There are now many papers reporting the generation of various types of neurons using permutations of diverse factors such as transcription factors, miRNAs, and small molecules. As discussed earlier some attempts have been made to generate specific neuronal subtypes with variable success. It has become more important than ever to properly define and characterize those iN cells. We have previously outlined gradual pan-neuronal parameters helping identify the maturation level of a given iN cell population [49]. Unlike other tissue systems that are made up of relatively homogenous populations of cells, the nervous system is bestowed with different neuronal subtypes formed by precise orchestrations of different morphogen gradients and transcription factors after early neural induction. Later in development, those different neuronal subtypes are further regionalized by transcription factors, morphogens and Hox gene expressions. All of these culminate into a complex neuronal network which scientists are just beginning to understand. It is conceivable that many neurological and neuropsychiatric diseases preferentially affect one neuronal subtype over others and that e.g. identical genetic lesions lead to different pathophysiological effects depending on the neuronal subtype. This has led to the motivation to generate specific neuronal subtypes.
