|MadSci Network: Development|
Your question addresses an excellent scientific aspect of stem cell function that is often obscured by the current focus on their potential for therapeutic applications. Optimistic predictions for these applications often do describe a fairly simplistic scenario in which the stem cells are delivered to the internal site in need of repair, where they almost magically change into newer, healthier cells of that tissue.
However, specialization of pluripotent stem cells is the end result of a very complex cellular process known as differentiation. As explained in the following Stem Cell Basics Primer from the Nat'l Institutes of Health, "scientists are just beginning to understand the signals inside and outside cells that trigger stem cell differentiation". Differentiation is controlled by a variety of molecular signals, some of which are secreted by neighboring cells & some of which may be delivered from more distant sources in the body through the bloodstream. The summary of a Harvard Univ. research study on the response of human embryonic stem cells to 8 different growth factors in the lab provides an example of the complexity of this differentiation process. It also explains how these factors help to regulate growth & development of an organism through stem cell differentiation, & how studies such as this may eventually help to discover how we can use them in directing stem cells to repair diseased tissues in the body.
I encourage you to continue seeking out the actual scientific basis behind the general media hype over many biomedical 'discoveries'. Even scientists themselves can be misled by an incomplete review of the current experimental findings. Thanks for the great question,
Jeff Buzby, Ph.D.
CHOC Research Institute
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