What is an adult stem cell?
• Adult Stem Cells can proliferate without differentiating for a long period (a characteristic referred to as Long-Term Self-Renewal), and they can give rise to mature cell types that have characteristic shapes and specialized functions. • Some adult stem cells have the capability to differentiate into tissues other than the ones from which they originated; this is referred to as Plasticity. • Adult stem cells are rare. Often they are difficult to identify and their origins are not known. Current methods for characterizing adult stem cells are dependent on determining cell Surface Markers and observations about their Differentiation patterns in test tubes and culture dishes. • To date, published scientific literature indicates that adult stem cells have been derived from brain, bone marrow, peripheral blood, dental pulp, spinal cord, blood vessels, skeletal muscle, epithelia of the skin and digestive system, cornea, retina, liver, and pancreas; thus, adult stem cells have been found in
A. Adult stem cells, also known as tissue-specific stem cells, are present in adults, children, newborn infants and developing fetuses. Adult stem cells are more limited and specialized than embryonic stem cells. They have the ability to make just one or two kinds of tissue, such as blood and immune system cells, brain or muscle cells. Adult stem cells also have a more limited capacity to replace themselves than do embryonic stem cells.
Adult stem cells, like all stem cells, share at least two characteristics. First, they can make identical copies of themselves for long periods of time; this ability to proliferate is referred to as long-term self-renewal. Second, they can give rise to mature cell types that have characteristic morphologies (shapes) and specialized functions. Typically, stem cells generate an intermediate cell type or types before they achieve their fully differentiated state. The intermediate cell is called a precursor or progenitor cell. Progenitor or precursor cells in fetal or adult tissues are partly differentiated cells that divide and give rise to differentiated cells. Such cells are usually regarded as “committed” to differentiating along a particular cellular development pathway, although this characteristic may not be as definitive as once thought [82] (see Figure 4.1. Distinguishing Features of Progenitor/Precursor Cells and Stem Cells). Figure 4.1. Distinguishing Features of Progenitor/Prec
