Here we show that expression of three transcription factors can rapidly and efficiently convert mouse fibroblasts into functional neurons (iN cells). While the single factor Ascl1 was sufficient to induce immature neuronal features, the additional expression of Brn2 and Myt1l generated mature iN cells with efficiencies of up to 19.5% (Supplementary Fig. 6b). Three factor iN cells displayed functional neuronal properties such as the generation of trains of action potentials and synapse formation. These transcription factors were identified from a total of nineteen candidates that we selected because of their specific expression in neural cell types or their roles in reprogramming to pluripotency (see Methods).
