ARX regulates cortical interneuron differentiation and migration

Abstract

Mutations in the aristaless-related homeobox (ARX) gene are associated with a spectrum of neurodevelopmental disorders with neurologic phenotypes including epilepsy, intellectual disabilities and autism spectrum disorders, with or without structural malformations. Some features of these disorders have been linked to abnormal cortical interneuron (IN) development and function. Currently, more than 50 subtypes of cortical INs have been identified thanks to the single cell transcriptomics. The existence of these many IN subtypes, with differing functions, raise the likelihood that distinct phenotypic dysfunction be associated with specific IN subtype defects. Despite the functional significance of each IN subtype, the molecular mechanisms underlying their development remain incompletely understood. To further extend our understanding of IN subtype development and to evaluate the implications of subtype defects, different types of Arx mutation models were investigated: conditional loss of function mutations of Arx (Arx cKO) driven by three IN-specific Cre lines (Gad2Cre, Nkx2.1Cre, and SstCre) and a poly-alanine tract expansion mutation (Arx(GCG)7). Single cell as well as total transcriptomic analysis, along with ARX chromatin immunoprecipitation sequencing (ChIP-seq), reveal that ARX regulates transcription of cortical IN development- and migration-associated genes. Our data obtained in embryonic and perinatal stage indicate that the relatively early loss of ARX in the progenitor cells or immature INs leads to IN subtype changes and migration defects, whereas its loss in postmitotic INs did not. On the other hand, the poly-alanine tract expansion mutation results in IN migration defects without affecting IN subtype development during embryonic stages, although postnatal reduction of certain subtypes of INs were detected. Our data provide new insights into how different mutations in the same gene can result in a spectrum of clinical phenotypes.