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How the kinetochore couples microtubule force and centromere stretch to move chromosomes

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ABSTRACT

The Ndc80 complex (Ndc80, Nuf2, Spc24, Spc25) is a highly conserved kinetochore protein essential for end-on anchorage to spindle microtubule plus-ends and for force generation coupled to plus-end polymerization and depolymerization. Spc24/Spc25 at one end of the Ndc80 complex binds the kinetochore. The N-terminal tail and CH domains of Ndc80 bind microtubules, and an internal domain binds microtubule-associated proteins (MAPs) such as the Dam1 complex. To determine how the microtubule and MAP binding domains of Ndc80 contribute to force production at the kinetochore in budding yeast, we have inserted a FRET tension sensor into the Ndc80 protein about halfway between its microtubule binding and internal loop domains. The data support a mechanical model of force generation at metaphase where the position of the kinetochore relative to the microtubule plus-end reflects the relative strengths of microtubule depolymerization, centromere stretch and microtubule binding interactions with Ndc80 and Dam1 complexes.

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Schematic of Force Coupler model in budding yeast metaphaseModels for the Ndc80 force coupler during polymerization in wild-type, partial and whole N-terminal tail deletion mutants. The N-terminal tail has a critical role in Ndc80 tension. Normal mean K-K stretch was maintained despite reduction (partial tail deletion) or lack (whole N-terminal tail deletion) of tension in Ndc80 at the position of the FRET sensor. During depolymerization, forces from peeling protofilaments push the Dam1 and Ndc80 complexes along kMTs toward the pole to stretch the centromere; the MTBDs of both Dam1 and Ndc80 are under compression. During polymerization, force from centromere stretch pulls the Ndc80 force coupler along kMTs with the MTBDs of Dam1 and Ndc80 under tension.
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Figure 7: Schematic of Force Coupler model in budding yeast metaphaseModels for the Ndc80 force coupler during polymerization in wild-type, partial and whole N-terminal tail deletion mutants. The N-terminal tail has a critical role in Ndc80 tension. Normal mean K-K stretch was maintained despite reduction (partial tail deletion) or lack (whole N-terminal tail deletion) of tension in Ndc80 at the position of the FRET sensor. During depolymerization, forces from peeling protofilaments push the Dam1 and Ndc80 complexes along kMTs toward the pole to stretch the centromere; the MTBDs of both Dam1 and Ndc80 are under compression. During polymerization, force from centromere stretch pulls the Ndc80 force coupler along kMTs with the MTBDs of Dam1 and Ndc80 under tension.

Mentions: Although the yeast N-terminal tail of Ndc80 is considered not essential33, our results show that the N-terminal tail of Ndc80 is critical to the timely progression through mitosis and distribution of force like mammalian Ndc80/Hec1. Tension is borne within the unstructured tail itself43 or via interactions with the CH domain8. Our measurements do not distinguish whether the reduced tension with tail deletion is through the loss of tail-MT interactions or the inability of the CH domain to establish robust MT binding (Fig. 7).


How the kinetochore couples microtubule force and centromere stretch to move chromosomes
Schematic of Force Coupler model in budding yeast metaphaseModels for the Ndc80 force coupler during polymerization in wild-type, partial and whole N-terminal tail deletion mutants. The N-terminal tail has a critical role in Ndc80 tension. Normal mean K-K stretch was maintained despite reduction (partial tail deletion) or lack (whole N-terminal tail deletion) of tension in Ndc80 at the position of the FRET sensor. During depolymerization, forces from peeling protofilaments push the Dam1 and Ndc80 complexes along kMTs toward the pole to stretch the centromere; the MTBDs of both Dam1 and Ndc80 are under compression. During polymerization, force from centromere stretch pulls the Ndc80 force coupler along kMTs with the MTBDs of Dam1 and Ndc80 under tension.
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Related In: Results  -  Collection

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Figure 7: Schematic of Force Coupler model in budding yeast metaphaseModels for the Ndc80 force coupler during polymerization in wild-type, partial and whole N-terminal tail deletion mutants. The N-terminal tail has a critical role in Ndc80 tension. Normal mean K-K stretch was maintained despite reduction (partial tail deletion) or lack (whole N-terminal tail deletion) of tension in Ndc80 at the position of the FRET sensor. During depolymerization, forces from peeling protofilaments push the Dam1 and Ndc80 complexes along kMTs toward the pole to stretch the centromere; the MTBDs of both Dam1 and Ndc80 are under compression. During polymerization, force from centromere stretch pulls the Ndc80 force coupler along kMTs with the MTBDs of Dam1 and Ndc80 under tension.
Mentions: Although the yeast N-terminal tail of Ndc80 is considered not essential33, our results show that the N-terminal tail of Ndc80 is critical to the timely progression through mitosis and distribution of force like mammalian Ndc80/Hec1. Tension is borne within the unstructured tail itself43 or via interactions with the CH domain8. Our measurements do not distinguish whether the reduced tension with tail deletion is through the loss of tail-MT interactions or the inability of the CH domain to establish robust MT binding (Fig. 7).

View Article: PubMed Central - PubMed

ABSTRACT

The Ndc80 complex (Ndc80, Nuf2, Spc24, Spc25) is a highly conserved kinetochore protein essential for end-on anchorage to spindle microtubule plus-ends and for force generation coupled to plus-end polymerization and depolymerization. Spc24/Spc25 at one end of the Ndc80 complex binds the kinetochore. The N-terminal tail and CH domains of Ndc80 bind microtubules, and an internal domain binds microtubule-associated proteins (MAPs) such as the Dam1 complex. To determine how the microtubule and MAP binding domains of Ndc80 contribute to force production at the kinetochore in budding yeast, we have inserted a FRET tension sensor into the Ndc80 protein about halfway between its microtubule binding and internal loop domains. The data support a mechanical model of force generation at metaphase where the position of the kinetochore relative to the microtubule plus-end reflects the relative strengths of microtubule depolymerization, centromere stretch and microtubule binding interactions with Ndc80 and Dam1 complexes.

No MeSH data available.


Related in: MedlinePlus