The neuronal progenitor cells of the forebrain subventricular zone: intrinsic properties in vitro and following transplantation

During the development of the central nervous system, progenitor cells, located within distinct germinal zones, produce presumptive neurons that migrate to their destinations and differentiate. Recent studies have demonstrated that a discrete region of the anterior part of the postnatal subventricular zone (SVZa) comprises neuronal progenitor cells whose progeny are fated to become the interneurons of the olfactory bulb. The SVZa is of particular interest because it is one of few germinal zones to persist postnatally and may be the only postnatal germinal zone to give rise exclusively to neurons. To the extent that the SVZa is unique among proliferative zones, the SVZa progeny are unique among neurons. First, unlike most cortical neurons, the SVZa-derived cells do not rely on radial glia-assisted migration when traveling to their target region. Second, the SVZa progeny continue to proliferate as they migrate to their target region. And third, the SVZa progeny express early neuron-specific antigens prior to their final division and, therefore, prior to reaching their destination where they will terminally differentiate. To better understand the capacity of the SVZa progeny to concurrently proliferate, migrate, and differentiate, we studied the cells in vitro and following transplantation into the neonatal SVZa and adult striatum. In each setting, we found that the SVZa cells continue both to proliferate and to differentiate into neurons. In addition, after homotopic and heterotopic transplantation, we found that the SVZa cells maintain their ability to migrate. These results suggest that the unique features of the SVZa progeny are specified intrinsically rather than by their extrinsic environment.