A microtubule-binding myosin required for nuclear anchoring and spindle assembly

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Abstract
Proper spindle positioning and orientation are essential for asymmetric cell division and require microtubule–actin filament (F-actin) interactions in many systems1,2. Such interactions are particularly important in meiosis3, where they mediate nuclear anchoring4,5,6, as well as meiotic spindle assembly and rotation7,8, two processes required for asymmetric cell division. Myosin-10 proteins are phosphoinositide-binding9, actin-based motors that contain carboxy-terminal MyTH4 and FERM domains of unknown function10. Here we show that Xenopus laevis myosin-10 (Myo10) associates with microtubules in vitro and in vivo, and is concentrated at the point where the meiotic spindle contacts the F-actin-rich cortex. Microtubule association is mediated by the MyTH4-FERM domains, which bind directly to purified microtubules. Disruption of Myo10 function disrupts nuclear anchoring, spindle assembly and spindle–F-actin association. Thus, this myosin has a novel and critically important role during meiosis in integrating the F-actin and microtubule cytoskeletons.