Fig. 1.

Direct conversion of human skin fibroblasts to tripotent iNPCs. (A) Schematic of the conversion process from fibroblasts to induced neuronal progenitor cells (iNPCs). Fibroblasts were transduced with retroviral vectors containing four reprogramming factors (Sox2, KLF4, Oct3/4, c-Myc). (B and C) Within 6–10 d, cells underwent marked morphological changes from a fibroblastic spindle like shape (B) to a sphere-like form commonly seen with NPCs (C). (D and E) Immunofluorescence of cultures at day 12 reveals expression of the NPC markers Pax6 and Nestin, as shown in red. DAPI staining (blue) was used to visualize nuclei. (F) iNPCs can form and grow as neurospheres when plated in uncoated dishes. (G) RT-PCR analysis demonstrates a strong up-regulation of the prototypic NPC markers NCAN and NKX2-2 in iNPCs. β-Actin was used as loading control. (H–J) iNPCs are tripotent and upon differentiation they can give rise to oligodendrocytes (H), neurons (I), and astrocytes (J). (Scale bars: black, 100 µm; white, 50 μm.) Fibro, fibroblast.