Oral or Poster Presentation
Concurrent Session 3D - Neo Neurosciences & Neuro Critical Care
Introduction: Recessive mutations in TRIO are associated with several neurodevelopmental disorders (NDD), including intellectual deficiency, autism and epileptic encephalopathies. TRIO is a dual guanine nucleotide exchange factor (GEF) that activates Rac1 and RhoA, two Rho-GTPases fundamental for cytoskeletal remodelling and neuronal migration. While Trio is known to regulate the development of excitatory neurons, its roles in GABAergic interneurons (INs) are unknown. Given the implication of IN pathologies in NDD, we hypothesized that Trio might be a central regulator of IN development.
Methods: We generated Dlx5/6-Cre;Trio-c/c;RCE-EGFP mutant mice carrying a conditional deletion of Trio in GABAergic INs. We investigated the impact on IN migration and cortical inhibition using confocal microscopy, live-cell imaging, patch-clamp physiology and EEG recordings. For all experiments, mutant mice were compared to wildtype littermates.
Results: We find a delay in tangential migration in Trio mutant mice, as shown by a 50% decrease in the number of INs at the migration front at e13.5 and 15.5. Time-lapse imaging of acute organotypic slices at e13.5 reveals disrupted migration dynamics in mutant INs, with 30% slower and less frequent nucleokinesis. Further, 3-D reconstitutions of migrating INs reveal morphological aberrations: mutant INs present a multipolar phenotype along with a 2-fold increase in the complexity of the leading and trailing processes. Electroporation in mutant INs of a mutated version of Trio cDNA lacking the GEF1 domain, thus presumably still able to activate RhoA but not Rac1, completely rescues the morphological deficits. Finally, patch-clamp recordings in the somatosensory cortex at P30 shows a 60% reduction in IPSCs frequency in mutants, whereas EEG recordings reveal daily spontaneous tonic-clonic seizures in mutants.
Conclusion: Altogether, our data suggest that TRIO loss-of-function mutations impact the migration of cortical INs, disrupting cortical inhibitory networks, which results in epilepsy. Our work provides functional evidence for the implication of TRIO as a novel NDD gene.