# Focal DEPDC5 loss without disruption to cerebral cortical neuron migration recapitulates DEPDC5-related focal epilepsy

## TL;DR

Deleting the DEPDC5 gene in mice after early brain development causes epilepsy, showing that early brain defects aren't always needed.

## Contribution

Shows postnatal DEPDC5 loss alone can cause epilepsy without disrupting early brain development.

## Key findings

- Postnatal DEPDC5 loss leads to mTOR hyperactivation and epilepsy in mice.
- Cortical lamination remains intact despite postnatal DEPDC5 deletion.
- Mice with DEPDC5 loss show increased seizures and seizure-related deaths.

## Abstract

Focal cortical dysplasia (FCD) is a major cause of refractory epilepsy and is associated with pathogenic variants in mTOR pathway genes, including DEPDC5, the most common cause of familial focal epilepsy. The mechanisms of epileptogenesis associated with FCD and hyperactive mTOR signaling remain unclear in DEPDC5-related epilepsy. To test whether DEPDC5 loss leading to seizures requires in utero cortical developmental defects or whether postnatal neuronal dysfunction of mTORC1 is sufficient to drive seizures, we developed a postnatal focal cortical Depdc5-knockout mouse model. Postnatal day 0–1 Depdc5-floxed mice received unilateral motor cortex injections of either AAV-Cre-GFP or control AAV-GFP. The AAV-Cre-GFP–injected hemisphere had decreased DEPDC5 levels with hyperactivation of mTOR that increased with age compared with both the contralateral hemisphere and the AAV-GFP–injected mice. Cortical lamination was not disrupted by postnatal DEPDC5 loss. Pathologic hallmarks of FCDs were identified in the Depdc5-knockout hemisphere, including increased SMI-311 neurofilament staining, hypomyelination, astrogliosis, and microglial activation. Mice with postnatal cortical DEPDC5 loss exhibited lower seizure thresholds, increased focal seizures, and increased rates of seizure-induced death compared with control mice. This study demonstrates that postnatal DEPDC5 loss and subsequent mTOR hyperactivation without disruption of cortical migration is sufficient to cause epilepsy.

<strong>Loss of DEPDC5 gene function after early brain development can still lead to epilepsy in mice providing critical insight into the developmental windows that lead to epilepsy and implications for genetic rescue.</strong>