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Elasticity and structure of eukaryote chromosomes studied by micromanipulation and micropipette aspiration.

Houchmandzadeh B, Marko JF, Chatenay D, Libchaber A - J. Cell Biol. (1997)

Bottom Line: Larger deformations of 10 to 100 times irreversibly and progressively transform the chromosomes into a "thin filament," parts of which display a helical organization.Chromosomes break for elongations of the order of 100 times, at which time the applied force is around 100 nanonewtons.Knowing the Young modulus allows us to estimate that the force exerted by the spindle on a newt chromosome at anaphase is roughly one nanonewton.

View Article: PubMed Central - PubMed

Affiliation: Centre National de la Recherche Scientifique (CNRS), Laboratoire de Spectrométrie Physique, Saint-Martin-d'Hères, France. bahram@coucou.ujf-grenoble.fr

ABSTRACT
The structure of mitotic chromosomes in cultured newt lung cells was investigated by a quantitative study of their deformability, using micropipettes. Metaphase chromosomes are highly extensible objects that return to their native shape after being stretched up to 10 times their normal length. Larger deformations of 10 to 100 times irreversibly and progressively transform the chromosomes into a "thin filament," parts of which display a helical organization. Chromosomes break for elongations of the order of 100 times, at which time the applied force is around 100 nanonewtons. We have also observed that as mitosis proceeds from nuclear envelope breakdown to metaphase, the native chromosomes progressively become more flexible. (The elastic Young modulus drops from 5,000 +/- 1,000 to 1,000 +/- 200 Pa.) These observations and measurements are in agreement with a helix-hierarchy model of chromosome structure. Knowing the Young modulus allows us to estimate that the force exerted by the spindle on a newt chromosome at anaphase is roughly one nanonewton.

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The state of the chromosome after different cycles of deformation– release, when the pipette is brought back  near the cell. (a) ε = 10, similar to Fig. 1 e;  (b) ε = 15; (c) ε = 20; and (d) ε = 55. During the last cycle (bottom), the chromosome broke and was released from the pipette. The shape observed is stable over at  least 1 h. Bar, 10 μm.
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Figure 2: The state of the chromosome after different cycles of deformation– release, when the pipette is brought back near the cell. (a) ε = 10, similar to Fig. 1 e; (b) ε = 15; (c) ε = 20; and (d) ε = 55. During the last cycle (bottom), the chromosome broke and was released from the pipette. The shape observed is stable over at least 1 h. Bar, 10 μm.

Mentions: For ε < 10, the chromosome is highly elastic, relaxing to its initial “native” length and appearance (Fig. 2 a). Such a large range of elasticity is rare (most materials are elastic only for ε < 0.01) but is characteristic of polymer gels (Horkay et al., 1989) or of extensible elastic objects, such as a helical spring (Love, 1944). The elastic Poisson coefficient can be evaluated directly from the images (the diameter of the chromosome decreases as ε increases) giving 0.20 ± 0.05. This regime of perfect elasticity indicates that there is a well-defined elastic modulus for a chromosome.


Elasticity and structure of eukaryote chromosomes studied by micromanipulation and micropipette aspiration.

Houchmandzadeh B, Marko JF, Chatenay D, Libchaber A - J. Cell Biol. (1997)

The state of the chromosome after different cycles of deformation– release, when the pipette is brought back  near the cell. (a) ε = 10, similar to Fig. 1 e;  (b) ε = 15; (c) ε = 20; and (d) ε = 55. During the last cycle (bottom), the chromosome broke and was released from the pipette. The shape observed is stable over at  least 1 h. Bar, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2139812&req=5

Figure 2: The state of the chromosome after different cycles of deformation– release, when the pipette is brought back near the cell. (a) ε = 10, similar to Fig. 1 e; (b) ε = 15; (c) ε = 20; and (d) ε = 55. During the last cycle (bottom), the chromosome broke and was released from the pipette. The shape observed is stable over at least 1 h. Bar, 10 μm.
Mentions: For ε < 10, the chromosome is highly elastic, relaxing to its initial “native” length and appearance (Fig. 2 a). Such a large range of elasticity is rare (most materials are elastic only for ε < 0.01) but is characteristic of polymer gels (Horkay et al., 1989) or of extensible elastic objects, such as a helical spring (Love, 1944). The elastic Poisson coefficient can be evaluated directly from the images (the diameter of the chromosome decreases as ε increases) giving 0.20 ± 0.05. This regime of perfect elasticity indicates that there is a well-defined elastic modulus for a chromosome.

Bottom Line: Larger deformations of 10 to 100 times irreversibly and progressively transform the chromosomes into a "thin filament," parts of which display a helical organization.Chromosomes break for elongations of the order of 100 times, at which time the applied force is around 100 nanonewtons.Knowing the Young modulus allows us to estimate that the force exerted by the spindle on a newt chromosome at anaphase is roughly one nanonewton.

View Article: PubMed Central - PubMed

Affiliation: Centre National de la Recherche Scientifique (CNRS), Laboratoire de Spectrométrie Physique, Saint-Martin-d'Hères, France. bahram@coucou.ujf-grenoble.fr

ABSTRACT
The structure of mitotic chromosomes in cultured newt lung cells was investigated by a quantitative study of their deformability, using micropipettes. Metaphase chromosomes are highly extensible objects that return to their native shape after being stretched up to 10 times their normal length. Larger deformations of 10 to 100 times irreversibly and progressively transform the chromosomes into a "thin filament," parts of which display a helical organization. Chromosomes break for elongations of the order of 100 times, at which time the applied force is around 100 nanonewtons. We have also observed that as mitosis proceeds from nuclear envelope breakdown to metaphase, the native chromosomes progressively become more flexible. (The elastic Young modulus drops from 5,000 +/- 1,000 to 1,000 +/- 200 Pa.) These observations and measurements are in agreement with a helix-hierarchy model of chromosome structure. Knowing the Young modulus allows us to estimate that the force exerted by the spindle on a newt chromosome at anaphase is roughly one nanonewton.

Show MeSH