Dynamics of interphase microtubules in Schizosaccharomyces pombe

Background: Microtubules in interphase Schizosaccharomyces pombe are essent ial for maintaining the linear growth habit of these cells. The dynamics of assembly and disassembly of these microtubules are so far uncharacterised. Results: Live cell confocal imaging of ctl tubulin tagged with enhanced gre en fluorescent protein revealed longitudinally oriented, dynamically unstab le interphase microtubule assemblies (IMAs). The IMAs were uniformly bright along their length apart from a zone of approximately doubly intense fluor escence commonly present close to their centres. The ends of each IMA switc hed from growth (similar to 3.0 mu m/min) to shrinkage (similar to 4.5 mu m /min) at 1.0 events per minute and from shrinkage to growth at 1.9 events p er minute, and the two ends were equivalently dynamic, suggesting equivalen t structure. We accordingly propose a symmetrical model for microtubule pac king within the IMAs, in which microtubules are plus ends out and overlap c lose to the equator of the cell. IMAs may contain multiple copies of this m otif; if so, then within each IMA end, the microtubule ends must synchronis e catastrophe and rescue. When both ends of an IMA lodge in the hemispheric al cell ends, the IMAs start to bend under compression and their overall gr owth rate is inhibited about twofold. Similar microtubule dynamics were obs erved in cells ranging in size from half to twice normal length. Patterned photobleaching indicated no detectable treadmilling or microtubule sliding during interphase. Conclusions: The consequence of the mechanisms described is continuous recr uitment of microtubule ends to the ends of growing cells, supporting microt ubule-based transport into the cell ends and qualitatively accounting for t he essential role for microtubules in directing linear cell growth in S. po mbe. (C) 2000 Elsevier Science Ltd. All rights reserved.