4E-BP1 Expression in Embryonic Postmitotic Neurons Mitigates MTORC1-induced Cortical Malformations and Behavioral Seizure Severity but Does Not Prevent Epilepsy in Mice

Hyperactivation of the mechanistic target of rapamycin complex 1 (mTORC1) pathway during neurodevelopment leads to focal cortical malformations associated with intractable seizures. Recent evidence suggests that dysregulated cap-dependent translation downstream of mTORC1 contributes to cytoarchitectural abnormalities and seizure activity. Here, we examined whether reducing cap-dependent translation by expressing a constitutively active form of the translational repressor, 4E-BP1, downstream of mTORC1 would prevent the development of cortical malformations and seizures. 4E-BP1 was expressed embryonically either in radial glia (neural progenitor cells) that generate cortical layer 2/3 pyramidal neurons or in migrating neurons destined to layer 2/3 using a conditional expression system. In both conditions, 4E-BP1 expression reduced mTORC1-induced neuronal hypertrophy and alleviated cortical mislamination, but a subset of ectopic neurons persisted in the deep layers and the white matter. Despite the above improvements, 4E-BP1 expression in radial glia had no effects on seizure frequency and further exacerbated behavioral seizure severity associated with mTORC1 hyperactivation. In contrast, conditional 4E-BP1 expression in migratory neurons mitigated the severity of behavioral seizures but the seizure frequency remained unchanged. These findings advise against targeting 4E-BPs by 4E-BP1 expression during embryonic development for seizure prevention and suggest the presence of a development-dependent role for 4E-BPs in mTORC1-induced epilepsy.