Dr. Young's reply to "a stem cell is a stem cell"
From dschroed:
"I was told by an oncologist that a stem cell is a stem cell, no matter how it is derived. I need to do extensive research before I make a decision of course to understand the process."
I want to thank Dr. Young for taking time from his ultra busy schedule to refute the comment that a stem cell is a stem cell. His reply will cause your brain to wither, but he has won the argument hands down I think you all will agree.
Dear Forum members,
Having spent over 30+ years studying adult stem cells, the oncologist's statement "... a stem cell is a stem cell, no matter how it is derived" is wrong.
There are many different varieties of stem cells and each one has a different function. The most differentiated "stem cells", also called progenitor cells or "-blast cells" are the immediate stem cells for differentiated tissue types, i.e., osteoblasts for bone, chondroblasts for cartilage, myoblasts for muscle, hepatoblasts for liver cells, pacreatoblasts for pancreas cells, neuroblasts for neurons, glioblasts for glial cells, keratinoblasts for skin cells, and the list goes on and on. For every differentiated cell type, there is a progenitor (-blast) cell for it.
As you develop from your embryonic through fetal stages there are three germ layer lineages formed: ectoderm, mesoderm, and endoderm. Each one of these germ layer lineages only forms tissues within their own distinct lineage. Moreover, there are stem cells for each one of these lineages, i.e., ectodermal stem cells, mesodermal stem cells, and endodermal stem cells.
Ectodermal lineage cells (and their stem cells) will only form cells belonging to the nervous system, such as your brain, spinal cord, neurons, glial cells, sensory nerve endings, ganglion cells, pituitary gland, hypothalamus, adrenal medulla, and cells belonging to the outer covering of your body, i.e., skin cells, hair cells, sweat gland cells, the enamel of your teeth, etc.
Mesodermal lineage cells (and their stem cells) will only form cells belonging to your muscle, bone, cartilage, connective tissue stroma (capsules, trabeculae, scar tissue, dermis, etc.), blood vessels, hematopoietic (blood) cells, lymphoid tissues, kidneys, ureters, urinary bladder, urethra, ovaries, testicles, adrenal cortex, spleen, etc.
And endodermal lineage cells (and their stem cells) will only form cells belonging to the parenchyma (actively functioning portion of the) liver, gall bladder, lung, stomach, small intestine, large intestine, rectum, pancreas (exocrine and endocrine), thyroid gland, parathyroid glands, etc.
During your development into an embryo there is the change of cell types from a single-cell called the ?zygote? to a solid ball of blastomeres to a blastocyst (a hollow ball of cells) that contain an inner cell mass (embryo proper), germ cells and the trophoblast (forming the placenta). There are two sets of stem cells given off during this transition as well. The inner cell mass will form pluripotent stem cells that will form every tissue type in the body except the germ cells (sperm and ova) and the placenta. The blastomeres will form totipotent stem cells that will form every cell type of the body, including germ cells and the placenta.
So the idea "... a stem cell is a stem cell, no matter how it is derived" is WRONG.
The identity of a particular stem cell depends on the following criteria. 1) What tissues the stem cells are isolated from and how the stem cells are isolated. 2) The cell surface markers the stem cells express. 3) Do the stem cells have the ability to self-renew themselves past a set biological clock (50-70 cell doublings in humans)? And 4) what tissues the cells will form. Those criteria dictate the identity of stem cell, i.e., progenitor (-blast) cells, ectodermal germ layer lineage stem cells, mesodermal germ layer lineage stem cells, endodermal germ layer lineage stem cells, pluripotent stem cells, and totipotent stem cells. Moreover, the above are just the adult-derived stem cells. Then you also have cells derived from the embryo (embryonic stem cells), and stem cells derived from cells floating in the amniotic fluid (i.e., aminiocytes).
In addition, to make matters a bit more confusing with respect to the adult stem cells, more than one stem cell type can exist next to another stem cell type. So isolating pure populations of stem cells can be a challenge.
I refer you to two published papers that discuss the adult stem cells in more detail, i.e., Young et al., Anatomical Record 276A 75-102, 2004 and Young and Black, Minerva Biotech 17:55-63, 2005. I have PDF's of the articles if you would like me to send them to you. You can make your request either to me or to the website and I will forward them to you.
Dr. Young
Know your model system and Tissue never lies - P.M. Johnston
Knowledge without an imagination is worthless - Albert Einstein
Adult stem cells do it better - H.E. Young