Striatal precursors adopt cortical identities in response to local cues

One of the early steps in the regionalization of the CNS is the subdivision of the forebrain into dorsal and basal telencephalic ventricular zones. These ventricular zones give rise to the cortex and striatum respectively, in the mature brain. Previous work suggests that while neural precursors are able to move within both the dorsal cortical and basal striatal ventricular zones, they are unable to cross the boundary area between them. To determine if the regional identities of the cells in these ventricular zones are restricted, cells from the basal striatal ventricular zone were either transplanted back into their original environment or into the dorsally adjacent cortical ventricular zone. Use of in vitro explants of mouse telencephalon demonstrated that striatal precursors are able to integrate heterotopically within 12 hours of being placed onto the surface of cortical ventricular zone. To examine whether heterotopically placed neural precursors have phenotypes appropriate to their host or donor environment, in vivo transplants in rats were performed. Striatal ventricular zone cells transplanted to a striatal environment adopt morphologies and axonal projections characteristic of striatal cells. In contrast, striatal ventricular zone cells transplanted in vivo to a cortical environment acquired morphologies and axonal projections specific to cortex. These findings suggest that within forebrain, position-specific cues play an instructive role in determining critical aspects of regional phenotype.