Reversible in vitro polymerization of tubulin from a cultured cell line (rat glial cell clone C6).

Tubulin from cultures of the rat glial cell clone C6 could be polymerized in vitro into intact microtubules. The polymerization was reversible and spontaneous, i.e., no addition of heterologous nucleation centers was necessary. Two cycles of polymerization/depolymerization yielded tubulin preparations of 95% purity as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Electron microscopy was used to show that the microtubules assembled in vitro by two cycles of polymerization/depolymerization were morphologically intact and temperature sensitive. In contrast, tubulin from neuroblastoma cells, clone Neuro-2A, could not be polymerized in a reversible fashion. The discovery of a cell line from which tubulin can be reversibly polymerized in vitro establishes a model system for studies of cell-cycle- and cell-type-dependent regulatory mechanisms controlling the assembly of microtubules.