Mechanisms specifying area fate in cortex include cell-cycle-dependent decisions and the capacity of progenitors to express phenotype memory.

Progenitor cells in the early developing cerebral cortex produce neurons destined for discrete functional areas in response to specific inductive signals. Using lineage analysis, we show that cortical progenitor cells at different fetal ages retain the memory of an area-specific inductive signal received in vivo, even though they may pass through as many as two cell cycles in the absence of the signal in culture. When exposed to inductive signals in vitro, only those progenitors that progress through at least one complete cell cycle alter their areal phenotype. Our findings suggest that induction of an areal phenotype is linealy inherited, with the phenotype specified prior to the final cell cycle.