The main function of the mitotic spindle is to accurately segregate replicated chromosomes during cell division. This dynamic, microtubule-based structure is assembled by a dividing cell and facilitates the orchestrated movement of chromosomes that is the hallmark of mitosis. Steady-state spindle size and morphology are relatively constant for cells of a specified type but vary considerably from one cell type to the next. Despite these differences, all eukaryotic spindles share basic architectural similarities, perhaps the most important of which is bipolar symmetry. At its core, assembling a bipolar spindle is a mechanical process that requires dynamic microtubules be moved and arranged to realize some ultimate functional form. These movements are the result of forces generated either by microtubule polymer dynamics or molecular motors. In this review we focus specifically on the motor-dependent mechanisms that shape the spindle and defer a more comprehensive treatment of spindle assembly and other motor functions during mitosis to others [1]
