Kinetochore motors drive congression of peripheral polar chromosomes by overcoming random arm-ejection forces

Abstract

Accurate chromosome segregation during cell division in metazoans relies on proper chromosome congression at the equator. Chromosome congression is achieved after bi-orientation to both spindle poles shortly after nuclear envelope breakdown, or by the coordinated action of motor proteins that slide misaligned chromosomes along pre-existing spindle microtubules. These proteins include the minus-end-directed kinetochore motor dynein, and the plus-end-directed motors CENP-E at kinetochores and chromokinesins on chromosome arms. However, how these opposite and spatially distinct activities are coordinated to drive chromosome congression remains unknown. Here we used RNAi, chemical inhibition, kinetochore tracking and laser microsurgery to uncover the functional hierarchy between kinetochore and arm-associated motors, exclusively required for congression of peripheral polar chromosomes in human cells. We show that dynein poleward force counteracts chromokinesins to prevent stabilization of immature/incorrect end-on kinetochore-microtubule attachments and random ejection of polar chromosomes. At the poles, CENP-E becomes dominant over dynein and chromokinesins to bias chromosome ejection towards the equator. Thus, dynein and CENP-E at kinetochores drive congression of peripheral polar chromosomes by preventing arm-ejection forces mediated by chromokinesins from working in the wrong direction.

Dynein prevents erroneous kinetochore-microtubule attachments in mitosis

“…By backtracking these polar chromosomes to their original positions at NEB, we found that they initially occupied a peripheral region outside the interpolar spindle ellipsoid, and were always significantly closer to one of the poles. 5 In contrast, chromosomes that were already positioned in the interpolar region at NEB were easily accessible by microtubules from both spindle poles and became bi-oriented soon after NEB. Importantly, these chromosomes completed alignment in the absence of all 3 motor activities.…”

“…Importantly, these chromosomes completed alignment in the absence of all 3 motor activities. 5 Thus, we concluded thatonly peripheral chromosomes that cannot bi-orient soon after NEB require motor proteins to congress.…”

“…[36][37][38] Once chromosomes become bi-oriented and tension is applied between sister kinetochores, Ndc80 moves away from Aurora B, resulting in kinetochoremicrotubule attachment stabilization. 39,40 Here we elaborate on recent studies that demonstrated a role of Dynein, 5 chromokinesins 5,41 and Aurora A kinase 5,41,42 in the prevention and correction of erroneous kinetochore-microtubule attachments during chromosome congression.…”

“…1,2 Chromosome movements during congression are driven by 2 main mechanisms: microtubule polymerization/depolymerization-based motion 3 and motor-dependent transport along microtubules. [4][5][6] The latter is mainly achieved through the coordinated activities of cytoplasmic Dynein, CENP-E and chromokinesins. 5 Cytoplasmic Dynein (from here on referred as Dynein) is a large protein complex (1.6 MDa) consisting of several subunits: 2 heavy chains containing ATPase motor domains, 2 intermediate chains, 2 light intermediate chains and 3 different types of light chains.…”

“…[4][5][6] The latter is mainly achieved through the coordinated activities of cytoplasmic Dynein, CENP-E and chromokinesins. 5 Cytoplasmic Dynein (from here on referred as Dynein) is a large protein complex (1.6 MDa) consisting of several subunits: 2 heavy chains containing ATPase motor domains, 2 intermediate chains, 2 light intermediate chains and 3 different types of light chains. 7 Dynein interacts with many different proteins that regulate its activity and localization, enabling Dynein to perform its various cellular tasks.…”