Astral microtubule asymmetry provides directional cues for spindle positioning in budding yeast.

Cortical force generators play a central role in the orientation and positioning of the mitotic spindle. In higher eukaryotes, asymmetrically localized cortical polarity determinants recruit or activate such force generators, which, through interactions with astral microtubules, position the mitotic spindle at the future site of cytokinesis. Recent studies in budding yeast have shown that, rather than the cell cortex, the astral microtubules themselves may provide polarity cues that are needed for asymmetric pulling on the mitotic spindle. Such asymmetry has been shown to be required for proper spindle positioning, and consequently faithful and accurate chromosome segregation. In this review, we highlight results that have shed light on spindle orientation in this classical model of asymmetric cell division, and review findings that may shed light on similar processes in higher eukaryotes.