Midzone microtubule dynamics in anaphase cells.

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During anaphase, antiparallel overlapping midzone microtubules elongate, contributing to chromosome segregation and specify of the location where the contractile ring will form. Midzone microtubules are dynamic in early anaphase, but not in late anaphase, when they appear to be stabilized. The kinetics and mechanisms of this stabilization are not completely understood. Here, we quantify of midzone microtubule dynamics using a photoactivatable-GFP tubulin expressed in LLCPk1 cells. We find that immediately after anaphase onset, a single highly dynamic population of microtubules is present, but as anaphase progresses, both a dynamic and more stable population of microtubules coexist, with a gradual increase in the dissipation half-time for the slower population. By the middle of cytokinesis, only static microtubules are detected. We examined the microtubule dynamics during furrowing examining the effects of actin and midzone-associated proteins. Blocking furrow ingression using either C3 or latrunculin treatment resulted in two spatially distinct microtubule populations in telophase cells: peripheral microtubules that were highly dynamic and central microtubules with fast and slow populations that never transition to a static array. Depletion of midzone microtubule-associate proteins, PRC1 or Kif4a, did not block furrow ingression in most cells and prevented formation of a static array in telophase cells. Although microtubules were partially stabilized similar to mid-anaphase cells. Quantification of the length of PRC1 decorated microtubule overlaps showed that static arrays are characterized by short highly compacted zones. These results demonstrate that dynamic turnover and sliding of midzone microtubules is gradually reduced as anaphase progresses and microtubules are further stabilized during cytokinesis. These data reveal the importance of the PRC1/KIF4A module and midzone microtubule compaction in generating a static midzone.