Precisely arranged cytoarchitectures such as layers and nuclei depend on neuronal migration, of which many in vitro studies have revealed the mode and underlying mechanisms. However, how neuronal migration is achieved in vivo remains unknown. Here we established an imaging system that allows direct visualization of cortical interneuron migration in living mouse embryos. We found that during nucleokinesis, translocation of the Golgi apparatus either precedes or occurs in parallel to that of the nucleus, suggesting the existence of both a Golgi/centrosome-dependent and -independent mechanism of nucleokinesis. Changes in migratory direction occur when the nucleus enters one of the leading process branches, which is accompanied by the retraction of other branches. The nucleus occasionally swings between two branches before translocating into one of them, the occurrence of which is most often preceded by Golgi apparatus translocation into that branch. These in vivo observations provide important insight into the mechanisms of neuronal migration and demonstrate the usefulness of our system for studying dynamic events in living animals.cortex | GABAergic interneuron | in utero electroporation | in vivo imaging N euronal migration is a critical step in the construction of the nervous system. During development, neurons migrate from the sites of their birth to their final destinations, where they form neuronal architectures, such as laminated structures and nuclei, that are necessary for information processing in the nervous system.Because neuronal migration is a dynamic phenomenon, realtime imaging could provide important insight into its mechanisms. Studies using real-time imaging of neurons in dissociated culture have demonstrated various aspects of neuronal migration, including the fact that radial fibers (1) and neighboring cells (2) act as the substrate for migration and the molecular mechanisms driving nucleokinesis (3, 4). Real-time imaging has also helped reveal the dynamics and roles of cytoplasmic organelles and cytoskeletal components, such as the centrosome (5-9), microtubules (9), and even of some molecules like calcium (10) and actin (7,11,12) during migration. In addition, slice and explant preparations have demonstrated aspects of migratory behaviors, including locomotion and translocation (13), branch-induced changes in migratory direction (14), multidirectional migration (15), random-walk-like behavior (16), pausing behavior, and the transition from tangential to radial migration (17).However, as informative as these neural migration studies are, they are limited because they are all in vitro and do not necessarily show neuronal behaviors in vivo. Here, we observed migrating neurons in the brain of living mouse embryos and analyzed their behavior, including the dynamics of the nucleus and the Golgi apparatus. We took advantage of the fact that cortical interneurons tangentially migrate near the surface of the cortex. These neurons are generated in the ganglionic eminences (GEs) in the basal forebrain a...
