To estimate the conversion efficiency, we first determined how many of the MEF-derived iN cells divided after induction of the viral transgenes by treating the cells with BrdU throughout the duration of the culture period and beginning one day after gene induction. The results showed that the vast majority of iN cells became postmitotic by 24 hours after transgene activation (Fig. 3h–i). This allowed us to roughly estimate the conversion efficiency of our method by quantifying the total number of Tuj1-positive iN cells in the entire dish on day twelve, and dividing this number by the number of plated cells (see methods). Using this method, the efficiency ranged from 1.8–7.7% in MEF and TTF-iN cells (Fig. 3j) presumably due to slight variations in titers of the viruses. These calculations might be an underestimation of the true conversion rate because not all cells receive the necessary complement of viral transgenes.
