
At the final stage of cell division, an actin-myosin ring forms around the cortex of the cell, which constricts to form a cleavage furrow and pinch the cell in two. What signals initiate and position the cleavage furrow? In nematodes, two signals seem to be important – one from the microtubule asters (the radial arrays of microtubules emanating from the centrosomes), and one from the spindle midzone (where microtubules from opposite poles overlap). On p. 1772, Koen Verbrugghe and John White describe a new model for how the cleavage furrow is positioned. An important player is the centralspindlin complex, which was previously thought not to be needed for furrow formation, only for the completion of cytokinesis. Now, Verbrugghe and White show that centralspindlin localises to the furrow and find that furrowing fails to occur when centralspindlin is missing along with two proteins involved in spindle elongation: PAR-2 and trimeric G-protein Gα. The researchers argue that the stability of the midzone microtubules is crucial for furrow formation. Since PAR-2 is thought to affect microtubule stability at the cortex, they propose that PAR-2 and centralspindlin act redundantly to stabilise microtubules in this region.
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