Interneuron migration defects during corticogenesis contribute to Dyrk1a haploinsufficiency syndrome pathogenesis.

Interneuron development is a crucial step of brain corticogenesis. When affected it often leads to brain dysfunctions like epilepsy, intellectual disabilities and autism spectrum disorder. Such defects are observed in the DYRK1A-haploinsufficiency syndrome, caused by mutations in DYRK1A, and commonly associated to cortical excitatory/inhibitory imbalance. However, how this imbalance is established in this syndrome remains elusive. Here, using mouse models and live imaging, we demonstrate that Dyrk1a specifically regulates the development of the cortical GABAergic system. We show that, unlike projection excitatory neurons, interneuron tangential migration relies on Dyrk1a dosage and kinase activity. We further reveal that Dyrk1a regulates actomyosin cytoskeleton remodeling during interneuron migration. Interestingly, mice with heterozygous inactivation of Dyrk1a in interneurons exhibited decreased interneuron density together with behavioral defects and epileptic activity, recapitulating phenotypes observed in human patients. Altogether, these data highlight the critical role of Dyrk1a in the development of the GABAergic system and the pathophysiology of DYRK1A-haploinsufficiency syndrome.