| 3581. |
- Renault, Valérie, et al.
(författare)
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Regenerative potential of human skeletal muscle during aging
- 2002
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Ingår i: Aging Cell. - : Wiley-Blackwell. - 1474-9718 .- 1474-9726. ; 1:2, s. 132-139
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we have investigated the consequences of aging on the regenerative capacity of human skeletal muscle by evaluating two parameters: (i) variation in telomere length which was used to evaluate the in vivo turn-over and (ii) the proportion of satellite cells calculated as compared to the total number of nuclei in a muscle fibre. Two skeletal muscles which have different types of innervation were analysed: the biceps brachii, a limb muscle, and the masseter, a masticatory muscle. The biopsies were obtained from two groups: young adults (23 +/- 1.15 years old) and aged adults (74 +/- 4.25 years old). Our results showed that during adult life, minimum telomere lengths and mean telomere lengths remained stable in the two muscles. The mean number of myonuclei per fibre was lower in the biceps brachii than in the masseter but no significant change was observed in either muscle with increasing age. However, the number of satellite cells, expressed as a proportion of myonuclei, decreased with age in both muscles. Therefore, normal aging of skeletal muscle in vivo is reflected by the number of satellite cells available for regeneration, but not by the mean number of myonuclei per fibre or by telomere lengths. We conclude that a decrease in regenerative capacity with age may be partially explained by a reduced availability of satellite cells.
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| 3582. |
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| 3583. |
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| 3584. |
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| 3585. |
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| 3586. |
- Rietdorf, Jens, et al.
(författare)
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Kinesin-dependent movement on microtubules precedes actin-based motility of vaccinia virus
- 2001
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Ingår i: Nature Cell Biology. - : Nature Publishing Group. - 1465-7392 .- 1476-4679. ; 3:11, s. 992-1000
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Tidskriftsartikel (refereegranskat)abstract
- Vaccinia virus, a close relative of the causative agent of smallpox, exploits actin polymerization to enhance its cell-to-cell spread. We show that actin-based motility of vaccinia is initiated only at the plasma membrane and remains associated with it. There must therefore be another form of cytoplasmic viral transport, from the cell centre, where the virus replicates, to the periphery. Video analysis reveals that GFP-labelled intracellular enveloped virus particles (IEVs) move from their perinuclear site of assembly to the plasma membrane on microtubules. We show that the viral membrane protein A36R, which is essential for actin-based motility of vaccinia, is also involved in microtubule-mediated movement of IEVs. We further show that conventional kinesin is recruited to IEVs via the light chain TPR repeats and is required for microtubule-based motility of the virus. Vaccinia thus sequentially exploits the microtubule and actin cytoskeletons to enhance its cell-to-cell spread.
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| 3587. |
- Rilfors, Leif, et al.
(författare)
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Regulation of lipid composition in biological membranes-biophysical studies of lipids and lipid synthesizing enzymes
- 2002
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Ingår i: Colloids and Surfaces B: Biointerfaces. - 0927-7765. ; 26:1, s. 112-24
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Tidskriftsartikel (refereegranskat)abstract
- The study of the role played by membrane lipids, functional lipidomics, has become increasingly important in membrane biology. The physico-chemical properties of the lipids in biological membranes are subject to some fundamental requirements. In general, the acyl chains shall be in a liquid-like state to keep the membrane proteins active, and the lipids must form a bilayer structure in order for the membrane to be an insulating barrier. However, a potential ability of the lipids to form nonbilayer structures seems to be a prequisite for several membrane-associated cell processes. Therefore, organisms exposed to changes in the environmental conditions, such as temperature and uptake of fatty acids, adjust their membrane lipid composition. Examples of prokaryotic organisms that have been studied in this respect are the cell wall-less bacterium Acholeplasma laidlawii, the Gram-negative bacterium Escherichia coli, and the Gram-positive bacteria Bacillus megaterium and Clostridium butyricum, and among eukaroytic organisms are found fungi, higher plants, and poikilothermic animals. By synthesizing a proper combination of acyl chain and polar head group structures, the organisms modify the phase transition temperatures of the membrane lipids so that they are maintained in a lamellar liquid crystalline phase, and the formation of a lamellar gel phase as well as reserved nonlamellar phases is avoided. It has been shown that A. laidlawii and E. coli maintain a balance between lamellar-formed and nonlamellar-forming lipids. A growing body of evidence shows that nonlamellar-forming membrane lipids play essential roles in many aspects of membrance functioning. Short-lived nonbilayer structures are probably formed in the processes of fusion and fission of lipid bilayers, and long-lived bilayer structures with a small radius of curvature occur in several types of biological membranes (e.g. smooth endoplasmic reticulum, inner mitochondrial membrane, and prolamellar bodies). The activity of membrane-associated proteins can be modulated by adding detergents or nonlamellar-forming lipids to bilayers. Some examples are the regeneration of denatured bacteriorphodopsin, and the activities of protein kinase C, some phospholipases, and some key lipid synthases involved in the lipid metabolism of eukaryotic cells, A. laidlawii, and E. coli. The physico-chemical properties of the lipid matrix can be a direct feed-back signal on the activity of the lipid synthases. Finally, nonlamellar-forming lipids are essential for a proper cell division, and an efficient translocation of proteins across the plasma membrane, of E. coli cells.
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| 3588. |
- Rilla, Kirsi, et al.
(författare)
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Changed lamellipodial extension, adhesion plaques and migration in epidermal keratinocytes containing constitutively expressed sense and antisense hyaluronan synthase 2 (Has2) genes.
- 2002
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Ingår i: Journal of Cell Science. - Cambridge : The Company of Biologists. - 0021-9533 .- 1477-9137. ; 115, s. 3633-3643
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Tidskriftsartikel (refereegranskat)abstract
- Hyaluronan is a major component of the epidermal extracellular matrix, is actively synthesized by keratinocytes and shows fast matrix turnover in the stratified epithelium. We probed the importance of hyaluronan synthesis in keratinocytes by establishing cell lines carrying the exogenous hyaluronan synthase 2 (Has2) gene in sense and antisense orientations to increase and decrease their hyaluronan synthesis, respectively. Compared with cell lines transfected with the vector only, most clones containing the Has2 sense gene migrated faster in an in vitro wounding assay, whereas Has2 antisense cells migrated more slowly. Has2 antisense clones showed delayed entry into the S phase of cell cycle following plating, smaller lamellipodia and less spreading on the substratum. The decrease of hyaluronan on the undersurface of Has2 antisense cells was associated with an increased area of adhesion plaques containing vinculin. Exogenous hyaluronan added to the keratinocyte cultures had a minor stimulatory effect on migration after wounding but did not restore the reduced migratory ability of Has2 antisense cells. Hyaluronan decasaccharides that displace receptor bound hyaluronan in keratinocytes, and Streptomyces hyaluronidase sufficient to remove most cell surface hyaluronan had little effect on cell migration. The results suggest that the dynamic synthesis of hyaluronan directed by Has2, rather than the abundance of pericellular hyaluronan, controls keratinocyte migration, a cell function vital for the repair of squamous epithelia following wounding.
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| 3589. |
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| 3590. |
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