If the cell types produced in vitro mimic those produced in vivo, we would expect unventralized telencephalic (PAX6+) and mitotic MGE progenitors (NKX2-1+) early, followed by immature MGE-like neurons and intermediate progenitors (DLL1+, ASCL1+, CCND2+), with functionally mature interneurons, and glia produced at the latest timepoints. Therefore, we assigned putative cell type identities to each cluster produced based on important developmental regulators (Figure 5A). We observed three categories of Cit− cells: PAX6+ clusters, which were deemed telencephalic progenitors (pTEL); NKX2-1+ clusters; and clusters negative for both. NKX2-1+ progenitors were further divided into ASCL1− MGE progenitors (pMGE) and ASCL1+ intermediate MGE progenitors (ipMGE). NKX2-1 and PAX6 negative cells were further divided into ASCL1− progenitors (p) and ASCL1+ intermediate progenitors (ip). Four main categories of Cit+ clusters emerged: GAD1+,PAX6+, SP8+ clusters were deemed LGE neurons (nLGE); ERBB4−,GAD1+ clusters were called MGE neurons (nMGE); ERBB4+, GAD1+ clusters were categorized as cortical interneurons (nCTX); while clusters that expressed OLIG1 and PDGFRα were classified as oligodendrocyte precursors (oMGE).
