A few overall trends emerged from these analyses (Figure 5B). PAX6+ progenitors (pTEL) were observed from D24 to D100, with peak production at D24. The only progenitor type observed at every timepoint was the pMGE, NKX2-1+ progenitor, which constituted 37% of all Cit− cells collected and profiled. ASCL1+ intermediate MGE progenitors (ipMGE), were observed only during the initial 54 days of culture, whereas PAX6−NKX2-1− progenitors (p, ip) were only observed from D100 through D125, possibly indicating a switch from neurogenesis to gliogenesis. In addition to the expression of ASCL1, clusters classified as intermediate progenitors also tended toward higher expression of DLL, DLL3 and CCND2 (Figure 4A). Previous work has indicated that CCND2 expression indicates intermediate progenitor status, and may bias interneuron progenitors toward the PVALB fate (Glickstein et al., 2007; Petros et al., 2015).
