Composition and organization of the SCZ: a large germinal layer containing neural stem cells in the adult mammalian brain.

Two known germinal zones continue to generate new neurons and glia in the adult mammalian brain: the subventricular zone (SVZ), lining the lateral walls of the lateral ventricle, and the subgranular zone of the dentate gyrus. Here we describe a region we will refer to as the subcallosal zone (SCZ). The SCZ is a caudal extension of the SVZ that is no longer associated to an open ventricle. It lies between the hippocampus and the corpus callosum. Cells isolated from the SCZ and cultured as neurospheres behave as neural stem cells in vitro. Using electron and light microscopy, we describe the cell types present in this region and how their organization differs from that of the SVZ. Using retroviral labeling and homotypic-homochronic microtransplantation techniques, we show that the majority of cells born in the SCZ migrate into the corpus callosum to become oligodendrocytes in vivo. This study defines the organization and fate of cells born in a large germinal region of the adult forebrain.