Dynactin targets Pavarotti-KLP to the central spindle during anaphase and facilitates cytokinesis in Drosophila S2 cells

The dynactin complex cooperates with the dynein complex in various systems for mitotic completion. Here we analysed the mitotic phenotype of Drosophila S2 cells following the knockdown of the dynactin subunit p150(Glued). We found that p150(Glued)-depleted cells were delayed in metaphase and that the centrosomes were poorly connected to mitotic spindle poles. In addition, anaphase occurred with asynchronous chromosome segregation. Although cyclin B was degraded in these anaphase cells, Aurora B, MEI-S322 and BubR1 were not released from the non-segregating chromosomes. We also found that the density and organisation of the central spindle were compromised, with Aurora B and polo kinases absent from the diminished number of microtubules. Pavarotti-KLP, a component of the centralspindlin complex required for the formation of stable microtubule bundles, was not immediately targeted to the plus ends of the microtubules following anaphase onset as happened in controls. Instead, it accumulated transiently at the cell cortex during early anaphase and its targeting to the central spindle was delayed. These data suggest that the dynactin complex contributes to cytokinesis by promoting stable targeting of the centralspindlin complex to microtubule plus ends at anaphase onset. The contribution of the dynein-dynactin complex to synchronous chromosome segregation and cytokinesis is discussed.