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6AIST TODAY 2013-1life-liaison-ml@aist.go.jpFor inquiries about this article : Research Planning Office of Life Science and BlotechnologyFig. 1 Pluripotent cell mass in the embryo of a vertebrate animal Egg yolkAnimal capAfrican clawed frogNewt(amphibian)Chicken(bird)MouseHuman(mammal)EpiblastInner cell massIntroductionResearch on stem cells including those of humans or research on regenerative science have recently attracted a great deal of attention. The fact is, however, that these fields have a long history from a biological standpoint, having already been researched since the 18th century.Regenerative phenomena are phenomena in life science that most typically represent the essence of life. They are broadly categorized into two types: physiological regeneration and damage regeneration.Physiological regeneration is a process that takes place in the human body on a daily basis. Take blood cells, for example. Some 60 million of these cells are produced and destroyed every second. In the entire human body, about 120 million cells are produced and destroyed every second, but your body today does not seem any different from how it was yesterday.Then there is the other phenomenon, damage regeneration. When we receive a cut on our hand or foot, the cut will heal on its own. If our liver is cut to one-third the original size by a surgical operation, the remaining one-third has the capability of returning to its original size. When one of the two kidneys is removed, the remaining kidney will increase in size to the equivalent of two kidneys (which is a type of damage regeneration and is technically due to metabolic hypertrophy). A newt, for example, regenerates the original form and function of limbs even when they are severed.As explained above, our body metabolizes all the time by its very nature, with old cells constantly being replaced by new cells. Even though we may suffer damage from some physical cause, we have the capability to restore the damaged part. Research is being carried out to clarify the actors that accomplish this capability (that is, stem cells and others) and its mechanism, so that the findings of this research can be applied to practical medical treatment.Stem cells in regenerationThe body is thought to heal itself in two ways when it suffers damage. One is the process in which a cell, which has already been differentiated, becomes temporarily dedifferentiated and is then differentiated again. The theoretical mechanism of regeneration for a newt whose limb has been severed then later repaired and regenerated to its original form is that the cells of muscles or bones at the severed part are dedifferentiated into mesenchymal stem cells and then redifferentiated into muscles or bones as required to deal with the cut surface. On the other hand, it is known that there are undifferentiated stem cells (somatic stem cells or tissue stem cells) throughout our body from the top of our head down to the tips of our toes. Even adults are known to have large numbers of stem cells in the skin, heart, bone marrow, muscles, brain, and almost all tissues and organs of the body. It is believed that these somatic stem cells are deeply related to the repair of damaged parts.What is a “pluripotent stem cell”?Stem cells, which are being actively investigated today, are broadly classified into three categories in terms of characteristics.In the process of embryogenesis, a cell, after fertilization, divides into a larger number of cells. When cell cleavage reaches the blastocyst stage, Current State and Future Prospects of Stem Cell Research

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