The Shapeshifting Stem Cell

Shapeshifting has been a common theme in ancient mythology as well as modern folklore (i.e. comic books). It may help if you keep Terminator 2000 from T3 or Mystique from X-Men in mind as you think about stem cells and what they do.

Let's get some technical jargon straight first. To stem cell biologists, a "stem cell" is strictly defined as a cell that is capable of both self-renewal and pluripotency. That basically means that a stem cell can divide asymmetrically and yield a single daughter stem cell to maintain the stem cell pool (self-renewal), and another daughter cell that will potentially become any cell type in a process called differentiation. Stem cells can divide symmetrically too, in theory, when a large reservoir of stem cells is needed during organ formation. Why the large reservoir? That's because matured, differentiated cells tend to have a limited number of cell divisions. So they cannot multiply enough to form the mature tissue. A delicate balance exists between the immature, pluripotent state vs. the mature, differentiated state in terms of proliferation. Pluripotent stem cell division is carefully controlled so that such malleable cells do not overwhelm the organism, and may result in some freaky situations. At the same time, a stable pluripotent reservoir of cells is maintained that contributes to early development, wound healing, and tissue turnover.

There is precious little understanding of what actually happens between stem cells and the fully mature differentiated cells. Some people think this gap contains a rainbow of immature cells that are poised to become their fated mature selves, but have not received the final go ahead. This cellular no man's land is rich with possibilities, which I'll tackle in my next few posts.

Now, for a thought experiment that will help illustrate a few key points about stem cell. For those of you not nerdy enough to know about X-Men lore, the mutant Mystique possesses shapeshifting and unlimited healing abilities. Under this premise, what kinds of cells would Mystique possess? I would guess that Mystique has a self-renewing pool of stem cells or immature, partly differentiated cells that are somehow psychically linked to her mind. She has the unique ability to command her cells to become any cell type and direct their migration around her body when she shapeshifts.

I know it's impossible to mentally direct the function of several million cells, but bear with me here. Stem cells have some complicated biology and I figured it best to present it in bite-sized chunks. So, for now, just spend a little time imagining possible scenarios that a group of shapshifting cells can do in a human body. I'll be sharing my thoughts in the next few posts (coupled with some hard core biology, of course).

Photo credit: Neurons differentiated from neural stem cells HCN-A94 with an unnatural amino acid incorporated. Courtesy of Dr. Bin Shen, Chemical Biology and Proteomics Laboratory, the Salk Institute for Biological Studies (http://wang.salk.edu)