There are stem cells, and then there are embryonic stem cells. The two are not the same. They are quite different. The former have always been part of the body tissues; the latter are, essentially, synthetic, so to speak; that is, man-made.
The term embryonic stem cell (esc) has been ingrained in the present day scientific jargon and has become the most advertised scientific research area cited by the mainstream media, politicos and pundits. This popularity has been strengthened even more so since Martin Evans was awarded the 2007 Nobel prize in medicine for the successful culture of mouse embryonic cells into pluripotent cell lines in 19811.
Wikipedia (author unknown) credits Gail R. Martin with coining the term embryonic stem cells, also in 19812. In fact, Martin states "Such cells were termed embryonic stem cells (ESC) to denote their origin directly from embryos. ." and puts the term in italics. The resultant cells are identified as pluripotent cell lines derived from the inner cell mass (ICM) in the mouse.
Thomson et al. was the first to derive pluripotent cell lines from the ICM in human blastocysts. When kept in culture for 4 to 5 months they could be directed to differentiate into several definitive tissue type cells3.
Unfortunately, the claim has been made that the ICM, or even earlier blastomeres, are actually "embryonic stem cells"4, and a New York Times issue on Health of 28 March, 2008 declares: "Stem cells are how we all begin." Furthermore, a review of "Stem Cell Research", published by RD Systems, states: ". . stem cells can only be defined functionally, not morphologically or phenotypically"5.
Not only are such definitions confusing, but they are incorrect. This terminology conflicts with what has previously been known about the early human embryo and what is known about stem cells.
The term stem cell first appeared in a text of Developmental Anatomy by Leslie Arey in 1954 in a subheading entitled: "Stem cell of the neural wall"6. Later, it appeared indexed in histology texts7,8. Prior to this time they were known as reparative, or, regenerative cells. The term first appeared in published research in the 1960s9.
Condic rightly separates the two types, but errs in defining the stem cell as "a general type of cell"10. In actuality stem cells are very specific types of cells and many can be readily identified morphologically, either by light microscopy or electron microscopy.For example: the satellite cell in human skeletal muscle, mucous neck cells in the human stomach, and basal cells of the epidermis in the human, not to mention the oogonia and spermatogonia, are clear examples of morphologically defined stem cells. Their purpose is to replenish the stem cell pool with one daughter cell, while the other daughter cell replaces lost definitive cells in the resident tissue.With the possible exception of the hematopoietic stem cell, they are not known to produce pluripotent cell lines.
These cells are derived sometime during development (or maybe after birth) partially differentiate, then are arrested in their resident, definitive tissue, available to be stimulated under appropriate means to undergo further differentiation to their definitive tissue type. Even though they would probably be produced during embryogenesis, or in the fetal period, they would be, de facto, adult stem cells. They would not be the same as embryonic stem cells, because the two different types have different courses of differentiation. Furthermore, there is no evidence, to date, that cultures of embryonic stem cells derive any true stem cells.
Pare and Sherley have derived a procedure (SACK) to ensure the culture of adult stem cells11. This is important because the steps of differentiation and arrest of these cells can then be determined.
That is what is supremely important: to understand the steps of differentiation, which, apparently, are active in the culture of embryonic stem cells, while deriving definitive tissues, but which have not yet been identified.
With increased manipulations of embryonic stem cells, and derivations from exotic cloning procedures, such as, the reprogramming of adult skin cells to act like embryonic stem cells [induced pluripotent cells, iPs]12, there is the potential that the benefits of true stem cells will be overlooked.