Specific neuroblast-derived signals control both cell migration and fate in the rostral migratory stream

Functional neuronal circuits require neuroblasts migrate to appropriate locations and then differentiate into neuronal subtypes. However, it remains unknown how neuroblasts in the subventricular zone (SVZ) are guided through the rostral migratory stream (RMS) to the olfactory bulb (OB). Here we define EphB2 as a neuroblast-derived cue that controls migration along the RMS and helps to determine cell fate. Within the RMS, EphB2 is expressed selectively in, kinase-active in, and required for the migration of neuroblasts. As neuroblasts enter the OB and differentiate, EphB kinase activity is down-regulated, and in the granule cell layer (GCL), EphB2 expression is down-regulated. Blocking EphB kinase activity or knocking down EphB2 results in defects in migration and premature cellular differentiation in the RMS. Unexpectedly, premature loss of EphB2 expression causes neuroblasts to stop migrating and differentiate into astrocyte-like cells. Thus, EphB2 kinase activity and expression are linked to migration and specification of neuroblast fate.