We also observed temporal changes within cluster types (Figure 5C, D). At D24, pTEL progenitor clusters expressed slightly higher levels of MKI67 and GPC3, indicating these early populations are mitotically active (Filmus, 2001; Scholzen and Gerdes, 2000). By D54 and D100, pTEL progenitor clusters express NFIA and HOPX, consistent with a transition to astrogliogenesis and/or outer radial glial cell production (Deneen et al., 2006; Pollen et al., 2015; Shu et al., 2003; Thomsen et al., 2016). After D54, pMGE clusters also express higher levels of HOPX, in addition to AQP4, S100B, ANXA1, and S100A10 compared to earlier clusters. These genes have been implicated in astrocyte differentiation and/or function, another indication that progenitors in vitro make the transition to gliogenesis at late stages, as occurs in vivo (Donato et al., 2013; Eberhard et al., 1994; Nielsen et al., 1997).
