Motoring to the Finish: Kinesin and Dynein Work Together to Orient the Yeast Mitotic Spindle

Two papers in this issue of The Journal of Cell Biology address the question of how the mitotic spindle is oriented within a dividing cell (5, 6). In this brief review, these new results will be placed in the context of other work on this topic. Spindle orientation is one of the essential roles of the cytoskeleton in all eukaryotic cells. Two broad classes of mitotic division illustrate the importance of this process: (a) asymmetric division, in which some aspect of the cell is differentially apportioned between the two products of division, and (b) symmetric division within an asymmetric cell, in which a cellular component, such as the nucleus, must be segregated equally to two cells that are unequal in size and/or shape. In the first case, the plane of division is determined by the orientation of the mitotic spindle, as...