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7AIST TODAY 2013-1life-liaison-ml@aist.go.jpFor inquiries about this article : Research Planning Office of Life Science and Blotechnologyhttp://unit.aist.go.jp/scrc/cie/index_en.htmlFor inquiries about this article : Research Center for Stem Cell EngineeringFig. 2 Classification of human stem cells and research issuesFig. 3 Measurement of stem cells for standardization of stem cellsClassification of human stem cells and research issuesStem cell: A cell capable of differentiating into various types of cells (pluripotency) while maintaining an undifferentiated stateIn this approach, how stem cells form organs is being analyzed using various stem cells, and the mechanism of stem cells’ organ formation is being investigated based on the analysis results to gain an understanding of functional differentiation and apply the technique to practical fields.Embryonic stem cell (ES cell)・Has totipotency .・An ethical problem occurs in the case of humans as ES cells originate from embryos.・Cancer may occur after transplantation.Induced pluripotent stem cell (iPS cell)・Has totipotency and has no ethical problem.・Gene transfer is used.・Cancer may occur after transplantation.・Large variations exist among cells.Somatic stem cell (mesenchymal stem cell or tissue stem cell)・Has multipotency.・Causes no ethical problem.・Poor in proliferating ability. Does not cause cancer.Measurement of cellsEpigenome analysisApplication to standardizationof stem cellsCellCell membraneSurface proteinsCell surface sugar chainsProteomicsProtein marker analysisMicroarray analysisNucleus/DNACytoplasmetc.Use of next-generation supercomputeretc.etc.a collective mass of undifferentiated or pluripotent cells is seen in part of the embryo. Examples of such a cluster include animal cap cells in the animal pole during the blastocyst stage of a frog, blastodermal cells in chicken embryos, and inner clumps of cells in mammals such as human beings or mice (Fig. 1). When an inner mass of cells of a mouse, for example, is taken out and cultivated, it becomes embryonic stem cells (ES cells). These cells are capable of differentiating into any type of cells that constitute a body; that is, they are pluripotent in differentiation (Fig. 2). However, there is an ethical issue under discussion with respect to these ES cells because they are produced from embryos, each of which may become an individual life.In one of the fields of recent regeneration research, some researchers are working on dedifferentiation of already differentiated cells in the tissues or organs of a mature body, such as that of an adult human.In 1953, King and Briggs of the United States took out the nuclei of cells in the blastocyst stage, which are divided somatic cells, in a frog egg, put them in an enucleated unfertilized egg, and successfully turned the differentiated cells back into undifferentiated cells. In 1963, Gurdon of the United Kingdom cloned a frog by transferring a cell nucleus in the intestines of a tadpole into an enucleated unfertilized egg, turning the differentiated nucleus back into an undifferentiated state, then fertilizing the egg to restart embryogenesis and create a tadpole. This process is called reprogramming, as it uses the power of the cellular cytoplasm of the unfertilized egg to dedifferentiate differentiated cells.A recent ongoing study focuses on a method that uses transcription genes to reprogram differentiated cells into undifferentiated cells with multipotency or pluripotency. These cells are known as induced pluripotent stem cells (iPS cells). Yamanaka et al. transferred four genes, Sox2, Oct3/4, c-Myc, and Klf4, into a fibroblast and created undifferentiated cells with induced pluripotency.This means that iPS cells reprogrammed differentiated cells into totipotent cells. Unlike ES cells, iPS cells cause no ethical problems. As this technique creates iPS cells from the cells of a patient, it can promote research that reflects the condition of the patient’s disease or facilitate the development of cell transplant therapy with

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