Embryonic stem cell.

Mouse embryonic stem (ES) cells are the cells that possess pluripotential differentiation activity into not only all somatic cells but also germ cells. Genetic alteration of mouse ES cells can be easily achieved and such genetic modification can be introduced into the animal, since ES cells are differentiated into germ cells in vivo. This technology enables us to analyze the function of any particular genes of interest in mice. And in vitro differentiation induction of mouse ES cells into various cell lineages, such as blood cells, neural cells, and cardiac muscle cells, has been studied. In vitro hematopoietic differentiation experiments were carried out most extensively and can be regarded as a model system of induction. Recently, human ES cells have been established. Many scientists, clinicians and even mass media have entertained the idea that human ES cells can be used after changing the cells into lineage-specific stem cells or progenitor cells such as hematopoietic stem cells and neural progenitor cells.