Localization of a collagenous protein in the organic matrix of spicules from the octocoral Leptogorgia virgulata (Cnidaria: Gorgonacea)

Calcareous body inclusions are commonly found throughout the invertebrate taxa. Elaborately structured calcium carbonate spicules are the major mineralized body inclusions of the gorgonian, Leptogorgia virgulata. Spicule formation in this octocoral, as well as other calcium carbonate invertebrate structures, is apparently regulated by the intra-spicule organic matrix. Recent findings show that the insoluble fraction of the spicule organic matrix is collagenous. Collagen, although integral to calcium phosphate structures found in vertebrates is not usually associated with the formation of invertebrate calcium carbonate structures. Interestingly, collagen is present in the organic matrix during the summer but absent in winter. This suggests that there is a seasonal turnover of collagen. Antibodies (supplied by Dr. N. Watabe, University of South Carolina) were directed against the purified collagenous fractions from summer samples. Immunocytochemical techniques were subsequently employed at the electron microscope level and localization of this collagen fraction was determined in animals collected throughout the year. The location of the collagenous fraction of the organic matrix was determined from the time of the initial disappearance from spicules in winter to its reappearance during the following spring and summer. Several mechanisms addressing the fate of the collagen during the winter months are discussed. In addition this study also produced the first evidence for extracellular spicule growth in L. virgulata

A Tale of Two Systems: Principals’ Concerns with NCLB Testing and School Resource Availability

This study examined the patterns, and discrepancies regarding concerns of principals with NCLB annual testing and school resource availability. An ethnographic approach was used to determine the attitudes of eight middle school principals from high resource availability, average resource availability, and low resource availability. From the responses of the participants, one of the themes that emerged was concerns with NCLB testing. The patterns which emerged for concerns with NCLB testing were: stress, finances, and content. Principals from all resource groups other than high resources spoke in detail about the stress that they felt NCLB testing was creating within their schools. Principals from high resource schools spoke about the financial impact that NCLB testing brought upon their budgets. Principals from high and low resource schools spoke from different perspectives about their concerns with the content of annual state tests

Myelin-associated glycoprotein and myelin galactolipids stabilize developing axo-glial interactions

We have analyzed mice that lack both the myelin-associated glycoprotein (MAG) and the myelin galactolipids, two glial components implicated in mediating axo-glial interactions during the myelination process. The single-mutant mice produce abnormal myelin containing similar ultrastructural abnormalities, suggesting that these molecules may play an overlapping role in myelin formation. Furthermore, the absence of the galactolipids results in a disruption in paranodal axo-glial interactions, and we show here that similar, albeit less severe, abnormalities exist in the developing MAG mutant. In the double-mutant mice, maintenance of axo-glial adhesion is significantly more affected than in the single mutants, supporting the overlapping function hypothesis. We also show that independently of MAG, galactolipids, and paranodal junctional components, immature nodes of Ranvier form normally, but rapidly destabilize in their absence. These data indicate that distinct molecular mechanisms are responsible for the formation and maintenance of axo-glial interactions

Axo-Glial Interactions Regulate the Localization of Axonal Paranodal Proteins

Mice incapable of synthesizing the abundant galactolipids of myelin exhibit disrupted paranodal axo-glial interactions in the central and peripheral nervous systems. Using these mutants, we have analyzed the role that axo-glial interactions play in the establishment of axonal protein distribution in the region of the node of Ranvier. Whereas the clustering of the nodal proteins, sodium channels, ankyrinG, and neurofascin was only slightly affected, the distribution of potassium channels and paranodin, proteins that are normally concentrated in the regions juxtaposed to the node, was dramatically altered. The potassium channels, which are normally concentrated in the paranode/juxtaparanode, were not restricted to this region but were detected throughout the internode in the galactolipid-defi- cient mice. Paranodin/contactin-associated protein (Caspr), a paranodal protein that is a potential neuronal mediator of axon-myelin binding, was not concentrated in the paranodal regions but was diffusely distributed along the internodal regions. Collectively, these findings suggest that the myelin galactolipids are essential for the proper formation of axo-glial interactions and demonstrate that a disruption in these interactions results in profound abnormalities in the molecular organization of the paranodal axolemma

Glial βii spectrin contributes to paranode formation and maintenance

Action potential conduction along myelinated axons depends on high densities of voltage-gated Na channels at the nodes of Ranvier. Flanking each node, paranodal junctions (paranodes) are formed between axons and Schwann cells in the peripheral nervous system (PNS) or oligodendrocytes intheCNS. Paranodal junctions contribute to both no deassembly and maintenance. Despitetheir importance, the molecular mechanisms responsible for paranode assembly and maintenance remain poorly understood. βII spectrin is expressed in diverse cells and is an essential part of the submembranous cytoskeleton. Here, we show that Schwann cell βII spectrin is highly enriched at paranodes. To elucidate the roles of glial βII spectrin, we generated mutant mice lacking βII spectrin in myelinating glial cells by crossing mice with a floxed allele of Sptbn1 with Cnp-Cre mice, and analyzed both male and female mice. Juvenile (4 weeks) and middle-aged (60 weeks) mutant mice showed reduced grip strength and sciatic nerve conduction slowing, whereas no phenotype was observed between 8 and 24 weeks of age. Consistent with these findings, immunofluorescence microscopy revealed disorganized paranodes in the PNS and CNS of both postnatal day 13 and middle-aged mutant mice, but not in young adult mutant mice. Electron microscopy confirmed partial loss of transverse bands at the paranodal axoglial junction in the middle-aged mutant mice in both the PNS and CNS. These findings demonstrate that a spectrin-based cytoskeleton in myelinating glia contributes to formation and maintenance of paranodal junctions.Fil: Susuki, Keiichiro. Baylor College of Medicine; Estados UnidosFil: Zollinger, Daniel R.. Baylor College of Medicine; Estados UnidosFil: Chang, Kae Jiun. Baylor College of Medicine; Estados UnidosFil: Zhang, Chuansheng. Baylor College of Medicine; Estados UnidosFil: Huang, Claire Yu Mei. Baylor College of Medicine; Estados UnidosFil: Tsai, Chang Ru. Baylor College of Medicine; Estados UnidosFil: Galiano, Mauricio Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; Argentina. Baylor College of Medicine; Estados UnidosFil: Liu, Yanhong. Baylor College of Medicine; Estados UnidosFil: Benusa, Savannah D.. Virginia Commonwealth University; Estados UnidosFil: Yermakov, Leonid M.. Wright State University; Estados UnidosFil: Griggs, Ryan B.. Wright State University; Estados UnidosFil: Dupree, Jeffrey L.. Virginia Commonwealth University; Estados UnidosFil: Rasband, Matthew N.. Baylor College of Medicine; Estados Unido

Oligodendrocytes assist in the maintenance of sodium channel clusters independent of the myelin sheath

To ensure rapid and efficient impulse conduction, myelinated axons establish and maintain specific protein domains. For instance, sodium (Na+) channels accumulate in the node of Ranvier; potassium (K+) channels aggregate in the juxtaparanode and neurexin/caspr/paranodin clusters in the paranode. Our understanding of the mechanisms that control the initial clustering of these proteins is limited and less is known about domain maintenance. Correlative data indicate that myelin formation and/ or mature myelin-forming cells mediate formation of all three domains. Here, we test whether myelin is required for maintaining Na+ channel domains in the nodal gap by employing two demyelinating murine models: (1) cuprizone ingestion, which induces complete demyelination through oligodendrocyte toxicity; and (2) ceramide galactosyltransferase deficient mice, which undergo spontaneous adult-onset demyelination without oligodendrocyte death. Our data indicate that the myelin sheath is essential for long-term maintenance of sodium channel domains; however, oligodendrocytes, independent of myelin, provide a partial protective influence on the maintenance of nodal Na+ channel clusters. Thus, we propose that multiple mechanisms regulate the maintenance of nodal protein organization. Finally, we present evidence that following the loss of Na+ channel clusters the chronological progression of expression and reclustering of Na+ channel isoforms during the course of CNS remyelination recapitulates development

Nodes of Ranvier Act as Barriers to Restrict Invasion of Flanking Paranodal Domains in Myelinated Axons

Accumulation of voltage gated sodium (Nav) channels at nodes of Ranvier is paramount for action potential propagation along myelinated fibers, yet the mechanisms governing nodal development, organization and stabilization remain unresolved. Here, we report that genetic ablation of the neuron-specific isoform of Neurofascin (NfascNF186) in vivo results in nodal disorganization, including loss of Nav channel and ankyrin-G (AnkG) enrichment at nodes in the peripheral (PNS) and central (CNS) nervous systems. Interestingly, the presence of paranodal domains failed to rescue nodal organization in the PNS and the CNS. Most importantly, using ultrastructural analysis, we demonstrate that the paranodal domains invade the nodal space in NfascNF186 mutant axons and occlude node formation. Our results suggest that NfascNF186-dependent assembly of the nodal complex acts as a molecular boundary to restrict the movement of flanking paranodal domains into the nodal area, thereby facilitating the stereotypic axonal domain organization and saltatory conduction along myelinated axons

Spatiotemporal ablation of myelinating glia-specific neurofascin (Nfasc NF155 ) in mice reveals gradual loss of paranodal axoglial junctions and concomitant disorganization of axonal domains

The evolutionary demand for rapid nerve impulse conduction led to the process of myelination-dependent organization of axons into distinct molecular domains. These domains include the node of Ranvier flanked by highly specialized paranodal domains where myelin loops and axolemma orchestrate the axoglial septate junctions. These junctions are formed by interactions between a glial isoform of neurofascin (NfascNF155) and axonal Caspr and Cont. Here we report the generation of myelinating glia-specific NfascNF155 null mouse mutants. These mice exhibit severe ataxia, motor paresis, and death before the third postnatal week. In the absence of glial NfascNF155, paranodal axoglial junctions fail to form, axonal domains fail to segregate, and myelinated axons undergo degeneration. Electrophysiological measurements of peripheral nerves from NfascNF155 mutants revealed dramatic reductions in nerve conduction velocities. By using inducible PLP-CreER recombinase to ablate NfascNF155 in adult myelinating glia, we demonstrate that paranodal axoglial junctions disorganize gradually as the levels of NfascNF155 protein at the paranodes begin to drop. This coincides with the loss of the paranodal region and concomitant disorganization of the axonal domains. Our results provide the first direct evidence that the maintenance of axonal domains requires the fence function of the paranodal axoglial junctions. Together, our studies establish a central role for paranodal axoglial junctions in both the organization and the maintenance of axonal domains in myelinated axons