Recent studies in desmin (−/−) mice have shown that the targeted ablation of desmin leads to pathological changes of the extrasarcomeric intermediate filament cytoskeleton, as well as structural and functional abnormalities of mitochondria in striated muscle. Here, we report on a novel heterozygous single adenine insertion mutation (c.5141_5143insA) in a 40-year-old patient with a distal myopathy. The insertion mutation leads to a frameshift and a truncated desmin (K239fs242). Using transfection studies in SW13 and BHK21 cells, we show that the K239fsX242 desmin mutant is incapable of forming a desmin intermediate filament network. Furthermore, it induces the collapse of a pre-existing desmin cytoskeleton, alters the subcellular distribution of mitochondria and leads to abnormal cytoplasmic protein aggregates reminiscent of desmin-immunoreactive granulofilamentous material seen in the ultrastructural analysis of the patient's muscle. Analysis of mitochondrial function in isolated saponin-permeablized skeletal muscle fibres from our patient showed decreased maximal rates of respiration with the NAD-dependent substrate combination glutamate and malate, as well as a higher amytal sensitivity of respiration, indicating an in vivo inhibition of complex I activity. Our findings suggest that the heterozygous K239fsX242 desmin insertion mutation has a dominant negative effect on the polymerization process of desmin intermediate filaments and affects not only the subcellular distribution, but also biochemical properties of mitochondria in diseased human skeletal muscle. As a consequence, the intermediate filament pathology-induced mitochondrial dysfunction may contribute to the degeneration/regeneration process leading to progressive muscle dysfunction in human desminopathies.
Atmospheric particles in urban and rural areas in Shenzhen city were collected in summer and winter 2004. The particles were analyzed using a scanning electron microscope equipped with an energy dispersive X‐ray spectrometer. The fine particles (<1 μ m) were categorized into chain‐like, elongated, rounded, and others on the basis of their morphology. Chain‐like particles were likely soot aggregates. In summer and winter, chain‐like particles accounted for 43% and 42% of total particles in the urban area, and 22% and 43% in the rural area, respectively. The elongated particles were mixtures of aged sea salts and ammonium sulfate, suggesting an aqueous phase reaction mechanism, i.e., in‐cloud sulfate formation. Such particles occupied 12% of total particles in the urban area in the summer and were rarely observed in the wintertime samples. The rounded particles were mainly composed of sulfate and/or carbon. Their number concentration in the urban area was more than three times higher in the winter. In addition, we found that air masses from northern inland contained much higher concentrations of particles than those from the ocean. This was particularly evident in the rural area, where concentrations of chain‐like and rounded particles were eight times higher in the continental air masses. These results suggest the strong influence of regional pollution on the particle number concentrations in the coastal city.
Connexin 31(Cx31) is one of the human genetic deafness disease genes. To determine the structure and function of Cx31 gene of mouse, the mouse Cx31 gene clone was screened from the genomic library with the probe obtained according to the sequence of the mouse Cx31 gene cDNA. Cx31 gene was mapped to the center of mouse chromosome 4 by fluorescence in situ hybridization. The present study lays a foundation for researches on structure and function of Cx31 gene, as well as establishment of the relative transgenic mice and gene knockout mice.
The mechanisms regulating the intermediate filament (IF) protein assembly are complex and not yet fully understood. All vertebrate cytoplasmic IF proteins have a central α-helical rod domain flanked by variable head and tail domains. The IF protein synemin cannot homopolymerize to form filament networks; it needs an appropriate copolymerization partner. To elucidate the roles of the vimentin head domain, the TAAL motif in the 2A region, and the TYRKLLEGEE motif in the 2B region of the rod domain in synemin filament formation, we have prepared a series of synemin constructs by site-directed mutagenesis and chimeric synemins having the vimentin head domain. The assembly properties of synemin constructs were assessed by the immunofluorescence of transient transfection into cultured SW13 cells without endogenous IFs. Our data showed that the formation of a filamentous network required at least the vimentin-like head domain and both the 2A and 2B regions of the rod domain.
Plusieurs réseaux de filaments composent le cytosquelette intracellulaire, d’abord caractérisés par microscopie électronique, puis par immuno-détection, et enfin par détermination des séquences des gènes et des protéines. Les microtubules forment des réseaux de 25 nanomètres de diamètre, c’est le réseau le plus dynamique, impliqué dans la division cellulaire. Les micro-filaments d’actine de 5 nanomètres de diamètre sont contrôlés par de nombreuses protéines associées qui modulent leurs interactions et leurs formes. Il a fallu un certain temps avant de réaliser que des filaments de 10 nanomètres, les filaments intermédiaires (IFs), formaient un troisième réseau du cytosquelette en plus des microtubules et des filaments d’actine. Différentes selon le type cellulaire mais de structures similaires, les protéines constituant les IFs s’auto-assemblent en homo- ou hétéro-polymères élastiques pour remplir des fonctions liées à la plasticité cellulaire, à la fixation des organites, mais aussi à la signalisation et au contrôle de l’activité génique. Multi-organisateurs des processus cellulaires, l’importance des filaments intermédiaires résulte de leur expression dans tous les tissus. Les revues qui suivent illustrent comment les mutations affectent la structure et l’assemblage des IFs, la formation d’inclusions et les perturbations du métabolisme cellulaire provoquant des pathologies graves. Les relations entre les nombreuses mutations identifiées dans les gènes codant les IFs avec le type et la sévérité des pathologies constituent encore un champ d’étude important.
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