Finally an Answer....See My Ask a Scientist Response!

Megan, thank you for submitting the following question to the
Howard Hughes Medical Institute's Ask a Scientist website:


How do stem cells decide what type of cell they are going to turn into and what type of cell is the initial one that we start out with in life? As an extension to this question: When a person is given stem cells, do the doctors decide what kind of cells they turn into in advance or does the body of the individual make that decision when the cells enter the human body system based on where there is a need?

Here is a response provided by one of our volunteer scientists:


This is a fabulous question and one that many great minds continue to investigate, because we do not yet know the complete answer. There are three general areas of biology that dictate a cell's fate. The first and most obvious is the DNA. All the information is encoded in the DNA, not only what cell type but how the cell can respond to signals it receives. The second are those signals. Signaling might be something as simple as 'inside' or 'outside'. Those first few divisions of identical cells in a developing embryo produce a ball of cells, with some facing the outside, and some completely surrounded by other cells. That difference triggers a whole new pattern of gene expression in the cells. The outside cells are now destined to become a different tissue than those inside the ball of cells. So, a simple external signal operates an incredibly complicated signal cascade that determines cell fate. The third contribution has only been appreciated recently, and that is that there are molecules carried in the fertilized egg that direct development also. These may be RNA molecules, proteins and enzymes that can alter which genes may be switched on or off, another level of regulation of cell fate.

Stem cell therapy will likely involve replacing or supplementing cells that have already undergone a certain amount of specialization. For example, our skin has many stem cells that for much of our life can constantly replace worn out cells. These skin stem cells are less differentiated than other skin cells, but are different from blood stem cells that replenish the blood. In the laboratory it is possible to take skin stem cells and revert them to an earlier developmental stage. When these stem cells are placed into the right environment they can then form many different types of cells, but not all.
Now, in the healthy person, our own tissues provide cues and support to our own stem cells naturally. The trouble is, that stem therapy is treating something that went wrong. So, the disease could be because the stem cells are all gone (attacked by the own body, they die too soon, or because of damage), the signals are not being sent to the stem cells, or the stem cells can no longer respond properly to the signals. As you can imagine, the stem cell therapy has to be carefully tailored to the specific disease so that any stem cells get to the right place, become the right cell type, they survive and start working properly. This is why to date, stem cell therapy is still only experimental. For more information try the NIH website:
http://stemcells.nih.gov/info/basics/defaultpage.asp


We welcome feedback from you about this answer to your question and
appreciate your interest in Ask a Scientist.


Ask a Scientist Coordinator