Otx2's incredible journey.

A surprising new mechanism that regulates the plasticity of postnatal neurons is reported in this issue by Sugiyama et al. (2008). These authors show in mice that visual experience triggers cell-to-cell transfer of the homeoprotein Otx2 to cortical interneurons, where it promotes maturation of inhibitory neural circuitry and opens the critical period for plasticity in the visual cortex.