Molecular and cellular characterization of epi-NSCs. (A–B′) Neur expression (Neur-GFP, green) only partially overlapped with expression of the NSC markers Ase (red, A) and Hth (red, B). Arrows point to the nuclei of several medial TZ cells. (C–C″) TZ cells (L’sc, red) expressed CycB (green), supporting that they are in G2 phase. In contrast, heterogenous CycB expression is seen in the NE. (D–D″′) Cross-section view showing a small basal cell at the medial edge of the TZ (arrow) expressing Pros (red), Neur-GFP (green), and Hth (blue). This cell likely corresponds to a GMC derived from the asymmetric division of an epi-NSC. (E–H) Snapshots of a time-lapse video tracking an epi-NSC (Neur-GFP, green) entering mitosis (His2Av-RFP, red) and dividing asymmetrically to producing a large apical cell (E) and a small basal cell (F). Arrows point to the dividing epi-NSC and its progeny cells. (I–J′) Snapshots of a time-lapse video showing a surface view of the TZ (E-cad-mCherry, red). E-cad is retained apically as the epi-NSC (Neur-GFP, green; arrow) undergoes mitotic rounding. Scale bars = 10 µm.