To further characterize the migration behavior, we performed 4-D (x, y, z, t) imaging of live hfMCOs near the fusion border at 2 weeks after fusion (Movie S4). We found two key features of migrating NKX2-1-GFP+ cells in hfMCOs: (1) directed forward extension of leading process (Figure 7F), and (2) nucleokinesis following the leading process (Figure 7G). Importantly, cytoplasm elongation was often observed preceding nucleokinesis (Figure 7G). These behaviors are remarkably similar to previous reports of interneuron migration in live mouse embryos, mouse MGE explant models, and postmortem human brain sections (Bellion et al., 2005; Ma et al., 2013; Paredes et al., 2016; Yanagida et al., 2012), demonstrating the suitability of using hfMCOs to study human interneuron migration.
