The following method was used to calculate the efficiency of neuronal induction. The total number of Tuj1+ cells with a neuronal morphology, defined as cells having a circular, three dimensional appearance that extend a thin process at least three times longer than their cell body, were quantified twelve days after infection. This estimate was based on the average number of iN cells present in 30 randomly selected 20× visual fields. The area of a 20× visual field was then measured, and we used this estimated density of iN cells to determine the total number of neurons present in the entire dish. We then divided this number by the number of cells plated before infection to get a percentage of the starting population of cells that adopted neuron-like characteristics.
