Loss of Slc35a2 alters development of the mouse cerebral cortex

Brain somatic variants in SLC35A2, an intracellular UDP-galactose transporter, are commonly identified mutations associated with drug-resistant neocortical epilepsy and developmental brain malformations, including focal cortical dysplasia type I and mild malformation of cortical development with oligodendroglial hyperplasia in epilepsy (MOGHE). However, the causal effects of altered SLC35A2 function on cortical development remain untested. We hypothesized that focal Slc35a2 knockout (KO) or knockdown (KD) in the developing mouse cortex would disrupt cortical development and change network excitability. Through two independent studies, we used in utero electroporation (IUE) to introduce CRISPR/Cas9/targeted guide RNAs or short-hairpin RNAs into the embryonic mouse brain at day 14.5-15.5 to achieve Slc35a2 KO or KD, respectively, from neural precursor cells. Slc35a2 KO or KD caused disrupted radial migration of electroporated neurons evidenced by heterotopic cells located in lower cortical layers and in the sub-cortical white matter. Slc35a2 KO in neurons did not induce changes in oligodendrocyte number, importantly suggesting that the oligodendroglial hyperplasia observed in MOGHE originates from distinct cell autonomous effects of Slc35a2 mutations. Adult KO mice were implanted with EEG electrodes for 72-hour continuous recording. Spontaneous seizures were not observed in focal Slc35a2 KO mice, but there was reduced seizure threshold following pentylenetetrazol injection. Here we demonstrate that focal Slc35a2 KO or KD in vivo disrupts corticogenesis through altered neuronal migration and that KO leads to reduced seizure threshold. Together these results demonstrate a direct causal role for SLC35A2 in cortical development.