In vitro reprogramming of fibroblasts into a pluripotent ES-cell-like state

Nuclear transplantation can reprogramme a somatic genome back into an embryonic epigenetic state, and the reprogrammed nucleus can create a cloned animal or produce pluripotent embryonic stem cells. One potential use of the nuclear cloning approach is the derivation of ‘customized’ embryonic stem (ES) cells for patient-specific cell treatment, but technical and ethical considerations impede the therapeutic application of this technology. Reprogramming of fibroblasts to a pluripotent state can be induced in vitro through ectopic expression of the four transcription factors Oct4 (also called Oct3/4 or Pou5f1), Sox2, c-Myc and Klf4. Here we show that DNA methylation, gene expression and chromatin state of such induced reprogrammed stem cells are similar to those of ES cells. Notably, the cells—derived from mouse fibroblasts—can form viable chimaeras, can contribute to the germ line and can generate live late-term embryos when injected into tetraploid blastocysts. Our results show that the biological potency and epigenetic state of in-vitro -reprogrammed induced pluripotent stem cells are indistinguishable from those of ES cells. Stem cells with potential The search for new ways of coaxing readily available cells to show the pluripotent activity of embryonic stem cells — the potential to differentiate into virtually any cell type — continues. The stakes are high, since if it can be achieved safely for human cells, cell transplantation therapy, even patient-specific therapy, will have come a step closer. Two groups now report an important advance in this direction: the creation of pluripotent stem cells from mouse fibroblasts. The epigenetic reprogramming requires the expression of four transcription factors, Oct3/4, Sox2, c-Myc and Klf4. The resulting cells resemble embryonic stem cells in both biological potency and epigenetic state. Four transcription factors Oct4, Sox2, c-Myc and Klf4 are known to convert fibroblasts to pluripotent stem cells, if Fbx 15 expression is also selected. But the induced stem cells were shown to be distinct from normal embryonic stem cells. However, if cells expressing Nanog and Oct4 are selected, then the reprogrammed fibroblasts are similar to embryonic stem cells in both biological potency and epigenetic state.