Stem cells in the developing and adult nervous system

Abstract

The fertilized egg is a totipotent stem cell that can produce all cell types of the organism, including the embryonic and the extraembryonic tissues. As development proceeds, cells lose their capacity to proliferate and differentiate into different cell types, and gain specialization. However, advances in stem cell biology have provided new insights into development and regenerative medicine. For example, neural stem/progenitor cells have been found to exist not only during embryonic development, but also in the adult nervous system of mammals. Moreover, although development of an organism proceeds irreversibly from embryo to adult with cells differentiating progressively toward specialized cell types, somatic cells can be artificially reprogrammed to adopt a different cell fate, as exemplified by induced pluripotent stem cells (iPS cells) and induced neuronal cells (iN cells). Complex 3D tissue including the retina, cortex and adenohypophysis can be generated from pluripotent stem cells in vitro . Notably, autologous transplantation of an iPS cellderived retinal pigment epithelium sheet was carried out for patients with aged macular degeneration in Japan in 2014. iPS cell technology is opening a new era in regenerative medicine and drug discovery. Here, we summarize the current views of stem cell biology during embryogenesis and adult neurogenesis, and then discuss therapeutic potential of stem cells, focusing on retinal development and regeneration.