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Direct observation of microtubule dynamics at kinetochores in Xenopus extract spindles: implications for spindle mechanics.

Maddox P, Straight A, Coughlin P, Mitchison TJ, Salmon ED - J. Cell Biol. (2003)

Bottom Line: At anaphase onset, kinetochores switched to depolymerization of microtubule plus ends, resulting in chromosome-to-pole rates transiently greater than flux.Kinetochores switched from persistent depolymerization to persistent polymerization and back again during anaphase, bistability exhibited by kinetochores in vertebrate tissue cells.These results provide the most complete description of spindle microtubule poleward flux to date, with important implications for the microtubule-kinetochore interface and for how flux regulates kinetochore function.

View Article: PubMed Central - PubMed

Affiliation: Cell Division Group, Marine Biological Laboratory, Woods Hole, MA 02543, USA.

ABSTRACT
Microtubule plus ends dynamically attach to kinetochores on mitotic chromosomes. We directly imaged this dynamic interface using high resolution fluorescent speckle microscopy and direct labeling of kinetochores in Xenopus extract spindles. During metaphase, kinetochores were stationary and under tension while plus end polymerization and poleward microtubule flux (flux) occurred at velocities varying from 1.5-2.5 micro m/min. Because kinetochore microtubules polymerize at metaphase kinetochores, the primary source of kinetochore tension must be the spindle forces that produce flux and not a kinetochore-based mechanism. We infer that the kinetochore resists translocation of kinetochore microtubules through their attachment sites, and that the polymerization state of the kinetochore acts a "slip-clutch" mechanism that prevents detachment at high tension. At anaphase onset, kinetochores switched to depolymerization of microtubule plus ends, resulting in chromosome-to-pole rates transiently greater than flux. Kinetochores switched from persistent depolymerization to persistent polymerization and back again during anaphase, bistability exhibited by kinetochores in vertebrate tissue cells. These results provide the most complete description of spindle microtubule poleward flux to date, with important implications for the microtubule-kinetochore interface and for how flux regulates kinetochore function.

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Related in: MedlinePlus

Updated models for the kinetochore–microtubule interface that include contributions from flux. Drawings in A–C are modified from Rieder and Salmon (1998). OP is a cross section of one microtubule attachment site in the outer plate of the kinetochore, and IP is a cross section of the inner plate. The stretch of the centromere beyond its rest length indicates the tension generated. Microtubule attachment and resistance to translocation through the attachment site may be provided by the microtubule motors CENP-E and cytoplasmic dynein, the nonmotor microtubule–binding domain of CENP-E, the microtubule binding domain of the p150 component of the dynactin complex bound to dynein, and unknown microtubule-binding proteins within the attachment site (see text for details).
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fig4: Updated models for the kinetochore–microtubule interface that include contributions from flux. Drawings in A–C are modified from Rieder and Salmon (1998). OP is a cross section of one microtubule attachment site in the outer plate of the kinetochore, and IP is a cross section of the inner plate. The stretch of the centromere beyond its rest length indicates the tension generated. Microtubule attachment and resistance to translocation through the attachment site may be provided by the microtubule motors CENP-E and cytoplasmic dynein, the nonmotor microtubule–binding domain of CENP-E, the microtubule binding domain of the p150 component of the dynactin complex bound to dynein, and unknown microtubule-binding proteins within the attachment site (see text for details).

Mentions: Because microtubule plus ends polymerize at metaphase kinetochores, the primary source of kinetochore tension must be the spindle mechanisms that produce microtubule poleward flux and not a kinetochore-based mechanism. We infer that the kinetochore resists translocation of kinetochore microtubules through their attachment sites as a function of translocation velocity and the molecular viscosity of attachment (Howard, 2001). The idea that microtubule binding sites within the kinetochore produce molecular friction to a moving microtubule lattice was conceptualized by Hill (1985). The resistance at polymerizing kinetochores may be generated by transient linkages between dimers in the microtubule lattice and motor or nonmotor linker molecules within the kinetochore outer plate (see diagram in Fig. 4).


Direct observation of microtubule dynamics at kinetochores in Xenopus extract spindles: implications for spindle mechanics.

Maddox P, Straight A, Coughlin P, Mitchison TJ, Salmon ED - J. Cell Biol. (2003)

Updated models for the kinetochore–microtubule interface that include contributions from flux. Drawings in A–C are modified from Rieder and Salmon (1998). OP is a cross section of one microtubule attachment site in the outer plate of the kinetochore, and IP is a cross section of the inner plate. The stretch of the centromere beyond its rest length indicates the tension generated. Microtubule attachment and resistance to translocation through the attachment site may be provided by the microtubule motors CENP-E and cytoplasmic dynein, the nonmotor microtubule–binding domain of CENP-E, the microtubule binding domain of the p150 component of the dynactin complex bound to dynein, and unknown microtubule-binding proteins within the attachment site (see text for details).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172681&req=5

fig4: Updated models for the kinetochore–microtubule interface that include contributions from flux. Drawings in A–C are modified from Rieder and Salmon (1998). OP is a cross section of one microtubule attachment site in the outer plate of the kinetochore, and IP is a cross section of the inner plate. The stretch of the centromere beyond its rest length indicates the tension generated. Microtubule attachment and resistance to translocation through the attachment site may be provided by the microtubule motors CENP-E and cytoplasmic dynein, the nonmotor microtubule–binding domain of CENP-E, the microtubule binding domain of the p150 component of the dynactin complex bound to dynein, and unknown microtubule-binding proteins within the attachment site (see text for details).
Mentions: Because microtubule plus ends polymerize at metaphase kinetochores, the primary source of kinetochore tension must be the spindle mechanisms that produce microtubule poleward flux and not a kinetochore-based mechanism. We infer that the kinetochore resists translocation of kinetochore microtubules through their attachment sites as a function of translocation velocity and the molecular viscosity of attachment (Howard, 2001). The idea that microtubule binding sites within the kinetochore produce molecular friction to a moving microtubule lattice was conceptualized by Hill (1985). The resistance at polymerizing kinetochores may be generated by transient linkages between dimers in the microtubule lattice and motor or nonmotor linker molecules within the kinetochore outer plate (see diagram in Fig. 4).

Bottom Line: At anaphase onset, kinetochores switched to depolymerization of microtubule plus ends, resulting in chromosome-to-pole rates transiently greater than flux.Kinetochores switched from persistent depolymerization to persistent polymerization and back again during anaphase, bistability exhibited by kinetochores in vertebrate tissue cells.These results provide the most complete description of spindle microtubule poleward flux to date, with important implications for the microtubule-kinetochore interface and for how flux regulates kinetochore function.

View Article: PubMed Central - PubMed

Affiliation: Cell Division Group, Marine Biological Laboratory, Woods Hole, MA 02543, USA.

ABSTRACT
Microtubule plus ends dynamically attach to kinetochores on mitotic chromosomes. We directly imaged this dynamic interface using high resolution fluorescent speckle microscopy and direct labeling of kinetochores in Xenopus extract spindles. During metaphase, kinetochores were stationary and under tension while plus end polymerization and poleward microtubule flux (flux) occurred at velocities varying from 1.5-2.5 micro m/min. Because kinetochore microtubules polymerize at metaphase kinetochores, the primary source of kinetochore tension must be the spindle forces that produce flux and not a kinetochore-based mechanism. We infer that the kinetochore resists translocation of kinetochore microtubules through their attachment sites, and that the polymerization state of the kinetochore acts a "slip-clutch" mechanism that prevents detachment at high tension. At anaphase onset, kinetochores switched to depolymerization of microtubule plus ends, resulting in chromosome-to-pole rates transiently greater than flux. Kinetochores switched from persistent depolymerization to persistent polymerization and back again during anaphase, bistability exhibited by kinetochores in vertebrate tissue cells. These results provide the most complete description of spindle microtubule poleward flux to date, with important implications for the microtubule-kinetochore interface and for how flux regulates kinetochore function.

Show MeSH
Related in: MedlinePlus