In the OSVZ-like area of hMGEOs, we observed a migratory stream of progenitor cells, either towards or parallel to the surface of hMGEOs (Figure S1F and S1G). The stream contained SOX2+/NKX2-1-GFP- cells, SOX2+/NKX2-1-GFP+ cells, and SOX2-/NKX2-1-GFP+ cells, which coalesced into migratory streaks (Figure 2K). Neuropilin-1 (NRP1)+ and CXCR4+ cells were present in the migratory streaks, further confirming their migrating properties (Figure 2L and 2M). Similarly, migrating cell clusters were observed in MGE domain of human fetal brain tissues in previous studies (Hansen et al., 2013). Thus, cells in hMGEOs may adopt intrinsic migration programs during development, resembling their in vivo counterparts. We also found that a core region underwent cell death during long-term culture of hMGEOs (Figure S1H and S1I). However, a number of DLX2+ cells were still detected in the region (Figure S1I), indicating that differentiated interneurons existed before cell death.
