Where Can Stem Cells Be Obtained, and How Do Various Types of Stem Cells Differ?
Once an embryo implants in the uterus and begins to make specific organs, at about 25 days after fertilization, separate groups of more mature stem cells take up residence in the different organs (blood, skin, brain, etc.) and contribute to making the cells of each organ. These cells remain in the organ throughout life and can be obtained at any time in development as well as in adulthood, but are more abundant early during development, when the fetus is growing. These later cells are called organ-restricted, “multipotent” stem cells (sometimes referred to as adult stem cells, because a limited number remain in and can be isolated from adult organs). Great interest and effort are being put into investigating both ES cells and multipotent stem cells, but it is not clear whether the multipotent (adult stem) cells live as long or are as viable as the pluripotent ES cells. Research shows that multipotent cells are certainly not as versatile or potent as ES cells. Our knowledge is currently
