Any one figure out how stem cells differentiate yet?

The best way to understand this is to look at drosophila developmental genetics, or chick limb development.

Essentially, though the cells are "all the same", their environment is *not*. So (in mammals) when a blastocyst implants itself in the wall of the uterus, it suddenly has 2 sides: the one touching the uterine wall, and the one free in the uterine lumen. So the cells on those 2 sides receive different signals, and begin to differentiate into different cell types (only 2 at this stage).

Then, all of a sudden, there are different signals received: some cells are only touching cells that are exactly identical, while others are touching cells that are different (along the seam between the 2 sides). More different environment means more cell types (now 4).

Further along, you will get cells that release a diffusable factor into their environment. Perhaps the cells immediately adjacent receive 10 equivalent amounts (ea) of this factor, while cells further away receive 5ea, and those even further away reveive 1ea. As the cells can detect how much of the factor they are receiving, they can therefore differentiate down yet further pathways, into more cell types (and how they differentiate will depend what partial-differentiation steps they had already taken).

Add into that that the original ovum was *already* polarised (it had one end where the cytoplasm is qualitatively different from the other), and this polarisation is maintained when the cells portion-up that cytoplasm by dividing, and further complexity is added.

Understand that it's been a while since I took any development lectures - but this kind of patterning is the basic theory.

And I know you are asking about stem cells, rather than ova, but the principle holds.

Other sources of variation in stem cell populations are also possible: for example, what stage of the cell cycle they are in when any particular signal is received.

It's all about signalling cascades. Even though all the cells are at a brief point in development all totipotent, then pluripotent/multipotent, nurse cells from the mother make contact with the cells and form a chemical gradient that induces the cells to differentiate more and more. For a very good illustration, the wiki article on how the anterior-posterior axis in drosophila is perfect:

http://en.wikipedia.org/wiki/Morphogenesis#Anterio...

Once each cell receives the signal, different genes within that cell are turned on and transcription and translation occur to produce further signalling molecules that then impacts its neighbors. Many of these genes (notch, fgf, bmp) self regulate or regulate each other so that very specific and very controlled differentiation can occur.

Of course, there's still a lot of research being done on the specific pathways, but a LOT is already known. We can induce different body parts on a number of different animals (chicken beaks on ducks, extra or missing segments in insects, a wing where an arm should be, etc). If you want more specifics in how the signalling works. Look up notch signalling, or bone morphogenic protein, fibroblast growth factors, and bicoid gradients to start with. :) Have fun and hope this helped.

stems cells have the means to change into any human body area (pores and skin, heart, liver, and so on). it might want to stay away from in case you advance leukemia or want a sparkling liver interior the destiny. really, making an investment in stem cellular study can save lives.

my theory is because it is a stem cell and it has 0 specific destination until its given one