Stem Cell Definition
Stem cells are the mother cells from which all other cells in the organism come. In early human development in the first 12 weeks of pregnancy embryonic stem cells have the ability to develop into all the cells that make up the embryo and placenta. (See: Embryological Development page) Later in the postnatal period so-called somatic adult stem cells are responsible for replenishing and repairing adult tissues like skin, blood vessel lining and the blood cells themselves. Stem cells are characterized by their ability to indefinitely reproduce themselves by dividing, self-renewing and by producing progenitor cells. The environment in which stem cells live plays an important role in determining what type of cell they develop into.
|What is a stem cell?|
There are several different types of stem cells. Stem calls are named based on their ability to differentiate into different types of tissues.
- Toti-potent stem cells are capable of developing into all types of cells, hence their name “toti” from total. Totipotent stem cells include spores of zygotes and in human embryos are present in its earliest stages of development.
- Pleuri-potent stem cells also known as embryonic stem cells, are characterized by 2 unique properties, their ability to develop into many different cell types and their ability to replicate indefinitely. In humans these cells come from an inner cell mass of the early embryo at about 1 week after fertilization and go on to develop into all the tissues of the body.
- Multi-potent stem cells can develop into cells from multiple, but a limited number of lineages. An example of a multipotent stem cell is the mesenchymal stem cell (MSC), which can differentiate into osteoblasts, chondrocytes, and adipocytes but cannot develop into muscle or other types of cells.
|Mesenchymal Stem Cell (MSC)|
|(Source: Dr Dirk Henrich)|
- Oligo-potent stem cells have the ability to differentiate into a few cell types. Examples of Oligopotent stem cells are stem cells in the vascular system that have the capacity to become both endothelial and smooth muscle cells.
- Induced Pluripotent Stem Cells (iPSC) are cells that have been taken from adults or children and genetically modified to behave like embryonic stem cells, i.e. they become pluripotent. As their name implies, iPSC are cells that have been induced to become pluripotent.
Stem Cells and Embryogenesis
Stem Cells and Embryogenesis
At the beginning of embryonic development there is just one stem cell, which forms the zygote. From the zygote the entire organism develops into over 200 different types of cells. During the first 5 days of development the zygote divides into stem cells, which later differentiate to embryonic stem cells and form the inner cell mass of the blastocyst.
|A single fertilized cell forms into a Zygote which gives rise
to the first stem cells which differentiated into embryonic stem cells
It is assumed that just the zygote and the stem cells from the first stages of the division are totipotent and can rebuild the entire organism from a single cell. In contrast embryonic stem cells, which develop later, are classified as pluripotent.
In embryogenesis embryonic stem cells undergo several differentiation processes, which lead to formation of several populations of highly differentiated cells. During this process embryonic stem cells loose their ability to differentiate into many different cell types and their high potential for self-renewal.
Adult vs. Embryonic Stem Cells
Adult stem cells exist in the fetus, children and in adults whereas embryonic stem cells exist only in the first 5 days of development. Adult stem cells are committed to becoming the type of cell of the their tissue of origin while embryonic stem cells are pluripotent and can differentiate into any cell type. In spite of being committed to being a cell type of its tissue of origin, adult stem cells can differentiate into different cell types within that tissue of origin. For example an adult stem cell in the vascular system can become an endothelial cell of the vessel wall or a smooth muscle cell from the vessel wall, but the same cell cannot become a bone cell. In contrast to embryonic stem cells, adult stem cells cannot be grown indefinitely in culture.
Very Small Embryonic Like (VSEL) stem cells
Studies have shown the presence of so-called Very Small Embryonic Like stem cells (VSEL) in adult tissues. These cells show a pluripotent ability committed to meso-, ecto- and endoderm differentiation. VSELs express several genes that are characteristic of pluripotent stem cells, like Oct4 and Nanog. The characterization of these stem cells in adult tissue requires immunological biomarkers and molecular tools like the fluorescence activated cell sorter (FACS), which permits analysis of several different markers on their surface simultaneously.
Therapeutic Applications of Stem Cells
Recent discoveries have led to a better understanding of the role stem cells play in tissue development, repair and regeneration. This has made it possible to use stem cells to treat a variety of different diseases. Bone marrow transplantation is a stem cell treatment that has been used to treat blood born cancers for more than 40 years. Other treatments, in the testing phase include for diabetes, other forms of cancer, Parkinson’s disease, ischemic heart disease, large bone defects, and many more.
As our knowledge of stem cells expands so will our ability to use them as in effective treatments. The potential for these treatments is tremendous. Stem cell therapy, for the first time in the practice of medicine, holds the promise of being able to cure disease, rather than just treat the symptoms.
Helpful related Links
A stem cell story. This 15-minute film provides an engaging, accessible and visually stunning introduction to the world of stem cell research. It uses innovative hand-drawn animation, beautiful cell photography and documentary interviews to capture the fascination and complexity of stem cells and regenerative medicine.
The California Institute for Regenerative Medicine (CIRM) was created in 2004 by a vote by the citizens of California in the USA, which authorized $3 billion in grants over ten years for embryonic stem cell and other biomedical research. It is claimed to be the world's largest single backer of stem cell research.
The Europe's stem cell hub, funded by the European Community, was established to help European citizens make sense of stem cells. It provides reliable, independent information and road-tested educational resources on stem cells and their impact on society.