The cloning of mammals from adult donor cells has demonstrated that the oocyte can reprogram a differentiated nucleus into a pluripotent embryonic state. Reprogramming of committed cells into pluripotent cells can also be achieved by the explantation of germ line cells and by the fusion of differentiated cells with embryonic cells. The future challenge will be to stably convert a differentiated cell into embryonic stem (ES) cells by the transient expression of defined genes. Recent findings suggest that the exposure of adult cells to a few defined factors can indeed induce a pluripotent-like state resembling that of ES cells. This approach may allow for the generation of patient-specific stem cells in order to study and treat degenerative diseases without recourse to nuclear transfer.
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