Chromosome Oscillations Research Articles

Molecular fluctuation in living cells

The concept of molecular fluctuation in living cells is introduced. Many apparently different experimental facts in living cells, including the velocity non-uniformity of organelle movement, the saltatory movement of transport vesicles in axoplasmic transport, the chromosome oscillation during metaphase in mitosis and the pauses in the chromosome movement during anaphase are explained using a unified viewpoint. A method of determination of average number of the attached motor protein molecules from the experimental data is also proposed.

Dynamic elastic behavior of alpha-satellite DNA domains visualized in situ in living human cells.

We have constructed a fluorescent alpha-satellite DNA-binding protein to explore the motile and mechanical properties of human centromeres. A fusion protein consisting of human CENP-B coupled to the green fluorescent protein (GFP) of A. victoria specifically targets to centromeres when expressed in human cells. Morphometric analysis revealed that the alpha-satellite DNA domain bound by CENPB-GFP becomes elongated in mitosis in a microtubule-dependent fashion. Time lapse confocal microscopy in live mitotic cells revealed apparent elastic deformations of the central domain of the centromere that occurred during metaphase chromosome oscillations. These observations demonstrate that the interior region of the centromere behaves as an elastic element that could play a role in the mechanoregulatory mechanisms recently identified at centromeres. Fluorescent labeling of centromeres revealed that they disperse throughout the nucleus in a nearly isometric expansion during chromosome decondensation in telophase and early G1. During interphase, centromeres were primarily stationary, although motility of individual or small groups of centromeres was occasionally observed at very slow rates of 7-10 microns/h.

The effects of diazepam on mitosis and the microtubule cytoskeleton II. Observations on newt epithelial and PtK1 cells

The effects of diazepam (DZP) on mitosis and the microtubule (MT) cytoskeleton were examined using live and fixed PtK1 and newt (Taricha granulosa) epithelial lung cells. DZP treatment caused rapid shortening of spindle MTs at prometaphase and metaphase, inducing movement of the poles together while chromosome oscillations continued. DZP treatment slowed the rate of anaphase A but did not detectably affect anaphase B, cell cleavage or interphase cells. Our results suggest that DZP inhibits mitosis by affecting prometaphase and metaphase MTs. Its action is not equivalent to that of common anti-MT drugs, since only a small subpopulation of MTs are significantly susceptible. Likewise, its effects are not equivalent to those generated by metabolic inhibitors. The related benzodiazepines, medazepam and oxazepam, induce effects equivalent to those of DZP.

Discussion on the Chromosome Oscillation During Metaphase

The chromosome oscillation during metaphase is explained as the result of fluctuation of forces exerted on the chromosome. In this letter a simple model for chromosome oscillation is proposed and the formulas of force fluctuation and the root mean square displacement of the chromosome in the oscillation are derived.

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

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.