Nuclear reprogramming of somatic cells to pluripotent stem cells

Nuclear Reprogramming is a phenomenon that fully differentiated somatic cells revert to pluripotent stem cells through change of epigenetic modifications without genetic alterations. This was first shown by successful production of cloned frogs by nuclear transfer of embryonic cells to UV-treated eggs in more than 50 years ago. Now, development of a micro-manipulation technology realize to generation of cloned mammals in various species. Furthermore, embryonic stem (ES) cells, which are indefinitely self-renewable pluripotent stem cells established in vitro from the inner cell mass cells of blastocysts, have a unique property of nuclear reprogramming of somatic nuclei by cell fusion. In ES-somatic. hybrid cells, somatic genomes are epigenetically and functionally closely similar to ES genomes as demonstrated by reactivation of pluipotent genes and repression of somatic genes. Reprogramming activity of ES cells indicate that full factors concerned with the reprogramming are contained in ES cells. Recently, it is highlighted that retroviral transduction of several defined factors isolated from ES cells are sufficient for generating pluripotent (iPS; induced pluripotent stem) cells from embryonic and adult somatic cells. Relaxation of nuclear chromatin is required prior to reactivation of pluripotent genes, although molecular mechanism of the reprogramming is not fully understood. ES and iPS cells have great potential for applying to regenerative and pharmaceutical medicines in near future.