Interphase microtubule dynamics are cell type-specific

The rate and pattern of microtubule polymer loss in interphase cells have been examined using nocodazole to block microtubule assembly. Cells were incubated with high concentrations of nocodazole for various times and the pattern of microtubule disassembly was determined using tubulin immunofluorescence. Polymer loss was quantitated by measuring the decrease in percentage of cell area occupied by microtubules. The results demonstrate that microtubules in diverse cells disassemble individually and asynchronously. In addition, these quantitative measurements reveal that epithelial and fibroblast cells display strikingly different kinetics of polymer loss. In fibroblasts, polymer loss is rapid, with a half-time of 4 min at 37 degrees C. In epithelial cells, loss of 60% of the microtubules occurs with a half-time of 18 min; the remaining 40% of the microtubules disassemble much more slowly (average half-time of 72 min). To demonstrate that these differences were not due to species differences among various cells assayed in these experiments, epithelial and fibroblast cells derived from primary cultures of newt lung have been examined. Again, fibroblast and epithelial cell microtubule dynamics could be readily distinguished. To determine if modifications to epithelial cell microtubules contribute to their stability, microtubules were completely disassembled and allowed to regrow. The rate of polymer loss for recently regrown microtubules was more rapid than microtubules in control cells, indicating that stability increases with time after assembly.