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Figure 1. Origin of pluripotent and multipotent stem cells. Pluripotent embryonic stem (ES) cells reside in the inner cell mass (ICM) of the blastocyst. The ICM that forms the human embryo can be isolated and expanded in vitro under appropriate culture conditions that include cells cultured at an appropriate density on plastic surfaces in the presence of soluble growth factors. Recently, the requirement for a mouse feeder-cell layer has been overcome [26]. Following insertion of murine ES cells into a blastocyst from a genetically distinct mouse, a chimeric offspring develops in which some of the cultured ES cells differentiate into each tissue. Multipotent stem cells are intermediate stem cells that are thought to be generally restricted to the lineage of a specific organ.
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