Nr-CAM and neurofascin interactions regulate ankyrin G and sodium channel clustering at the node of Ranvier

AbstractVoltage-dependent sodium (Na+) channels are highly concentrated at nodes of Ranvier in myelinated axons and play a key role in promoting rapid and efficient conduction of action potentials by saltatory conduction. The molecular mechanisms that direct their localization to the node are not well understood but are believed to involve contact-dependent signals from myelinating Schwann cells [1] and interactions of Na+ channels with the cytoskeletal protein, ankyrin G [2]. Two cell adhesion molecules (CAMs) expressed at the axon surface, Nr-CAM and neurofascin, are also linked to ankyrin G and accumulate at early stages of node formation, suggesting that they mediate contact-dependent Schwann cell signals to initiate node development [3]. To examine the potential role of Nr-CAM in this process, we treated myelinating cocultures of DRG (dorsal root ganglion) neurons and Schwann cells with an Nr-CAM-Fc (Nr-Fc) fusion protein. Nr-Fc had no effect on initial axon-Schwann cell interactions, including Schwann cell proliferation, or on the extent of myelination, but it strikingly and specifically inhibited Na+ channel and ankyrin G accumulation at the node. Nr-Fc bound directly to neurons and clustered and coprecipitated neurofascin expressed on axons. These results provide the first evidence that neurofascin plays a major role in the formation of nodes, possibly via interactions with Nr-CAM

Discovery and Functional Categorisation of Expressed Sequence Tags from Flowers of \u3cem\u3eEragrostis Curvula\u3c/em\u3e Genotypes Showing Different Ploidy Levels and Reproductive Modes

Two novel genotypes of weeping lovegrass (Eragrostis curvula) - a dihaploid strain obtained in vitro from an apomictic cultivar and a tetraploid plant derived from the dihaploid after chromosome duplication – have recently been developed. These materials represent an excellent system for the identification, through transcriptional profiling, of genes involved in diplospory and/or ploidy level gene regulation. The aim of this work was the discovery and functional classification of expressed sequence tags (ESTs) from immature inflorescences of the apomictic E. curvula cultivar Tanganyika (2n=4x=40), a dihaploid sexual strain derived from it (2n=2x=20) and a tetraploid sexual strain (2n=4x=40) obtained by colchicine duplication of the dihaploid

Segregation and ordering at the (1×2) reconstructed Pt80Fe20(110) surface determined by low-energy electron diffraction

The surface of an ordered Pt80Fe20(110) crystal exhibits (1×2) and (1×3) reconstructions depending on the annealing treatment after ion bombardment. The (1×3) structure occurs after annealing in the range 750 to 900 K. Annealing above 1000 K leads to the (1×2) structure, which is, from the present result, unambiguously attributed to the same geometrical reconstruction as Pt(110) but with smaller relaxation amplitudes: a detailed low-energy electron-diffraction analysis concludes to a missing-row structure with row pairing in layers 2 and 4 accompanied by a buckling in layers 3 and 5. The top layer spacing is contracted by 13%, and further relaxations are detectable down to the fifth layer. The specific diffraction spots associated with the bulk chemical ordering along the dense [1¯10] rows are very weak: The I(V) analysis shows that this chemical ordering is absent in the outermost ‘‘visible’’ rows but gradually recovers over five to six layers deep. General Pt enrichment is found in the surface ‘‘visible’’ rows (in layers 1–3), but segregation and order yield a subtle redistribution of Pt and Fe atoms in deeper rows: For example, in layer 2, the visible row is Pt rich, whereas the other row (buried under layer 1) is enriched with Fe. Because of the many parameters considered, a fit procedure was applied to a large data basis to solve the structure; the results were confirmed and illustrated subsequently by a standard I(V) analysis for the most relevant parameters. The final r factors are RDE=0.36, RP=0.34, and RZJ=0.14 for two beam sets at normal and oblique incidence consisting of 26 and 21 beams, respectively

Structure determination of the (1×2) and (1×3) reconstructions of Pt(110) by low-energy electron diffraction

The atomic geometry of the (1×2) and (1×3) structures of the Pt(100) surface has been determined from a low-energy electron-diffraction intensity analysis. Both structures are found to be of the missing-row type, consisting of (111) microfacets, and with similar relaxations in the subsurface layers. In both reconstructions the top-layer spacing is contracted by approximately 20% together with a buckling of about 0.17 Å in the third layer and a small lateral shift of about 0.04 Å in the second layer. Further relaxations down to the fourth layer were detectable. The surface relaxations correspond to a variation of interatomic distances, ranging from -7% to +4%, where in general a contraction of approximately 3% for the distances parallel to the surface occurs. The Pendry and Zanazzi-Jona R factors were used in the analysis, resulting in a minimum value of RP=0.36 and RZJ=0.26 for 12 beams at normal incidence for the (1×2) structure, and similar agreement for 19 beams of the (1×3) structure. The (1×3) structure has been reproducibly obtained after heating the crystal in an oxygen atmosphere of 5×10-6 mbar at 1200 K for about 30 min and could be removed by annealing at 1800 K for 45 min after which the (1×2) structure appeared again. Both reconstructed surfaces are clean within the detection limits of the Auger spectrometer. CO adsorption lifts the reconstruction in both structures. After desorption at 500 K the initial structures appear again, indicating that at least one of the reconstructions does not represent the equilibrium structure of the clean surface and may be stabilized by impurities

Q344ter Mutation Causes Mislocalization of Rhodopsin Molecules That Are Catalytically Active: A Mouse Model of Q344ter-Induced Retinal Degeneration

Q344ter is a naturally occurring rhodopsin mutation in humans that causes autosomal dominant retinal degeneration through mechanisms that are not fully understood, but are thought to involve an early termination that removed the trafficking signal, QVAPA, leading to its mislocalization in the rod photoreceptor cell. To better understand the disease mechanism(s), transgenic mice that express Q344ter were generated and crossed with rhodopsin knockout mice. Dark-reared Q344terrho+/− mice exhibited retinal degeneration, demonstrating that rhodopsin mislocalization caused photoreceptor cell death. This degeneration is exacerbated by light-exposure and is correlated with the activation of transducin as well as other G-protein signaling pathways. We observed numerous sub-micrometer sized vesicles in the inter-photoreceptor space of Q344terrho+/− and Q344terrho−/− retinas, similar to that seen in another rhodopsin mutant, P347S. Whereas light microscopy failed to reveal outer segment structures in Q344terrho−/− rods, shortened and disorganized rod outer segment structures were visible using electron microscopy. Thus, some Q344ter molecules trafficked to the outer segment and formed disc structures, albeit inefficiently, in the absence of full length wildtype rhodopsin. These findings helped to establish the in vivo role of the QVAPA domain as well as the pathways leading to Q344ter-induced retinal degeneration

Genome-Wide Profile of Pleural Mesothelioma versus Parietal and Visceral Pleura: The Emerging Gene Portrait of the Mesothelioma Phenotype

Malignant pleural mesothelioma is considered an almost incurable tumour with increasing incidence worldwide. It usually develops in the parietal pleura, from mesothelial lining or submesothelial cells, subsequently invading the visceral pleura. Chromosomal and genomic aberrations of mesothelioma are diverse and heterogenous. Genome-wide profiling of mesothelioma versus parietal and visceral normal pleural tissue could thus reveal novel genes and pathways explaining its aggressive phenotype.Well-characterised tissue from five mesothelioma patients and normal parietal and visceral pleural samples from six non-cancer patients were profiled by Affymetrix oligoarray of 38 500 genes. The lists of differentially expressed genes tested for overrepresentation in KEGG PATHWAYS (Kyoto Encyclopedia of Genes and Genomes) and GO (gene ontology) terms revealed large differences of expression between visceral and parietal pleura, and both tissues differed from mesothelioma. Cell growth and intrinsic resistance in tumour versus parietal pleura was reflected in highly overexpressed cell cycle, mitosis, replication, DNA repair and anti-apoptosis genes. Several genes of the “salvage pathway” that recycle nucleobases were overexpressed, among them TYMS, encoding thymidylate synthase, the main target of the antifolate drug pemetrexed that is active in mesothelioma. Circadian rhythm genes were expressed in favour of tumour growth. The local invasive, non-metastatic phenotype of mesothelioma, could partly be due to overexpression of the known metastasis suppressors NME1 and NME2. Down-regulation of several tumour suppressor genes could contribute to mesothelioma progression. Genes involved in cell communication were down-regulated, indicating that mesothelioma may shield itself from the immune system. Similarly, in non-cancer parietal versus visceral pleura signal transduction, soluble transporter and adhesion genes were down-regulated. This could represent a genetical platform of the parietal pleura propensity to develop mesothelioma.Genome-wide microarray approach using complex human tissue samples revealed novel expression patterns, reflecting some important features of mesothelioma biology that should be further explored

Variants of OTOF and PJVK Genes in Chinese Patients with Auditory Neuropathy Spectrum Disorder

BACKGROUND: Mutations in OTOF and PJVK genes cause DFNB9 and DFNB59 types of hearing loss, respectively. The patients carrying pathogenic mutations in either of these genes may show the typical phenotype of auditory neuropathy spectrum disorder (ANSD). The aim of the present study was to identify OTOF and PJVK mutations in sporadic ANSD patients. METHODS AND FINDINGS: A total of 76 unrelated Chinese non-syndromic ANSD patients were sequenced on the gene OTOF and PJVK exon by exon. Variants were valued in 105 controls with normal hearing to verify the carrying rate. We identified one pathogenic mutation (c.1194T>A) and three novel, possibly pathogenic, variants (c.3570+2T>C, c.4023+1 G>A, and c.1102G>A) in the OTOF gene, and one novel, possibly pathogenic, variant (c.548G>A) in PJVK. Moreover, we found three novel missense mutations within the exons of OTOF. CONCLUSIONS: As we identified 4 and 1 possible pathogenic variants of the OTOF gene and the PJVK gene, respectively, we believe that screening in these genes are important in sporadic ANSD patients. The pathogenicity of these novel mutations needs further study because of their single heterozygous nature. Knowledge on the mutation spectra of these genes in Chinese would be beneficial in understanding the genetic character of this worldwide disease

Identification of stable and metastable adsorption sites of K adsorbed on Al(111)

The adsorption of potassium on Al(111) at 90 K and at 300 K has been investigated by low-energy electron diffraction (LEED). Although a (√3 × √3 )R30° structure is formed at each temperature, a detailed LEED analysis has revealed that the adsorbate positions are quite different and unusual in each case. At 90 K the adatoms occupy on-top sites and at 300 K they occupy substitutional sites. An irreversible phase transformation from the former to the latter structure occurs on warming to 300 K. These results are discussed in the light of recent density-functional-theory calculations

Role for a Novel Usher Protein Complex in Hair Cell Synaptic Maturation

The molecular mechanisms underlying hair cell synaptic maturation are not well understood. Cadherin-23 (CDH23), protocadherin-15 (PCDH15) and the very large G-protein coupled receptor 1 (VLGR1) have been implicated in the development of cochlear hair cell stereocilia, while clarin-1 has been suggested to also play a role in synaptogenesis. Mutations in CDH23, PCDH15, VLGR1 and clarin-1 cause Usher syndrome, characterized by congenital deafness, vestibular dysfunction and retinitis pigmentosa. Here we show developmental expression of these Usher proteins in afferent spiral ganglion neurons and hair cell synapses. We identify a novel synaptic Usher complex comprised of clarin-1 and specific isoforms of CDH23, PCDH15 and VLGR1. To establish the in vivo relevance of this complex, we performed morphological and quantitative analysis of the neuronal fibers and their synapses in the Clrn1−/− mouse, which was generated by incomplete deletion of the gene. These mice showed a delay in neuronal/synaptic maturation by both immunostaining and electron microscopy. Analysis of the ribbon synapses in Ames waltzerav3J mice also suggests a delay in hair cell synaptogenesis. Collectively, these results show that, in addition to the well documented role for Usher proteins in stereocilia development, Usher protein complexes comprised of specific protein isoforms likely function in synaptic maturation as well

Channelopathies in Cav1.1, Cav1.3, and Cav1.4 voltage-gated L-type Ca2+ channels

Voltage-gated Ca2+ channels couple membrane depolarization to Ca2+-dependent intracellular signaling events. This is achieved by mediating Ca2+ ion influx or by direct conformational coupling to intracellular Ca2+ release channels. The family of Cav1 channels, also termed L-type Ca2+ channels (LTCCs), is uniquely sensitive to organic Ca2+ channel blockers and expressed in many electrically excitable tissues. In this review, we summarize the role of LTCCs for human diseases caused by genetic Ca2+ channel defects (channelopathies). LTCC dysfunction can result from structural aberrations within their pore-forming α1 subunits causing hypokalemic periodic paralysis and malignant hyperthermia sensitivity (Cav1.1 α1), incomplete congenital stationary night blindness (CSNB2; Cav1.4 α1), and Timothy syndrome (Cav1.2 α1; reviewed separately in this issue). Cav1.3 α1 mutations have not been reported yet in humans, but channel loss of function would likely affect sinoatrial node function and hearing. Studies in mice revealed that LTCCs indirectly also contribute to neurological symptoms in Ca2+ channelopathies affecting non-LTCCs, such as Cav2.1 α1 in tottering mice. Ca2+ channelopathies provide exciting disease-related molecular detail that led to important novel insight not only into disease pathophysiology but also to mechanisms of channel function