How the Aurora B kinase finds the spindle midzone in anaphase

Radhika Subramanian

Aurora B kinase must localize to the cell center for proper cytokinesis, the final and irreversible step of mitosis. Aurora B functions as part of the Chromosomal Passenger Complex (CPC), which concentrates at the spindle midzone - a narrow array of overlapping antiparallel microtubules that forms at the cell center during anaphase. How the CPC achieves this selective enrichment within the dense and heterogeneous spindle microtubule network remains unknown. Using a fully reconstituted system, we defined a minimal CPC enrichment module composed of PRC1, KIF4A, MKLP2, and CPC. We identified KIF4A as the molecular link that anchors CPC to PRC1-crosslinked microtubules, both in vitro and at the midzone in dividing cells. Maximum CPC enrichment results from the synergistic activity of KIF4A and MKLP2. Remarkably, this synergy arises from a partitioning of transport between the two motors, directed by local CPC density on microtubules. These findings uncover a cargo-density-dependent motor handoff mechanism that may represent a broader principle for precisely positioning signaling complexes within heterogeneous microtubule networks.