Asymmetric spindle positioning.

When a spindle is positioned asymmetrically in a dividing cell, the resulting daughter cells are unequal in size. Asymmetric spindle positioning is driven by regulated forces that can pull or push a spindle. The physical and molecular mechanisms that can position spindles asymmetrically have been studied in several systems, and some themes have begun to emerge from recent research. Recent work in budding yeast has presented a model for how cytoskeletal motors and cortical capture molecules can function in orienting and positioning a spindle. The temporal regulation of microtubule-based pulling forces that move a spindle has been examined in one animal system. Although the spindle positioning force generators have not been identified in most animal systems, the forces have been found to be regulated by both PAR polarity proteins and G-protein signaling pathways in more than one animal system.