Friday, August 17, 2007

The Stem Cell Delusion: Are They Still Stem Cells If They're Bacteria?

On a previous episode of the bayblab podcast, I argued (rather poorly) that so-called mammalian "stem" cells are not so magical and deterministic as we think (ie they do not "exist"). Rather, I attempted to argue, the stem cell illusion is an emergent property of fundamental cell population dynamics and is even exhibited by the lowly unicellular prokaryotes, as exemplified by the phenomenon of bacterial persistence. A new PLOSone paper explores the theoretical basis of bacterial persistence as population bet-hedging:

"Within a population of bacteria there exists a subgroup of cells that do not grow at the normal rate but exists in a quiescent, non-growing or slow-growing state. These cells are sometimes called persister cells [1], because they are able to persist in the face of catastrophic events such as antibiotic treatment...A key aspect of persister cells is that their resistance to antibiotic treatment is not genetically determined. Consequently, following antibiotic treatment, persisters give rise to new populations that have the same vulnerability to antibiotic treatment as the ancestral population [9]."

Sound familiar stem-cell believers? Slow growth, resistance to insult, and capable of repopulating diverse cell types. OK, so maybe bacteria have stem cells too. Maybe we should even think of them as multicellular organisms. But wait, now for the challenge to faith:

"The resistance of persister cells is therefore determined phenotypically, with cells switching between the alternative phenotypic states of persistence and normal growth [7], [11]."

What the !@#$& ?? Cells shape-shifting back and forth? Stem cell one minute, non-stem cell the next? Clearly mammalian cells are different. Once a stem cell always a stem cell. Right? Wrong. The stochastic outcome of asymetric stem cell division was one of the first properties described by McCulloch and Till soon after they discovered mammalian stem cells waaaaay back in the day.

Obviously then, "stem" cells do not exist....then they do....then they don't, then they do...., it's a wave....

Maybe it's not that bad. At least one might say there's a certain probability that a given cell will be "stem" at a certain point in space-time?


Anonymous Coward said...

bravo, stem cells denier unite!

Anonymous said...

sounds like all cells can be stem cells-what's to deny?!