Modeling and mechanical perturbations reveal how spatially regulated anchorage gives rise to spatially distinct mechanics across the mammalian spindle

TL;DR

This study combines modeling and mechanical perturbations to understand how spatially regulated anchorage in the mammalian spindle influences its mechanical behavior, revealing the importance of localized anchorage for proper spindle function.

Contribution

The paper introduces a coarse-grained model and experimental approach to identify the spatial regulation of anchorage in the spindle, highlighting the role of lateral anchorage near chromosomes.

Findings

Lateral anchorage near chromosomes is essential for maintaining spindle mechanics.

Forces at k-fiber ends alone are insufficient to explain observed shapes under manipulation.

Spatially regulated anchorage enables distinct mechanical responses across the spindle.

Abstract

During cell division, the spindle generates force to move chromosomes. In mammals, microtubule bundles called kinetochore-fibers (k-fibers) attach to and segregate chromosomes. To do so, k-fibers must be robustly anchored to the dynamic spindle. We previously developed microneedle manipulation to mechanically challenge k-fiber anchorage, and observed spatially distinct response features revealing the presence of heterogeneous anchorage (Suresh et al. 2020). How anchorage is precisely spatially regulated, and what forces are necessary and sufficient to recapitulate the k-fiber's response to force remain unclear. Here, we develop a coarse-grained k-fiber model and combine with manipulation experiments to infer underlying anchorage using shape analysis. By systematically testing different anchorage schemes, we find that forces solely at k-fiber ends are sufficient to recapitulate unmanipulated k-fiber shapes, but not manipulated ones for which lateral anchorage over a 3 $\mu$m length scale near chromosomes is also essential. Such anchorage robustly preserves k-fiber orientation near chromosomes while allowing pivoting around poles. Anchorage over a shorter length scale cannot robustly restrict pivoting near chromosomes, while anchorage throughout the spindle obstructs pivoting at poles. Together, this work reveals how spatially regulated anchorage gives rise to spatially distinct mechanics in the mammalian spindle, which we propose are key for function.