Microtubule-organizing centres: a re-evaluation.

The number, length, distribution and polarity of microtubules are largely controlled by microtubule-organizing centres, which nucleate and anchor microtubule minus ends in a process that requires gamma-tubulin. Here we discuss recent evidence indicating that gamma-tubulin-dependent formation of new microtubules is not restricted to conventional microtubule-organizing centres. These findings suggest that the spatio-temporal control of microtubule nucleation is more complex than previously thought, leading us to a re-evaluation of the concept of the microtubule-organizing center.