Cortical neuron specification: it has its time and place.

Cortical neurogenesis is a highly stereotyped process in which progenitor cells generate neurons destined for specific cortical layers depending on the timing of cell cycle exit. Previous work has shown that during corticogenesis, progenitors become progressively restricted in their developmental potential. Recent work has uncovered some of the intrinsic mechanisms that underlie this fate restriction. In addition to timing, new studies suggest that the location of cell cycle exit in the cortical germinal zone may also contribute to cortical neuron specification.