Relative contributions of chromatin and kinetochores to mitotic spindle assembly

During mitosis and meiosis in animal cells, chromosomes actively participate in spindle assembly by generating a gradient of Ran guanosine triphosphate (RanGTP). A high concentration of RanGTP promotes microtubule nucleation and stabilization in the vicinity of chromatin. However, the relative contributions of chromosome arms and centromeres/kinetochores in this process are not known. In this study, we address this issue using cells undergoing mitosis with unreplicated genomes (MUG). During MUG, chromatin is rapidly separated from the forming spindle, and both centrosomal and noncentrosomal spindle assembly pathways are active. MUG chromatin is coated with RCC1 and establishes a RanGTP gradient. However, a robust spindle forms around kinetochores/centromeres outside of the gradient peak. When stable kinetochore microtubule attachment is prevented by Nuf2 depletion in both MUG and normal mitosis, chromatin attracts astral microtubules but cannot induce spindle assembly. These results support a model in which kinetochores play the dominant role in the chromosome-mediated pathway of mitotic spindle assembly.

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Kinetochore-driven formation of kinetochore fibers contributes to spindle assembly during animal mitosis

The Journal of Cell Biology ◽

10.1083/jcb.200407090 ◽

2004 ◽

Vol 167 (5) ◽

pp. 831-840 ◽

Cited By ~ 199

Author(s):

Helder Maiato ◽

Conly L. Rieder ◽

Alexey Khodjakov

Keyword(s):

Mitotic Spindle ◽

Spindle Assembly ◽

Spindle Pole ◽

S2 Cells ◽

Spindle Poles ◽

Drosophila S2 Cells ◽

Mitotic Spindle Assembly ◽

Normal Mitosis ◽

Proper Orientation ◽

Dependent Mechanism

It is now clear that a centrosome-independent pathway for mitotic spindle assembly exists even in cells that normally possess centrosomes. The question remains, however, whether this pathway only activates when centrosome activity is compromised, or whether it contributes to spindle morphogenesis during a normal mitosis. Here, we show that many of the kinetochore fibers (K-fibers) in centrosomal Drosophila S2 cells are formed by the kinetochores. Initially, kinetochore-formed K-fibers are not oriented toward a spindle pole but, as they grow, their minus ends are captured by astral microtubules (MTs) and transported poleward through a dynein-dependent mechanism. This poleward transport results in chromosome bi-orientation and congression. Furthermore, when individual K-fibers are severed by laser microsurgery, they regrow from the kinetochore outward via MT plus-end polymerization at the kinetochore. Thus, even in the presence of centrosomes, the formation of some K-fibers is initiated by the kinetochores. However, centrosomes facilitate the proper orientation of K-fibers toward spindle poles by integrating them into a common spindle.

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Mitotic spindle assembly in animal cells: a fine balancing act

Nature Reviews Molecular Cell Biology ◽

10.1038/nrm.2016.162 ◽

2017 ◽

Vol 18 (3) ◽

pp. 187-201 ◽

Cited By ~ 175

Author(s):

Suzanna L. Prosser ◽

Laurence Pelletier

Keyword(s):

Mitotic Spindle ◽

Spindle Assembly ◽

Animal Cells ◽

Mitotic Spindle Assembly

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Mechanisms of chromosome biorientation and bipolar spindle assembly analyzed by computational modeling

eLife ◽

10.7554/elife.48787 ◽

2020 ◽

Vol 9 ◽

Cited By ~ 4

Author(s):

Christopher Edelmaier ◽

Adam R Lamson ◽

Zachary R Gergely ◽

Saad Ansari ◽

Robert Blackwell ◽

...

Keyword(s):

Mitotic Spindle ◽

Spindle Assembly ◽

Extensive Study ◽

Bipolar Spindle ◽

Microtubule Attachment ◽

Anaphase Onset ◽

Length Regulation ◽

Mitotic Spindle Assembly ◽

Early Mitosis ◽

Segregation Of Chromosomes

The essential functions required for mitotic spindle assembly and chromosome biorientation and segregation are not fully understood, despite extensive study. To illuminate the combinations of ingredients most important to align and segregate chromosomes and simultaneously assemble a bipolar spindle, we developed a computational model of fission-yeast mitosis. Robust chromosome biorientation requires progressive restriction of attachment geometry, destabilization of misaligned attachments, and attachment force dependence. Large spindle length fluctuations can occur when the kinetochore-microtubule attachment lifetime is long. The primary spindle force generators are kinesin-5 motors and crosslinkers in early mitosis, while interkinetochore stretch becomes important after biorientation. The same mechanisms that contribute to persistent biorientation lead to segregation of chromosomes to the poles after anaphase onset. This model therefore provides a framework to interrogate key requirements for robust chromosome biorientation, spindle length regulation, and force generation in the spindle.

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Mechanisms of chromosome biorientation and bipolar spindle assembly analyzed by computational modeling

10.1101/649913 ◽

2019 ◽

Cited By ~ 2

Author(s):

Christopher J. Edelmaier ◽

Adam R. Lamson ◽

Zachary R. Gergely ◽

Saad Ansari ◽

Robert Blackwell ◽

...

Keyword(s):

Mitotic Spindle ◽

Spindle Assembly ◽

Extensive Study ◽

Bipolar Spindle ◽

Microtubule Attachment ◽

Anaphase Onset ◽

Length Regulation ◽

Mitotic Spindle Assembly ◽

Early Mitosis ◽

Segregation Of Chromosomes

AbstractThe essential functions required for mitotic spindle assembly and chromosome biorientation and segregation are not fully understood, despite extensive study. To illuminate the combinations of ingredients most important to align and segregate chromosomes and simultaneously assemble a bipolar spindle, we developed a computational model of fission-yeast mitosis. Robust chromosome biorientation requires progressive restriction of attachment geometry, destabilization of misaligned attachments, and attachment force dependence. Large spindle length fluctuations can occur when the kinetochore-microtubule attachment lifetime is long. The primary spindle force generators are kinesin-5 motors and crosslinkers in early mitosis, while interkinetochore stretch becomes important after biorientation. The same mechanisms that contribute to persistent biorientation lead to segregation of chromosomes to the poles after anaphase onset. This model therefore provides a framework to interrogate key requirements for robust chromosome biorientation, spindle length regulation, and force generation in the spindle.

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