Differentiation of adult hippocampus-derived progenitors into olfactory neurons in vivo.

Neurogenesis continues throughout adulthood in discrete regions. Proliferative zones include the subependymal zone, from where progenitors migrate along the rostral migratory pathway to differentiate into neurons in the olfactory bulb, and the hippocampal subgranular zone, where they migrate and differentiate into granule neurons. Progenitors isolated from adult subependymal zone exhibit in vitro neurogenesis when stimulated with epidermal or fibroblast growth factor. Cultured adult rat hippocampal progenitors (AHPs) grafted to adult rat hippocampus show site-specific neuronal differentiation. Here we investigate determinants of multipotentiality in the adult central nervous system, by grafting AHPs into homotypic (hippocampus) or heterotypic (the rostral migratory pathway) neurogenic sites or a heterotypic, non-neurogenic site (the cerebellum). We found that grafts into neurogenic, but not nonneurogenic sites, showed neuronal differentiation. Furthermore, AHPs grafted in the rostral migratory pathway migrated into the olfactory bulb, differentiating into tyrosine-hydroxylase-positive neurons, a non-hippocampus phenotype. These results reveal that AHP populations can respond to persistent neuronal differentiation cues in the adult central nervous system.