The Basics of Stem Cells
The word stem is generally used in plant kingdom for plant’s aerial part which bears several diversified structures as leaves, flowers, fruits etc. and can regenerate all these structures after any injury, cut or senescence. Similarly several cells in animal kingdom also have capability to regenerate into similar types or different types of cell, tissue, organs and structures and are called Stem Cells.
Types of Stem Cells based on functional properties: –
Unipotent Stem Cells: –
Are type of stem cells having capability to regenerate into only one type of cells of its origin.
Example – Cardiac muscles, Kidney endothelial cells, Hepatic cells etc.
Pluripotent Stem Cells: –
These stem cells can regenerate into different types of cells. These cells have ability to develop into cells either of same origin or of different origin.
Example – Skin cells, Erythropoetic cells (Bonemarrow cells)
Multipotent Stem Cells: –
Are most advanced types of stem cell with capacity to generate all types of cell, tissues, organs and even whole organism.
Example – Embryonic stem cells (Blastocyst cell)
Cells – The Basic Unit of Life
Starting from the beginning, cells are the basic unit of all life. They contain DNA (deoxribonucleaic acid), which is all of the cell’s genetic material. They also have the ability to undergo cell division and replication, which creates two daughter cells with identical DNA. There are somatic cells and germline cells. Somatic cells make up every part of your body from your eyes, to your skin, to your heart. Somatic cells are also the type of cells that cancer research uses and the types of cells that were used in Dolly, the sheep clone. Germline cells are sex cells that are used in sexual reproduction with females and males carying different types. When a female germline cell (ova) and a male germline cell (spermatazoa) combine during sexual reproduction, they form a zygote. The zygote then goes through several divisions (showed below) to form into a ball of pluripotent cells called stem cells.
The yellow cells in the figure above are pluripotent stem cells, which means these cells have much potential to differentiate into any type of somatic cell in the body. Differentiation is a developmental process by which unguided cells “turn into” a specific somatic cell type, like a blood cell or a nerve cell. During embryonic development, the perfect amounts of stem cells differentiate into every type of tissue to create all of the wonderful organs in our body as demonstrated below. While healthy (non-cancerous) cells in the body go through only about 50 replication cycles and then naturally kill themselves (to prevent excessive genetic mutations), stem cell have the capacity to theoretically divide forever. They can go on through millions and billions of cycles developing new cells with no limit, if supplied with the proper environment.
Types of Stem Cells
There are three main types of stem cells which are all obtained differently, have diverse applications, and face various controversies.
Embryonic Stem (ES) Cells can be obtained from the early developing stages of an embryo as shown in the first figure with a blastocyst. Stem cells obtained from this newly developed bundle of cells have the full potential to differentiate into absolutely, positively anything in the human body. Many scientists believe that embryonic stem cell research could lead to therapies that have the potential to cure at least 120 million Americans. They believe that these cells have the potential to cure thousands of disorders and biomedical problems such as Parkinson’s Disease, Alzheimer’s Disease, spinal cord injury, and organ replacements. These are the types of stem cells that are under constant controversy because they are taken from a five to six day old embryo . President Bush has legalized approximately 60 genetically diverse stem cell lines that can legally be used in research laboratories in the United States. The constant struggle between science, the government, and religion is at the pinnacle of this controversy.
Adult Stem Cells can be obtained from full-grown adults, but not all of their cells are stem cells because the majority of them have already differentiated. Therefore stem cells have to be found in special parts of the body where they have been saved and undifferentiated, like in bone marrow or early stages of tissue development. These cells are not fully pluripotent and (so far) have only been able to differentiate into a limited number of tissues. However they have been used for various applications such as cloning, trying to cure diabetes, and artificial blood. A major controversy in adult stem cell research has been cloning and the effects of cloning. The biggest question that is pending is how far people will go with cloning as fears rise such as in the book Brave New World and the movie The Island. Cloning is limited to animal use only and it is strictly and absolutely unlawful to apply to human use…as of now.
Umbilical Cord Stem Cells can be obtained from the umbilical cord of a new born baby. Millions of multipotent (not as much potential as pluripotent, but more potential than differentiated cells) stem cells lie in the umbilical cord and the blood in it. These stem cells can be saved in a stem cell bank and later used for bone marrow, anemia, and cancer treatments. There is not much wide-spread controversy in these types of stem cells because the umbilical cord is usually thrown away after child birth. Therefore this stem cell bank idea utilizes trash and turns it into a potential life saver.
More information on stem cells can be obtained from National Institutes of Health, The White House’s Stem Cell Fact Sheet, TIME/CNN, and The University of California.