Microtubules get early release

The centrosome is a nucleating center for microtubules (MTs) and the hub of the MT aster. On page 731, Abal et al. report that the centrosome in fibroblasts also seeds a second population of short MTs that are released and transported to the periphery. Both anchored and free MTs are needed for cell migration.

Abal et al. distinguished the two MT populations using GFP-tagged EB1, a protein that associates with growing MT plus ends. Visualization of EB1 in fibroblasts revealed that one set of MTs moved away from the centrosome toward the cell membrane more rapidly than could be explained by polymerization alone. The speed of this faster group stemmed from active transport of short but growing MTs by the motor dynein. Inhibition of dynein greatly diminished...