II.What are the unique properties of all stem cells?
III. Types of stem cells
IV. What are the similarities and differences between embryonic and adult stem cells?
V. What are the potential uses of stem cells?
Stem cells are cells that have the remarkable potential to develop into many different cell types in the body during early life and growth
In addition, in many tissues they serve as a sort of internal repair system, dividing essentially without limit to replenish other cells as long as the person or animal is still alive
When a stem cell divides, each new cell has the potential either to remain a stem cell or become another type of cell with a more specialized function, such as a muscle cell, a red blood cell, or a brain cell
Stem cell research.
Research on stem cells with a primary goal to identify how undifferentiated stem cells become the differentiated cells that form the tissues and organs
Scientists know that turning genes on and off is central to this process. Some of the most serious medical conditions, such as cancer and birth defects, are due to abnormal cell division and differentiation .
A research for more complete understanding of the genetic and molecular controls of these processes may yield information about how such diseases arise and suggest new strategies for therapy
Stem cells are distinguished from other cell types by two important characteristics.
i.They are unspecialized cells capable of renewing themselves through cell division, sometimes after long periods of inactivity
ii. Under certain conditions, they can be induced to become tissue- or organ-specific cells with special functions.
In some organs, such as the gut and bone marrow, stem cells regularly divide to repair and replace worn out or damaged tissues
In other organs, however, such as the pancreas and the heart, stem cells only divide under special conditions.
II.What are the unique properties of all stem cells?
All stem cells—regardless of their source—have three general properties:
They are capable of dividing and renewing themselves for long periods
They are unspecialized
They can give rise to specialized cell types.
Potency specifies the differentiation potential (the potential to differentiate into different cell types) of the stem cell
Totipotent (a.k.a omnipotent) stem cells can differentiate into embryonic and extraembryonic cell types. Such cells can construct a complete, viable organism. These cells are produced from the fusion of an egg and sperm cell.
Pluripotent stem cells are the descendants of totipotent cells and can differentiate into nearly all cells, i.e. cells derived from any of the three germ layers
Multipotent stem cells can differentiate into a number of cells, but only those of a closely related family of cells.
Oligopotent stem cells can differentiate into only a few cells, such as lymphoid or myeloid stem cells.
Unipotent cells can produce only one cell type, their own,but have the property of self-renewal which distinguishes them from non-stem cells (e.g. muscle stem cells).
Types of stem cells
Often based on where in the body or what stage in development they come from
1. Embryonic Stem Cells
Embryonic stem cells are derived from very early embryos and can in theory give rise to all cell types in the body.
However, coaxing these cells to become a particular cell type in the laboratory is not trivial.
Furthermore, embryonic stem cells carry the risk of transforming into cancerous tissue after transplantation
The morula‘s cells are totipotent, able to become all tissues and a placenta.
2. Adult Stem Cells or Tissue-specific Stem Cells
Many adult tissues contain stem cells that can replace cells that die or restore tissue after injury.
Skin, muscle, intestine and bone marrow, for example, each contain their own stem cells. In the bone marrow, billions of new blood cells are made every day from blood-forming stem cells
Adult stem cells are tissue-specific, meaning they are found in a given tissue in our bodies and generate the mature cell types within that particular tissue or organ.
It is not clear whether all organs, such as the heart, contain stem cells. The term ‘adult stem cells’ is often used very broadly and may include fetal and cord blood stem cells
a. Fetal Stem Cells
As their name suggests, fetal stem cells are taken from the fetus.
The developing baby is referred to as a fetus from approximately 10 weeks of gestation.
Most tissues in a fetus contain stem cells that drive the rapid growth and development of the organs
Like adult stem cells, fetal stem cells are generally tissue-specific, and generate the mature cell types within the particular tissue or organ in which they are found.
b. Cord Blood Stem Cells
At birth the blood in the umbilical cord is rich in blood-forming stem cells.
The applications of cord blood are similar to those of adult bone marrow and are currently used to treat diseases and conditions of the blood or to restore the blood system after treatment for specific cancers.
Like the stem cells in adult bone marrow, cord blood stem cells are tissue-specific
To be used in cell transplant treatments the cells will most likely need to be directed into a more mature cell type, both to be therapeutically effective and to minimize risk that cancers develop.
There are currently no treatments using embryonic stem cells accepted by the medical community.
3. Induced Pluripotent Stem Cells (iPS cells)
In 2006, scientists discovered how to “reprogram” cells with a specialized function (for example, skin cells) in the laboratory, so that they behave like an embryonic stem cell.
These cells, called induced pluripotent cells or iPS cells, are created by inducing the specialized cells to express genes that are normally made in embryonic stem cells and that control how the cell functions.
Shinya Yamanaka and his colleagues at Kyoto University used the transcription factors Oct3/4, Sox2, c-Myc, and Klf4 to induce epithelial cells to be like embryonic stem cells.
Embryonic stem cells and iPS cells share many characteristics, including the ability become the cells of all organs and tissues, but they are not identical and can sometimes behave slightly differently.
IPS cells are a powerful method for creating patient- and disease-specific cell lines for research. However, the techniques used to make them need to be carefully refined before they can be used to generate iPS cells suitable for safe and effective therapies
5. Potential uses of stem cells
Human stem cells could be used to test new drugs. For example, new medications could be tested for safety on differentiated cells generated from human pluripotent cell lines.
Generation of cells and tissues that could be used for cell-based therapies.e.g Today, donated organs and tissues are often used to replace ailing or destroyed tissue, but the need for transplantable tissues and organs far outweighs the available supply
Stem cells, directed to differentiate into specific cell types, offer the possibility of a renewable source of replacement cells and tissues to treat diseases including, spinal cord injury, burns, heart disease, diabetes, osteoarthritis, and rheumatoid arthritis.
Figure 1. Strategies to repair heart muscle with adult stem cells. 07/16/11
To be useful for transplant purposes, stem cells must be reproducibly made to:
-Proliferate extensively and generate sufficient quantities of tissue.
-Differentiate into the desired cell type(s).
-Survive in the recipient after transplant.
-Integrate into the surrounding tissue after transplant.
-Function appropriately for the duration of the recipient's life.
Stem cells offer exciting promise for future therapies, but significant technical hurdles remain that will only be overcome through years of intensive research