The prevalent genetic defects and acquired injuries of the peripheral nervous system (PNS) cause a significant socioeconomic issue on our healthcare system. However, there are relatively few detailed studies of human PNS tissues, due to the difficulty to obtaining patient samples. We have shown that peripheral neurons and Schwann cells can be derived from human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs); however, the process is arduously long (at least over 5 months). Recently we developed an alternative, a new method that directly converts human fibroblasts into induced neural crest (iNC) in only two weeks. Our iNC population exhibits neural crest- specific cellular and molecular characteristics. Although the iNC population shows multipotency in a single cell level, they are more prone to a sensory neuron fate, rather than autonomic neuron lineages. During development, cell fates are determined by cell extrinsic factors, such as growth factors and morphogens. If such cell extrinsic factors also govern cell fates during generation of iNC, we may be able to change the differentiation potential of the iNC. This hypothesis incites a question, whether modulation of cell extrinsic factors (such as ventralization and/or caudalization cues) can influence the cellular fate during direct conversion, in the same way that this mechanism operates in developmental cell determination. Currently direct conversion, exemplified by our iNC, is dependent on transcription factors delivered by oncogenic viral transduction. Our second question is whether and how `non-genetic' small molecules can achieve sufficient direct conversion of human fibroblasts to induced neural crest? Our current iNC induction system is suitable for investigating these fundamental questions about cell fate plasticity, because it employs only a single transcription factor, along with highly quantitative detection method (SOX10::GFP detection by FACS). Our proposed experiments are expected to: (i) expand and strengthen our current conception of general `genetic factor-dependent' direct conversion, and (ii) accelerate a wide range of research on PNS disorders, e.g. by providing disease-specific Schwann cells or sympathetic neurons directly from fibroblasts of Charcot-Marie- Tooth1A (CMT1A) or familial dysautonomia patients.
Neural crest cells have involved various types of human genetic diseases such as craniofacial abnormality, pediatric cancers and human genetic neuropathy, but due to the scarcity of human NC cells, the extensive study of these disease and efforts to discover potential drug have been delayed. With minimal genetic cue and/or chemical compound(s), we propose the development of innovative scheme for derivation of peripheral neurons and Schwann cells in patient-specific manner. Our new protocols will provide human neural crest cells, which is potentially useful to understand pain sensation and to further regenerative medicine.
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