Neuroblasts arising in the adult forebrain that travel to the olfactory bulb use two modes of migration: tangentially, along the rostral migratory stream, and radially, in the core of the olfactory bulb where they start to ascend to the outer layers. Although the mechanisms of tangential migration have been extensively studied, the factors controlling radial migration remain unexplored. Here we report that the extracellular matrix glycoprotein tenascin-R, expressed in the adult mouse olfactory bulb, initiates both the detachment of neuroblasts from chains and their radial migration. Expression of tenascin-R is activity dependent, as it is markedly reduced by odor deprivation. Furthermore, grafting of tenascin-R-transfected cells into non-neurogenic regions reroutes migrating neuroblasts toward these regions. The identification of an extracellular microenvironment capable of directing migrating neuroblasts provides insights into the mechanisms regulating radial migration in the adult olfactory bulb and offers promising therapeutic venues for brain repair.
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