I always was interested in cell differentiation, and it looks like some folks are getting ever closer to understanding the underlying mechanisms:
Biologists at the Broad and Whitehead Institutes in Cambridge, Mass., have now delved deep into this process and uncovered what seems to be a crucial feature of how a cell's fate is determined, even though much remains to be understood.
They have discovered a striking new feature of the chromatin, the specialized protein molecules that protect and control the giant molecules of DNA that lie at the center of every chromosome.
The feature explains how embryonic cells are kept in a poised state so that all of the genome's many developmental programs are blocked, yet each is ready to be executed if the cell is assigned to that developmental path.
They still don't understand what triggers differentiation - the signalling that leads to master regulator genes being turned on or off for a given cell, however. I don't know a lot about this (not a biologist or biochemist), but the environment of the cell (who its neighbors are) has a lot to do with the process, so I would think there has to be some mechanism for the chemical signals outside the cell to do something inside the cell (some protein gets made, perhaps) and this would affect what happens in these newly discovered "bivalent domains" on the chromosome, which causes a cascade of genes being turned on or off at different levels (the master regulatory genes control several secondary genes), which tells the cell what proteins to produce, and in effect what function it will have. Very cool stuff.