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71.
Engert JC Bérubé P Mercier J Doré C Lepage P Ge B Bouchard JP Mathieu J Melançon SB Schalling M Lander ES Morgan K Hudson TJ Richter A 《Nature genetics》2000,24(2):120-125
Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS or SACS) is an early onset neurodegenerative disease with high prevalence (carrier frequency 1/22) in the Charlevoix-Saguenay-Lac-Saint-Jean (CSLSJ) region of Quebec. We previously mapped the gene responsible for ARSACS to chromosome 13q11 and identified two ancestral haplotypes. Here we report the cloning of this gene, SACS, which encodes the protein sacsin. The ORF of SACS is 11,487 bp and is encoded by a single gigantic exon spanning 12,794 bp. This exon is the largest to be identified in any vertebrate organism. The ORF is conserved in human and mouse. The putative protein contains three large segments with sequence similarity to each other and to the predicted protein of an Arabidopsis thaliana ORF. The presence of heat-shock domains suggests a function for sacsin in chaperone-mediated protein folding. SACS is expressed in a variety of tissues, including the central nervous system. We identified two SACSmutations in ARSACS families that lead to protein truncation, consistent with haplotype analysis. 相似文献
72.
73.
A striking feature of the body plan of a majority of animals is bilateral symmetry. Almost nothing is known about the mechanisms controlling the symmetrical arrangement of the left and right body sides during development. Here we report that blocking the production of retinoic acid (RA) in chicken embryos leads to a desynchronization of somite formation between the two embryonic sides, demonstrated by a shortened left segmented region. This defect is linked to a loss of coordination of the segmentation clock oscillations. The lateralization of this defect led us to investigate the relation between somitogenesis and the left-right asymmetry machinery in RA-deficient embryos. Reversal of the situs in chick or mouse embryos lacking RA results in a reversal of the somitogenesis laterality defect. Our data indicate that RA is important in buffering the lateralizing influence of the left-right machinery, thus permitting synchronization of the development of the two embryonic sides. 相似文献
74.
Atomic ordering in network glasses on length scales longer than nearest-neighbour length scales has long been a source of controversy. Detailed experimental information is therefore necessary to understand both the network properties and the fundamentals of glass formation. Here we address the problem by investigating topological and chemical ordering in structurally disordered AX2 systems by applying the method of isotopic substitution in neutron diffraction to glassy ZnCl2. This system may be regarded as a prototypical ionic network forming glass, provided that ion polarization effects are taken into account, and has thus been the focus of much attention. By experiment, we show that both the topological and chemical ordering are described by two length scales at distances greater than nearest-neighbour length scales. One of these is associated with the intermediate range, as manifested by the appearance in the measured diffraction patterns of a first sharp diffraction peak at 1.09(3) A(-1); the other is associated with an extended range, which shows ordering in the glass out to 62(4) A. We also find that these general features are characteristic of glassy GeSe2, a prototypical covalently bonded network material. The results therefore offer structural insight into those length scales that determine many important aspects of supercooled liquid and glass phenomenology. 相似文献
75.
Kurth WS Gurnett DA Clarke JT Zarka P Desch MD Kaiser ML Cecconi B Lecacheux A Farrell WM Galopeau P Gérard JC Grodent D Prangé R Dougherty MK Crary FJ 《Nature》2005,433(7027):722-725
Saturn is a source of intense kilometre-wavelength radio emissions that are believed to be associated with its polar aurorae, and which provide an important remote diagnostic of its magnetospheric activity. Previous observations implied that the radio emission originated in the polar regions, and indicated a strong correlation with solar wind dynamic pressure. The radio source also appeared to be fixed near local noon and at the latitude of the ultraviolet aurora. There have, however, been no observations relating the radio emissions to detailed auroral structures. Here we report measurements of the radio emissions, which, along with high-resolution images of Saturn's ultraviolet auroral emissions, suggest that although there are differences in the global morphology of the aurorae, Saturn's radio emissions exhibit an Earth-like correspondence between bright auroral features and the radio emissions. This demonstrates the universality of the mechanism that results in emissions near the electron cyclotron frequency narrowly beamed at large angles to the magnetic field. 相似文献
76.
77.
Raghoebarsing AA Smolders AJ Schmid MC Rijpstra WI Wolters-Arts M Derksen J Jetten MS Schouten S Sinninghe Damsté JS Lamers LP Roelofs JG Op den Camp HJ Strous M 《Nature》2005,436(7054):1153-1156
Wetlands are the largest natural source of atmospheric methane, the second most important greenhouse gas. Methane flux to the atmosphere depends strongly on the climate; however, by far the largest part of the methane formed in wetland ecosystems is recycled and does not reach the atmosphere. The biogeochemical controls on the efficient oxidation of methane are still poorly understood. Here we show that submerged Sphagnum mosses, the dominant plants in some of these habitats, consume methane through symbiosis with partly endophytic methanotrophic bacteria, leading to highly effective in situ methane recycling. Molecular probes revealed the presence of the bacteria in the hyaline cells of the plant and on stem leaves. Incubation with (13)C-methane showed rapid in situ oxidation by these bacteria to carbon dioxide, which was subsequently fixed by Sphagnum, as shown by incorporation of (13)C-methane into plant sterols. In this way, methane acts as a significant (10-15%) carbon source for Sphagnum. The symbiosis explains both the efficient recycling of methane and the high organic carbon burial in these wetland ecosystems. 相似文献
78.
Cellular biochemical networks have to function in a noisy environment using imperfect components. In particular, networks involved in gene regulation or signal transduction allow only for small output tolerances, and the underlying network structures can be expected to have undergone evolution for inherent robustness against perturbations. Here we combine theoretical and experimental analyses to investigate an optimal design for the signalling network of bacterial chemotaxis, one of the most thoroughly studied signalling networks in biology. We experimentally determine the extent of intercellular variations in the expression levels of chemotaxis proteins and use computer simulations to quantify the robustness of several hypothetical chemotaxis pathway topologies to such gene expression noise. We demonstrate that among these topologies the experimentally established chemotaxis network of Escherichia coli has the smallest sufficiently robust network structure, allowing accurate chemotactic response for almost all individuals within a population. Our results suggest that this pathway has evolved to show an optimal chemotactic performance while minimizing the cost of resources associated with high levels of protein expression. Moreover, the underlying topological design principles compensating for intercellular variations seem to be highly conserved among bacterial chemosensory systems. 相似文献
79.
80.
Nobushigé Ikushima 《Cellular and molecular life sciences : CMLS》1959,15(12):475-476
Zusammenfassung Stücke aus der dorsalen Randzone der frühen Gastrula vonHynobius nebulosus wurden in Holtfreterscher Lösung auf Kollodiummembranen gezüchtet. In dreieckigen Explantaten entstehen öfters zwei Chordastränge, während in viereckigen Explantaten stets nur ein Chordastrang gebildet wird. Diese Tatsachen weisen auf die Möglichkeit hin, dass Gestaltungsbewegungen des Explantates bei der Determination der Chordaanlage eine wichtige Rolle spielen. 相似文献