FATE DETERMINATION AND MIGRATION OF PROGENITORS IN THE POSTNATAL MAMMALIAN CNS

Using replication-deficient retroviruses to transfer marker genes into immature cells, we have characterized spatial and temporal patterns o f glial progenitor migration and differentiation in the early postnata l rat forebrain and cerebellum, and interneuron differentiation in the cerebellum. Progenitors do not migrate randomly, but follow discrete paths, largely confined to a coronal plane in forebrain and a sagittal plane in cerebellum. Radial glia provide one substrate for migration. In vitro studies suggest that radial glia contribute a permissive pat hway along which migratory progenitors can travel and that contact wit h radial glia keeps progenitors in an immature, migratory state. Local environmental cues that progenitors encounter during migration may in fluence fate decisions substantially. Not all progenitors differentiat e; some remain in an immature, proliferative state in which they do no t complete differentiation, but can be induced to do so by pathologica l conditions.