Ubiquitination Inhibits Neuronal Exit

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Science  24 Dec 2010:
Vol. 330, Issue 6012, pp. 1754-1755
DOI: 10.1126/science.1200475

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In the developing brain, neurons increase their numbers in an “amplification compartment,” from which they emigrate to colonize distant brain structures. How young neurons leave these compartments, however, has been unclear, although researchers have hypothesized that they turn on a biochemical “migration program” that enables them to exit. On page 1834 of this issue, however, Famulski et al. (1) show that one common type of neuron uses an opposite strategy. To exit, young cerebellar granule neurons shut down a protein ubiquitination mechanism that inhibits the formation of a molecular complex that controls adhesion and allows the neurons to migrate to a final destination. Granule cells, a large population of small neurons in the central nervous system, proliferate at the surface of the developing cerebellum. They then undergo a transient phase of “tangential” migration near the cerebellar surface before extending a radial process (sprout-like extension) and migrating to deeper layers farther from their birthplace (see the figure). The mechanisms that control the onset of radial migration are poorly understood. In their study, Famulski et al. explore the role of ubiquitination, a common cellular process in which the protein ubiquitin bonds to proteins, marking them for destruction and recycling. Research is revealing that ubiquitination is as important as phosphorylation in regulating biological processes. Early analyses of ubiquitination's role in cell migration, for instance, showed that it can activate the intracellular trafficking and recycling of adhesion molecules (which enable cells to stick to each other or to extracellular products) and regulate actin cytoskeleton dynamics (2, 3). In the cerebral cortex, researchers have suggested that polyubiquitination and degradation arrests the radial migration of neurons (4).