embryonic stem cell research

bone marrow contains many differenttypes of cells several of which have specialized roles in the blood. in the early 1960s it was shown that if bone marrow was taken from one mouse and transplanted into another, rare andunspecialized cells could travel to the spleen where they woulddivide and form small colonies these colonies contained a mixture of different blood cell types. incredibly when these colonies wereremoved and retransplanted these rare cells formed new colonies in the spleen of a second mouse. these experiments reveal two definingproperties of a stem cell

first a stem cell must be able to self renew. that is, it must be able to divide and give rise to more cells like itself. second, it must be able to differentiatein other words it must be able to divide and give rise to specialized cells. since these early experiments many different types of stem cells havebeen discovered and this general definition applies toall of them. following fertilization, the developingembryo contains a group of cells known as the "inner cell mass" that will eventually go on to form all tissues in the body. however at theearly stage of development

these cells have not yet committed tobecome a specific type of cell and are said to be in an undifferentiated state. if the cells of the "inner cell mass" are isolated they can grow indefinitely in a plasticdish and maintain this undifferentiated state. these cells are known as "embryonic stem cells" or es cells like cells in the developing embryo es cells retain the ability to form any type of cell in the adult body thus es cells are said to be "pluripotent" by studying the signals required tocontrol how es cells develop into specific cell types

scientists may be able to developtherapies capable of restoring damaged tissues most of the cells in our bodies are notstem cells. for example blood and skin cells have become specialized toperform a specific function in the body. by a process known as differentiation,that is normally not reversible. however, if some adults are taken grown in plastic dishes and given specific genetic instructions over time, a small number of these cells will reverse from their differentiated state and develop the ability to redifferentiate into any cell type in the body. thisnewfound ability

is known as "pluripotentcy", and therefor these cells are known as "induced pluripotent stem cells" or ips cells. the creation of ips cells from individual patients may one day allows us to develop replacement tissues that are a perfect genetic match to the patient. in addition, thecreation of ips cells from patients with specific diseases will allow scientists to develop newdrugs to treat a wide variety of disorders