scholarly journals Location of actin, myosin, and microtubular structures during directed locomotion of Dictyostelium amebae.

1984 ◽  
Vol 98 (2) ◽  
pp. 382-390 ◽  
Author(s):  
S Rubino ◽  
M Fighetti ◽  
E Unger ◽  
P Cappuccinelli
Keyword(s):  
Immunofluorescence Microscopy ◽  
The Other ◽  
Microtubule Organizing Center ◽  
Fixed Position ◽  
Microtubule Network ◽  
Cellular Slime Mould ◽  
Organizing Center ◽  
Cellular Slime ◽  
Microtubular Structures

During their life cycle, amebae of the cellular slime mould Dictyostelium discoideum aggregate to form multicellular structures in which differentiation takes place. Aggregation depends upon the release of chemotactic signals of 3',5'-cAMP from aggregation centers. In response to the signals, aggregating amebae elongate, actively more toward the attractive source, and may be easily identified from the other cells because of their polarized appearance. To examine the role of cytoskeletal components during ameboid locomotion, immunofluorescence microscopy with antibodies to actin, myosin, and to a microtubule-associated component was used. In addition, rhodamine-labeled phallotoxin was employed. Actin and myosin display a rather uniform distribution in rounded unstretched cells. In polarized locomoting cells, actin fluorescence (due to both labeled phallotoxin and specific antibody) is prevalently concentrated in the anterior pseudopod while myosin fluorescence appears to be excluded from the pseudopod. Similarly, microtubules in locomoting cells are excluded from the leading pseudopod. The cell nucleus is attached to the microtubule network by way of a nucleus-associated organelle serving as a microtubule-organizing center and seems to be maintained in a rather fixed position by the microtubules. These findings, together with available morphological and biochemical evidences, are consistent with a mechanism in which polymerized actin is moved into the pseudopod through its interaction with myosin at the base of the pseudopod. Microtubules, apparently, do not actively participate in movement but seem to behave as anchorage structures for the nucleus and possibly other cytoplasmic organelles.

The role of phosphodiesterase in aggregation of Dictyostelium discoideum

1978 ◽  
Vol 31 (1) ◽  
pp. 233-243
Author(s):  
M. Darmon ◽  
J. Barra ◽  
P. Brachet
Keyword(s):  
Dictyostelium Discoideum ◽  
Direct Contact ◽  
Signal To Noise Ratio ◽  
Signal To Noise ◽  
Extracellular Medium ◽  
Camp Phosphodiesterase ◽  
Cellular Slime Mould ◽  
Cellular Slime ◽  
Mutant Cells

The role of cAMP phosphodiesterase in the cAMP-mediated aggregation of the cellular slime mould Dictyostelium discoideum was investigated with a morphogenetic mutant defective in phosphodiesterase production. Mutant cells become capable of aggregating normally when incubated in the presence of exogenous phosphodiesterase isolated from Idictyostelium or rat brain. Direct contact between enzyme and the cell membrane is not required for this phenotypic suppression. The aggregateless character of this strain presumably results from an over-accumulation of cAMP in the extracellular medium since aggregation can be induced in the absence of added phosphodiesterase under conditions facilitating diffusion of the nucleotide. This suggests that phosphodiesterase is not involved in the generation or recognition of cAMP signals, but that the enzyme is essential in the control of the cAMP signal-to-noise ratio.

Variable pathways for developmental changes in composition and organization of microtubules in Physarum polycephalum

1990 ◽  
Vol 96 (3) ◽  
pp. 383-393
Author(s):  
L. Solnica-Krezel ◽  
M. Diggins-Gilicinski ◽  
T.G. Burland ◽  
W.F. Dove
Keyword(s):  
Physarum Polycephalum ◽  
Microtubule Organizing Center ◽  
Developmentally Regulated ◽  
Tubulin Isotypes ◽  
Cellular Events ◽  
Organizing Center ◽  
Cytoplasmic Microtubules ◽  
Beta 2 ◽  
Rare Cells ◽  
Microtubular Structures

The development of uninucleate amoebae into multinucleate plasmodia in myxomycetes is called the amoebal-plasmodial transition (APT). During the APT in Physarum polycephalum the ability to form flagellar axonemes is lost; the astral, open mitosis is replaced by the anastral, closed mitosis; and cytoskeletal microtubules disappear. These changes are accompanied by alterations in the repertoire of expressed tubulins. Using immunofluorescence microscopy we have studied the timing of loss and accumulation of developmentally regulated tubulin isotypes in relation to other cellular events during the APT. We specifically asked whether changes in the composition of microtubules are correlated with changes in their organization. The plasmodium-specific beta 2-tubulin can first be detected in microtubules of uninucleate cells after they become committed to plasmodium formation. However, rare cells are observed that exhibit beta 2-tubulin at earlier or only at later stages of development. Amoeba-specific acetylated alpha 3-tubulin disappears gradually during development. Individual cells differ in the timing of loss of this isotype: alpha 3-tubulin is present in the majority of uninucleate cells, in a fraction of binucleate and quadrinucleate cells, and is absent from larger multinucleate cells. Cytoplasmic microtubules in uninucleate cells are organized by a single microtubule-organizing center (MTOC) juxtaposed to the nucleus. Binucleate cells and quadrinucleate cells exhibit variable numbers of MTOCs. Cytoplasmic microtubules persist during the APT until the stage of plasmodia containing at least 100 nuclei. The lack of a strict correlation between the changes in tubulin composition and changes in organization of microtubular structures indicates that accumulation of beta 2-tubulin and disappearance of alpha 3-tubulin isotypes are not sufficient to bring about reorganization of microtubules during development. Individual cells in a developing population differ not only in the succession of accumulation and loss of developmentally regulated tubulins, but also in the sequences of other cellular changes occurring during the APT.

In vitro nucleation of microtubules from microtubule-organizing center prepared from cellular slime mold

Cell Motility ◽  
1982 ◽  
Vol 2 (3) ◽  
pp. 257-272 ◽  
Author(s):  
Ryoko Kuriyama ◽  
Chikako Sato ◽  
Yoshio Fukui ◽  
Soryu Nishibayashi
Keyword(s):  
Slime Mold ◽  
Cellular Slime Mold ◽  
Microtubule Organizing Center ◽  
Organizing Center ◽  
Cellular Slime

scholarly journals The role of the ameiotic1 gene in the initiation of meiosis and in subsequent meiotic events in maize.

Genetics ◽  
1993 ◽  
Vol 135 (4) ◽  
pp. 1151-1166 ◽  
Author(s):  
I Golubovskaya ◽  
Z K Grebennikova ◽  
N A Avalkina ◽  
W F Sheridan
Keyword(s):  
Meiotic Division ◽  
Higher Plants ◽  
Gene Interaction ◽  
Microtubule Organizing Center ◽  
Spindle Fiber ◽  
Chromosome Synapsis ◽  
Organizing Center ◽  
Relationship Of ◽  
The Relationship

Abstract Understanding the initiation of meiosis and the relationship of this event with other key cytogenetic processes are major goals in studying the genetic control of meiosis in higher plants. Our genetic and structural analysis of two mutant alleles of the ameiotic1 gene (am1 and am1-praI) suggest that this locus plays an essential role in the initiation of meiosis in maize. The product of the ameiotic1 gene affects an earlier stage in the meiotic sequence than any other known gene in maize and is important for the irreversible commitment of cells to meiosis and for crucial events marking the passage from premeiotic interphase into prophase I including chromosome synapsis. It appears that the period of ameiotic1 gene function in meiosis at a minimum covers the interval from some point during premeiotic interphase until the early zygotene stage of meiosis. To study the interaction of genes in the progression of meiosis, several double meiotic mutants were constructed. In these double mutants (i) the ameiotic1 mutant allele was brought together with the meiotic mutation (afd1) responsible for the fixation of centromeres in meiosis; and with the mutant alleles of the three meiotic genes that control homologous chromosome segregation (dv1, ms43 and ms28), which impair microtubule organizing center organization, the orientation of the spindle fiber apparatus, and the depolymerization of spindle filaments after the first meiotic division, respectively; (ii) the afd1 mutation was combined with two mutations (dsy1 and as1) affecting homologous pairing; (iii) the ms43 mutation was combined with the as1, the ms28 and the dv1 mutations; and (iv) the ms28 mutation was combined with the dv1 mutation and the ms4 (polymitotic1) mutations. An analysis of gene interaction in the double mutants led us to conclude that the ameiotic1 gene is epistatic over the afd1, the dv1, the ms43 and the ms28 genes but the significance of this relationship requires further analysis. The afd gene appears to function from premeiotic interphase throughout the first meiotic division, but it is likely that its function begins after the start of the ameiotic1 gene expression. The afd1 gene is epistatic over the two synaptic mutations dsy1 and as1 and also over the dv1 mutation. The new ameiotic*-485 and leptotene arrest*-487 mutations isolated from an active Robertson's Mutator stocks take part in the control of the initiation of meiosis.

scholarly journals Centriole and Golgi microtubule nucleation are dispensable for the migration of human neutrophil-like cells

2021 ◽  
pp. mbc.E21-02-0060
Author(s):  
Lucas C. Klemm ◽  
Ryan A. Denu ◽  
Laurel E. Hind ◽  
Briana L. Rocha-Gregg ◽  
Mark E. Burkard ◽  
...  
Keyword(s):  
Cell Line ◽  
Host Defense ◽  
Human Neutrophil ◽  
Microtubule Organizing Center ◽  
Microtubule Nucleation ◽  
Directed Migration ◽  
Inhibitory Role ◽  
Organizing Center ◽  
Cytoskeletal Rearrangements

Neutrophils migrate in response to chemoattractants to mediate host defense. Chemoattractants drive rapid intracellular cytoskeletal rearrangements including the radiation of microtubules from the microtubule-organizing center (MTOC) towards the rear of polarized neutrophils. Microtubules regulate neutrophil polarity and motility, but little is known about the specific role of MTOCs. To characterize the role of MTOCs on neutrophil motility we depleted centrioles in a well-established neutrophil-like cell line. Surprisingly, both chemical and genetic centriole depletion increased neutrophil speed and chemotactic motility, suggesting an inhibitory role for centrioles during directed migration. We also found that depletion of both centrioles and GM130-mediated Golgi microtubule nucleation did not impair neutrophil directed migration. Taken together, our findings demonstrate an inhibitory role for centrioles and a resilient MTOC system in motile human neutrophil-like cells. [Media: see text] [Media: see text] [Media: see text]

The Role of the Centrosome in Development and Progression of Breast Cancer

2001 ◽  
Vol 7 (S2) ◽  
pp. 582-583
Author(s):  
W. Lingle ◽  
J. Salisbury ◽  
S. Barrett ◽  
V. Negron ◽  
C. Whitehead
Keyword(s):  
Mitotic Spindle ◽  
Mammalian Cells ◽  
Microtubule Organizing Center ◽  
Daughter Cells ◽  
Spindle Poles ◽  
Sister Chromatids ◽  
Close Proximity ◽  
Interphase Cells ◽  
Organizing Center

The centrosome is the major microtubule organizing center in most mammalian cells, and as such it determines the number, polarity, and spatial distribution of microtubules (MTs). Interphase MTs, together with actin and intermediate filaments, constitute the cell's cytoskeleton, which dynamically maintains cell polarity and tissue architecture. Interphase cells begin Gl of the cell cycle with one centrosome. During S phase, the centrosome duplicates concomitantly with DNA replication. Duplicated centrosomes usually remain in close proximity to one another until late G2, at which time they separate and then move during prophase to become the poles that organize the bipolar mitotic spindle. During the G2/M transition, interphase MTs depolymerize and a new population of highly dynamic mitotic MTs are nucleated at the spindle poles. The bipolar mitotic spindle apparatus constitutes the machinery that partitions and separates sister chromatids equally between two daughter cells.

scholarly journals A Note on the Role of Mean Flows in Doppler-Shifted Frequencies

2013 ◽  
Vol 43 (2) ◽  
pp. 432-441 ◽  
Author(s):  
Theo Gerkema ◽  
Leo R. M. Maas ◽  
Hans van Haren
Keyword(s):  
Doppler Shift ◽  
Wave Dispersion ◽  
The Other ◽  
Mean Flow ◽  
Fixed Position ◽  
Doppler Shifts ◽  
The Mean ◽  
The Difference ◽  
The One

Abstract The purpose of this paper is to resolve a confusion that may arise from two quite distinct definitions of “Doppler shifts”: both are used in the oceanographic literature but they are sometimes conflated. One refers to the difference in frequencies measured by two observers, one at a fixed position and one moving with the mean flow—here referred to as “quasi-Doppler shifts.” The other definition is the one used in physics, where the frequency measured by an observer is compared to that of the source. In the latter sense, Doppler shifts occur only if the source and observer move with respect to each other; a steady mean flow alone cannot create a Doppler shift. This paper rehashes the classical theory to straighten out some misconceptions. It is also discussed how wave dispersion affects the classical relations and their application.

scholarly journals Visualization of the intracellular behavior of HIV in living cells

2002 ◽  
Vol 159 (3) ◽  
pp. 441-452 ◽  
Author(s):  
David McDonald ◽  
Marie A. Vodicka ◽  
Ginger Lucero ◽  
Tatyana M. Svitkina ◽  
Gary G. Borisy ◽  
...  
Keyword(s):  
Life Cycle ◽  
Cytoplasmic Dynein ◽  
Living Cells ◽  
Microtubule Organizing Center ◽  
Microtubule Network ◽  
Organizing Center ◽  
Infected Cells ◽  
Resolution Imaging ◽  
Transcription Complexes ◽  
Hiv 1

To track the behavior of human immunodeficiency virus (HIV)-1 in the cytoplasm of infected cells, we have tagged virions by incorporation of HIV Vpr fused to the GFP. Observation of the GFP-labeled particles in living cells revealed that they moved in curvilinear paths in the cytoplasm and accumulated in the perinuclear region, often near the microtubule-organizing center. Further studies show that HIV uses cytoplasmic dynein and the microtubule network to migrate toward the nucleus. By combining GFP fused to the NH2 terminus of HIV-1 Vpr tagging with other labeling techniques, it was possible to determine the state of progression of individual particles through the viral life cycle. Correlation of immunofluorescent and electron micrographs allowed high resolution imaging of microtubule-associated structures that are proposed to be reverse transcription complexes. Based on these observations, we propose that HIV uses dynein and the microtubule network to facilitate the delivery of the viral genome to the nucleus of the cell during early postentry steps of the HIV life cycle.

scholarly journals Inflammasome activation in neutrophils of patients with severe COVID-19

2022 ◽  
Author(s):  
Karen Aymonnier ◽  
Julie Ng ◽  
Laura E Fredenburgh ◽  
Katherin Zambrano-Vera ◽  
Patrick Münzer ◽  
...  
Keyword(s):  
Time Lapse ◽  
Sterile Inflammation ◽  
Inflammasome Activation ◽  
Microtubule Organizing Center ◽  
Reporter Mice ◽  
Organizing Center ◽  
Monocytes And Macrophages ◽  
Histone Citrullination ◽  
Net Release

Infection by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) engages the inflammasome in monocytes and macrophages and leads to the cytokine storm in COVID-19. Neutrophils, the most abundant leukocytes, release neutrophil extracellular traps (NETs), which have been implicated in the pathogenesis of COVID-19. Our recent study shows that activation of the NLRP3 inflammasome is important for NET release in sterile inflammation. However, the role of neutrophil inflammasome formation in human disease is unknown. We hypothesized that SARS-COV-2 infection may induce inflammasome activation in neutrophils. We also aimed to assess the localization of inflammasome formation, (i.e. ASC speck assembly), and timing relative to NETosis in stimulated neutrophils by real time video microscopy. Neutrophils isolated from severe COVID-19 patients demonstrated that approximately 2% of neutrophils in both the peripheral blood and tracheal aspirates presented ASC speck. ASC speck was observed in neutrophils with an intact poly-lobulated nucleus, suggesting early formation during neutrophil activation. Additionally, 40% of nuclei were positive for citrullinated histone H3, and there was a significant correlation between speck formation and nuclear histone citrullination. Time-lapse microscopy in LPS-stimulated neutrophils from fluorescent ASC reporter mice showed that ASC speck formed transiently and at the microtubule organizing center, long before NET release. Our study shows that ASC speck is present in neutrophils from COVID-19 patients with respiratory failure and that it forms early in NETosis. Our findings suggest that inhibition of neutrophil inflammasomes may be beneficial in COVID-19.

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