Phosphatase Receptor Type G in Neural Tissues.

Protein-tyrosine phosphatase receptor type G (RPTPγ/PTPRG) interacts in vitro with contactin-3-6 (CNTN3-6), a group of glycophosphatidylinositol-anchored cell adhesion molecules involved in the wiring of the nervous system. In addition to PTPRG, CNTNs associate with multiple transmembrane proteins and signal inside the cell via cis-binding partners to alleviate the absence of an intracellular region. Here, we use comprehensive biochemical and structural analyses to demonstrate that PTPRG·CNTN3-6 complexes share similar binding affinities and a conserved arrangement. Furthermore, as a first step to identifying PTPRG·CNTN complexes in vivo, we found that PTPRG and CNTN3 associate in the outer segments of mouse rod photoreceptor cells. In particular, PTPRG and CNTN3 form cis-complexes at the surface of photoreceptors yet interact in trans when expressed on the surfaces of apposing cells. Further structural analyses suggest that all CNTN ectodomains adopt a bent conformation and might lie parallel to the cell surface to accommodate these cis and trans binding modes. Taken together, these studies identify a PTPRG·CNTN complex in vivo and provide novel insights into PTPRG- and CNTN-mediated signaling

Hepatic protein tyrosine phosphatase receptor gamma links obesity-induced inflammation to insulin resistance

During obesity, chronic inflammation leads to insulin resistance and diabetes. Here, Brenachot et al. show that Protein Tyrosine Phosphatase Receptor Gamma is upregulated in obesity by inflammatory signals and correlates with insulin resistance in humans. Its deletion in mouse models of obesity and inflammation ameliorates insulin resistance by suppressing glucose production

Pleiotrophin Regulates the Retention and Self-Renewal of Hematopoietic Stem Cells in the Bone Marrow Vascular Niche

The mechanisms through which the bone marrow (BM) microenvironment regulates hematopoietic stem cell (HSC) fate remain incompletely understood. We examined the role of the heparin-binding growth factor, pleiotrophin (PTN), in regulating HSC function in the niche. PTN(−/−) mice displayed significantly decreased BM HSC content and impaired hematopoietic regeneration following myelosuppression. Conversely, mice lacking the protein tyrosine phosphatase receptor-zeta (PTPRZ), which is inactivated by PTN, displayed significantly increased BM HSC content. Transplant studies revealed that PTN action was not HSC-autonomous but rather was mediated by the BM microenvironment. Interestingly, PTN was differentially expressed and secreted by BM sinusoidal endothelial cells within the vascular niche. Furthermore, systemic administration of anti-PTN antibody in mice substantially impaired both the homing of hematopoietic progenitor cells to the niche and the retention of BM HSCs in the niche. PTN is a secreted component of the BM vascular niche which regulates HSC self-renewal and retention in vivo

Proliferation and tyrosine phosphorylation in OS cell lines.

<p>(A) Proliferative capacity of tumor cells derived from <i>Trp53</i>-heterozygous mice with either one <i>Ptprz1</i> allele (+/-) or with <i>Ptprz1</i>-deficiency (-/-). The growth curves (left) and the BrdU incorporation assays (right) demonstrate increased proliferation in the cases of <i>Ptprz1</i>-deficiency. Bars represent mean ± SD (n≥3). Asterisks indicate significant differences between the two genotypes (p<0.05, two-way ANOVA followed by Bonferroni’s post-test (left panel) or two-tailed Student’s <i>t</i>-test (right panel)). (B) SH2 profiling with different SH2 domains reveals differences in tyrosine phosphorylation of specific proteins (indicated by arrowheads). Re-probing of stripped membranes with anti ß-actin mAb served as control for equal loading. Analyses were performed in duplicate with cell extracts harvested at different cell densities.</p