To expand the panel of markers, we performed single-cell qPCR on AD-iN cells at 5 WPI. Confirming our immunostaining results, ~80% of the cells that expressed any Ca2+-binding proteins or SST (41 cells) expressed either CB (22 cells), CR (4 cells), or SST (7 cells) (Fig. 2k). We also found several cells expressing CCK, a gene frequently expressed among human cortical interneurons17. The low frequency of PV-positive neurons was potentially due to the late developmental expression of this marker1,2,4,18. Previous studies showed that accelerated generation of motor neurons from PSCs could be achieved by the use of Notch inhibitors19. Indeed, when we treated AD-iN cells with a γ-secretase inhibitor (DAPT), we observed improved complexity of the neuronal morphology in terms of neurite arborization (Supplementary Fig. 5). However, DAPT treatment did not enhance the appearance of PV-expressing cells.
