Direct conversion. a Schematic of the experimental protocol. b Cells probed with a mature neuronal marker anti-MAP2 (green) and a tubulin marker anti-TUJ1 (red) revealed that mature iNeurons are detected from day 7. Cells were counter stained with the nuclear marker DAPI (blue). Scale bars = 250 μm. c Expression of mature neuronal markers in iNeurons. Green: MAP2, NeuN, Synapsin; red: TUJ1; blue: DAPI. Scale bars: 50 μm. d Quantification of iNeurons based on TUJ1-positive cells divided by the number of initial plating cells in response to PTBP1 shRNA. Cells untreated with shPTBP1 had no TUJ1-positive staining. Data are from three experiments (the mean ± SEM, n = 30–82).