| Abstract |
Cytokinesis in myosin II-null (mhcA-) cells of Dictyostelium discoideum requires adhesion to a substratum. Moreover, such myosin II-independent, adhesion-dependent cytokinesis can be divided into two distinct classes: a cell cycle-coupled form (cytokinesis B) and a cell cycle-independent form (cytokinesis C). To better understand the mechanisms underlying cytokinesis B and C, we introduced mutations into mhcA- cells and isolated clones that consistently gave rise to large, multinucleated cells. One such clone was found to have a disrupted talA gene, which codes for one of two Dictyostelium homologues of talin. Time-lapse observation revealed that cytokinesis B is partially impaired in mhcA-/talA- cells and that cytokinesis C is completely blocked. MhcA-/talA- cells took significantly longer to complete cytokinesis B than mhcA- cells on regular polystyrene surfaces, but not on a more adhesive surface. During cytokinesis B in mhcA- cells, GFP-TalA localized in the cortex and in dot-like structures on the ventral surface. Like vertebrate talin, these TalA dots may be involved in substrate adhesion and provide the traction needed to efficiently carry out cytokinesis B. During cytokinesis C in mhcA- cells, GFP-TalA was localized in the cortex of future furrow regions, and was highly enriched in cytoplasmic bridges that formed as the furrowing proceeded. Analysis of furrows in which GFP-TalA concentrations were asymmetric suggested that cortical TalA prevents formation of leading edges in regions where its concentration is high and indirectly promotes formation of leading edges elsewhere, which causes passive furrowing of the TalA-rich regions.
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