During anaphase, microtubules (green) are released from the centromere and move toward the poles.

Centrosomes spit out microtubules to thin out their load at the end of mitosis, as illustrated by Rusan and Wadsworth on page 21. This reorganization helps reestablish the interphase microtubule array and may contribute to localizing the cytokinetic ring.

Centrosomes nucleate many more microtubules during mitosis than they do in interphase. The new results show that the extra load is lightened in mammalian cells at late anaphase, when microtubules were released both individually and in clusters. The clusters carried with them centrosomal proteins such as γ-tubulin, the microtubule nucleator. The release of microtubules is prevented by CDK activity, as nondegradable cyclin B inhibited the disassembly after chromosome separation.

Microtubules were released and actively transported outwards in the direction of the cell poles (away from the chromosomes), where microtubules were previously scarce. Because the freed microtubules are not protected at their minus ends, they are more dynamic and turn over more rapidly than attached microtubules. The microtubules or their subunits are probably used to reform the interphase array.

The bias in turnover also creates an asymmetry in the array that might be important for directing cytokinesis to a central location. The attached, stable microtubules (those pointing inward) are more likely to transport signals that might stimulate the formation of the cytokinetic ring.