Model for spindle length regulation by F-actin and Myo10. F-actin and Myo10 function antagonistically to contribute to spindle length control. F-actin promotes spindle lengthening, perhaps through interactions with astral microtubules at the cell cortex, whereas Myo10 provides a counteracting spindle shortening function. The F-actin spindle lengthening is independent of Myo10, as knockdown of Myo10 results in longer spindles. In contrast, the shortening function of Myo10 requires F-actin because disrupting both F-actin and Myo10 gives normal length spindles.