The actin cytoskeleton in spindle assembly and positioning

The most dramatic changes in eukaryotic cytoskeletal organization and dynamics occur during passage through mitosis. Although both spindle self-organization and actin-dependent cytokinesis have long been the subject of intense investigation, it has only recently become apparent that the actin cortex also has a key role during early mitosis. This is most striking in animal cells, in which changes in the actin cytoskeleton drive mitotic cell rounding and cortical stiffening. This mitotic cortex then functions as a foundation for spindle assembly and to guide spindle orientation with respect to extracellular chemical and mechanical cues. Here, we discuss this recent work and the possible role of crosstalk between the mitotic actin cortex and the plus ends of astral microtubules in this process.