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

Proper spindle positioning and orientation are essential for asymmetric cell division and require microtubule-actin filament (F-actin) interactions in many systems(1,2). Such interactions are particularly important in meiosis(3), where they mediate nuclear anchoring(4-6), as well as meiotic spindle assembly and rotation(7,8), two processes required for asymmetric cell division. Myosin-10 proteins are phosphoinositide-binding(9), actin-based motors that contain carboxy-terminal MyTH4 and FERM domains of unknown function(10). 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.