What are stem cells ?

by KakashiNar

An article containing all the basic info about stem cells. Explains what they are, their properties, how many types exist, where they extracted from etc.

Stem cells are one of the many different types of cells, most if not all complex organisms have. They are undifferentiated cells, with the capacity to transform into all the other more specialized cells, like muscle, neural and blood cells. Stem cells are usually divided into 2 very broad categories:
1) Embryonic stem cells
2) Adult stem cells

Lately a third category of stem cells has also arised, called induced pluripotent stem cells.

Embryonic stem cell colony
Embryonic stem cell colony

Adult stem cells (ASCs) are stem cells found in juvenile and adult individuals whereas embryonic stem cells (ESCs) are stem cells found, as suggested by their name, in embryos.

ASCs are mainly responsible for replenishing and regenerating dying cells and tissues. On the other hand, ESCs participate in the process of embryogenesis. All tissues and organs are initially created by ESCs.

As mentioned before there is also a third type of stem cells, called induced pluripotent stem cells. These stem cells don’t occur naturally and are created in the lab via a method called transfection. Essentially, they are somatic cells (specialized cells like neurons) that have been reversed to a stem cell-like nature. They are pluripotent and very similar to ESCs. 

Stem cells have two specific attributes that make them unique when compared to other types of cells. The first attribute is called potency and the second self-renewal.


What is potency ?

In simple words, potency refers to a stem cell’s capacity to transform into other, different and more specific cells. The higher the potency the higher the number of different cells a stem cell can differentiate into. Potency is divided into the following degrees:

  1. Totipotent
  2. Pluripotent
  3. Multipotent
  4. Oligopotent

Totipotent stem cells can transform into all the different cells an organism has. Embryonic stem cells derived from a morula  are totipotent

Pluripotent stem cells can again transform into all kinds of cells, with one exception, the cells from which the placenta is comprised of.

Multipotent stem cells can transform into many different cells,  that belong to the same organ/tissue. For example mesenchymal stem cells (which can be found in the bone marrow) can develop into all skeletal cells, for example osteoblasts, chondrocytes and muscle cells.

Oligopotent stem cells can develop into just a handful of different cells, again of the same  organ/tissue. An indicative  example, are vascular stem cells which can only become  endothelial or smooth muscle cells. 

What is self renewal ?

Self renewal refers to the ability stem cells have to replenish their numbers. Theoretically and under the proper circumstances a stem cell can divide into more and more stem cells indefinitely. The derived cells are essentially the same as the original one.

A mesenchymal stem cell
A mesenchymal stem cell

Where are stem cells extracted from?

Embryonic stem cells are extracted from very “young” embryos. More specifically:

  • Morula, very early embryos comprised of only 32-64 cells. ESCs taken from a morula are totipotent in nature
  • Blastocyst, the next embryonic stage after the morula, only 4-5 days old. ESCs taken from blastocysts are pluripotent

Adult stem cells have been successfully extracted from many different sources. The bone marrow by itself can be used to extract three different types of ASCs:

  • Mesenchymal stem cells
  • Hematopoietic stem cells
  • Endothelial stem cells

Some other sources for adult stem cells are the following:

  • Adipose tissue  
  • Skin
  • Brain
  • Blood

Stem cell applications

As of 2013, stem cell applications are very limited. The only FDA-approved stem cell treatment is called hematopoietic stem cell transplantation and has been around for more than 30 years. However this is expected to change very soon as there are many clinical applications running both on humans and animals examining the efficacy of various types of stem cells for treating many different conditions. 

Many researchers believe that stem cells, whether they are ASC,ESCs or IPSCs, will allow us to treat many currently untreatable conditions including:

  • Alzheimer
  • Parkinson
  • Osteoarthritis
  • Amyotrophic lateral sclerosis
  • Debilating injuries like spinal cord injuries

Researchers also believe that stem cells will one day be a better option for treating even simpler conditions like osteoporosis and severe myopia.

Finally, it is expected that ESC research will give us a better understanding of how tumors and cancers initially develop, thus allowing the production of better and more effective anti-cancer drugs.

Updated: 03/13/2013, KakashiNar
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katiem2 on 02/25/2013

Stem cells in itself is a word more commonly spoken and yet there is rarely a good description as to what these vital cells actually are and what they can do. It's still a topic needed more light shed on it. You've done a very good job of clearing any confusion I had as to the what and why of stem cells I thank you. :)K

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