Impaired Reelin-Dab1 Signaling Contributes to Neuronal Migration Deficits of Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is associated with neurodevelopmental abnormalities, including defects in neuronal migration. However, the alterations in cell signaling mechanisms critical for migration and final positioning of neurons in TSC remain unclear. Our detailed cellular analyses reveal that reduced Tsc2 in newborn neurons causes abnormalities in leading processes of migrating neurons, accompanied by significantly delayed migration. Importantly, we demonstrate that Reelin-Dab1 signaling is aberrantly regulated in TSC mouse models and in cortical tubers from TSC patients owing to enhanced expression of the E3 ubiquitin ligase Cul5, a known mediator of pDab1 ubiquitination. Likewise, mTORC1 activation by Rheb overexpression generates similar neuronal and Reelin-Dab1 signaling defects, and directly upregulates Cul5 expression. Inhibition of mTORC1 by rapamycin treatment or by reducing Cul5 largely restores normal leading processes and positioning of migrating neurons. Thus, disrupted Reelin-Dab1 signaling is critically involved in the neuronal migration defects of TSC.