The Art of Healing. The Science of Regeneration.
What is a Stem Cell?
A stem cell is a non-specialized (undifferentiated) cell which is capable of two processes: self-renewal and differentiation.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -What is the difference between Self Renewal & Differentiation?
Self-renewal is the ability of stem cells to replicate and create multiple, identical copies of the non-specialized cell. Differentiation is the ability of stem cells to develop into the specialized cell types found throughout the body including osteoblasts, chondrocytes, blood cells, epithelial cells, etc.. Stem cells can be considered totipotent, pluripotent, multipotent, bipotent, and unipotent. The two main types of stem cells are embryonic stem cells (ESCs) and adult stem cells. Embryonic stem cells are present during embryo and fetal development. Adult stem cells are found in tissues of the body and are necessary for tissue repair, maintenance, and growth throughout life. [1-5]
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Figure 1. |
Toti-, Pluri-, Multi-potent…What’s the difference?
Stem cells are classified based on their differentiation potential. Some stem cells are able to develop into each of the 200 cell types found in the body while others can only differentiate into one cell type.
Pluripotent cells are capable of forming any cell found in the body however, they are not capable of forming an entire organism. Embryonic stem cells are pluripotent cells.
Totipotent cell is capable of developing into a complete organism. [1-6] In order to form a complete organism, the development of structures which allow for implantation into the uterine wall are necessary. Placental development is also essential for delivering nutrients to the fetus. Only totipotent cells are capable of forming these structures. [7]
The zygote and early cells arising from zygotes known as blastomeres are truly totipotent cells. [8]
Multipotent is a term used to describe stem cells which are capable of differentiating into cells belonging to a particular lineage. For example, mesenchymal stem cells are capable of differentiating into cells of the mesodermal lineage. Hematopoietic stem cells are also multipotent stem cells which give rise to all mature blood cells. [1-6]
Bipotent is a term used to describe stem cells which are capable of differentiating into two cell types. Lymphoid progenitor cells can develop into T cells and B cells. [2]
Unipotent is a term used to describe stem cells which are capable of differentiating into only one mature, terminally differentiated cell type. Spermatagonial stem cells are unipotent and only capable of developing into sperm cells. [1-6]
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Figure 2. |
What is the difference between Embryonic Stem Cells, Adult Stem Cells, and iPS cells?
Embryonic Stem Cells (ESCs) are undifferentiated, pluripotent cells isolated from the inner cell mass (ICM) of the blastocyst during embryo development and expanded using in vitro culture methods. ESCs are capable of differentiating into all of the cell types found in the body. Ethical concerns surround the potential use of ESCs in the fields of regenerative medicine, tissue engineering, and cellular therapeutics. Furthermore, ESCs have the potential of developing into tumors and invoking an immune response. [1-6]
Adult Stem Cells are undifferentiated, multipotent cells located throughout differentiated tissues in the body. Adult stem cells are capable restricted to differentiating into cells of a particular tissue. While adult stem cells are rare, they function to repair and replace damaged tissue resulting from injury, disease, or aging. [1, 4,7,8]
Figure 3. Difference in Stem Cells Chart
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