Classification of Stem Cells Based on Potential
Stem Cell potency is the ability of stem cells to be able to differentiate into specialized cell types. Cells with higher potency are able to generate more varied cell types than those with lower potency.
Totipotent Stem Cells
Totipotent stem cells have the highest versatility amongst the stem cell types. When a sperm and an ovum unite, they form a one-celled zygote. This cell is considered to be totipotent, which means that it has the potential to give rise to any and all cells of the entire body, such as the brain, skin, blood, etc. It has the ability to give rise to an entire functional organism through differentiation and self-renewal. The first few cell divisions of the zygote during embryonic development produce the most number of totipotent cells. After the fourth day of embryonic development, the cells start to specialize and become pluripotent stem cells.
Pluripotent Stem Cells
Pluripotent stem cells are similar to totipotent stem cells in that they can produce all types of tissues. But unlike totipotent stem cells, they cannot generate the body of an entire organism. On the fourth day of development, the cells of the embryo arrange themselves into two distinct layers, an outer layer which will become the placenta, and an inner mass that will form the tissues and eventually the organs of the human body. Though they can form nearly any human tissue, these inner cells, cannot do so without the presence of the outer cell layer; hence they are not considered totipotent but are pluripotent in nature. As these pluripotent stem cells continue to divide and differentiate, they begin to specialize giving further cell types.
Multipotent Stem Cells
Multipotent cells have less plasticity and are more differentiated than pluripotent stem cells. They can divide to produce a limited range of cells that belong to a particular type of tissue. The daughter cells of the pluripotent cells will eventually become the progenitors of cell lines such as blood cells, nerve cells, and skin cells. At this stage, they can give rise to one of several types of cells within a given organ and/or tissue. For instance, multipotent blood stem cells can give rise to many types of cells present in the blood such as red blood cells, white blood cells or platelets. These type of stem cells are also referred to as oligopotent stem cells.
Adult Stem Cells
An adult stem cell can either be a unipotent progenitor stem cell, which means that it can give rise to cells belonging to a single specific lineage or a specialized multipotent stem cell that can produce cells of a very limited type. in adult humans, these kinds of stem cells are used to replace cells that have either died or lost their function. They are undifferentiated cells present in a microenvironment of differentiated tissue known as a stem cell niche. They can renew themselves and can specialize to yield all cell types present within the tissue niche. Thus far, adult stem cells have been isolated from many tissue types such as the hematopoietic (blood), neural, endothelial, muscle, mesenchymal, gastrointestinal, and epidermal cells, etc.
These types of stem cells are also sometimes referred to as unipotent stem cells as they are able to contribute to the productions of only one mature cell type.