PP6-regulated Aurora A activity towards NDC80 limits mitotic spindle size to prevent micronucleation

Amplification of the mitotic kinase Aurora A or loss of its regulator protein phosphatase 6 (PP6) promote micronucleation and related nuclear structure defects, changes that have emerged as drivers of genome instability. Using functional genomics to shed light on the processes underpinning these changes, we discover synthetic lethality between PPP6C, the catalytic subunit of PP6, and the kinetochore protein NDC80. We find that during spindle formation, NDC80 is phosphorylated at microtubule-attached kinetochores carrying the PP6-regulated pool of Aurora A, and this phosphorylation persists until spindle disassembly in telophase. Expression of Aurora-phosphorylation-deficient NDC80-9A or phospho-mimetic NDC80-9D results in reduced or enlarged spindle size, respectively. PPP6C-knockout results in enlarged spindles which fail to hold chromosomes tightly together in anaphase, causing defective nuclear structure, and remarkably NDC80-9A rescues micronucleation and defective nuclear structure in these cells. These results demonstrate that NDC80 is a target of the Aurora A-PP6 pathway and underline the importance of spindle size control for the fidelity of cell division. ### Competing Interest Statement The authors have declared no competing interest.