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 neuro ns destined for discrete functional areas in response to specific indu ctive signals. Using lineage analysis, we show that cortical progenito r cells at different fetal ages retain the memory of an area-specific inductive signal received in vivo, even though they may pass through a s many as two cell cycles in the absence of the signal in culture. Whe n exposed to inductive signals in vitro, only those progenitors that p rogress through at least one complete cell cycle alter their areal phe notype. Our findings suggest that induction of an areal phenotype is l inealy inherited, with the phenotype specified prior to the final cell cycle.