Directly generating terminally differentiated neurons could be useful in disease modeling and transplantation studies. However, a clear limitation of postmitotic iN cells is the inability to expand once reprogrammed. Large numbers of cells will be required for cell replacement-based therapies in a clinical setting, or for drug screening. Therefore, it would be desirable to induce expandable neural precursor cells directly from fibroblasts. Recently, Ding and colleagues successfully converted mouse fibroblasts to induced neural precursor cells (iNPCs) (Kim et al., 2011). In this study, the recipe for reprogramming was not tailored to the target cell type but instead identical to the iPS cell reprogramming factors (Figure 2). However, unlike for iPS cell formation, the factors were induced only for a short time, and the cells were then exposed to media favoring the growth of neural progenitor cells. After optimization of timing and culture conditions, colonies appeared that closely resembled neural rosette cells and expressed several relevant markers. Upon spontaneous differentiation, these iNPCs could give rise to multiple neuronal subtypes and astrocytic cells, indicating that the iNPCs were at least bi-potential neural
