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Friday, November 12, 2010

The Potential of Stem Cells: from the embryo to the adult

We all know that we grow in our mother's bellies and begin as a tiny little egg in their womb. We know that it took 9 months to change this tiny little egg into a complete human being with arms, legs, eyes and ears. We know that when we are born we pretty much have all the right pieces in all the right places. And we know that although we continue to grow, develop and mature as we age, these changes are nothing compared to the growth, development and maturation that occurs before birth. Today, we will discuss why that is true.

Here we will discuss Embryonic Stem Cells- we will consider what they are, how they are different from adult stem cells (discussed in the earlier post: Stem Cells - what are they and why do i care?), and why they are a source of much contention.

Early cell divisions following fertilization generate a mass
of embryonic stem cells that continue to divide and
differentiate into all the tissues of an adult human being
I think the best way to discuss this topic is to start at the beginning, the very beginning, and then finish somewhere around the end.

So, how do we begin? Well... with the miraculous act of conception, right? Right! When the sperm (containing your Dad's DNA) and the egg (which contains your Mom's DNA) come together for the very first time a complex chemical reaction starts the process of creating a human being. This process begins with cell divisions- lots and lots and lots of divisions that transform that single cell into many, many cells. These very first cells are the embryonic stem cells, and these cells are able to make all the different tissues, organs, and systems of a functioning human being.

A single embryonic stem cell can make ANY cell type in our entire body!

Let me repeat that, just to make sure you realize how important that really is. Embryonic stem cells can make any cell- this includes a blood cell, a bone cell, a liver cell, an eye cell, a skin cell, or even a brain cell. They are completely undetermined and have tonnes of potential! All they need is a little direction, or the right nudge, to 'differentiate' and become a specific cell type.

Stem cell diagram illustrates a human fetus st...Image via Wikipedia
One might say that embryonic stem cells are like a fresh mound of rainbow-coloured Playdoh that can be transformed into any shape or form with the right kind of manipulation. Embryonic stem cells have virtually unlimited potential.

And this fact is why embryonic stem cells are different from adult stem cells. If you recall from the previous post, adult stem cells are present in the adult body and are present in many different tissues. These stem cells are also capable of generating many cell types, but adult stem cells have restricted potential and can only make specific cells for a specific tissue. For instance skin has skin stem cells and blood has blood stem cells and the brain has brain stem cells, and each of these stem cell will only make cells for that specific type of adult tissue. A skin stem cell maintains our skin but not our blood because a skin stem cell is specific and restricted to only skin. Adult stem cells are specific to only one kind of adult tissue.

Adult stem cells are required to maintain and repair our body as we age, and although adult stem cells have very important uses (ex. using skin stem cells to generate new skin for burn victims), their use in research and medicine is much more limited than their embryonic counterparts. And this is solely due to the fact that the potential of adult stem cells is limited, while embryonic stem cell potential is unlimited.

Return to our Playdoh analogy. While an embryonic stem cell is like fresh, rainbow-coloured Playdoh capable of forming anything, an adult stem cell is more like stiff, green Playdoh that is more difficult to manipulate and resistant to new shapes; it's potential is more restricted.

Although we have a rough understanding of the different
developmental stages a human embryo progresses through,
the details of this development remains very poorly defined.
The fact that embryonic stem cells can make any cell type in the human body means they have many important uses in research and medicine. For instance, embryonic stem cells can help us study human development. We currently have very little knowledge of how groups of cells in an embryo are able to become functioning organs in the adult. By studying embryonic stem cells we can better understand how humans transform from a single cell into a complex, multicelled organism. And by understanding how humans develop normally we will be able to identify when this development goes wrong. Imagine, one day we might actually be able to stop birth defects and disabilities before they even happen.

Stem cells are also very important in medicine since they can be used to repair injuries and cure diseases. For instance, a patient with leukemia (blood cancer) can be given healthy, undiseased blood stem cells that will generate healthy, undiseased blood and this will cure the cancer. Also, a patient with a paralyzing spinal cord injury can regain movement if brain stem cells are used to grow new, uninjured neurons. These examples use adult stem cells, but imagine if we had a cell type that could create both new blood cells for a leukemia patient and a new spinal cord for a car crash victim. But... wait a minute.... we do have that kind of cell type! We have embryonic stem cells!

In theory, a single embryonic stem cell can be used to repair and cure any injury or disease that a person may encounter. In theory, that single embryonic stem cell can even be used to regrow an entire organ (such as new eyes for the blind) or an entire appendage (like a new leg for an amputee)! All we have to do is learn how to manipulate these cells and learn how to mould them into these different forms or tissues.

Diseases and conditions where stem cell treatm...Image via Wikipedia
As you can imagine, while embryonic stem cells have amazing potential for health, they also have amazing potential for harm.  And this is why the ethical debates surrounding these cells are ongoing.

Because a single embryonic stem cell can be used to grow an entire human being there are many concerns about human cloning. Some say that if research using full-grown humans is illegal and unethical so is research using human embryonic stem cells. This relates to the question: 'When does an embryo, a cluster of cells, become a human being with thoughts and rights?' There are also issues of accessibility. Who will benefit from the medicines and therapies developed from embryonic stem cell research? And who will regulate this research? Will only the rich few that have enough money to pay for the treatment be allowed to access the technology? And who will ensure that everyone, including the poorest people in the poorest countries, benefits from these medicines?


Here is a discussion on the history of stem cell research. This 'fire-side chat' is between leading scientists James Till and Janet Rossant who helped found the stem cell field.



StemCellTalks Fireside Chat with Jim Till and Janet Rossant from Stem Cell Network on Vimeo.



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1 comment:

  1. This other article here was written a while ago in another blog but I think it is certainly relevant :)

    Reprogramming Skin Cells into Stem Cells

    http://www.nextnature.net/2009/07/reprogramming-skin-cells-into-stem-cells/

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