Measurements of the yield of iN cell conversion in three stem cell lines, H1 ES cells and two different iPS cells lines, showed that nearly 100% of surviving lentivirally infected ES and iPS cells were converted into neurons, revealing an unprecedented efficiency of conversion (Fig. 2D). When we calculated the number of iN cells generated as a function of starting ES or iPS cells, we observed an apparent increase with H1 ES-cell derived iN cells but not with the two iPS cell line derived iN cells (Fig. 2D). The increase in cell numbers in H1 ES-cell derived iN cells is due to the continuing division of H1 cells after plating; iPS-cell derived iN cells do not show such increased cell numbers because they exhibit some cell death in response to culture splitting and lentiviral infection, resulting in a partial loss of the iPS cells as iN cells are being generated. Overall, these data demonstrate that forced expression of a single transcription factor –Ngn2– induces neuronal differentiation with high yield.
