Neural Induction and Patterning in Mammalian Pluripotent Stem Cells

Embryonic stem (ES) cells are derived from the inner cell mass (ICM) of blastocyst stage embryos, while induced pluripotent stem (iPS) cells are generated from somatic cells through transient overexpression of defined transcription factors. When transplanted into a preimplantation embryo, ES cells and iPS cells can differentiate into any cell type, including germ cells. Moreover, they can grow in culture indefinitely while maintaining pluripotency. In vitro differentiation of ES cells and iPS cells recapitulates many aspects of in vivo embryogenesis. The acquisition of neural fates (neural induction) in ES cells can be controlled by bone morphogenetic protein (BMP), fibroblast growth factor (FGF), and Wnt signaling, while the production of specific neural cell types (neural patterning) can be controlled by exogenous patterning signals such as Wnt, BMP, Shh, FGF, and retinoic acid. In response to these signals, ES cells can differentiate into a wide range of neural cell types that correlate with their positions along the anterior-posterior and dorsal-ventral axes. ES cell and iPS cell culture systems will provide materials for cell replacement therapy, and can be used as in vitro models for disease and drug testing as well as development. Here we review spatiotemporal control of neural differentiation of mammalian pluripotent stem cells, with a special emphasis on the relationship between in vivo embryogenesis and in vitro ES cell differentiation. Retinal differentiation from ES cells and iPS cells is also outlined.