I’d like to point to very interesting discussion that questioned “Is ‘stem cell’ concept holding back biology?” A professor Arthur Lander  from University of California Irvine in his article  argues that:
… after 45 years, we have been unable to place the general notion of ‘stemness’ on a purely molecular footing. Of course, the fact that a goal has not been achieved after a long time does not mean that the answer in not around the corner. But it does give one cause to wonder whether something we are doing needs to change, either the question we are asking or the way we are approaching it.
In an online interview for “The Scientist”  journal, Dr. Lander pointed out that current status of the stem cell concept is misguided.
We want to nail down the concept, but we need to nail it down in a different way. So if this is really a network property — that is, a property at a higher level than the cell itself — then nailing down the concept means knowing something about molecular properties of the cell and molecular properties of cell types it produces, the molecular properties of things that they produce that then feed back on the stem cells? It’s a system level property, so we need to have information about a whole system.
I shared discussion on FriendFeed  and started to comment:
If we come back to the article, we can see that Dr. Lander doesn’t actually argue the existence of stem cells per se, but offers an alternative way to explain how this system functions:
The jury is still out on whether all self-maintaining tissues exploit stochastic renewal with feedback or whether some, do in fact rely on invariant asymmetric stem cell divisions.
…the fact that stem cells very often do divide asymmetrically in no way implies that asymmetric division is the mechanism of tissue homeostasis. One can achieve homeostasis through feedback control, and still expect to see frequent (albeit not obligatory) asymmetric division, especially in tissues with rapid turnover in which stem cells must divide many times during the lifetime of the organism.
So the discussion turned into an assessment of our way to study and explain stem cell functions and characteristics – “stochastic model with feedback control” versus “asymmetrically dividing defining stem cell population” withing a given tissue. You can find a more detailed explanation of stochastic model of renewing withing the lineage in Lander’s recent article .
The final point of the article that was made:
In summary, it would seem that the concept of stem cell indeed has the potential to hold us back – especially if we focus on demanding from it things it cannot give. But if we can re-fashion our thinking at a different level – in which systems relationships and dynamics take the place of molecular signatures and simple gene regulatory circuits – then there is a chance that the concept of stem cell will continue to light the path toward biological understanding.
I don’t think that stem cell concept is “holding back biology”. I think it’s evolved. I’d agree with Dr. Lander that it’s a “natural course of science” and current findings and discussions like this will guide us in the way of approaching the problem in the future.
I disagree that most of stem cell biologists are “stuck in searching molecular signature of stemness”. I’m a stem cell researcher and don’t care much about it. The field is so broad. The system approach of studying adult stem cell was very well known and established. We know that stem cell lives in populations dependent on environmental cues (niches). We knew that there is a heterogeneity within the population and frequently pure stem cell can not represent the whole population.
I’m so glad that during the last week this discussion was so productive and useful for me. It was broadcast-ed , blogged , twittered , shared , interviewed , podcasted  and commented  in open science manner. It is a great example how scientific discussion should be done online!