In the mouse forebrain, interneurons (INs) are born in the ganglionic eminences and preoptic area, and migrate from there to the cortex and other brain regions. The medial ganglionic eminence produces most INs of the neocortex – particularly the early born ones – whereas a minority of later-born cortical INs, as well as INs of other brain regions, derive from the caudal ganglionic eminence (CGE). What specifies the different populations of INs and how they reach their targets, is still incompletely understood. Michèle Studer and colleagues now (p. ) analyse IN migration from the CGE, finding that, in addition to the well-known caudal migratory stream (CMS), populations of INs also migrate rostrally by taking medial and lateral paths (the MMS and LMS, respectively). INs in the different paths appear to express different subsets of transcription factors and give rise to distinct sub-populations of mature INs. The authors identify the COUP-TFI nuclear receptor as a key regulator of identity and fate of the MMS and LMS INs. These data uncover an unexpected complexity in the migratory paths of CGE-derived INs that might be crucial for defining the huge diversity of mature IN types in the brain.
