RESTRICTION OF LATE CEREBRAL CORTICAL PROGENITORS TO AN UPPER-LAYER FATE

Early in development, neural progenitors in cerebral cortex normally p roduce neurons of several layers during successive cell divisions. The laminar fate of their daughters depends on environmental cues encount ered just before mitosis. At the close of neurogenesis, however, corti cal progenitors normally produce neurons destined only for the upper l ayers. To assess the developmental potential of these cells, upper-lay er progenitors were transplanted into the cerebral colter of younger h osts, in which deep-layer neurons were being generated. These studies reveal that late cortical progenitors are not competent to generate de ep-layer neurons and are instead restricted to producing the upper lay ers.