A stem cell is a relatively undifferentiated cell that can divide to produce more differentiated tissue cells, by following a genetic program of one-time gene expression that often leads to programmed cell death in the differentiated cells.
Stem cells have two important characteristics that distinguish them from other types of cells. First, they are unspecialized cells that renew themselves for long periods through cell division. The second is that under certain physiologic or experimental conditions, they can be induced to become cells with special functions such as the beating cells of the heart muscle or the insulin-producing cells of the pancreas.
Stem cells are important for living organisms for many reasons. In the 3- to 5-day-old embryo, called a blastocyst, embryonic stem cells in developing tissues give rise to the multiple specialized cell types that make up the heart, lung, skin, and other tissues. In some adult tissues, such as bone marrow, muscle, and brain, discrete populations of adult stem cells generate replacements for cells that are lost through normal wear and tear, injury, or disease.
Stem cells from skin cells breakthrough
In November 2007, two independent teams of researchers, from Kyoto University and the University of Wisconsin in Madison, announced that they had managed to turn ordinary skin cells into cells that look and behave like embryonic stem cells. Both teams used four genes to transform fibroblasts into what are called induced pluripotent (iPS) cells – similar to human embryonic cells. This major breakthrough will enable patient- and disease-specific stem cells to be produced without using human eggs or embryos.