摘要:

AbstractAs an alternative to swimming through liquid medium by the coordinated bending activity of its two flagella,Chlamydomonascan exhibit whole cell gliding motility through the interaction of its flagellar surfaces with a solid substrate. The force transduction occurring at the flagellar surface can be visualized as the saltatory movements of polystyrene microspheres. Collectively, gliding motility and polystyrene microsphere movements are referred to as flagellar surface motility. The principal concanavalin A binding, surface‐exposed glycoproteins of theChlamydomonas reinhardtiiflagellar surface are a pair of glycoproteins migrating with apparent molecular weight of 350 kDa. It has been hypothesized that these glycoproteins move within the plane of the flagellar membrane during the expression of flagellar surface motility. A novel mutant cell line ofChlamydomonas(designated L‐23) that exhibits increased binding of concanavalin A to the flagellar surface has been utilized in order to restrict the mobility of the concanavalin A‐binding flagellar glycoproteins. Under all conditions where the lateral mobility of the flagellar concanavalin A binding glycoproteins is restricted, the cells are unable to express whole cell gliding motility or polystyrene microsphere movements. Conversely, whenever cells can redistribute their concanavalin A binding glycoproteins in the plane of the flagellar membrane, they express flagellar surface motility. Since the 350 kDa glycoproteins are the major surface‐exposed flagellar proteins, it is likely that most of the signal being followed using fluorescein isothiocyanate (FITC)‐concanavalin A is attributable to these high molecular weight glycoproteins. Therefore, it is likely that the 350 kDa glycoproteins are the ones that must move laterally in the plane of the flagellar membrane in order for the cell to express whole cell gliding motility and microsphere movements along the flagellar surface. This study represents one of the first demonstrations, in any cell type, that whole cell locomotion requires glycoprotein movement within the plane of the plasma

ISSN:0886-1544    

DOI:10.1002/cm.970130102

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe cytoskeleton of goldfish xanthophores contains an abundance of unique dense structures (400 nm in diameter) that are absent in goldfish nonpigment cells and are probably remnants of pterinosomes. No major difference in protein composition between xanthophores and nonpigment cells (without these structures) was found that could account for these structures. In xanthophores, these structures are foci of radiating filaments. The addition or withdrawal of ACTH causes a radical rearrangement of the xanthophore Cytoskeleton accompanying redistribution of carotenoid droplets, namely, the virtual exclusion of these dense bodies with associated filaments from the space occupied by the carotenoid droplet aggregate vs. a relatively even cytoplasmic distribution of these structures when the carotenoid droplets are dispersed. These changes in cytoskeletal morphology are not accompanied by any major changes in the protein or phosphoprotein composition of the cytoskeleton.

ISSN:0886-1544    

DOI:10.1002/cm.970130103

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

年代:1989

数据来源: WILEY

摘要:

AbstractTriton‐insoluble cytoskeleton of nonpigment cells has bound protein kinase that phosphorylates, with or without added cAMP, tubulins and the intermediate filament proteins p60, p56, p53, and p45a to give multiple charge variants. In the absence of 8‐Br‐cAMP, Triton‐insoluble cytoskeletons from xanthophores also phosphorylate p60, p56, and p45a, but not p53; tubulin phosphorylation may also be reduced. In the presence of 8‐Br‐cAMP, p53, as well as several other peptides, are phosphorylated. One of these latter peptides was identified as the carotenoid droplet (pigment organelle) protein p57, whose phosphorylation and dephosphorylation precede pigment dispersion and aggregation respectively (Lynch et al.: J. Biol. Chem. 261:4204–4211, 1986). The amount of pp57 produced depends on the state of pigment distribution in the xanthophores used to prepare the cytoskeletons for labeling. With cytoskeletons from xanthophores with aggregated pigment, pp57 is a major labeled phosphoprotein seen in two‐dimensional gels. With cytoskeletons prepared from xanthophores with dispersed pigment, the yield of labeled pp57 is greatly reduced (by at least 90%). Together with earlier results, we propose that, in the aggregated state, p57 serves to bind carotenoid droplets to the cytoskeletons, most likely the microtubules. The significance of other cAMP‐dependent phosphorylation reactions is unknown but may be related to cAMP‐induced cytoskeleton rearrangement in

ISSN:0886-1544    

DOI:10.1002/cm.970130104

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe micronuclear spindle apparatus in Paramecium bursaria was studied by electron microscopy during prophase, metaphase, and anaphase of the first meiotic division. During prophase, the spindle apparatus consists mostly of intermediate‐like filaments, relatively few spindle microtubules, and unique cone‐shaped structures termed microlamellae. Microlamellae join the ends of chromosomes to the fibrous elements of the spindle. The capacity to preserve the intermediate‐like filaments is largely dependent upon the use of collidine buffer during fixation. In contrast, during metaphase and anaphase, microtubules are the dominant fibrous element of the spindle. The microtubules interact with chromosomes during these phases by joining to true kinetochores. Neither treatment with cytochalasin B or fixation with a low concentration of osmium tetroxide affects the development of intermediate filaments during prophase. Because intermediate‐like filaments are abundant during prophase and microtubules are more common during metaphase and anaphase, the structural differences may reflect differences in the mechanisms for chromosome m

ISSN:0886-1544    

DOI:10.1002/cm.970130105

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

年代:1989

数据来源: WILEY

摘要:

AbstractA hallmark feature of parasitic platyhelminths is a cytoarchitecturally unusual syncytial epidermis composed of a peripheral layer of continuous cytoplasm (the ectocytoplasm) connected to underlying nucleated cell bodies by small cytoplasmic bridges. The helminth epidermis, or tegument, plays important roles in protection and nutrient acquisition; cestodes, in fact, completely lack a gastrointestinal tract and absorb all nutritive material through the tegument. Perhaps not surprisingly, the cestode tegument bears certain resemblances to the mucosal epithelium of the vertebrate small intestine, including the possession of a microvillous brush border upon the surface of the ectocytoplasm. In contrast to the intestinal epithelial cell, however, very little is known concerning the nature and organization of the cytoskeleton within the helminth epidermis. Therefore, a number of different microscopical preparative techniques were used to examine the tegument of the tapewormHymenolepis diminutafor the presence and distribution of microfilaments, intermediate filaments, and microtubules. It was found that both actin‐containing microfilaments and intermediate‐sized filaments are present but are restricted to specific locations along the plasmalemmae of the ectocytoplasm. In contrast, microtubules are found throughout the tegument, and are concentrated in the supranuclear regions of the perikarya and in the cytoplasmic bridges interconnecting the perikarya and ectocytoplasm. Unlike brush borders of most other epithelia, the cestode epidermal brush border lacks a filamentous terminal web and is instead associated with microtubules. A network of fine filaments, 5–8 nm in diameter but distinct from actin‐containing microfilaments, runs throughout the ectocytoplasm and appears to interlink tegumental vesicles. These fine filaments may represent the primary “skeletal” system responsible for maintaining the structure of the tegumenta

ISSN:0886-1544    

DOI:10.1002/cm.970130106

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

年代:1989

数据来源: WILEY

摘要:

AbstractTriton‐insoluble cytoskeletons were isolated fromDictyostelium discoideumAX3 cells prior to and following stimulation with 2′deoxy cyclic adenosine monophos‐phate (cAMP). Temporal changes in the content of actin and a 120,000 dalton actin‐binding protein (ABP‐120) in cytoskeletons following stimulation were monitored. Both actin and ABP‐120 were incorporated into the cytoskeleton at 30–40 seconds following stimulation, which is cotemporal with the onset of pseudopod extension during stimulation of amoebae with chemoattraciants. Changes in the content of total cytoskeletal protein and cytoskeletal myosin were determined under the same experimental conditions as controls. These proteins exhibited different kinetics from those of cytoskeletal ABP‐120 and actin following the addition of 2′deoxy cAMP. The authors concluded that the association of ABP‐120 with the cytoskeleton is regulated during cAMP signalling. Furthermore, these results indicate that ABP‐120 is involved in cross‐linking newly assembled actin filaments into the cytoskeleton during chemoattractant‐stimu

ISSN:0886-1544    

DOI:10.1002/cm.970130107

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

年代:1989

数据来源: WILEY

ISSN:0886-1544    

DOI:10.1002/cm.970130101

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

年代:1989

数据来源: WILEY