F-actin-binding protein drebrin has two major isoforms: drebrin A and drebrin E. Drebrin A is the major isoform in the adult brain and is highly concentrated in dendritic spines, regulating spine morphology and synaptic plasticity. Conversely, drebrin E is the major isoform in the embryonic brain and regulates neuronal morphological differentiation, but it is also expressed in neurogenic regions of the adult brain. The subventricular zone (SVZ) is one of the brain regions where adult neurogenesis occurs. Neuroblasts migrate to the olfactory bulb (OB) and integrate into existing neuronal networks, after which drebrin expression changes from E to A, suggesting that drebrin E plays a specific role in neuroblasts in the adult brain. Therefore, to understand the role of drebrin E in the adult brain, we immunohistochemically analyzed adult neurogenesis using drebrin-null-mutant (DXKO) mice. In DXKO mice, the number of neuroblasts and cell proliferation decreased, although cell death remained unchanged. These results suggest that drebrin E regulates cell proliferation in the adult SVZ. Surprisingly, the decreased number of neuroblasts in the SVZ did not result in less neurons in the OB. This was because the survival rate of newly generated neurons in the OB increased in DXKO mice. Additionally, when neuroblasts reached the OB, the change in the migratory pathway from tangential to radial was partly disturbed in DXKO mice. These results suggest that drebrin E is involved in a chain migration of neuroblasts.
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