Next, we assessed the kinetics and efficiency of 5F-induced neuronal conversion. In MEFs, Tuj1-positive cells with immature neuron-like morphology were found as early as three days after infection (Fig. 3a). After five days, neuronal cells with long, branching processes were readily detected, and over time increasingly complex morphologies were evident, suggesting an active process of maturation in newly formed iN cells (Fig. 3a). Similarly, we detected TauEGFP expression as early as day five (Supplementary Fig. 3h). The fraction of TauEGFP-positive cells remained similar at eight and thirteen days post-infection, as determined by FACS analysis suggesting no de-novo generation of iN cells after day 8 (Fig. 3b). Electrophysiological parameters such as action potential height, resting membrane potential, membrane input resistance, and membrane capacitance also showed signs of maturation over time (Fig. 3c–g, Supplementary Tables 2,3).
