Human stem cells as a model of motoneuron development and diseases.

Human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) possess the potential to become all cell and tissue types of the human body. Under chemically defined culture systems, hESCs and hiPSCs have been efficiently directed to functional spinal motoneurons and astrocytes. The differentiation process faithfully recapitulates the developmental process predicted from studies in vertebrate animals and human specimens, suggesting the usefulness of stem cell differentiation systems in understanding human cellular development. Motoneurons and astrocytes differentiated from genetically altered hESCs or disease hiPSCs exhibit predicted phenotypes. They thus offer a simplified dynamic model for analyzing pathological processes that lead to human motoneuron degeneration, which in turn may serve as a template for pharmaceutical screening. In addition, the human stem cell-derived motoneurons and astrocytes, including those specifically derived from a patient, may become a source for cell therapy.