Distinct Roles of RZZ and Bub1-KNL1 in Mitotic Checkpoint Signaling and Kinetochore Expansion
Author(s)Rodriguez-Rodriguez, Jose-Antonio; Lewis, Clare; McKinley, Kara Lavidge; Sikirzhytski, Vitali; Corona, Jennifer; Maciejowski, John; Khodjakov, Alexey; Cheeseman, Iain M; Jallepalli, Prasad V.; ... Show more Show less
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The Mad1-Mad2 heterodimer is the catalytic hub of the spindle assembly checkpoint (SAC), which controls M phase progression through a multi-subunit anaphase inhibitor, the mitotic checkpoint complex (MCC) [1, 2]. During interphase, Mad1-Mad2 generates MCC at nuclear pores . After nuclear envelope breakdown (NEBD), kinetochore-associated Mad1-Mad2 catalyzes MCC assembly until all chromosomes achieve bipolar attachment [1, 2]. Mad1-Mad2 and other factors are also incorporated into the fibrous corona, a phospho-dependent expansion of the outer kinetochore that precedes microtubule attachment [4–6]. The factor(s) involved in targeting Mad1-Mad2 to kinetochores in higher eukaryotes remain controversial [7–12], and the specific phosphorylation event(s) that trigger corona formation remain elusive [5, 13]. We used genome editing to eliminate Bub1, KNL1, and the Rod-Zw10-Zwilch (RZZ) complex in human cells. We show that RZZ's sole role in SAC activation is to tether Mad1-Mad2 to kinetochores. Separately, Mps1 kinase triggers fibrous corona formation by phosphorylating two N-terminal sites on Rod. In contrast, Bub1 and KNL1 activate kinetochore-bound Mad1-Mad2 to produce a “wait anaphase” signal but are not required for corona formation. We also show that clonal lines isolated after BUB1 disruption recover Bub1 expression and SAC function through nonsense-associated alternative splicing (NAS). Our study reveals a fundamental division of labor in the mammalian SAC and highlights a transcriptional response to nonsense mutations that can reduce or eliminate penetrance in genome editing experiments. Rodriguez-Rodriguez et al. identify distinct roles for Bub1, KNL1, and RZZ in SAC signaling and fibrous corona formation. They also show that BUB1-disrupted clones re-express Bub1 and regain SAC function via nonsense-associated alternative splicing, an often-overlooked transcriptional response that can limit penetrance in genome editing experiments.
DepartmentMassachusetts Institute of Technology. Department of Biology
Rodriguez-Rodriguez, Jose-Antonio et al. "Distinct Roles of RZZ and Bub1-KNL1 in Mitotic Checkpoint Signaling and Kinetochore Expansion." Current Biology 28, 21 (November 2018): P3422-3429.e5 © 2018 Elsevier
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