Aurora A kinase-coated beads function as microtubule-organizing centers and enhance RanGTP-induced spindle assembly

The roles of the kinase Aurora A (AurA) in centrosome function and spindle assembly [1-3] have been established in Drosophila[4,5], C. elegans[6], and Xenopus egg extracts [7-9]. Recently, we have shown that AurA acts downstream of the RanGTPase signaling pathway to stimulate spindle assembly in mitosis [110]. However, it is still not clear whether AurA can stimulate the formation of microtubule organizing centers (MTOC) on its own. Moreover, whether AurA is essential for spindle assembly in the absence of centrosomes has remained unclear [10, 11]. Here, we report the development of functional assays that allow us to show that activation of AurA by TPX2 is essential for Ran-stimulated spindle assembly in the presence or absence of centrosomes. Furthermore, AurA-coated magnetic beads function as MTOCs in the presence of RanGTP in Xenopus; egg extracts and RanGTP stimulates AurA to recruit activities responsible for both MT nucleation and organization to the beads. The MTOC function of AurA-coated beads require both MT nucleators and motors. Compared to XMAP215-coated beads [112], AurA-coated beads increase the rate of bipolar spindle assembly in the presence of RanGTP, and the kinase activity of AurA is essential for the beads to function as MTOCs.