RESUMEN
Genome-wide association studies and copy number variation analyses have linked contactin associated protein 2 (Caspr2, gene name Cntnap2) with autism spectrum disorder (ASD). In line with these findings, mice lacking Caspr2 (Cntnap2(-/-)) were shown to have core autism-like deficits including abnormal social behavior and communication, and behavior inflexibility. However the role of Caspr2 in ASD pathogenicity remains unclear. Here we have generated a new Caspr2:tau-LacZ knock-in reporter line (Cntnap2(tlacz/tlacz)), which enabled us to monitor the neuronal circuits in the brain expressing Caspr2. We show that Caspr2 is expressed in many brain regions and produced a comprehensive report of Caspr2 expression. Moreover, we found that Caspr2 marks all sensory modalities: it is expressed in distinct brain regions involved in different sensory processings and is present in all primary sensory organs. Olfaction-based behavioral tests revealed that mice lacking Caspr2 exhibit abnormal response to sensory stimuli and lack preference for novel odors. These results suggest that loss of Caspr2 throughout the sensory system may contribute to the sensory manifestations frequently observed in ASD.
Asunto(s)
Encéfalo/metabolismo , Proteínas de la Membrana/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Neuronas/metabolismo , Percepción Olfatoria/fisiología , Animales , Trastorno del Espectro Autista/genética , Trastorno del Espectro Autista/metabolismo , Proteínas de la Membrana/genética , Ratones , Ratones Transgénicos , Proteínas del Tejido Nervioso/genética , OdorantesRESUMEN
The Kv7 (KCNQ) family of voltage-gated K(+) channels regulates cellular excitability. The functional role of Kv7.2 has been hampered by the lack of a viable Kcnq2-null animal model. In this study, we generated homozygous Kcnq2-null sensory neurons using the Cre-Lox system; in these mice, Kv7.2 expression is absent in the peripheral sensory neurons, whereas the expression of other molecular components of nodes (including Kv7.3), paranodes, and juxtaparanodes is not altered. The conditional Kcnq2-null animals exhibit normal motor performance but have increased thermal hyperalgesia and mechanical allodynia. Whole-cell patch recording technique demonstrates that Kcnq2-null sensory neurons have increased excitability and reduced spike frequency adaptation. Taken together, our results suggest that the loss of Kv7.2 activity increases the excitability of primary sensory neurons.
Asunto(s)
Ganglios Espinales/citología , Regulación de la Expresión Génica/genética , Canal de Potasio KCNQ2/metabolismo , Potenciales de la Membrana/genética , Proteínas del Tejido Nervioso/metabolismo , Células Receptoras Sensoriales/fisiología , Animales , Moléculas de Adhesión Celular Neuronal/metabolismo , Femenino , Hiperalgesia/genética , Canal de Potasio KCNQ2/genética , Canal de Potasio KCNQ3/metabolismo , Masculino , Potenciales de la Membrana/efectos de los fármacos , Ratones , Ratones Noqueados , Actividad Motora/genética , Mutación/genética , Proteínas del Tejido Nervioso/genética , Factor de Transcripción PAX3 , Umbral del Dolor/fisiología , Factores de Transcripción Paired Box/genética , Factores de Transcripción Paired Box/metabolismo , Bloqueadores de los Canales de Potasio/farmacología , Células Receptoras Sensoriales/efectos de los fármacos , Tetraetilamonio/farmacología , Canales de Sodio Activados por Voltaje/metabolismoRESUMEN
The interaction between myelinating Schwann cells and the axons they ensheath is mediated by cell adhesion molecules of the Cadm/Necl/SynCAM family. This family consists of four members: Cadm4/Necl4 and Cadm1/Necl2 are found in both glia and axons, whereas Cadm2/Necl3 and Cadm3/Necl1 are expressed by sensory and motor neurons. By generating mice lacking each of the Cadm genes, we now demonstrate that Cadm4 plays a role in the establishment of the myelin unit in the peripheral nervous system. Mice lacking Cadm4 (PGK-Cre/Cadm4(fl/fl)), but not Cadm1, Cadm2, or Cadm3, develop focal hypermyelination characterized by tomacula and myelin outfoldings, which are the hallmark of several Charcot-Marie-Tooth neuropathies. The absence of Cadm4 also resulted in abnormal axon-glial contact and redistribution of ion channels along the axon. These neuropathological features were also found in transgenic mice expressing a dominant-negative mutant of Cadm4 lacking its cytoplasmic domain in myelinating glia Tg(mbp-Cadm4dCT), as well as in mice lacking Cadm4 specifically in Schwann cells (DHH-Cre/Cadm4(fl/fl)). Consistent with these abnormalities, both PGK-Cre/Cadm4(fl/fl) and Tg(mbp-Cadm4dCT) mice exhibit impaired motor function and slower nerve conduction velocity. These findings indicate that Cadm4 regulates the growth of the myelin unit and the organization of the underlying axonal membrane.
Asunto(s)
Moléculas de Adhesión Celular/deficiencia , Moléculas de Adhesión Celular/genética , Enfermedad de Charcot-Marie-Tooth/genética , Enfermedad de Charcot-Marie-Tooth/metabolismo , Eliminación de Gen , Inmunoglobulinas/deficiencia , Inmunoglobulinas/genética , Fibras Nerviosas Mielínicas/metabolismo , Animales , Enfermedad de Charcot-Marie-Tooth/patología , Ratones , Ratones de la Cepa 129 , Ratones Noqueados , Ratones Transgénicos , Vaina de Mielina/genética , Vaina de Mielina/metabolismo , Fibras Nerviosas Mielínicas/patologíaRESUMEN
Saltatory conduction requires high-density accumulation of Na(+) channels at the nodes of Ranvier. Nodal Na(+) channel clustering in the peripheral nervous system is regulated by myelinating Schwann cells through unknown mechanisms. During development, Na(+) channels are first clustered at heminodes that border each myelin segment, and later in the mature nodes that are formed by the fusion of two heminodes. Here, we show that initial clustering of Na(+) channels at heminodes requires glial NrCAM and gliomedin, as well as their axonal receptor neurofascin 186 (NF186). We further demonstrate that heminodal clustering coincides with a second, paranodal junction (PNJ)-dependent mechanism that allows Na(+) channels to accumulate at mature nodes by restricting their distribution between two growing myelin internodes. We propose that Schwann cells assemble the nodes of Ranvier by capturing Na(+) channels at heminodes and by constraining their distribution to the nodal gap. Together, these two cooperating mechanisms ensure fast and efficient conduction in myelinated nerves.
Asunto(s)
Axones/metabolismo , Moléculas de Adhesión Celular Neuronal/metabolismo , Moléculas de Adhesión Celular/metabolismo , Nódulos de Ranvier/metabolismo , Células de Schwann/metabolismo , Canales de Sodio/metabolismo , Potenciales de Acción/fisiología , Análisis de Varianza , Animales , Western Blotting , Moléculas de Adhesión Celular Neuronal/genética , Células Cultivadas , Electrofisiología , Técnica del Anticuerpo Fluorescente , Ratones , Ratones Noqueados , Microscopía Electrónica , Vaina de Mielina/metabolismo , Fibras Nerviosas Mielínicas/metabolismo , Factores de Crecimiento Nervioso/metabolismo , Conducción Nerviosa , ARN Mensajero/genética , ARN Mensajero/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
Three cell adhesion molecules are present at the axoglial junctions that form between the axon and myelinating glia on either side of nodes of Ranvier. These include an axonal complex of contacin-associated protein (Caspr) and contactin, which was proposed to bind NF155, an isoform of neurofascin located on the glial paranodal loops. Here, we show that NF155 binds directly to contactin and that surprisingly, coexpression of Caspr inhibits this interaction. This inhibition reflects the association of Caspr with contactin during biosynthesis and the resulting expression of a low molecular weight (LMw), endoglycosidase H-sensitive isoform of contactin at the cell membrane, which remains associated with Caspr but is unable to bind NF155. Accordingly, deletion of Caspr in mice by gene targeting results in a shift from the LMw- to a HMw-contactin glycoform. These results demonstrate that Caspr regulates the intracellular processing and transport of contactin to the cell surface, thereby affecting its ability to interact with other cell adhesion molecules.
Asunto(s)
Moléculas de Adhesión Celular Neuronal/deficiencia , Moléculas de Adhesión Celular Neuronal/metabolismo , Moléculas de Adhesión Celular/metabolismo , Adhesión Celular/genética , Vaina de Mielina/metabolismo , Factores de Crecimiento Nervioso/metabolismo , Animales , Moléculas de Adhesión Celular Neuronal/genética , Comunicación Celular/fisiología , Membrana Celular/metabolismo , Contactinas , Marcación de Gen , Glicosilación , Ratones , Ratones Noqueados , Modelos Biológicos , Peso Molecular , Vaina de Mielina/ultraestructura , Fibras Nerviosas Mielínicas/metabolismo , Fibras Nerviosas Mielínicas/ultraestructura , Neuroglía/metabolismo , Neuroglía/ultraestructura , Unión Proteica/fisiología , Isoformas de Proteínas/metabolismo , Transporte de Proteínas/fisiologíaRESUMEN
In myelinated axons, K+ channels are concealed under the myelin sheath in the juxtaparanodal region, where they are associated with Caspr2, a member of the neurexin superfamily. Deletion of Caspr2 in mice by gene targeting revealed that it is required to maintain K+ channels at this location. Furthermore, we show that the localization of Caspr2 and clustering of K+ channels at the juxtaparanodal region depends on the presence of TAG-1, an immunoglobulin-like cell adhesion molecule that binds Caspr2. These results demonstrate that Caspr2 and TAG-1 form a scaffold that is necessary to maintain K+ channels at the juxtaparanodal region, suggesting that axon-glia interactions mediated by these proteins allow myelinating glial cells to organize ion channels in the underlying axonal membrane.
Asunto(s)
Axones/metabolismo , Moléculas de Adhesión Celular Neuronal/metabolismo , Proteínas de la Membrana , Fibras Nerviosas Mielínicas/metabolismo , Proteínas del Tejido Nervioso/deficiencia , Canales de Potasio/metabolismo , Nódulos de Ranvier/metabolismo , Animales , Axones/ultraestructura , Comunicación Celular/genética , Contactina 2 , Marcación de Gen , Ratones , Ratones Noqueados , Microscopía Electrónica , Mutación/genética , Fibras Nerviosas Mielínicas/ultraestructura , Proteínas del Tejido Nervioso/genética , Conducción Nerviosa/genética , Neuroglía/metabolismo , Neuroglía/ultraestructura , Canales de Potasio/genética , Nódulos de Ranvier/ultraestructura , Canales de Potasio de la Superfamilia ShakerRESUMEN
The NCP family of cell-recognition molecules represents a distinct subgroup of the neurexins that includes Caspr and Caspr2, as well as Drosophila Neurexin-IV and axotactin. Here, we report the identification of Caspr3 and Caspr4, two new NCPs expressed in nervous system. Caspr3 was detected along axons in the corpus callosum, spinal cord, basket cells in the cerebellum and in peripheral nerves, as well as in oligodendrocytes. In contrast, expression of Caspr4 was more restricted to specific neuronal subpopulations in the olfactory bulb, hippocampus, deep cerebellar nuclei, and the substantia nigra. Similar to the neurexins, the cytoplasmic tails of Caspr3 and Caspr4 interacted differentially with PDZ domain-containing proteins of the CASK/Lin2-Veli/Lin7-Mint1/Lin10 complex. The structural organization and distinct cellular distribution of Caspr3 and Caspr4 suggest a potential role of these proteins in cell recognition within the nervous system.