DIRECT EVIDENCE FOR HOMOTYPIC, GLIA-INDEPENDENT NEURONAL MIGRATION

Neuronal precursors born in the subventricular zone (SVZ) of the neona tal and adult rodent brain migrate 3-8 mm from the walls of the latera l ventricle into the olfactory bulb. This tangentially oriented migrat ion occurs without the guidance of radial glia or axonal processes. Th e cells move closely associated, forming elongated aggregates called c hains, which are ensheathed by astrocytes. We have developed a culture system in which postnatal mouse SVZ neuronal precursors assemble into chains with ultrastructural and immunocytochemical characteristics eq uivalent to those in vivo but without the astrocytic sheath. Time-laps e videomicrography revealed that individual cells migrate along the ch ains very rapidly (similar to 122 mu m/hr) in both directions. Periods of cell body translocation were interspersed with stationary periods. This saltatory behavior was similar to radial glia-guided migration b ut similar to 4 times faster. Neuronal precursors isolated from embryo nic cortical ventricular zone or cerebellar external granule layer did not form chains under these conditions, suggesting that chain migrati on is characteristic of SVZ precursors. This study directly demonstrat es that SVZ neuronal precursors migrate along each other without the a ssistance of astrocytes or other cell types. (Additional data are pres ented in www.cell.com).