Much of the debate over stem cell research centers on how words are defined. In our battle to preserve an ethic of life, it is important for us to understand some of the basic terms that are often misused in the media.
Why should I care how the terms are defined?
Media reports often discuss stem cells with ambiguity or in misleading ways that do not reflect current scientific knowledge. Without an accurate understanding of the language of stem cells it is easy to assume that the only promising research is in the area of destructive embryonic stem cell research.
How should “stem cells” be defined?
Even within the scientific community there is confusion over how stem cells should be defined. Different experimental techniques can lead to varied conclusions over what constitutes a stem cell. To add to the confusion, evidence is mounting that some mature human cells seem to be able to revert back to a stem cell in certain situations and under certain conditions. This holds great promise for medical therapies in the future, but can make it difficult to decide what exactly constitutes a stem cell.
Based on scientific literature and medical textbooks, a stem cell can be defined simply as an unspecialized cell that can duplicate itself and grow into many different kinds of mature cells.
Terms of the Debate1
A new human life begins with the fertilization of a mature egg by a sperm; the result is a single, new cell called a zygote. A new zygote is the ultimate stem cell. It is totipotent. A totipotent cell can produce new and different cells unlike itself – these cells can become a complete, unique human being. For example, the new totipotent zygote is capable of generating the placenta, other tissues necessary for the growth of the embryo, as well as every type of cell found in the body.
When this new life is about four days old, the cells begin to commit to different cell types. Some form an outer layer that will become the placenta; others make the inner cell mass which will continue to form the embryo. The inner mass consists of pluripotent stem cells that can make any component of the embryo but cannot give rise to extra-embryonic tissue such as the placenta. These pluripotent stem cells can be extracted from the inner cell mass (destroying the embryo in the process) to generate a collection of embryonic stem cells.
As the embryo continues to grow and parts of the body start to emerge, the stem cells within each future organ become more specialized and are only capable of producing specific cells. Eventually, as a stem cell keeps dividing into two cells, at some point in development one or both of the daughter cells becomes ‘committed’ to a certain type of tissue and are incapable of further division. These committed daughter cells become the normal functioning cells of the heart, skin, brain, and other organs. These stem cells are multipotent. Adults still have multipotent stem cells in their bodies – we call these adult stem cells or non-embryonic stem cells.
In addition to the multipotent adult stem cells that are found in adult bodies, a growing number of studies have found pluripotent stem cells in adults. These flexible stem cells have the ability to specialize into every cell type of the body - just like embryonic stem cells. For more information on these exciting new studies, see What the Media Won't Tell You About Stem Cell Research
Dawn Vargo is a research assistant in the Public Policy Division of Focus on the Family.
Defining the Stem Cell Controversy
Do you know what the terms of the stem cell debate actually mean?
1 These terms were developed using information from: The Oxford Companion to the Body, edited by Colin Blakemore and Sheila Jennet, 2001
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