Figure 1.

Routes of cell fate conversion. (a) Reversion to a totipotent state can be achieved by somatic cell nuclear transfer, whereas reversion to a pluripotent state is accomplished by iPS cell reprogramming, or cell fusion with ESCs. (b) Direct conversion of fate between two differentiated states without de-differentiation. Examples of direct conversion include fibroblast to neuron, hepatocyte or cardiomyocyte lineages. (c) De-differentiation to a progenitor state, as exemplified by loss of Pax5 expression in mature B cells. (d) Transdetermination of an adult stem cell from its normal lineage into a closely related lineage. Each sphere represents a distinct stage of cell differentiation, with the most brightly colored spheres corresponding to mature cells. Directed differentiation directs cells down this natural cascade of fate specification.