How does the kinetochore stretching occur?
One intuitive possibility is that stretching is caused by microtubules mechanically pulling the kinetochores. In this mechanical stretching model, kinetochore deformation is based on the elastic properties that kinetochores might have. Alternatively, kinetochore stretching might be the result of conformational rearrangements of the kinetochore components. In this case, the kinetochore stretching does not necessarily reflect the presence of tension. Both models are possible and will be perturbed with a microtubule poison. The results that centromere integrity is required for kinetochore stretching (Fig. 3 D) seemingly favor the mechanical stretching model, but it does not preclude the second model. Conversely, the kinetochore stretching in monooriented chromosomes (Fig. 5 C) can be better explained by the rearrangement model. However, it would be difficult to precisely assess the presence of tension at kinetochores because when chromosomes are pulled toward the pole, they must simultane
