A radial glia-specific role of RhoA in double cortex formation.

The positioning of neurons in the cerebral cortex is of crucial importance for its function as highlighted by the severe consequences of migrational disorders in patients. Here we show that genetic deletion of the small GTPase RhoA in the developing cerebral cortex results in two migrational disorders: subcortical band heterotopia (SBH), a heterotopic cortex underlying the normotopic cortex, and cobblestone lissencephaly, in which neurons protrude beyond layer I at the pial surface of the brain. Surprisingly, RhoA(-/-) neurons migrated normally when transplanted into wild-type cerebral cortex, whereas the converse was not the case. Alterations in the radial glia scaffold are demonstrated to cause these migrational defects through destabilization of both the actin and the microtubules cytoskeleton. These data not only demonstrate that RhoA is largely dispensable for migration in neurons but also showed that defects in radial glial cells, rather than neurons, can be sufficient to produce SBH.