Localized Aurora B activity spatially controls non-kinetochore microtubules during spindle assembly

Efficient spindle assembly involves the generation of spatial cues around chromosomes that locally stabilize microtubule (MT) plus-ends. In addition to the small GTPase Ran, there is evidence that Aurora B kinase might also generate a spatial cue around chromosomes but direct proof for this is still lacking. Here, we find that the Aurora B substrate MCAK localizes to MT plus-ends throughout the mitotic spindle, but its accumulation is strongly reduced on MT plus-ends near chromatin, suggesting that a signal emanating from chromosomes negatively regulates MCAK plus-end binding. Indeed, we show that Aurora B is the kinase responsible for producing this chromosome-derived signal. These results are the first to visualize spatially restricted Aurora B kinase activity around chromosomes on an endogenous substrate and explain how Aurora B could spatially control the dynamics of non-kinetochore MTs during spindle assembly

A Complex of Kif18b and MCAK Promotes Microtubule Depolymerization and Is Negatively Regulated by Aurora Kinases

SummaryIntroductionSpindle assembly requires tight control of microtubule (MT) dynamics. This is dependent on a variety of MT binding proteins and their upstream regulators. The Aurora kinases have several well-described functions during cell division, but it remains unclear whether they control global spindle microtubule dynamics.ResultsHere, we find that simultaneous inhibition of Aurora A and B results in a dramatic decrease in spindle MT stability, and we identify the uncharacterized kinesin-8 Kif18b as a mediator of this effect. In interphase, Kif18b is nuclear, but upon nuclear envelope breakdown, Kif18b binds to astral MT plus ends through an interaction with EB1. Surprisingly, Kif18b also binds to the kinesin-13 motor MCAK, and this interaction is required for robust MT depolymerization. Furthermore, the Kif18b-MCAK interaction is negatively regulated by Aurora kinases through phosphorylation of MCAK, indicating that Aurora kinases regulate MT plus-end stability in mitosis through control of Kif18b-MCAK complex formation.ConclusionTogether, these results uncover a novel role for Aurora kinases in regulating spindle MT dynamics through Kif18b-MCAK and suggest that the Kif18b-MCAK complex constitutes the major MT plus-end depolymerizing activity in mitotic cells

Kif15 Cooperates with Eg5 to Promote Bipolar Spindle Assembly

SummaryBackgroundThe formation of a bipolar spindle is an essential step during cell division. Bipolar spindle assembly is driven by the highly conserved microtubule motor Eg5 (kinesin-5), which can slide antiparallel microtubules apart to drive centrosome separation. However, it is currently unclear whether and how additional motors can contribute to centrosome separation and bipolar spindle formation.ResultsWe have developed a novel assay to identify motors involved in spindle bipolarity; via this assay, we identify Kif15/Hklp2 (kinesin-12, hereafter referred to as Kif15). Kif15 is not required for spindle bipolarity in cells with full Eg5 activity but becomes essential when Eg5 is partially inhibited. We show that the primary function of Kif15 is to promote spindle elongation and to ensure maintenance of spindle bipolarity. Nonetheless, ectopic expression of Kif15 can fully reconstitute bipolar spindle assembly in the absence of Eg5 activity, demonstrating that Kif15 can replace all essential functions of Eg5 in bipolar spindle assembly. Importantly, this activity of Kif15 depends on its interaction with the microtubule-associated protein TPX2, indicating that a Kif15-TPX2 complex promotes centrosome separation.ConclusionsThese findings show that, similar to Eg5, Kif15 can drive centrosome separation during bipolar spindle assembly. For this activity, Kif15 requires both its motor domain and its interaction with TPX2. Based on these data, we propose that a complex of Kif15 and TPX2 can crosslink and slide two antiparallel microtubules apart, thereby driving centrosome separation

Single-Molecule Imaging Uncovers Rules Governing Nonsense-Mediated mRNA Decay

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Antiviral responses are shaped by heterogeneity in viral replication dynamics

Antiviral signalling, which can be activated in host cells upon virus infection, restricts virus replication and communicates infection status to neighbouring cells. The antiviral response is heterogeneous, both quantitatively (efficiency of response activation) and qualitatively (transcribed antiviral gene set). To investigate the basis of this heterogeneity, we combined Virus Infection Real-time IMaging (VIRIM), a live-cell single-molecule imaging method, with real-time readouts of the dsRNA sensing pathway to analyse the response of human cells to encephalomyocarditis virus (EMCV) infection. We find that cell-to-cell heterogeneity in viral replication rates early in infection affect the efficiency of antiviral response activation, with lower replication rates leading to more antiviral response activation. Furthermore, we show that qualitatively distinct antiviral responses can be linked to the strength of the antiviral signalling pathway. Our analyses identify variation in early viral replication rates as an important parameter contributing to heterogeneity in antiviral response activation

Cyclin G-associated kinase promotes microtubule outgrowth from chromosomes during spindle assembly

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Wee1 controls genomic stability during replication by regulating the Mus81-Eme1 endonuclease

Wee1 is essential for normal DNA replication and for genomic stability, at least in part by inhibiting a general DNA damage response induced by the Mus81-Eme1 endonuclease

Bicaudal D2, Dynein, and Kinesin-1 Associate with Nuclear Pore Complexes and Regulate Centrosome and Nuclear Positioning during Mitotic Entry

Mammalian Bicaudal D2 is the missing molecular link between cytoplasmic motor proteins and the nucleus during nuclear positioning prior to the onset of mitosis