1. A method of separating multipotential neural progenitor cells from a mixed population of cell types, said method comprising: selecting a promoter which functions selectively in the neural progenitor cells; introducing a nucleic acid molecule encoding a fluorescent protein under control of said promoter into all cell types of the mixed population of cell types; allowing only the neural progenitor cells, but not other cell types, within the mixed population to express said fluorescent protein; identifying cells of the mixed population of cell types that are fluorescent, which are restricted to the neural progenitor cells; and separating the fluorescent cells from the mixed population of cell types, wherein the separated cells are restricted to the neural progenitor cells.