Connections distributed within 3 μm of chromosomes are necessary and sufficient for the kinetochore-fiber's robust anchorage in the mammalian spindle

Abstract

In mammalian cells, kinetochore-fibers are responsible for moving chromosomes within the spindle. To perform this task, they must generate and respond to forces while maintaining their connection to the spindle. Yet, how and where along their length they are anchored in the spindle, and which connections are necessary and sufficient remains unknown. Recent advances using microneedle manipulation opened new avenues in directly challenging kinetochore-fiber anchorage and revealed that anchorage near chromosomes restricts kinetochore-fiber pivoting there. To determine the components of this anchorage necessary and sufficient to locally restrict pivoting and maintain kinetochore-fiber orientation in the spindle center under force, we develop a theoretical framework using Euler-Bernoulli beam theory. We determine that highly localized anchorage just at the chromosome end fails to preserve kinetochore-fiber orientation in the spindle center. Similarly, global uniform anchorage fails to capture the localized resistance to pivoting by uniformly preserving structure everywhere. Instead, we show that local anchorage distributed within 3 μm of chromosomes is both necessary and sufficient for kinetochore-fibers to locally preserve their orientation under force. Together, our work indicates that while kinetochore-fibers have connections all along their length, not all connections are mechanically equivalent. Our model establishes the relationship between spindle architecture and the mechanics underlying kinetochore-fiber anchorage, and can be expanded to diverse spindle architectures across evolution.

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