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Pole-to-chromosome movements induced at metaphase: sites of microtubule disassembly
1University of Wisconsin Madison, Laboratory of Molecular Biology 53706.
Abstract:
Metaphase spindles can be induced to shrink by treating cells with microtubule-depolymerizing agents. During treatment, the paired sister chromatids remain at the metaphase plate and the poles move toward them. The question we asked is whether this pole-to-chromosome movement was accompanied by a loss of subunits from the kinetochore ends of the microtubules, the polar ends, or both ends. LLC-PK cells were injected at late prometaphase with Xrhodamine tubulin and at metaphase the fluorescent spindles were marked by photobleaching a bar between one pole and the chromosomes. Nocodazole at low concentrations was briefly applied to the cells to induce the shortening of the spindle and movement of the poles inward toward the chromosomes. In the induced shortening, the distance between the photobleached bar and the chromosomes decreased substantially while the distance between the bar and the pole showed a smaller change. Upon reversal from nocodazole, new polymer was added to the spindle as determined by recovery of fluorescence, and the cells progressed through mitosis and cytokinesis. We conclude that the movement of the poles to the chromosomes induced by nocodazole treatment during metaphase is similar to the chromosome-to-pole movement occurring during anaphase in that under both conditions the primary site for kinetochore microtubule disassembly is at the kinetochore.
Insights
During metaphase arrest, spindle poles move poleward via kinetochore microtubule disassembly. This disassembly primarily occurs at the kinetochore, mirroring anaphase chromosome-to-pole movement.
Area of Science:
- Cell Biology
- Molecular Biology
Background:
- Metaphase spindles can shrink when cells are treated with microtubule-depolymerizing agents.
- During this process, sister chromatids stay at the metaphase plate while poles move inward.
Purpose of the Study:
- To determine if pole-to-chromosome movement during spindle shortening involves microtubule subunit loss at kinetochore or polar ends, or both.
Main Methods:
- LLC-PK cells were injected with Xrhodamine tubulin.
- Fluorescent spindles were photobleached.
- Low concentrations of nocodazole induced spindle shortening and pole movement.
- Changes in photobleached bar distance to chromosomes and poles were measured.
Main Results:
- Pole-to-chromosome movement during nocodazole-induced spindle shortening showed a greater decrease in distance between the photobleached bar and chromosomes than between the bar and the pole.
- Reversal of nocodazole treatment allowed new microtubule polymerization and cell cycle progression.
Conclusions:
- Nocodazole-induced pole movement to chromosomes during metaphase involves kinetochore microtubule disassembly primarily at the kinetochore.
- This mechanism is analogous to chromosome-to-pole movement during anaphase.