scholarly journals Microtubule assembly and kinetochore directional instability in vertebrate monopolar spindles: implications for the mechanism of chromosome congression

1994 ◽  
Vol 107 (1) ◽  
pp. 285-297 ◽  
Author(s):  
L. Cassimeris ◽  
C.L. Rieder ◽  
E.D. Salmon
Keyword(s):  
Constant Velocity ◽  
Metaphase Plate ◽  
Lung Epithelial Cells ◽  
Microtubule Assembly ◽  
Pole Motion ◽  
Chromosome Congression ◽  
Chromosome Position ◽  
Lung Epithelial ◽  
Sister Kinetochore ◽  
Bipolar Spindles

We have proposed previously a kinetochore motor-polar ejection model for chromosome congression to the metaphase plate where forces generated at the kinetochore are antagonized by away-from-the pole forces generated within each half-spindle on the chromosome arms. This model was based in large part on observations of the behavior of chromosomes on monopolar spindles. In these cells chromosomes typically become attached to the pole by only one kinetochore fiber. These mono-oriented chromosomes move to positions away from the pole even though they are pulled poleward at their kinetochores. Their arms are also ejected away from the pole when severed from the centromere. Here we have characterized further the properties of monopolar spindles in newt lung epithelial cells to determine the similarities between monopolar and bipolar spindles. We found no significant differences between monopolar and bipolar spindles over the parameters examined, which included: microtubule dynamics as measured by fluorescence redistribution after photobleaching; the ability of polar microtubule arrays to push chromosome arms away from the pole; the dependence of chromosome position relative to the pole on microtubule assembly; the number of kinetochore microtubules per kinetochore; and the directional instability of kinetochore motion during chromosome oscillations poleward and away-from-the-pole. As in bipolar spindles, kinetochore directional instability is characterized by abrupt switching between constant velocity phases of poleward and away-from-the-pole motion. From these data we conclude that the mechanism(s) responsible for chromosome positioning in monopolar spindles are fundamentally the same as those in bipolar spindles; only the geometry of the two spindle forms and the interplay between sister kinetochore directional instabilities are different. We also found no correlation in the kinetochore-to-pole distance with kinetochore microtubule number in monopolar spindles, but a strong qualitative correlation with microtubule density. This finding indicates that oscillations of mono-oriented chromosomes in both monopolar and bipolar spindles occur because chromosomes persist in poleward motion until they reach a density of polar microtubules sufficiently high to promote switching to away-from-the-pole motion. As the kinetochore and chromosome arms move away-from-the-pole, microtubule density decreases and the kinetochore switches to poleward motion, pulling the chromosome arms back into regions of higher microtubule density. The mechanism regulating kinetochore switching between poleward and away-from-the-pole motion is poorly understood, but may depend on tension at the kinetochore generated by pushing forces on the chromosome arms produced by the polar microtubule arrays.

scholarly journals Motile kinetochores and polar ejection forces dictate chromosome position on the vertebrate mitotic spindle

1994 ◽  
Vol 124 (3) ◽  
pp. 223-233 ◽  
Author(s):  
CL Rieder ◽  
ED Salmon
Keyword(s):  
Mitotic Spindle ◽  
Constant Velocity ◽  
Molecular Mechanisms ◽  
Dynamic Instability ◽  
Microtubule Dynamic ◽  
Pole Motion ◽  
Microtubule Motors ◽  
Chromosome Position ◽  
Pulling Forces

We argue that hypotheses for how chromosomes achieve a metaphase alignment, that are based solely on a tug-of-war between poleward pulling forces produced along the length of opposing kinetochore fibers, are no longer tenable for vertebrates. Instead, kinetochores move themselves and their attached chromosomes, poleward and away from the pole, on the ends of relatively stationary but shortening/elongating kinetochore fiber microtubules. Kinetochores are also "smart" in that they switch between persistent constant-velocity phases of poleward and away from the pole motion, both autonomously and in response to information within the spindle. Several molecular mechanisms may contribute to this directional instability including kinetochore-associated microtubule motors and kinetochore microtubule dynamic instability. The control of kinetochore directional instability, to allow for congression and anaphase, is likely mediated by a vectorial mechanism whose magnitude and orientation depend on the density and orientation or growth of polar microtubules. Polar microtubule arrays have been shown to resist chromosome poleward motion and to push chromosomes away from the pole. These "polar ejection forces" appear to play a key role in regulating kinetochore directional instability, and hence, positions achieved by chromosomes on the spindle.

scholarly journals On the mechanism of anaphase A: evidence that ATP is needed for microtubule disassembly and not generation of polewards force.

1987 ◽  
Vol 105 (4) ◽  
pp. 1691-1705 ◽  
Author(s):  
T P Spurck ◽  
J D Pickett-Heaps
Keyword(s):  
Epithelial Cells ◽  
Cold Treatment ◽  
Metaphase Plate ◽  
Lung Epithelial Cells ◽  
Chromosome Movement ◽  
High Calcium ◽  
Lung Epithelial ◽  
Nucleotide Triphosphates ◽  
Gamma S ◽  
Initial Movement

As anaphase began, mitotic PtK1 and newt lung epithelial cells were permeabilized with digitonin in permeabilization medium (PM). Permeabilization stopped cytoplasmic activity, chromosome movement, and cytokinesis within about 3 min, presumably due to the loss of endogenous ATP. ATP, GTP, or ATP-gamma-S added in the PM 4-7 min later restarted anaphase A while kinetochore fibers shortened. AMPPNP could not restart anaphase A; ATP was ineffective if the spindle was stabilized in PM + DMSO. Cells permeabilized in PM + taxol varied in their response to ATP depending on the stage of anaphase reached: one mid-anaphase cell showed initial movement of chromosomes back to the metaphase plate upon permeabilization but later, anaphase A resumed when ATP was added. Anaphase A was also reactivated by cold PM (approximately 16 degrees C) or PM containing calcium (1-10 mM). Staining of fixed cells with antitubulin showed that microtubules (MTs) were relatively stable after permeabilization and MT assembly was usually promoted in asters. Astral and kinetochore MTs were sensitive to MT disassembly conditions, and shortening of kinetochore MTs always accompanied reactivation of anaphase A. Interphase and interzonal spindle MTs were relatively stable to cold and calcium until extraction of cells was promoted by longer periods in the PM, or by higher concentrations of detergent. Since we cannot envisage how both cold treatment or relatively high calcium levels can reactivate spindle motility in quiescent, permeabilized, and presumably energy-depleted cells, we conclude that anaphase A is powered by energy stored in the spindle. The nucleotide triphosphates effective in reactivating anaphase A could be necessary for the kinetochore MT disassembly without which anaphase movement cannot proceed.

scholarly journals Kinetochore motility after severing between sister centromeres using laser microsurgery: evidence that kinetochore directional instability and position is regulated by tension

1995 ◽  
Vol 108 (7) ◽  
pp. 2537-2548 ◽  
Author(s):  
R.V. Skibbens ◽  
C.L. Rieder ◽  
E.D. Salmon
Keyword(s):  
Laser Ablation ◽  
Constant Velocity ◽  
Somatic Cells ◽  
Metaphase Plate ◽  
Fundamental Property ◽  
The Other ◽  
Centromeric Chromatin ◽  
Laser Microbeam ◽  
Differential Movement ◽  
Sister Kinetochore

During mitosis in vertebrate somatic cells, the single attached kinetochore on a mono-oriented chromosome exhibits directional instability: abruptly and independently switching between constant velocity poleward and away from the pole motility states. When the non-attached sister becomes attached to the spindle (chromosome bi-orientation), the motility of the sister kinetochores becomes highly coordinated, one moving poleward while the other moves away from the pole, allowing chromosomes to congress to the spindle equator. In our kinetochore-tensiometer model, we hypothesized that this coordinated behavior is regulated by tension across the centromere produced by kinetochore movement relative to the sister kinetochore and bulk of the chromosome arms. To test this model, we severed or severely weakened the centromeric chromatin between sister kinetochores on bi-oriented newt lung cell chromosomes with a laser microbeam. This procedure converted a pair of tightly linked sister kinetochores into two mono-oriented single kinetochore-chromatin fragments that were tethered to their chromosome arms by thin compliant chromatin strands. These single kinetochore-chromatin fragments moved substantial distances off the metaphase plate, stretching their chromatin strands, before the durations of poleward and away from the pole movement again became similar. In contrast, the severed arms remained at or moved closer to the spindle equator. The poleward and away from the pole velocities of single kinetochore-chromatin fragments in prometaphase were typical of velocities exhibited by sister kinetochores on intact chromosomes from prometaphase through midanaphase A. However, severing the chromatin between sister kinetochores uncoupled the normally coordinated motility of sister kinetochores. Laser ablation also uncoupled the motilities of the single kinetochore fragments from the bulk of the arms. These results reveal that kinetochore directional instability is a fundamental property of the kinetochore and that the motilities of sister kinetochores are coordinated during congression by a stiff centromere linkage. We conclude that kinetochores act as tensiometers that sense centromere tension generated by differential movement of sister kinetochores and their chromosome arms to control switching between constant velocity P and AP motility states.

scholarly journals MAST/Orbit has a role in microtubule–kinetochore attachment and is essential for chromosome alignment and maintenance of spindle bipolarity

2002 ◽  
Vol 157 (5) ◽  
pp. 749-760 ◽  
Author(s):  
Helder Maiato ◽  
Paula Sampaio ◽  
Catarina L. Lemos ◽  
John Findlay ◽  
Mar Carmena ◽  
...  
Keyword(s):  
Metaphase Plate ◽  
Microtubule Associated Proteins ◽  
New Family ◽  
Chromosome Congression ◽  
Chromosome Alignment ◽  
Associated Proteins ◽  
In Vivo Analysis ◽  
Bipolar Spindles ◽  
Functional Kinetochore

Multiple asters (MAST)/Orbit is a member of a new family of nonmotor microtubule-associated proteins that has been previously shown to be required for the organization of the mitotic spindle. Here we provide evidence that MAST/Orbit is required for functional kinetochore attachment, chromosome congression, and the maintenance of spindle bipolarity. In vivo analysis of Drosophila mast mutant embryos undergoing early mitotic divisions revealed that chromosomes are unable to reach a stable metaphase alignment and that bipolar spindles collapse as centrosomes move progressively closer toward the cell center and eventually organize into a monopolar configuration. Similarly, soon after depletion of MAST/Orbit in Drosophila S2 cells by double-stranded RNA interference, cells are unable to form a metaphase plate and instead assemble monopolar spindles with chromosomes localized close to the center of the aster. In these cells, kinetochores either fail to achieve end-on attachment or are associated with short microtubules. Remarkably, when microtubule dynamics is suppressed in MAST-depleted cells, chromosomes localize at the periphery of the monopolar aster associated with the plus ends of well-defined microtubule bundles. Furthermore, in these cells, dynein and ZW10 accumulate at kinetochores and fail to transfer to microtubules. However, loss of MAST/Orbit does not affect the kinetochore localization of D-CLIP-190. Together, these results strongly support the conclusion that MAST/Orbit is required for microtubules to form functional attachments to kinetochores and to maintain spindle bipolarity.

scholarly journals Analysis of the treadmilling model during metaphase of mitosis using fluorescence redistribution after photobleaching.

1986 ◽  
Vol 102 (3) ◽  
pp. 1032-1038 ◽  
Author(s):  
P Wadsworth ◽  
E D Salmon
Keyword(s):  
Lung Epithelial Cells ◽  
Microtubule Assembly ◽  
Fluorescence Recovery ◽  
Laser Microbeam ◽  
Culture Cells ◽  
First Order Kinetics ◽  
Lung Epithelial ◽  
Fluorescent Analog Cytochemistry ◽  
Micron Diameter ◽  
Rate Of Recovery

One recent hypothesis for the mechanism of chromosome movement during mitosis predicts that a continual, uniform, poleward flow or "treadmilling" of microtubules occurs within the half-spindle between the chromosomes and the poles during mitosis (Margolis, R. L., and L. Wilson, 1981, Nature (Lond.), 293:705-711). We have tested this treadmilling hypothesis using fluorescent analog cytochemistry and measurements of fluorescence redistribution after photobleaching to examine microtubule behavior during metaphase of mitosis. Mitotic BSC 1 mammalian tissue culture cells or newt lung epithelial cells were microinjected with brain tubulin labeled with 5-(4,6-dichlorotriazin-2-yl) amino fluorescein (DTAF) to provide a fluorescent tracer of the endogenous tubulin pool. Using a laser microbeam, fluorescence in the half-spindle was photobleached in either a narrow 1.6 micron wide bar pattern across the half-spingle or in a circular area of 2.8 or 4.5 micron diameter. Fluorescence recovery in the spindle fibers, measured using video microscopy or photometric techniques, occurs as bleached DTAF-tubulin subunits within the microtubules are exchanged for unbleached DTAF-tubulin in the cytosol by steady-state microtubule assembly-disassembly pathways. Recovery of 75% of the bleached fluorescence follows first-order kinetics and has an average half-time of 37 sec, at 31-33 degrees C. No translocation of the bleached bar region could be detected during fluorescence recovery, and the rate of recovery was independent of the size of the bleached spot. These results reveal that, for 75% of the half-spindle microtubules, FRAP does not occur by a synchronous treadmilling mechanism.

Legionella pneumophila induced microRNA expression in human lung epithelial cells

Pneumologie ◽  
2010 ◽  
Vol 64 (S 03) ◽  
Author(s):  
B Schmeck ◽  
B Dolniak ◽  
I Pollock ◽  
C Schulz ◽  
W Bertrams ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Legionella Pneumophila ◽  
Human Lung ◽  
Microrna Expression ◽  
Lung Epithelial Cells ◽  
Lung Epithelial ◽  
Human Lung Epithelial Cells

Microscopy study on the interaction of silica nanoparticles with lung epithelial cells

Pneumologie ◽  
2013 ◽  
Vol 67 (12) ◽  
Author(s):  
H Peuschel ◽  
T Ruckelshausen ◽  
C Cavelius ◽  
A Kraegeloh
Keyword(s):  
Epithelial Cells ◽  
Silica Nanoparticles ◽  
Microscopy Study ◽  
Lung Epithelial Cells ◽  
Lung Epithelial
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