摘要:

AbstractAfter the infectious bacterium,Listeria monocytogenes, is phagocytosed by a host cell, it leaves the lysosome and recruits the host cell's cytoskeletal proteins to assemble a stationary tail composed primarily of actin filaments cross‐linked with alpha‐actinin. The continual recruitment of contractile proteins to the interface between the bacterium and the tail accompanies the propulsion of the bacterium ahead of the elongating tail. When a bacterium contacts the host cell membrane, it pushes out the membrane into an undulating tubular structure or filopodium that envelops the bacterium at the tip with the tail of cytoskeletal proteins behind it. Previous work has demonstrated that alpha‐actinin can be cleaved into two proteolytic fragments whose microinjection into cells interferes with stress fiber integrity. Microinjection of the 53 kD alpha‐actinin fragment into cells infected withListeria monocytogenes, induces the loss of tails from bacteria and causes the bacteria to become stationary. Infected cells that possess filopodia when injected with the 53 kD fragment lose their filopodia. These results indicate that intact alpha‐actinin molecules play an important role in the intracellular motility ofListeria, presumably by stabilizing the actin fibers in the stationary tails that are required for the bacteria to move forward. Fluorescently labeled vinculin associated with the tails when it was injected into infected cells. Talin antibody staining indicated that this protein, also, is present in the tails. These observations suggest that the tails share properties of attachment plaques normally present in the host cells. This model would explain the ability of the bacterium (1) to move within the cytoplasm and (2) to push out the surface of the cell to form a filopodium. The attachment plaque proteins, alpha‐actinin, talin, and vinculin, may bind and stabilize the actin filaments as they polymerize behind the bacteria and additionally could also enable the tails to bind to the cell membrane in the filopodia. © 1994 Wil

ISSN:0886-1544    

DOI:10.1002/cm.970280202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractWe describe the purification of microtubule proteins fromXenopusegg extracts by temperature‐dependent assembly and disassembly in the presence of dimethyl sulfoxide and identify a number of presumptive microtubule‐associated proteins (MAPs). One of these proteins has a molecular weight of 230 kDa and is immunologically related to HeLa MAP4. We show that this MAP is heat stable and phosphorylated, and that it promotes elongation of microtubules from axonemes. © 1994 Wiley‐Lis

ISSN:0886-1544    

DOI:10.1002/cm.970280203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractDamage to the cardiac myocyte sarcolemma following any of several pathological insults such as ischemia (anoxia) alone or followed by reperfusion (reoxygenation), is most apparent as progressive sarcolemmal blebbing, an event attributed by many investigators to a disruption in the underlying cytoskeletal scaffolding. Scanning electron microscopic observation of tissue cultured rat neonatal cardiomyocytes indicates that exposure of these cells to the toxic aldehyde 4‐hydroxynonenal (4‐HNE), a free radical‐‐induced, lipid peroxidation product, results in the appearance of sarcolemmal blebs, whose ultimate rupture leads to cell death. Indirect immunofluorescent localization of a number of cytoskeletal components following exposure to 4‐HNE reveals damage to several, but not all, key cytoskeletal elements, most notably microtubules, vinculin‐containing costameres, and intermediate filaments. The exact mechanism underlying the selective disruption of these proteins cannot be ascertained at this time. Colocalization of actin indicated that whereas elements of the cytoskeleton were disrupted by increasing length of exposure to 4‐HNE, neither the striated appearance of the myofibrils nor the lateral register of neighboring myofibrils was altered. Monitoring systolic and diastolic levels of intracellular calcium ([Ca2+]i) indicated that increases in [Ca2+]ioccurred after considerable cytoskeletal changes had already taken place, suggesting that damage to the cytoskeleton, at least in early phases of exposure to 4‐HNE, does not involve Ca2+‐dependent proteases. However, 4‐HNE–induced cytoskeletal alterations coincide with the appearance of, and therefore suggest linkage to, sarcolemmal blebs in cardiac myocytes.Although free radicals produced by reperfusion or reoxygenation of ischemic tissue have been implicated in cellular damage, these studies represent the first evidence linking cardiomyocyte sarcolemmal damage to cytoskeletal disruption produced by a free radical product.

ISSN:0886-1544    

DOI:10.1002/cm.970280204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractSpermatozoa of the small myzostomid wormMyzostomum cirriferumusually swim with the flagellum foremost but occasionally stop and then swim with the head foremost. The spermatozoa have axoneme of the 9+0 type; thus each lacks the central pair microtubules. The flagellum emerges in the anterior end of the cell body and attaches to it with junctions. To understand the mechanism regulating the swimming direction of the spermatozoa, we recorded the sperm and their flagellar movements using a video camera with a high‐speed shutter. The effects of calcium and viscosity on these movements were also examined.The cell body with the flagellum attached to it formed a curved plate during beating, while the free portion of the flagellum beats with small helical bends. Motive force to propel a spermatozoon was mainly due to the bends in the cell body. The spermatozoa reversed the direction of their swimming as a result of a change in the direction of bend propagation. The direction of bend propagation was regulated by calcium; the bends in the cell body propagated from the end of the head toward the free portion of the flagellum at low concentrations of Ca2+, whereas the direction of bend propagation was reversed at high concentrations of this ion. High viscosity of the medium stimulated a change in the direction of bend propagation. © 1994 Wiley‐Liss,

ISSN:0886-1544    

DOI:10.1002/cm.970280205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe neuronal microtubule‐associated protein tau has been implicated in the development of axonal morphology including the organization of microtubules into a uniformly oriented array of microtubules commonly referred to as “bundle.” Determination of the functional organization of tau has revealed that regions of tau protein which flank the microtubule‐binding domain affect the bundling of microtubules in vitro with a microtubule‐binding fragment of tau being most effective [Brandt and Lee, 1993:J. Biol. Chem.268:3414‐3419]. In order to study the relation of microtubule bundles that form in vitro to those observed in the axon, we determined the orientation of individual microtubules in bundles and the effects of bundling on microtubule assembly and stability in cell‐free assembly reactions. Here we report that bundles induced by a microtubule‐binding fragment of tau contain randomly oriented microtubules as determined by using the difference in growth rates at microtubule plus and minus ends. We demonstrate that in vitro bundling increases microtubule growth (about 30%), stabilizes microtubules against dilution‐ and cold‐induced disassembly, and allows microtubule nucleation despite the absence of a tau region which has previously been shown to be required for tau‐dependent microtubule nucleation. We conclude that conditions that stabilize microtubules can lead to bundle formation and allow microtubule assembly by a mechanism different from that employed by microtubule‐associated proteins. The data also support the view that additional mechanisms besides the action of tau and tubulin exist in order to organize microtubules in the axon.

ISSN:0886-1544    

DOI:10.1002/cm.970280206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractF‐actin is a major component of the neutrophil (PMN) cytoskeleton. In basal PMNs, F‐actin exists in two structurally and functionally distinct pools: Triton insoluble F‐actin (TIF)–cold insensitive, not depolymerizable by dilution, and distributed in pseudopods and submembranous locations; and Triton soluble F‐actin (TSF)–unstable in cold, diffusely distributed, and gelsolin enriched. The element(s) conferring these unique properties to the Triton insoluble F‐actin pool are unknown, but logically include distinct actin regulatory proteins. To study the morphologic and functional determinants of the Triton insoluble F‐actin pool, the distribution and quantity of three candidate regulatory proteins, α‐actinin, tropomyosin (TM), and actin binding protein (ABP‐280), were compared in F‐actin (Triton insoluble and Triton soluble) and G‐actin pools isolated from basal and chemotactic factor activated human PMNs in suspension, using immunoblots and ionic extraction. F‐actin content was measured by NBDphallacidin binding and gel scans. The results show that: (1) α‐actinin, actin binding protein 280, and tropomyosin are localized to TIF and excluded from TSF; (2) TM, α‐actinin, and ABP 280 are required to stabilize fractions of Triton insoluble F‐actin in PMNs; and (3) chemotactic factor activation results in release of a fraction of TM from the Triton insoluble F‐actin pool in temporal association with F‐actin polymerization in the Triton insoluble F‐actin pool. Shifts in ABP 280 or α‐actinin do not occur. The results suggest that TM, α‐actinin, and ABP 280 provide structure to TIF and that TM release from TIF is involved in chemotactic factor induced actin

ISSN:0886-1544    

DOI:10.1002/cm.970280207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThree dimensional (3‐D) reconstruction of four mitotic WISH cells from ultrathin sections gave an informative representation of the spatial distribution of keratin densities in these cells. The correspondence between the densities as studied by transmission electron microscopy (TEM) and the Keratin bodies initially revealed by immunoflourescent colabeling of cultures, was confirmed by immunoelectron‐microscopy. The smaller, and sometimes more elongated densities, were relatively abundant just beneath the subplasmalemmal microfilament band; and at certain levels of the mitotic cell they were observed to be connected to neighboring densities by intact intermediate filaments (IFs). The larger and more spherical densities appeared to be somewhat more discrete and randomly distributed. Other observed associations of the keratin densities included the telophase contractile ring of microfilaments, chromosomes, the reformed telophase nucleus, and desmosomal junctions with neighboring interphase cells. Cytochalasin D (CD) treatment of cells displaced the peripheral keratin densities toward the cell membrane. The density volume constituted 0.52% to 1.57% of the total cell volume, and the proportional density size was decreased in the cells that had progressed into anaphase and telophase. The observed formation and subsequent dissolution of keratin densities during mitosis may represent a dynamic mechanism of restructuring the keratin cytoskeleton in an unpolymerized form in order to allow for rapid reformation of interphase cell junctions. The physical associations observed between intact IFs and the keratin densities may provide support at certain depths of the mitotic cell, and the juxtaposition of densities with nuclear components suggests a possible source of and role for keratin IFs during nuclear events. © 1994 Wiley‐Lis

ISSN:0886-1544    

DOI:10.1002/cm.970280208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractWe studied the organization of acetylcholine receptor (AChR) clusters by shearing culturedXenopusmuscle cells with a stream of buffer, and preparing rotary replicas of the exposed cytoplasmic surface of the sarcolemma. AChR clusters contained numerous particles that protruded from the sarcolemma and formed an irregular array composed of discrete aggregates. AChR were located within these particle aggregates, as shown by comparison of the replicas to labeling by fluorescent α‐bungarotoxin, and by immunogold cytochemistry with antibodies specific for the receptor. The aggregates were cross‐linked by a dense network of 7 nm filaments that replicated with the banded pattern characteristic of actin microfilaments. The organization of receptors into the small aggregates was independent of the organization of these aggregates into clusters, as alkaline extraction removed the microfilament network and disrupted the irregular array of particle aggregates, but did not disperse individual receptors from the aggregates. We conclude that two levels of interactions organize AChR clusters inXenopusmuscle cells: short‐range interactions that assemble individual AChR into small aggregates, and long‐range interactions, perhaps mediated by actin microfilaments, that anchor the aggregates into larger clusters. © 1994 Wiley

ISSN:0886-1544    

DOI:10.1002/cm.970280209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:0886-1544    

DOI:10.1002/cm.970280201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY