Abstract: Once neurons are lost because of injury or degeneration, they hardly ever regenerate in most mammalian central nervous system (CNS) regions. In adult rodents, some brain regions, such as the subventricular zone of the lateral ventricle and the subgranular zone of the dentate gyrus, retain neural stem cells (NSCs) and generate new neurons. Although a small population of new neurons derived from NSCs migrate toward lesion sites after brain injury, they are insufficient to completely restore neuronal functions. Cell transplantation using induced pluripotent stem cells (iPSCs) or embryonic stem cells (ESCs) has become an attractive therapeutic strategy for nerve injury or degeneration (Barker et al., 2015; Huang and Zhang, 2019). For Parkinson’s disease, transplantation of dopaminergic neurons from human ESCs or iPSCs is emerging as a therapeutic approach (Li and Chen, 2016). However, the risks of immune rejection and tumorigenesis remain substantial drawbacks of this therapeutic approach.