skeletal muscle lineage, can induce many features of muscle cells in fibroblasts in the late 1980s, several other examples of remarkable cell-fate changes have been observed in response to forced expression of transcriptional regulators, but until recently it was assumed that this phenomenon is limited to closely related cell lineages (for discussion and historical background, see Graf, 2011, in this issue). After the initial description of iN cells, additional studies showed that fibroblasts can be directly converted to a diverse range of cell types, such as cardiomyocytes (Ieda et al., 2010;), blood cell progenitors (Szabo et al., 2010) and hepatocytes (Huang et al., 2011; Sekiya and Suzuki, 2011). In this review, we discuss the recent advances in direct lineage reprogramming towards the neuronal lineage and propose criteria that can be used to identify successfully reprogrammed iN cells.
