Encyclopedia of Stem Cell Research
What is a stem cell? We have a basic working definition, but the way we observe a stem cell function in a dish may not represent how it functions in a living organism. Only this is clear: Stem cells are the engine room of multicelluar organisms for both plants and animals. They live in cave-like “niches,” surrounded by intricate signals that allow them to divide—either to make more of themselves (self-renew), or to produce a progeny that can go on to make a specific type of tissue. They can often be plucked from this environment and placed in a nutrient broth at body temperature and encouraged to divide, although the niche is generally lost and their characteristics often change.