Developmental anatomy of the dentate gyrus

The dentate gyrus is the entrance gate of neuronal information into the hippocampal formation. Recent studies suggested that functions of dentate neural stem cells is essential for cellular mechanisms of memory formation and psychiatric diseases. Development of the dentate gyrus is unique in terms of that the neural stem cells migrate out from their origin in the medio-caudal neuroepithelium of the embryonic telencephalon and produce the dentate granule cells, the principal neurons of the dentate gyrus. The pioneering works by Joseph Altman and his colleagues suggested some anatomical structures transiently appear during development of the dentate gyrus by basic histological methods, and discussed the migratory route of the mitotic cells. Here, we describe recently obtained information about development of the dentate gyrus from studies of genetically engineered mouse lines and observations of molecules, which allow us to identify distinct stages during the process of granule cell differentiation and lineage of the neuronal subtypes in the hippocampal formation.