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Microtubule Arrays (microtubule + array)

Distribution by Scientific Domains

Life Sciences	80%

Selected Abstracts

Microtubule arrays in fucoid zygotes are sensitive to cytoplasmic pH

PHYCOLOGICAL RESEARCH, Issue 1 2001
David C. Henderson
SUMMARY Regulation of microtubule (MT) arrays and embryo-genesis by cytoplasmic pH (pHc) was investigated in zygotes of the brown alga Pelvetia compressa (J. Agardh) De Toni. pHc was clamped to (set to) acidic values using a weak acid, propionic acid (PA), and to alkaline values using a weak base, methylamine (MA). Acidification of pHc from the normal value of 7.4,7.5 to about 7.0 caused disruption of microtubule arrays. The nucleating activity was delocalized from the centrosomes and dispersed over the nuclear envelope, the number of MTs decreased, and MTs failed to extend into the cell cortex. Alkalinization to about pH 8.0 also caused dispersal of nucleating activity, but distinct centrosomes remained. MTs coursed in various directions following MA treatment, giving the array a disorganized appearance. Two MT-dependent processes, rhizoid morphogenesis and cell division, were found to be perturbed by small changes in pHc. [source]

The contributions of microtubule stability and dynamic instability to adenovirus nuclear localization efficiency

CYTOSKELETON, Issue 9 2007
James C. Warren
Abstract Adenoviruses (Ads) utilize host cell microtubules to traverse the intracellular space and reach the nucleus in a highly efficient manner. Previous studies have shown that Ad infection promotes the formation of stable, posttranslationally modified microtubules by a RhoA-dependent mechanism. Ad infection also shifts key parameters of microtubule dynamic instability by a Rac1-dependent mechanism, resulting in microtubules with lower catastrophe frequencies, persistent growth phases, and a bias toward net growth compared to microtubules in uninfected cells. Until now it was unclear whether changes in RhoGTPase activity or microtubule dynamics had a direct impact on the efficiency of Ad microtubule-dependent nuclear localization. Here we have performed synchronous Ad infections and utilized confocal microscopy to analyze the individual contributions of RhoA activation, Rac1 activation, microtubule stability, dynamic behavior, and posttranslational modifications on Ad nuclear localization efficiency (NLE). We found that drug-induced suppression of microtubule dynamics impaired Ad NLE by disrupting the radial organization of the microtubule array. When the microtubule array was maintained, the suppression or enhancement of microtubule turnover did not significantly affect Ad NLE. Furthermore, RhoA activation or the formation of acetylated microtubules did not enhance Ad NLE. In contrast, active Rac1 was required for efficient Ad nuclear localization. Because Rac1 mediates persistent growth of microtubules to the lamellar regions of cells, we propose that Ad-induced activation of Rac1 enhances the ability of microtubules to "search and capture" incoming virus particles. Cell Motil. Cytoskeleton 2007. © 2007 Wiley-Liss, Inc. [source]

MAP65 in tubulin/colchicine paracrystals of Vigna sinensis root cells: Possible role in the assembly and stabilization of atypical tubulin polymers,

CYTOSKELETON, Issue 3 2010
Emmanuel Panteris
Abstract Members of the MAP65 family, colocalizing with microtubule arrays, have been identified in Vigna sinensis root cells by Western blotting and immunofluorescence. MAP65 proteins were also found in tubulin/colchicine paracrystals, which were formed during colchicine treatment by both immunofluorescence and immunogold microscopy. During recovery from colchicine, MAP65 signal was depleted from disintegrating paracrystals appearing in the reinstating microtubule arrays. MAP65-free perinuclear tubulin/colchicine aggregates were observed in plasmolyzed colchicine-treated cells. Deplasmolysis of the above cells resulted in the formation of MAP65-decorated paracrystals. As confirmed by appropriate biochemical assays with the Phos-tag reagent, MAP65 proteins underwent phosphorylation during plasmolysis, which was reversible by deplasmolysis. According to the effect of the mitogen-activated protein kinase (MAPK) inhibitor UO126, the phosphorylation status of MAP65, as well as its presence in tubulin/colchicine polymers is probably controlled by MAPK-mediated phosphorylation. According to the above, it seems likely that apart from binding to microtubules, MAP65 proteins may act as "tubulin associated proteins" in a broader manner, promoting the polymerization and/or stabilization of atypical polymers such as tubulin/colchicine paracrystals. © 2010 Wiley-Liss, Inc. [source]

Microtubule-dependent organization of subcortical microfilaments in the early Drosophila embryo

DEVELOPMENTAL DYNAMICS, Issue 3 2007
Maria Giovanna Riparbelli
Abstract Dynamic alterations in the spatial organization of cytoskeletal elements constitute a prominent morphological feature of the early, syncytial stages of embryogenesis in Drosophila. Here, we describe and characterize the dynamic behavior of cytoplasmic, subcortical microfilaments, which form a series of nucleus-associated structures, at different phases of the simultaneous nuclear division cycles characteristic of early Drosophila embryos. Remodeling of the cytoplasmic microfilament arrays takes place in parallel to the established cyclic reorganization of cortical microfilament structures. We provide evidence that the cortical and subcortical microfilament populations organize independently of each other, and in response to distinct instructive cues. Specifically, formation of subcortical microfilament structures appears to rely on, and spatially mirror, the organization of polarized microtubule arrays, while cortical microfilament restructuring constitutes a centrosome-dependent process. Genetic analysis identifies a requirement for SCAR, a key mediator of Arp2/3-based microfilament dynamics, in organization of subcortical microfilament structures. Developmental Dynamics 236:662,670, 2007. © 2007 Wiley-Liss, Inc. [source]

Towards correlative imaging of plant cortical microtubule arrays: combining ultrastructure with real-time microtubule dynamics

JOURNAL OF MICROSCOPY, Issue 3 2009
D.A. BARTON
Summary There are a variety of microscope technologies available to image plant cortical microtubule arrays. These can be applied specifically to investigate direct questions relating to array function, ultrastructure or dynamics. Immunocytochemistry combined with confocal laser scanning microscopy provides low resolution "snapshots" of cortical microtubule arrays at the time of fixation whereas live cell imaging of fluorescent fusion proteins highlights the dynamic characteristics of the arrays. High-resolution scanning electron microscopy provides surface detail about the individual microtubules that form cortical microtubule arrays and can also resolve cellulose microfibrils that form the innermost layer of the cell wall. Transmission electron microscopy of the arrays in cross section can be used to examine links between microtubules and the plasma membrane and, combined with electron tomography, has the potential to provide a complete picture of how individual microtubules are spatially organized within the cortical cytoplasm. Combining these high-resolution imaging techniques with the expression of fluorescent cytoskeletal fusion proteins in live cells using correlative microscopy procedures will usher in an radical change in our understanding of the molecular dynamics that underpin the organization and function of the cytoskeleton. [source]

Microtubule arrays in fucoid zygotes are sensitive to cytoplasmic pH

Identification of a novel family of 70 kDa microtubule-associated proteins in Arabidopsis cells

THE PLANT JOURNAL, Issue 4 2005
Andrey V. Korolev
Summary Most plant microtubule-associated proteins (MAPs) have homologues across the phylogenetic spectrum. To find potential plant-specific MAPs that will have evaded bioinformatic searches we devised a low stringency method for isolating proteins from an Arabidopsis cell suspension on endogenous taxol-microtubules. By tryptic peptide mass fingerprinting we identified 55 proteins that were enriched on taxol-microtubules. Amongst a range of known MAPs, such as kinesins, MAP65 isoforms and MOR1, we detected ,unknown' 70 kDa proteins that belong to a family of five closely related Arabidopsis proteins having no known homologues amongst non-plant organisms. To verify that AtMAP70-1 associates with microtubules in vivo, it was expressed as a GFP fusion. This confirmed that the protein decorates all four microtubule arrays in both transiently infected Arabidopsis and stably transformed tobacco BY-2 suspension cells. Microtubule-directed drugs perturbed the localization of AtMAP70-1 but cytochalasin D did not. AtMAP70-1 contains four predicted coiled-coil domains and truncation studies identified a central domain that targets the fusion protein to microtubules in vivo. This study therefore introduces a novel family of plant-specific proteins that interact with microtubules. [source]

Interactions of tobacco microtubule-associated protein MAP65-1b with microtubules

THE PLANT JOURNAL, Issue 1 2004
Catherine Wicker-Planquart
Summary Tobacco microtubule associated protein (MAP65) (NtMAP65s) constitute a family of microtubule-associated proteins with apparent molecular weight around 65 kDa that collectively induce microtubule bundling and promote microtubule assembly in vitro. They are associated with most of the tobacco microtubule arrays in situ. Recently, three NtMAP65s belonging to the NtMAP65-1 subfamily have been cloned. Here we investigated in vitro the biochemical properties of one member of this family, the tobacco NtMAP65-1b. We demonstrated that recombinant NtMAP65-1b is a microtubule-binding and a microtubule-bundling protein. NtMAP65-1b has no effect on microtubule polymerization rate and binds microtubules with an estimated equilibrium constant of dissociation (Kd) of 0.57 µm. Binding of NtMAP65-1b to microtubules occurs through the carboxy-terminus of tubulin, as NtMAP65-1b was no longer able to bind subtilisin-digested tubulin. In vitro, NtMAP65-1b stabilizes microtubules against depolymerization induced by cold, but not against katanin-induced destabilization. The biological implications of these results are discussed. [source]