A SHORT-RANGE SIGNAL RESTRICTS CELL-MOVEMENT BETWEEN TELENCEPHALIC PROLIFERATIVE ZONES

During telencephalic development, a boundary develops that restricts c ell movement between the dorsal cortical and basal striatal proliferat ive zones. In this study, the appearance of this boundary and the mech anism by which cell movement is restricted were examined through a num ber of approaches. The general pattern of neuronal dispersion was exam ined both with an early neuronal marker and through the focal applicat ion of Dil to telencephalic explants. Both methods revealed that, alth ough tangential neuronal dispersion is present throughout much of the telencephalon, it is restricted within the boundary region separating dorsal and ventral telencephalic proliferative zones. To examine the c ellular mechanism underlying this boundary restriction, dissociated ce lls from the striatum were placed within both areas of the boundary, w here dispersion is limited, and areas within the cortex, where signifi cant cellular dispersion occurs. Cells placed within the boundary regi on remain round and extend only thin processes, whereas progenitors pl aced onto the cortical ventricular zone away from this boundary are ab le to migrate extensively. This suggests that the boundary inhibits di rectly the migration of cells. To examine whether the signal inhibitin g dispersion within the boundary region acts as a long- or short-range cue, we apposed explants of boundary and nonboundary regions in vitro . Within these explants we found that migration was neither inhibited in nonboundary regions nor induced in boundary regions. This suggests that the boundary between dorsal and ventral telencephalon isolates th ese respective environments through either a contact-dependent or a sh ort-range diffusible mechanism.