Measuring microtubule thickness: an exercise in cooperativity.

Doublecortin (DCX), a microtubule-associated protein, is essential for neuronal migration, although a clear mechanistic understanding of this requirement remains elusive. In this issue of Developmental Cell, Bechstedt and Brouhard (2012) report that DCX relies on cooperative binding and an affinity for growing microtubule ends to nucleate and stabilize 13-protofilament microtubules.