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Abstract
Differentiated cells can be reprogrammed to an embryonic-like state by transfer of
nuclear contents into oocytes or by fusion with embryonic stem (ES) cells. Little
is known about factors that induce this reprogramming. Here, we demonstrate induction
of pluripotent stem cells from mouse embryonic or adult fibroblasts by introducing
four factors, Oct3/4, Sox2, c-Myc, and Klf4, under ES cell culture conditions. Unexpectedly,
Nanog was dispensable. These cells, which we designated iPS (induced pluripotent stem)
cells, exhibit the morphology and growth properties of ES cells and express ES cell
marker genes. Subcutaneous transplantation of iPS cells into nude mice resulted in
tumors containing a variety of tissues from all three germ layers. Following injection
into blastocysts, iPS cells contributed to mouse embryonic development. These data
demonstrate that pluripotent stem cells can be directly generated from fibroblast
cultures by the addition of only a few defined factors.