Successful cell division requires a tight regulation of chromosome motion via the activity of molecular motors. Many of the key players at the origin of the forces generating the movement have been identified, but their spatial and temporal organization remains elusive. The protein complex Kinetochore on the chromosome associates with microtubules emanating from one of the spindle poles and drives the chromosome toward the pole. Chromokinesin motors on the chromosome arms also interact with microtubules, ejecting the chromosome away from the pole. In animal cells, a monooriented chromosome (associated to a single pole) periodically switches between phases of poleward and away from the pole movement[, a behavior tentatively explained so far by the existence of a complex switching mechanism within the kinetochore itself. Here we show that the interplay between the morphology of the mitotic spindle and the collective kinetics of chromokinesins can account for the highly non-linear periodic chromosome motion. Our analysis provides a natural explanation for the origin of chromosome directional instability and for the mechanism by which chromosomes feel their position in space.

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