Stem cells in animals are major undifferentiated cells that retain the ability to divide and differentiate into other cell types. As these cells have the ability to divide and differentiate, they can be handy in repairing systems of the body.
It is believed that stem cell research has the potential to revolutionise the face of human disease by using it to repair specific tissues or to grow organs.
Stem cells differ from other kinds of cells in the body in more than one way. Regardless of their source, all stem cells have three general properties which is unique to them:
- Stem cells are capable of dividing and renewing themselves for long periods
Stem cells have the capability to replicate many times. This process of cell replication performed by themselves many times over, is called proliferation.The number of times proliferation can occur is simply unlimited. The same is not true for other type of cells. For example, muscle cells, blood cells, or nerve cells do not normally replicate themselves. In the laboratory, a starting population of stem cells can yield millions of cells through proliferation.
- Stem cells are unspecialized
One of the basic properties of a stem cell is that it is not specialized. It means that it does not have any tissue-specific structures that will allow it to perform specialized functions. It is in quite contrast to other cell type, which has a dedicated function. For example, a heart muscle cell is supposed to pump blood through the body. It can not be instrumental in other dissimilar activities.
Scientists have shown keen interest in the specific factors and conditions that allow stem cells to remain unspecialized. It has taken scientists many years of trial and error to learn to grow stem cells in the laboratory without stem cells being spontaneously differentiated into specific cell types. For example, it took 20 years to learn how to grow human embryonic stem cells in the laboratory following the development of conditions for growing mouse stem cells. Therefore, an important area of research is understanding the signals in a mature organism that cause a stem cell population to proliferate and remain unspecialized until the cells are needed for repair of a specific tissue. It is critical for scientists to have such information to be able to grow large numbers of unspecialized stem cells in the laboratory for further experimentation.
- Stem cells can give rise to specialized cell types
As discussed earlier, stem cells are unspecialized. But, they have the ability to give rise to specialized cells. This process is called differentiation. These are the early stages of research regarding differenriation. But, from whatever research material is available, it is apparent that there are some signals which trigger this process. The signals are both internal and external. The internal signals are controlled by a cell's genes, which are interspersed across long strands of DNA, and carry coded instructions for all the structures and functions of a cell. The external signals for cell differentiation include chemicals secreted by other cells, physical contact with neighboring cells, and certain molecules in the microenvironment. As per one study, in normal mammalian hematopoiesis, hematopoietic stem cells (HSCs) have the capacity to replenish the entire blood system. Consequently, mutation of stem cells has the potential to rapidly affect the entire hematopoietic system.
An interesting aspect about the stem cell is that embryonic stem cells can proliferate in a laboratory for more than one year without differentiation as it has unique immune-privileged properties. But, same is not true for Adult stem cells. Adult stem cells typically generate the cell types of the tissue in which they reside. For example, a blood-forming adult stem cell in the bone marrow normally gives rise to the many types of blood cells such as red blood cells, white blood cells and platelets. In recent times, researchers are vigorously exploring the possibility of using adult stem cells for cell-based therapies.
